AN INTERNAL SEAL FOR
REPAIRING NATURAL GAS MAINS
Samuel A. Cooper
Leon R. Glicksman
Carl R. Peterson
Energy Laboratory
Report No. MIT-EL-84-017
September 1984
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AN INTERNAL SEAL FOR REPAIRING
NATURAL GAS MAINS
ABSTRACT
Joint leakage from low gressu re natural gas distribution
mains (typical valu e: 0.25 ft /hr at 6 inwg ga s pressure) is a
persistent source of maintenance problems for utilities.
External encapsulat ion i s the usual choice for repairing leakIt is rel iable and exp ensive, about $1000 per
ing joints.
joint (80% of which is f or excavati on and resurfacing).
Consolidated E dison of New York is sponsoring a project
No current
to develop a chea p an d reliable joint seal.
sealing methods were found to be acceptable in Phase I.
Adhesion failures betwee n the seal and pipe were a major cause
Prel iminary Pha se II research recommended
of seal failure.
Such a seal
the development of an internal mec han ical seal.
would minimize exc avation and eliminate adhesion failures.
To complete Phase II, an internal mechanical seal was
The initial research indicated that cleaning of
developed.
the pipe interior had to be minimized or eliminated. Testing
demonstrated that a sealant, either asphalt or vulcanizing
silicone, greatly enhanced the sealing of uncleaned pipes,
This led to the
while permitting low stress levels.
seal concept for
mechanical
internal
development of a new
of 2 injected
tests
Joint
joints.
sealing uncleaned gas main
seal, which
1
Type
The
run.
were
silicone seal co ncepts
pipe
uncleaned
an
sealed
completely
filled the joint recess,
with
re
cess
joint
the
spanned
which
joint.
The Type 2 seal,
an elastomeric bri dge, had a leak rate of 0.000038 ft /hr at 6
The leakage was
inwg gas pressure from an uncleaned joint.
These flexible
bridge.
silicone
the
of
lity
permiabi
by
caused
and compliant sea Ils, clamped in place with retaining bands,
provide mechanical support for the sealant throughout the seal
life, and thus do not rely on adhesion.
__________I.
MIII
TABLE OF CONTENTS
Page
Abstract
2
Table of Contents
3
List of Tables
5
List of Figures
6
List of Photographs
7
Acknowledgments
8
1.0 INTRODUCTION.........................................
9
2.0 BACKGROUND AND ASSUMPTIONS.............................
12
2.1 Con Edison's Distribution System
12
2.2 Assumptions
13
3.0 PREVIOUS WORK........
................................
14
3.1 Phase I
14
3.2 Preliminary Phase II Research
16
3.2.1 Elastomer selection
17
3.2.2 Surface roughness and cleaning methods
18
3.2.3 Sealability and elastomer hardness
19
3.2.4 Baseline internal mechanical seal
20
3.2.5 Alternative seal concepts
21
3.2.6 Power transmission
22
3.2.7 Summary
22
4.0 EVALUATION AND TESTING OF CONCEPTS .....................
34
4.1 Concept Evaluation
34
4.2 Cleaning of Pipe Interiors
35
4.3 Seal Test Rig I
37
4.3.1 Description of apparatus
38
4.3.2 Test procedure
40
4.3.3 Silicone sponge and sealant results
41
4.3.4 Asphalt sealant results
42
4.3.5 Discussion of STR I test results
46
4.4 Retaining Bands
46
4.4.1 Retaining band issues
47
4.4.2 Mechanical Ratchet Retaining Band
48
4.4.3 Rejected alternatives
50
5.0 INTERNAL MECHANICAL SEAL PROTOTYPES..................
65
5.1 Choice of Curing Sealant
65
5.2 Seal Test Rig II
66
5.2.1 Description of apparatus
66
5.2.2 Pipe section characteristics
67
5.3 Injected Silicone Seals
68
5.3.1 Seal geometry and fabrication
68
5.3.2 Test procedure
69
5.3.3 Test results
70
5.4 Asphalt Seals
72
5.4.1 Seal geometry and fabrication
72
5.4.2 Test procedure
74
5.4.3 Test results
74
5.5 Discussion of STR II Results
6.0 INJECTED SILICONE SEAL JOINT TESTS...................
76
87
6.1 Seal Geometries
87
6.2 Test Joints
88
6.3 Type 1 Injected Silicone Seal Test
89
6.4 Type 2 Injected Silicone Seal Test
90
6.5 Discussion
90
7.0 SEAL DEPLOYMENT......................................
98
8.0 CONCLUSIONS AND RECOMMENDATIONS....................... 104
Appendix A - Materials Used for Seal Development
107
Appendix B - Retaining Band Force Derivation
109
Appendix C - Retaining Ring Analysis
110
Appendix D - Test Results Documentation
112
Appendix E - Phase I Supplemental Report
118
Appendix F - References
128
Appendix G - Deployment Mechanism
129
----'-------
-'
~"111
ImiY
,m
ini
LIST OF TABLES
No.
Title
3.1
Recommended Elastomers for Seals
24
3.2
Effectiveness of Cleaning Methods
25
3.3
Comparative Surface Roughness of Various
26
Page
Cleaning Methods
3.4
Estimation of Required Gasket Compressive
Stresses
27
to Achieve a Seal
4.1
Summary of STR I Test Results
52
5.1
Summary of STR II Test Results
79
6.1
Summary of Joint Test Results
92
__
_
LIST OF FIGURES
Page
No.
Title
1.1
Cast Iron Bell and Spigot Pipe Joint
11
3.1
Baseline Internal Mechanical Seal
28
3.2
Test Apparatus for Sealability Tests
29
3.3
Details of Rubber Gasket Used for
30
Sealability Tests
3.4
Inflatable Polyurethane Foam Seal Concepts
31
3.5
Beaded Gasket Concept
32
3.6
V-Groove Gasket Concept
32
3.7
Ridged Gasket Concept
33
4.1
Hypothetical Wire Wheel Cleaning Mechanism
53
4.2
Cross-Section of STR I Test Section
54
4.3
Water Tank Leak Measurement System
55
4.4
Schematic of Constant Pressure "Gas" System
55
4.5
Leak Rates of Sponge and Sponge/RTV
56
Gasket Materials
4.6
(STR I)
Leak Rate Decrease for Type B Asphalt
Seal,
First Test,
57
(STR I)
4.7
Joining Methods for Retaining Bands
58
4.8
Compressive Stress Distribution in a Sponge
59
Gasket Material Created by the Prototype
Retaining Band
4.9
Steel Tape Retaining Band Concept
60
4.10
Retaining Ring Applied Pressure
61
4.11
Hinged Retaining Ring Concept
62
4.12
Garter Spring Retaining Band Concept
62
5.1
Cross-Section of STR II Test Section
80
5.2
Seal Prototypes Tested in STR II
81
5.3
End View of Type 1 Injected Silicone Seal
82
6.1
Injected Silicone Seal Prototypes Tested in
93
Field Joints
7.1
Seal Packages for Deployment
102
LIST OF PHOTOGRAPHS
No.
Title
4.1
STR I Test Section
63
4.2
Prototype Retaining Bands
63
4.3
Contracted Prototype Retaining Bands
64
5.1
STR II
83
5.2
STR II Test Section, Type 1 Injected Silicone
Seal, Seal #2
83
5.3
Scale Size, Bottom of Pipe
84
5.4
Scale Size, Side of Pipe
84
5.5
Removed Type 1 Injected Silicone Seal Showing
Molding Ability of the Sealant, STR II, Seal #2
85
5.6
Asphalt Seal, STR II, Test #2
85
5.7
6.1
Seepage From Asphalt Seal, STR II,
Joint for Type 1 Seal Test
6.2
Pipe Scale for Type 1 Seal Test
94
6.3
Joint for Type 2 Seal Test
95
6.4
Pipe Scale for Type 2 Seal Test
Seepage From Type 1 Joint Test
95
6.6
Section Showing Joint Recess Filling by
Type 1 Injected Silicone Seal
96
6.7
Seepage From Type 2 Joint Test
97
6.8
Seepage Into Recess by Type 2 Injected
97
6.5
Page
Test Section and Apparatus
Test #2
86
94
96
Silicone Seal
7.1
7.2
Type 1 Silicone Seal in Package #2 Shape
Type 1 Silicone Seal in Package 44 Shape
103
103
ACKNOWLEDGMENTS
I
would
like
those who helped
to
me
take
in
this
opportunity
my stay at M.I.T.
to
and
thank
in
all
of
the prepara-
tion of this thesis.
I wish
and
Prof.
to thank
Carl
my
thesis
Peterson,
for
advisors, Dr.
their
ideas
and
Leon Glicksman
comments
which
guided this research over several developmental hurdles.
I thank the Consolidated Edison Company of New York which
sponsored
In
M.I.T.
Bob
this research,
particular,
Zlokovitz,
questions
that
and
I wish
Mr.
helped
enabling me to finish my stay at
to
Ben
thank Mr.
Lee
to guide
for
this work
Hans Mertens,
their
Mr.
comments
and
towards a practical
solution.
I
would
like
to
thank Mr.
Fred Johnson and
Mr.
Aubrey
Rigby who helped me in the fabrication of the test equipment.
I would
Kish,
and
Ms.
like
Joy
to
thank
Roller
Ms.
for
Kathleen Giordano, Ms.
their
assistance
in
Eva
preparing
reports and this thesis.
Finally,
Ashdown
House
I would
and
in
like
the
to
thank my
Heat Transfer
fellow collegues
Laboratory for
camaraderie that made my stay here more enjoyable.
in
their
U
CHAPTER 1
INTRODUCTION
Many
of
the
United
States'
older
cities
use
cast
iron
pipe as a major part of their low pressure natural gas distribution systems.
Most of these pipe systems were installed
under
city streets
at
least
several
decades
ago.
The
pipe
systems use bell and spigot joints with a lead and jute packing, see Figure 1.1, which seals the joint against leakage.
The distribution systems
gas,
which
had
heavy
originally carried manufactured
hydrocarbon
constituents
keep the jute packing moist and swollen.
that
acted
to
This swelling helped
to reduce the leakage rates at those joints where the lead did
not provide a positive seal.
As a result, system leakage was
minimal.
In the
1950's, many American
natural gas.
Natural gas
constituents.
This
some
joints
to
dry
utilities switched
over to
does not have heavy hydrocarbon
lack of moisturizers allowed the jute
in
up,
to
shrink,
and
leakage at the affected joints.
deteriorate,
The
leading
result was a rapid
in-
crease in system leakage a few years after the introduction of
natural gas.
Many solutions
tried.
After
the
to the problem of
drying out
of
the
system leakage were
jute
was
recognized,
various liquids and oils were used in mostly unsuccessful
attempts to moisturize and swell the jute.
Ultimately, many
of
the leaking
This
lowered
joints were encapsulated from the outside.
system
leakage
rates,
but
at
considerable
expense.
The Consolidated Edison Company of New York (Con Edison)
experienced
has
pushed
methods
their
the same
problem.
Since
the development
to cut
joint
leakage.
maintenance expenses
per encapsulated
of
joint,
the
more
The
1950's,
reliable
goal
has
from an approximate
$800
of
which
is
for
Con Edison
and
been
cheaper
to
cost of
reduce
$1000
excavation
and
These costs are so high
resurfacing of the street.1
little preventive
encapsulation
is done.2
are encapsulated only after they leak.
Generally,
the
joints are
automatically
joints
Exceptions occur when
joints are uncovered during other work on the system.
case
that
encapsulated
expense of having to excavate the joint again
to
In this
avoid
the
to seal it.
As part of this development effort, Con Edison has funded
research
at
the Massachusetts
Institute
of
Technology.
The
goal of this research is to develop a sealing method which
more reliable and economical
of
this project investigated all
determine
the
failure.
to
than available systems.
factors
Based on
Phase
II
its associated
contributing
to
called for
installation
IV would
their
success
or
this knowledge, a recommendation was made
design
internal mechanical
the development of
this
method.
would
the design and development of
Phase
Phase I
known sealing methods to
proceed with the development of an
seal.
is
Phase
III
seal
and
involve
the installation devices, while
the support
systems
and
implement
the
is
organized
as
main access method.
This
thesis
follows.
adresses
Phase
II
and
Chapter 2 describes Con Edison's system and the
restrictions
on
the
scope
of
the
research.
Chapter
3 des-
cribes the work done by Thomas Rogers on Phase I and the early
part of Phase II.1
Chapter 4 describes the work done
author to evaluate and
covers
cleaned
the
preliminary prototype
joint
Chapter 6.
test several seal concepts.
tests
with
seal
tests.
The
prototypes
by the
Chapter 5
successful
are
Chapter 7 deals with seal deployment.
covered
unin
The conclu-
sions and recommendations for further study are in Chapter 8.
--
--
106
I
11111N
-'
il fll
Cast Iron Spigot
Piece
Figure 1.1 : Cast Iron Bell and Spigot Pipe Joint.
11
1
CHAPTER 2
BACKGROUND AND ASSUMPTIONS
first
The
section
the
of
description
pertinent
presents
details
of
section
second
The
system.
distribution
chapter
this
of
short
a
Edison's
Con
describes
the
restrictions under which the research at M.I.T. was conducted.
2.1 CON EDISON'S DISTRIBUTION SYSTEM
A general characterization of Con
system is necessary to provide the
Conditions
project.
in
Edison's distribution
research
context for this
transmission
and
pipelines
service
lines will not be presented as these are outside the scope of
this study.
Edison's
Con
distribution
system
consists
of
cast
iron
pipe, 4 to 36 inches in diameter. The majority of lines are 4
to 8 inches in diameter. Gas pressures range from 4 inches of
The distribution mains tend to
water gage (inwg) to 25 psig.
expected to contain
1
Service taps can
branches, bends, reducers, tees, and traps.
be as frequent as one every 10 feet. The taps are usually in
follow
the streets.
The
system can be
the top of the main, although some may be located in the side
as much as a quarter of the circumference from the top of the
3
pipe.
The bell and spigot pipe joints occur about every 10
feet, with a maximum distance between joints of 12 feet. The
condition of the jute in the joints can vary from like new to
completely deteriorated.
heavily
contaminated
with
The jute can vary from clean to
old manufactured gas deposits or
Most of the joints will be lead backed, while some will
In most joints the backing can be
use a concrete backing.
1
expected to be loose or partially separated from the pipe.
tar.
The
comprised
pipe
of
interiors
rust
coated
typically
are
and manufactured gas
deposits.
can vary greatly in thickness and density.
12
with
The
scale
scale
There will also be
occasional tar deposits and casting burrs with large deposit
build-ups.
In addition,
carbo-seal,
water,
and
oil
fogging
1
may be present in liquid form at the bottom of the pipe.
Although most joints do not leak, those that do typically
have leak
joint
rates of 0.25 cubic
feet per hour
(ft3 /hr)
in a line containing natural gas at 6 inwg.4
from a
Leaks
of
this magnitude are repaired as soon as possible.
2.2 ASSUMPTIONS
This
research
project
will
be
limited
to
cast
distribution mains which are 6 and 8 inches in diameter.
internal
inwg.
natural gas pressure will
be assumed
iron
The
to be about
6
The conditions of the mains will be taken to be similar
to those described in the previous section.
CHAPTER 3
PREVIOUS WORK
t
This chapter describes the work which was done by Thomas
This work recommended
Rogers on this research project.
an
internal
mechanical
seal
be
developed as
the
that
solution
to
the problem of sealing leaking gas main joints.
3.1 PHASE I
ture
The Phase
I research
survey of
existing
was
primarily an extensive
leak sealing
technology. The
causing leak initiation were determined.
identify
most
the
factors
sealing
which
led
to
the
factors
Efforts were made to
premature
The major focus was
systems.
litera-
failure
to determine
of
the
applicability of existing sealing methods.
initiation
Leak
caused
by
in
the backing
of
bell
and
the
joint
separating from the pipe.
for natural
gas.
The
joints
spigot
(either
probably
is
lead or
concrete)
This could then become a leak path
cause for
the separation was either
improper construction or pipe stresses resulting from external
loadings
lead
or
strains
nor concrete
caused
backed
by
temperature
have
joints
bell
and
spigot
are
joints
no
Neither
very well
performed
laboratory simulations of field stresses.
that
changes.
in
It should be noted
longer
used
in
new
construction.
Leak
behavior
is dependent
the backing
severity of
separation
on
several
influences
as does the condition of the jute packing.
condition
may
deteriorated
provide
jute cannot.
some
sealing
There
is
factors.
the
The
leak rate,
Moist jute in good
ability,
also some
while
evidence
dry,
that
the type of soil around the pipe can influence the leak rate.
Loose, dry soils probably do
little to reduce
1
while clay soils probably do reduce leak rates.
leak rates,
The various joint sealing methods were classified in the
following
groups:
gas
conditioning,
14
jute
swellants,
mm
iI
aL
IllYIIYIYIIIYlull
I
fill-and-drain, bridge-the-gap, external, and insertion.
Gas
conditioning
humidification,
involves
oil
the
fogging
treatment
or
of
the
gas
monoethylene
by
glycol
vaporization. This treatment is meant to temporarily stop or
slow the deterioration of the jute by keeping it moist. None
of these methods was found to be very effective,
the jute had already deteriorated.
As
to
part
of
determine
zation
in
the
Phase
E.
reducing leakage
Edison
had
built
swellants
through the jute.
15%
also
field testing of glycol
Jute
Rogers
an
apparatus
The author com-
Monoethylene glycol vaporization was
to only produce a
Con
study,
the effectiveness of monoethylene glycol vapori-
pleted the test program.
found
I
especially if
1
leak
found
rate decrease,
very
see
Appendix
limited
effectiveness
liquids
which
in
vaporization.
are
into in-service mains.
mixtures
of
They are
intended
are
poured
to climb throughout
the
jute packing by capillary action, cause the jute to swell,
and
thereby
that
the
seal
the leak.
Field
experience has
jute swellants have inadequate
often
shown
climbing and swelling
capabilities.1
Fill-and-drain methods
fill
with
a rubber emulsion, which is
sion
is supposed
currently
in
to penetrate
the
pipe.
out-of-service main sections
then pressurized.
and
fill
all
After a suitable
of
the
The
emul-
leak paths
pressurization
time
the remaining emulsion is drained and the main is allowed to
cure.
These methods incur high
overhead costs.
They are
not
suitable for Con Edison's low pressure distribution system. 1
Bridge-the-gap
methods
involve
the
placement
internal seal at the joint, by either man or machine.
methods
extensive
require
removing
internal
the main
cleaning.
Cost
of
Current
from service as well
prohibits
the
an
adoption
currently available systems for Con Edison's situation.
as
of
1
External
methods
involve
either
encapsulation
or
mechanical clamping of the pipe joint exterior. This requires
excavation,
but
the
main
remains
in
service.
Excavation
resurfacing are about 80% ($800) of the total cost.
and
Currently
external methods are the most reliable, they are the preferred
sealing technique.
Insertion requires
existing one.
that a new pipe be pushed inside the
The main must be removed from service.
The old
service taps will require excavation so that they may be connected to the new pipe.
are
not
presently
Costs tend to be high.
appropriate
for
an
These methods
urban
distribution
system.1
Based on the research of Phase I, the desired characteristics of an alternate sealing system were outlined. 1
1) Internally seals the joints without relying on an
adhesive bond to the cast iron.
2) Requires a minimum of cleaning and surface
preparation.
3) Seals joints without taking the main out of service.
4) Requires a minimum of excavation.
5) Can be used in sections of mains with bends, branches,
service taps and tees.
6) Is simple to install and is not labor intensive.
7) Seal remains flexible and compliant, expanding and
contracting with pipe movement.
Gas pressure aids the
seal rather than forcing against it.
Seal does not
react with any chemical found in the pipe interior.
8) Allows for quality control by TV.
9) Overall system costs
(operational and social) are less
than existing systems.
3.2 PRELIMINARY PHASE II RESEARCH
The
preliminary
elastomers,
pipe
research
interior
for
Phase
cleaning methods,
II
investigated
the
relationship
between surface roughness and sealability, power transmission,
and
size
constraints
recommendations
were
due
to bend
made
for
clearances.
seal
concepts
As a
result,
and
design
criteria, and a feasible baseline internal mechanical seal was
developed.
This section will review and highlight the results of the
d
research
in each of
for
background
Phase
the
The purpose is
these areas.
II
which
research
to provide a
was
conducted
by
the author.
3.2.1 Elastomer selection
The
main
of
environment
considerably
is
fluid.
pressure
a
gasket
The gasket
from
must
seal
the
fluid
is
very low
at a
sealing
and/or
high
flange are
very
In a gas
roughness.
pressure
gas
natural
hot
a
of a
surfaces
a
common
more
smooth, about 60 micro-inches in surface
main
in
material
different
Usually
applications.
gasket
a
(less
than
1 psig)
and the sealing surface, cleaned or uncleaned, is usually much
rougher than a sealing
flange.
The low gas pressure and high
surface roughness both make a seal harder to achieve. 1
There are
choice of
rough pipe
an
two
important properties which dictate
elastomer as
surface,
the gasket
material.
the gasket material
must
irregular leak paths at the pipe surface.
must also
be
somewhat
expansion
in
the
material
types
flexible
pipe
(fibrous,
Of
metallic,
To seal a
fill all
of
the
The gasket material
to accomodate
joints.
the
the
four
movement and
major
elastomeric,
and
gasket
plastic)
only elastomers can satisfy both criteria. 1
The interior of a natural gas main is a harsh environment
for
an
methane,
and
elastomer.
tertiary
sulfides
(from
Some
butyl
the
of
the major
mercaptan
corrosive
(odorant),
deposits).
Most
of
elements
oils,
these
are
sulfates
corrosive
elements attack the sulfur bonds which serve to vulcanize most
elastomers into a usable solid material.
chemicals meant that the selected
Resistance to
elastomer had
to have
these
fully
saturated bonds. 1
To facilitate the elastomer selection process, a theoretical
baseline
baseline
seal
the pipe wall
internal
consisted
mechanical
of
by retaining
two
seal
hoops
bands.
A
of
was
conceived.
gasket
pressed
bridge was used
This
into
to span
the joint recess, see Figure 3.1.1
The
elastomer
selection
process
considered
a
number
of
important
material
properties.
sistance,
stress relaxation,
These
included:
creep, aging,
chemical
temperature
re-
range,
and gas permiability.
Stress relaxation is a reduction of the
stress
in
strain
both
a
material
under
under
constant
stress.
the
gasket
and
the
constant
The
while
recommended
membrane
The results are summarized
strain,
was
creep
elastomer
fluorocarbon
is
for
(Viton).
in Table 3.1.1
3.2.2 Surface roughness and cleaning methods
The development of a successful
quire
that
the
quantified.
with
a
and
each
run,
the free
signal
usually
the
valleys
root
should
visually.
was fed
about
the
be
felt
to
1
mean
be
believed
pipe
using
a
to re-
interiors be
cantilever beam
Strain gages were placed on the
to a
strip
of
chart
travel
(rms)
value
across
representative
of
the
was
valleys
and
pipe
peaks
Several
mean
and
For
the
calculated.
the
peaks
recorder.
deviation
was
First,
the
was
the
made
square
only
of
inch
noted.
Second,
were
end.
mean
from
factors
they
profilometer was
on
the
interior,
and
A
pin
beam,
surface roughness
seal
this
estimated
were
used
simplified
as
the
manual data reduction. 1
A number
interior
methods
was
(gpm).
tried
shards.
Water
at
were
2000 and
3000
sometimes.
sfpm
It
a
also created
would
have
effective
psi
A 4
5 gallons
psi was
(sfpm) usually removed
polished
dust.
Higher
the
hand
dusty, and
held wire
leaving
be
very
brush
sensitive
only
film
surface
cleaning
was
slow
and
rather
left
speeds
action.5
the
Chemical
ineffective.
lighter
scale,
cleaners were
The
of
An
It was
to balance and asperities.
removed
the harder deposits.
per
inch wire wheel with
hard
improved
at
abrasive grinding wheel was used with some difficulty.
effective,
the
cleaning
Sand blasting at 80
feet per minute
although
by treating
jet cleaning, with and without
effective.
surface
tested
The
It was effective, but dusty.
deposits,
7500
methods
pipe
It was
speed of 756
the
of
left bare metal.
tried.
a
cleaning
surface
an abrasive,
minute
of
A
always
found
effectiveness
to
of
-~
- ---
~111111
1~i I
in
Ii
each cleaning method is summarized in Table 3.2.1
The surface roughness produced by each cleaning method is
shown
in Table
which
result
3.3.
from
The wide
the
range
various
of
cleaning
surface
methods
roughnesses
is
obvious.
The smoothest surface is the most desirable one.
3.2.3 Sealability and elastomer hardness
For
an
elastomeric gasket
to
seal a
rough
surface,
the
elastomer must deform and flow into all of the surface asperities.
The ability to fill these asperities is affected by the
peak-to-valley
heights,
the
steepness
of
the
slopes
the peaks and valleys, and the elastomer hardness.
between
Hard elas-
tomers do not seal as well as soft ones, given the same conditions.
Thus harder elastomers
require higher compressive
stresses to force them into the surface asperities.1
The
rough
unusual
surfaces)
quantify
the
sealing
necessitated
elastomer
built,
see
Figure
an
hardness
stresses needed to seal
was
requirements
of
this
problem
experimental
approach
(durometer) and
various pipe surfaces.
3.2,
that
to
compressive
An apparatus
pressed a small
piece of rubber against a cleaned pipe shard.
rubber "gasket" are in Figure 3.3.
(very
rectangular
Details of the
Leakage out along the leak
paths was detected by a soap bubble solution.1
The geometry of the rubber gasket and pipe led to a nonuniform pressure distribution.
the
low pressure edges
Rubber cement was used to seal
rubber gasket, see Figure 3.3.
of the
Leakage
always occurred
cement.
The pressure distribution was approximated as
parabolic, varying only in
with
no
compressive
at the
the
stresses
inner edges
of
the rubber
being
circumferential direction and
at
the
measured compressive stresses required
edges.
Therefore,
to seal
the
the leak were
multiplied by a factor of 1.287 to adjust them. 1
The adjusted
leak paths are
compressive stresses necessary
to seal
the
shown in Table 3.4 as a function of durometer
and cleaning method.
The high compressive stresses which are
required for the rough surfaces left by water jet cleaning are
obvious.
the cleaning and sealability
the results of
Based on
the following recommendations were made. 1
tests,
1) The softest possible elastomer should be used.
2) Wire wheel cleaning has the best chance of success
because of low required gasket stresses and ease of
use.
3) Grinding wheels have similar required stresses, but
are harder to use.
4) Sandblasting is not recommended, it is too dusty.
5) Water jet cleaning is not recommended, it requires
too high a gasket compressive stress.
All
of the cleaning methods create dust
or debris which must
not be allowed to contaminate the natural gas in the main.
3.2.4 Baseline internal mechanical seal
To examine the feasibility
line
internal
of a mechanical
mechanical seal
design is shown in Figure 3.1.
seal,
a base-
design was developed.
This
The following assumptions were
made. 1
1) The pipe interior had been cleaned with a wire wheel.
2) The gasket material elastomer had a hardness of 30
durometer.
3) The nominal gasket compressive stress,
retaining band,
exerted by the
was 33 psi.
4) The gasket material was 0.25
inches thick.
5) The bridge material was an elastomer.
Because an elastomeric gasket degrades with time,
be
overstressed
lifetime.
initially
to
maintain
a
seal
for
it must
its
design
To accommodate property variations of the elastomer
required
15%
laxation
over
more stress
50 years
handle seasonal
than
the nominal
required
a
further
value.
10%
temperature variations required
Stress
increase.
reTo
that the ini-
tial gasket stress be increased to a final value of 46.7 psi.
The
retaining
joined ends
band was
assumed
to
be
(joining method unspecified).
a
metal
1
hoop with
The critical
fail-
__
I
I
I___
__I/
ure condition of the band was assumed to be elastic instability
or
buckling.
The critical
radial
load,
W
in lb/in,
is
related to the retaining band parameters by the following.
3EI
R3
The
required
section)
retaining
band
dimensions
for a 6 inch diameter
0.0625 in.
thick.
(rectangular
main were 1.0
in.
crosswide
by
The radial compressive load from the rubber
of 46.7 ib/in gave a tangential hoop stress of about 2000 psi
1
in the retaining band.
3.2.5 Alternative seal concepts
Rogers
which
also suggested
offered
potential,
suggestion was
to use
several
but
an
alternative seal
needed development.
expanded
elastomer
solid elastomer of the baseline seal.
rubber
has
a minimum
of 70
concepts
The
instead
first
of
the
Since fluorocarbon
durometer hardness,
the required
An
compressive stresses would be very large, see Table 3.4. 1
expanded elastomer, either open or closed-cell, is much softer
than
15
durometer rubber and
is
often
used
in
low pressure
sealing situations.
Foaming
polyurethanes
configurations.
gasket
with
were
suggested
for
two
possible
The first involved inflating cavities in the
the
polyurethane
foam.
The
expansion
would
produce the needed compressive stress in the gasket, a retaining band might or might not be used.
injected into the
joint recess.
The foam could also be
These concepts are shown in
Figure 3.4.1
Another
concept
was
to
use
beads of a less dense material.
stiffer
gasket
material
restrain
a gasket
containing
raised
The goal was to have the
the
softer
bead
while
the
bead provided the seal, see Figure 3.5.1
Gaskets
gested.
having
circumferential
ridges were also sug-
The first configuration had the ridge fitting into a
V-shaped groove machined around the pipe interior, see Figure
3.6.
Alternatively,
the
ridges
interior.
against the pipe
simply
be
could
pressed
could have
A soft material
been
installed between two ridges to improve the seal, see Figure
3.7.1
It was also suggested that a coating of sealant could be
applied
sealant
A properly designed
to the outer gasket surface.
(curing or
non-curing)
would be
to
used
improve
the
plugging of the leak paths while lowering the required gasket
compressive stress. 1
There
were
two
suggestions
which would have had the
for
retaining
band
necessary adjustability.
was to use an adhesively bonded lap joint.
designs
The first
The second was to
use a mechanical latching device with multiple stops, i.e.,
a
ratchet.
3.2.6 Power transmission
A short study was done to investigate methods of delivering power to a cleaning mandrel.
supply 0.25
hp
to a motor
mechanism.
For a hydraulic
Each method was assumed to
for driving
turbine,
a wire wheel
1.8
hp would
cleaning
have been
needed to pump 27.7 gpm of fluid either in or out through 1.0
in. i.d.
using
gas
hoses (several hundred feet long).
nitrogen gas,
to the turbine
9 hp would have
been needed
through similar hoses.
have been dumped into the natural gas
would have
For a gas turbine
to be explosion proof.
The
flow.
to pump the
exhaust would
Electric motors
But these
motors would be
small, flexible in use, readily available, and would require a
much
smaller
umbilical.
Consequently, electric
motors
were
recommended for use.
3.2.7 Summary
As
baseline
a
result
of
the
preliminary
internal mechanical
seal was
Achievable
stresses could
be used
joint.
was
that
It
concentrate on
recommended
minimizing
the
Phase
felt
II
research,
to be
the
reasonable.
to seal a cleaned pipe
further
cleaning
development
and
should
stress levels
--
- -------
I
--
required.1
The most promising concept was felt
panded elastomer as the gasket material.
to be using
an ex-
The seal would be
inserted into the main in a collapsed "U" shape.
This design
would minimize the cleaning and retaining band stresses which
would be needed.
The development of a sealant, to flow into
and fill the surface irregularities, was also recommended. 1
23
Table 3.1 : Recommended Elastomers for Seals.l
Elastomer
Common
Comments
Name
Gasket Material:
Fluorocarbon
Viton
Fluorosilicone
Epichlorohydrin
Hardness must be lowered by compounding, if possible
Resistant to fuels, high permeability,
set resistance must be tested
Hydrin
Silicone
Lowest 'ermeability, low temperature
use only (not with exothermic foam
systems); set and hardness must be
compounded/tested
Good set resistance, poor permeability,
must test effect of aliphatic gas/tar
on properties
Bridge Material:
Fluorocarbon
Viton
No Restrictions
Epichlorohydrin
Hydrin
Cannot Be Used with Foam System
Chlorosulfonated
polyethylene
Hypalon
Cannot Be Used with Foam System, Need
to Test effect of tertiary butyl
mercaptan
---
-----
mioIYIYYII
illl
----
, l
h
M110
m
Table 3.2 : Effectiveness of Cleaning Methods. 1
CLEANING METHOD
RESIDUE
RESII
RMOVED
REMA:
water at 3000 psi
X
at 2000 psi
X
water w/grit at 3000 psi
X
at 2000 psi
X
at 3000 psi at 1 in.
at 5 in.
X
X
X
by hand
X
grinding wheel
wire wheel
X
sand blasting
X
n l
Table 3.3 : Comparative Surface Roughness of
Cleaning Methods. 1
REPRESENTATIVE
ROUGHNESS NO.
d, /-in.
SAMPLES
DESCRIPTION
6000
3A, 2
3000 psi.
4800
LA (L)
2000 psi.
4880
4A
3000 psi.
3500
1A (R)
2000 psi.
hand wire brushing
4000
4B, 13
sand blasting
3200
wire wheel
2920
grinding wheel
2480
METHOD
water w/grit
water w/o grit
80 psi,
8 CFM
.
nMM
mIII
Table 3.4 : Estimation of Required Gasket Compressive
Stresses to Achieve a Seal. 1
CLEANING METHOD
RUBBER DUROMETER HARDNESS
15/20
30
40
60
Wire Wheel
33*
33
33
65
Grinding Wheel
33
33
33
65
Water Jet at
3000 psi
33
65
65
97
Water Jet at
3000 psi
w/grit
33
65
97**
Sandblast
33
33
65
130**
65
* Gasket Stresses are in psi that have been adjusted by a factor
of 1.287 as described in Section 7.5.4.
** Conservatively estimated.
Joint Recess
Gasket
IMaterial
Retaining
Band
Bridge
Material
Figure 3.1 : Baseline Internal Mechanical Seal.1
28
_
IYIIUlii
Radial
Arm Drill
Press Chuck
Aluminum
Block
Leak Locations
Rubber Bushing
-Support
Block
Cast Iron Pine Shard
Gasket Material
-
Gas Chamber
Lower Support Block
Gas Inlet
Dynamometer ""'
Figure 3.2 : Test Apparatus for Sealability Tests.l
Axial Direc tion
Elastomeric
Material
Cast Iron Pipe Shard
/---Cast Iron
Approximate
Leak Path
Pipe Shard
/
8
3
-in. Dia Hole
-
Approximate
Area Sealed
with Rubber
Cement
Gasket Area
-1.64 in2
Figure 3.3 : Details of Rubber Gasket Used for
Sealability Tests.1
--- -----
-----
-----
I
---------------I~I
i~/
/~~~I
Gasket with
Inflated
Compartments
Gasket with '
Uninflated
Compartments
a) Foam-Inflated Gasket.
Cast Iron
Pipe
Foam in
Joint Recess
Retaining
Bands
Gasket
Material
b) Foam in the Joint Recess.
Cast Iron Pipe
Gasket "
Material
0
Bridge
Material
Reinforced
Polyurethane
Foam
Elastomer
Tube
c) Unsupported Inflatable Gasket.
Figure 3.4 : Inflatable Polyurethane Foam Seal Concepts.1
Undensified
Bead
***
o*.
Figure 3.5 : Beaded Gasket Concept.l
Figure 3.6 : V-Groove Gasket Concept.l
-
--------
------------
UIhiI
---
Case Iron
Pipe
Soft
Insert
Retaining Band
Gasket Material
Molded
Ridges
Figure 3.7 : Ridged Gasket Concept. 1
CHAPTER 4
EVALUATION AND TESTING OF CONCEPTS
The initial research of the present author had to address
several
issues.
Cleaning of
Were
all
of
the
seal
concepts
viable?
the pipeline interior was clearly a major problem.
How much cleaning could be done with reasonable equipment in 6
and
8
inch pipe?
There
was
a
How much
need
for
quantitative
cylindrical pipe sections
expanded
needed
Finally,
to be
The
data
the
on
a
sealants
viable
on
for
require?
rates
for
The influence of
leak
design
seal
leak
instead of shards.
elastomers and
quantified.
cleaning should
rates
a
had
to be
retaining
band
found.
dominant
dependability.
theme
It
in
was
this
research
strongly
felt
was
simplicity
that
the
and
simplest
internal seal design would have the highest chance of success.
This concern for simplicity played a major role in many of the
design decisions which were made.
4.1
CONCEPT EVALUATION
Several
which used
concepts
seal
configurations were
foaming polyurethane,
suggested,
the
foam
see
suggested
Figure 3.4.
would
injection with a gaseous blowing agent
result
the
generate
cavity
the
needed
gasket stress
since
any
an
loads
would
cure
required
foam.
a
due
seal,
So,
the
stress.
to
all
of
in
foam would
the
initial
the cavity
structural
matrix
cannot
bear
structural
matrix
of
the
foam
Therefore,
high
the
stress-free
gasket stresses will
or by
By forcefully
polyurethane
But,
the
either
(typically Freon)
the gas pressure
polyurethane
itself.
to
the
gasket
would be
uncured
by
in
For
from
mixing the constituents inside the seal cavity.
filling
by Rogers
condition.
need high gas pressures
in
the
6
As the seal aged, the high pressure gas in the foam would
diffuse into the natural gas of
34
the main, and some natural gas
_~~I__
___I
_I
I
_
II
would diffuse into the foam. The result of the diffusion
would be a lowering of the gas pressure in the cavity. 7
As
the gas pressure lowered, the gasket stresses would start to
load and deflect the polyurethane structural matrix. The end
result would be a lowering of the gasket stress, independent
of gasket material stress relaxation, as the seal aged.
Because of the stress relaxation with aging as well as
the complexities and uncertainties of making a polyurethane
foam inside a seal cavity in a gas main, no further development of polyurethane foam seals was carried out.
The ridged gasket, using V-grooves machined into the
pipe, see Figure 3.6, would have required several pieces of
complex machinery.
First, a groove must be machined around
the pipe interior (which is often rough and not always
circular).
Dust control would require containment behind
sealing cuffs.
Precise control would be needed to carefully
position the seal ridges in the grooves. Finally, the stress
concentration in the relatively brittle pipe due to the
V-groove might lead to a failure of the pipe.
Because of the need for more complex machinery by this
sealing method compared to some of the alternatives, no
further development work on this concept was performed.
The
remaining seal concepts were carried forward for further
consideration.
4.2 CLEANING OF PIPE INTERIORS
The previous work of Rogers showed that cleaning the pipe
interior with a wire wheel had several advantages over other
methods. It would be easier to use because it is flexible and
produced a minimum of debris compared to sand or water grit
blasting. But, the dusty debris would require containment. A
wire wheel also produced a smoother surface.
ful seal was more likely and
Thus a success-
lower gasket stresses would be
required than with other cleaning techniques.
To
help
explore
the problems posed
by a wire wheel
cleaning system, some preliminary design was done.
The first
question raised was the size and number of wire wheels
used.
was
A wire wheel as large as the inner diameter of the pipe
ruled
bends
out.
Such
size
customer.
o.d.,
would
and obstructions.
service tap entrances,
By
using
inhibit
the
negotiation
of
Also, it would always pass over
leading
to dust contamination
two smaller wire
for the
wheels, about
1.0
in.
it would be easier to negotiate obstacles and avoid
taps.
service
directions,
By
rotating
torques on
or cancelled, making
and
to be
control.
the
wire
wheels
the cleaning mandrel
the cleaning mandrel
Accomodation
of
in
could
opposite
be reduced
easier to position
irregularities
in
the
pipe
radius would require either a soft wire wheel or a suspension
system.
Given the small size of the wire wheels and the high
rotational speeds needed,
while in use.
the wire wheels would be very stiff
Thus, a suspension system would be needed.
Because speed is important, it made sense
cleaning
mandrel
to move
the contamination
is
continuously.
Also,
at the bottom of the pipe,
to require the
since most
of
cleaning only
the bottom half would get most of the scale, allow the mandrel
to move faster, and leave the service taps undisturbed.
The
next requirement was some
form of sealing
system to
keep the dust generated by the wire wheels from contaminating
the natural
the
gas in
main.
The continuous movement of
the
cleaning mandrel dictated the use of flexible bristle skirts.
would provide a decent
These
skirts
would
have
to
be
seal
raised
to
The
over rough scale.
allow
the
mandrel
to
reverse.
These
preliminary
design
specifications
simple sketches for a cleaning apparatus.
in
Figure 4.1.
cleaning
in
a
These sketches
live
main
was
Sealing would be the main problem.
to
to
some
An example is shown
indicated
going
led
be
that wire wheel
very difficult.
There was also very little
space available for the required mechanism.
The complexity of
such
reliability.
a device was
not expected
to improve
The
other methods of cleaning promised even more difficulties.
Consequently,
it was obvious
that further seal
develop-
11WIY
W
IMil
m IIllhii
ment should focus on minimizing or eliminating cleaning of the
pipe. This could be done by using either expanded elastomers
as the gasket material, or a sealant to fill the irregularities of the pipe surface.
4.3 SEAL TEST RIG I
Early in the author's research, Dr. Fred McGarry of
M.I.T. was consulted.
He recommended the use of a thick,
fiber reinforced asphalt as a sealant.
Asphalt would not be
affected in a significant manner by the environment of a gas
main. By using a thick asphalt and fiber reinforcing, flow of
the asphalt would be minimized.
(Under constant stress, asphalt will "flow" like a viscous fluid to relieve the stress.)
Development efforts needed to be concentrated on selecting an
asphalt with an ability to fill the pipe surface irregularities without flowing excessively out from under the gasket
material.8
The sealability test apparatus built by Rogers, see
Figure 3.2, had provided a minimum of quantitative data.
It
did not give a realistic simulation of a gas main seal. A new
test apparatus was clearly needed to proceed with the development program.
Seal Test Rig I (STR I) was designed to provide quantitative data on leak rates so that the various sealing concepts
could be compared.
It used short cylindrical pipe sections
instead of the shards used by Rogers.
This allowed a better
approximation of pipe geometries and a more uniform pressure
distribution.
The other key feature was an elastomeric
diaphragm which provided controlled compressive stress on each
gasket material.
In this section the apparatus is described, typical test
procedures are outlined, test results on silicone sponge and a
silicone sealant are presented, and test results on fiberglass
reinforced asphalt are described.
are presented.
Finally, the conclusions
Description of apparatus
4.3.1
The
4.1.
test
It
used
diameter.
no.
section
The
is
actual
was
It
which was
from
was made
grooved
Figure
pipe
made
was
aluminum
in place
bonded
in
main
a
leak
and
from
with
a
The
in.
in
(model
reinforced
fabric
The endplate
plexiglass
window
The sealing
with silicone RTV.
path.
3
Inc.
from PVC plastic.
plate
Photograph
sections,
from aluminum as well.
to provide
4.2
by Bellofram,
made
The piston was made
fabricated
plate
gas
diaphragm was
4-250-250CAJ).
neoprene.
shown
The clamping ring was
two plates were clamped
together to maintain alignment.
When
port,
the
diaphragm
was
inflated by
the
high
pressure
the diaphragm exerted a compressive stress (equal to the
pressure
stress
axial
behind
the
diaphragm)
distribution was
and
because
believed
a
allows
gasket
the
to be
quantitative
material.
fairly uniform
directions.
circumferential
it
on
This
assesment
of
in
The
the
is
important
the
pressures
which are really needed to achieve a seal.
the natural gas
in a main.
By raising the
could be forced to leak out of the
paths
were
which
interface.
present
at
"gas" pressure, air
test section along any leak
the
By varying the diaphragm pressure,
relationship
between
"gas" leak rates
gasket
material
pressurizing
section.
a
relative
to
constant
pressurizing
the
leak rates
sighting
gas pressure
is shown
was
tube
supplied
of
the
main
to the
test
Leak rates were quantified by measuring the
(in
milliliters, ml)
tube, while maintaining a
the pressurizing tube
water
and
Leak rates were always measured at a constant "gas"
amount of water
main
stress
By maintaining a constant head of water in the
pressure, 6 inwg.
in
This allowed the
to be determined.
tube
tank,
the gasket
compressive
The water tank system used to measure
in Figure 4.3.
material
pipe-gasket
material compressive stress could be varied.
water
to simulate
"gas" pressure cavity was used
Air inside the
tank.
The
relative
water
which
added
over time
constant head of water
to the sighting
was
to the
added
to
tube of
the
the
pressur-
izing
equal
was
tube
the
to
at
gas,
constant
No correc-
the test section.
pressure, which leaked out of
to standard atmospheric conditions since
tions were made
The
been negligible.
correction factor would have
of
of
volume
advantage
this apparatus was its ability to measure very small
rates
at
"gas"
low
pressures.
the
leak
precision was about
The
2
significant figures in ml/sec.
constant
gas
pressure
in
the
system was
to
periods
long
for
section
test
The purpose of this constant
between leak rate measurements.
pressure
I which maintained
to STR
Later, a system was added
the
simulate
pressurized
natural
gas
which, in trying to leak past seals, may be causing some slow
displacement of
A schematic of the
the gasket materials.
constant gas pressure system is shown in Figure 4.4.
Valve #1
the desired
"gas"
throttled
the 5 psi air supply down to
pressure.
Valve #2 adjusted the amount of low pressure "gas"
which was vented to
"gas"
pressures
the room.
and
leak
This allowed a wide range of
rates
to
be
accomodated.
The
pressurized "gas" which was not vented would eventually get to
the
test section and leak out.
leak rates required that
Low
most of the "gas" be vented to the room.
The largest potential source of error with the apparatus
was
leakage past
To minimize any leakace at
interface.
interface
at
the gasket material
liberally coated
was
the gasket-diaphragm
this
the
vacuum grease.
silicone
with
junction,
The effectiveness of the vacuum qrease was checked by making a
simulated pipe section from a smooth aluminum tube of the
appropriate
section.
This
diameter.
The
diaphragm
was
tuhb
diaphragm was pressurized to 5 psi.
ft 3 /hr
was
quickly
the
test
to
the
pipe
material was used.
The
directly
seal1
surface with vacuum grease, no gask,*t
0.000016
in
was clamped
A negligible leak rate of
reached
in
indicated very good sealing, see AppeTnix D.
3
hours,
which
4.3.2 Test procedure
The typical test procedure was as follows.
meter
pipe
main.
section was
Usually the
plate was
out
of a
longer
pipe interior was
bonded with
sealed and
the pipe section.
cut
A 3 in.
specimen of
not cleaned.
After this had cured,
assembly
was
end
carefully
of
inserted
The Bellofram
into
the
pipe
The.test section
then clamped together and connected to the water tank
system.
psi
The
the gasket material
section inside the ring of gasket material.
was
gas
silicone RTV to one end
under test was inserted into the pipe section.
diaphragm
dia-
The diaphragm pressure was set as desired, usually 5
(which resulted in 5 psi compressive stress on the gasket
material).
The leak rate of the test section could now be measured.
Leak rates were measured as
follows.
pressurizing
water
tube
tube was more
sight tube.
was
the
than 6 in.
higher
level
than
in
the
pressurizing
the water level
in
(The extra height depended on the leak rate.
experimenter needs
cylinder at
till
Water was added to the
several
the top of
never more
seconds
to position
the pressurizing
than 12
in.,
the
The
the graduated
tube.
Total
height
and then only briefly.)
When
leakage brought the water level in the pressurizing tube back
to 6 in.
above
the water
level
in
the
sight tube
(this gave
the desired 6 inwg "gas" pressure in the water tank, which was
thus supplied
pressurizing
to the
tube
as
test section) water was added to
needed
to maintain
"gas" pressure in the water tank.
not
provide
a perfect
seal,
the
the
constant 6
the
inwg
If the gasket material did
leakage
during
a leak
test
would result in rising water levels in both the water tank and
the pressurizing
tube.
pressure differential
But,
could
by
be
adding
maintained
water a
to
constant
supply a known
quantity of "gas" at a constant pressure to the test section.
The leak rate was found by measuring the amount of water
added
during a
cylinder) and
test.
leak
test
dividing
it
(water was
by
the
added
time
a graduated
duration of
Time was measured with a stop watch.
40
from
The
the
leak
leak rates
were measured in milliliters per second, ml/sec, and then
converted to cubic feet per hour, ft3 /hr (1 ml/sec = 0.1271
ft3 /hr).
After the leak test the constant pressure system was
connected to the line between the water tank and the test
section. The continuous "gas" pressure was then adjusted to 6
inwg. The diaphragm pressure was left at its test value,
The apparatus was then left alone till the
usually 5 psi.
next leak measurement test. Time between tests was typically
1 day, but it ranged from several hours to several days. The
constant pressure system would be disconnected for the test.
In this manner the performance of the gasket material could be
measured over a long period of time.
4.3.3 Silicone sponge and sealant results
The first gasket material which was tested was silicone
The piece of sponge
sponge (closed cell, medium firmness).
was 1.0 in. wide by 0.20 in. thick (sanded down from 0.25
in.).
The sponge material used had 10% strain under 5.5 psi
The
compressive stress (measured in a stress-strain test).
material specifications can be found in Appendix A.
The pipe section which was used had been lightly scraped
with a spatula to remove some of the excess loose scale from
This had to be done to allow everything to
the pipe bottom.
fit inside the pipe section without having the diaphragm
directly compressing the sponge when the diaphragm was unpressurized. The pipe roughness was not measured.
The leak rate of "gas" past the sponge gasket material
was measured for several different values of sponge compressive stress (i.e., diaphragm pressure). The "gas" pressure was
6 inwg at all times. A plot of the leak rate as a function of
the compressive stress on the sponge is shown in Figure 4.5.
The leak rate was inversely related to the compressive stress,
as expected. At 5.0 psi compressive stress, the leak rate of
"gas" was 0.7 ft3 /hr.
The next test was done to determine the effect that a
41
sealant would have on the leak rate if it was used to fill the
leak paths
of
the
pipe-gasket material
interface.
pipe section and sponge gasket was used.
disassembled.
same
The test section was
Some silicone RTV sealant, see Appendix A, was
to the outside of the sponge gasket.
applied
The
The sponge was
then reinserted into the pipe, and the test section was reassembled.
After a
24
hour cure
the
leak rate was measured.
It should be noted that during the cure the "gas" pressure and
the diaphragm pressure were both zero.
shown
in
Figure 4.5.
very large drop in
sealant
had
At
5.0
The results are also
psi gasket
leak rate to 0.0045
obviously
filled many of
pipe-gasket material
interface.
stress
ft 3 /hr.
the
there was
The silicone
leak paths
This leak
a
in
rate was
the
much
smaller than the 0.25 ft3/hr from a typical leaking joint.
The test results are documented in Appendix D.
4.3.4 Asphalt sealant results
The first test used Type A asphalt which was fairly hard,
see Appendix A.
The gasket material was made by dipping a 1.0
in.
strip
by
0.2
asphalt.
of
of
fiberglass
mat
lb/ft 3 ) in
(2.9
hot
Fiberglass was chosen as a reinforcing fiber because
inertness and good wetting by asphalt.
its
fiberglass
when
in.
mat
cooled
was
not
to the
very
dense.
The
room temperature
This piece
impregnated
of
strip,
of 80 degrees F, was
placed in a pipe section which had been lightly scraped on the
bottom
with
a
to
spatula
provide
clearance.
The
Bellofram
assembly was inserted into the pipe section and pressurized to
5 psi.
days
"gas" pressure was applied.
No continuous
the
leak
rate was
measured.
It was
found
to
After 10
be
0.043
ft3/hr
at 6 inwg "gas" pressure.
The asphalt had apparently
not filled all of the surface irregularities.
Substantial
flow
of
the asphalt
had
occurred.
The
phalt gasket material was about one half its original
ness.
the
The cross-section was fairly uniform,
Bellofram diaphragm was
stress
field.
as-
thick-
suggesting that
indeed providing a very uniform
Small pieces were cut out of
42
the
deformed
asphalt gasket material from different areas.
These were
dissolved in solvent to see how much of the fiberglass mat was
in each piece.
The amount of fiberglass in each piece was
about the same.
The fiberglass mat was so thin that it was
slowly torn apart when the asphalt flowed. This mat therefore
could not restrain the flow of asphalt as much as was
necessary. A denser mat was used to provide more resistance
to asphalt flow for all of the subsequent tests.
Type A asphalt is much stiffer than many asphalts which
are available. Because of the results above, it was obvious
that a softer asphalt was necessary to fill the leak paths.
The subsequent tests were run to determine how effective
softer asphalts would be as a gasket material.
The second test used Type B asphalt, which was extremely
soft (a tacky residue was left on everything it touched), see
Appendix A.
The gasket material was made as above, except
that a much denser fiberglass mat (8.3 lb/ft 3 ) was used. The
seal was assembled, the diaphragm was pressurized to 5 psi.
No continuous "gas" pressure was supplied to the test section.
In this case the decrease in the leak rate over a number of
days was monitored, see Figure 4.6.
The leak rate decreased
roughly
linearly in the log-log plot.
The final value was
0.008 ft 3 /hr at 6 inwg "gas" pressure after 288 hours (12
days). The room temperature was about 80 degrees F during the
experiment.
Some of the leak rate measurements became erratic at
about 8 days into the test. The "gas" pressure was not immediately relieved after each leak test. Because of the low
leakage rates past the asphalt gasket, the seal was subjected
to a low continuous pressure while the "gas" pressure slowly
bled away. The leak rate on the eighth day was a lot higher
than it had been on the seventh day.
It was suspected that by
not relieving the "gas" pressure in the system, some asphalt
had been forced out of several leak paths by the low pressure,
thus raising the leak rate. For the remainder of the test the
"gas" pressure was relieved after each leak measurement. The
43
leak rate then returned to the linear reduction noted earlier
in the test.
the
of
Because
above,
noted
behavior
it
was
suspected
that continuous "gas" pressure, as of course it would occur in
The constant
use, might eventually lead to large leak rates.
pressure "gas" system was added to the test apparatus at this
Retesting the Type B seal with a continuous "gas"
time.
pressure of 6 inwg applied between leak rate measurements
After 44 hours, the
resulted in unacceptably high leak rates.
1.7
rate was
leak
a
to
subsequent
The
removal of
the
"gas" pressure allowed the leak rate to drop back
continuous
down
ft 3 /hr.
ft 3/hr,
0.004
level,
low
after
several
days.
However, just after the leak rate had been measured and while
there was still "gas" pressure in the test section, the water
in
level
very
dropped
tube
pressurizing
the
suddenly.
A
Remeasurement of the leak rate gave a value of 0.8 ft 3/hr.
very large leak path had been created by the "gas" pressure.
A second
specimen
the Type
of
B asphalt
and fiberglass
(8.3 lb/ft 3 ) gasket material was tested in the same pipe
The same procedure was used, except 6
section as the first.
mat
inwg
"gas" pressure was
immediately applied.
Initially
gasket material sealed fairly well, 0.005 ft 3/hr at 6
But, by 70 hours the
"gas" pressure after 7 minutes.
rate had risen to 0.96 ft 3/hr at 6 inwg "gas" pressure.
the
inwg
leak
The
room temperature was 85 degrees F.
Disassembly of the test sections revealed that very large
asphalt flows had occurred. The asphalt had been squeezed out
of
fiberglass mat.
the
irregularities,
against 6 inwg
Despite
filling
the pipe surface
the Type B asphalt would not hold a seal
"gas" pressure.
Because the room temperature
of 80 degrees F was within the conceivable operating range of
an internal joint seal, it was obvious that a thicker asphalt
would
be
needed
to hold a
seal while
under
"gas" pressure.
Subsequent tests used thicker asphalts.
A third test was run using Type C asphalt
stiffer
than Type B) as a sealant,
44
(a little
see Appendix A.
This
asphalt was tacky at room temperature.
The gasket material
was made in the same manner as previously, the denser mat (8.3
lb/ft 3 ) was used. The pipe section was the same one used for
the Type B asphalt tests described earlier.
The gasket was
installed in the test section,-the diaphragm assembly was
inserted, and the test section was clamped. The diaphragm was
pressurized to 5 psi.
The
leak
rate
showed
the expected decrease with time.
After 3 minutes (measured from when the diaphragm was
pressurized) the leak rate was 0.75 ft 3/hr at 6 inwg "gas"
pressure. After 24 hours it was 0.0019 ft 3 /hr, and at 42
hours it was 0.00032 ft3 /hr, both at 6 inwg "gas" pressure.
The continuous pressure system had been acting between leak
rate tests. The room temperature had been about 80 degrees F.
Disassembly of the seal after the test revealed substantial flow of the asphalt again.
The asphalt was again
squeezed out of the fiberglass mat by the compressive stress
which was exerted by the diaphragm.
It was concluded that
still thicker asphalt was needed.
A final test was run using Type D asphalt (thicker than
C, but a lot softer than A) as a sealant, see Appendix A.
This grade of asphalt was still slightly tacky to the touch at
80 degrees F. The gasket material was made in the same manner
as the Type B test, the denser fiberglass mat (8.3 lb/ft 3 ) was
used.
However, the impregnated fiberglass mat had an extra
layer of pure asphalt applied to it.
The pipe section which
was used was fresh and uncleaned.
The pipe section was
assembled as outlined previously. The extra asphalt layer was
installed so that it contacted the pipe surface. The intent
was to speed up the leak rate decrease.
The diaphragm was
pressurized to 5 psi.
The leak rate showed a very rapid decrease. After 5
minutes it was only 0.0047 ft 3 /hr at 6 inwg "gas" pressure.
After 26 hours, there was no discernable leak rate (observed
for 9 minutes).
The continuous pressure system had been acting between leak rate tests.
The room temperature had been
45
about 80 degrees F.
Disassembly
substantial
of
the
asphalt
seal
after
flow.
the
test
again
slowly
being
asphalt was
The
revealed
squeezed out of the fiberglass mat, although not as rapidly as
for
some
of
the softer asphalts.
Despite the asphalt
flow,
the excellent sealing job that this gasket material performed
was very encouraging.
The test results are documented in Appendix D.
4.3.5 Discussion of STR I test results
The
test results which were
summarized in Table 4.1.
obtained using
STR I are
The data clearly support the use of
a sealant to improve the sealing ability of a gasket material.
From the test results it was obvious that if asphalt was used
as a sealant, it would have to be mechanically constrained to
reduce
undesirable amounts
of
flow.
Silicone would also
benefit from being constrained, at least until it cured.
A
major goal
result
of
of
the
tests.
these
research program was
STR
I demonstrated
reached
that
as
the use
a
of
expanded elastomers and sealants could produce low leak rates
at
very
pipe
modest
sections.
compressive
Pipe
stresses
roughness was
in
poorly
now much
or
less
uncleaned
important.
Also, two different sealants, asphalt and silicone, were shown
to be viable choices.
tions
This would allow some major simplifica-
to be made for an internal mechanical seal and
its
installation hardware.
4.4 RETAINING BANDS
A mechanical
retaining band
serves
to
hold
in
In this way the
place initially and throughout the seal life.
sealant must act only to seal
the seal
leak paths and,
in particular,
it need not act as an adhesive.
This eliminates the adhesion
failures which
so
many
an
internal mechanical
have plagued
sealing
systems
in
the
seal
are
past.
The
critical
retaining bands
components.
of
The
simplicity
46
of
their
design
is
directly linked to the compressive stress levels that they are
required
to
exert
compressive stress
on
the
gasket
of
levels
material.
the baseline
eliminated many simple solutions.
The
seal
sealant
stress
cannot
levels
led
be
overstated.
to the
(46.7 psi)
The significance of the low
stress levels which were successfully used in the
a
high
This
successful
drastic
use
of a
tests using
reduction
thin
in
steel band
with a mechanical ratchet as a retaining band.
This section describes some
issues which
were of
natives, and some of
4.4.1 Retainin
parameters
they are
subjected
them.
These
the
retaining
of
installation
band based
alter-
the other designs which were rejected.
design
forces which
size
the steel
band issues
Crucial
install
importance,
of the retaining band design
forces
and
retaining
to and
affect
band
mechanism.
of
the
the
Appendix
B
the
bands
forces
are
needed
requirements
size and
contains
a
the
power
to
for
the
of
the
derivation
of
the static compressive force in a retaining band which results
from
the
radial
required force,
load exerted by
F (lb.),
the gasket
material.
The
is.
F = WR
Here W
is
is the radial
the
radius
of
load on the retaining band in lb/in and R
curvature
of
baseline internal mechanical
the
required
width.
compressive
the
seal, W
force was
band
= 46.7
140
lb.
The use of a sealant, based on the
gave a required compressive force of 15
in.).
in
inches.
lb/in,
per
For
the
R = 3 in.,
inch
of
band
results from STR I,
lb (W = 5 lb/in, R = 3
This is a significant drop.
A second issue was whether the retaining band should have
been rigid or springy.
A rigid band would be locked in place,
and
if
unable
to
expand
the
gasket
material
creeped.
springy band could expand as the gasket material creeped,
maintaining some pressure on the gasket.
only be
necessary if a
thus
A springy band would
significant amount
47
A
of gasket material
creep was expected.
sealant
The low stress levels allowed by using a
(resulting
in very
little
creep)
meant
that springy
bands were not needed.
4.4.2 Mechanical Ratchet Retaining Band
At
the
force
low
and
stress
levels
were
which
made
possible by the use of a sealant, steel bands offered a simple
An appropriate means
solution to the retaining band problem.
of
clamping
the ends
in
place
had to be found.
Three of the
possible solutions: a mechanical ratchet, adhesive lap joint,
and a spring, are shown in Figure 4.7.
The
selected
ratcheting
mechanical
because
of
its
was
end
favorable
which
the design
characteristics.
was
Such
a
band would be easily adjustable to a wide range of diameters.
The latch would not creep or decompose due to chemical attack.
The ratcheting mechanism is also fairly robust.
It is however
a rigid band.
The adhesive lap joint was eliminated from consideration
because the adhesive would have had to function
in a hostile
chemical environment while being under constant shear stress.
Contamination
during
installation
would
have
also been
a
problem.
The
spring end
than
attachment was abandoned
more
complex
the mechanical
have
the ability to be
wound
ratchet.
down
to half
because
it
was
It also did
not
of
its
installed
radius.
Several prototypes of a mechanical ratchet retaining band
were
made from
steel
in.,
9/16
wide),
in.,
easily wound
up
to
hose
clamps
(0.025
in.
see Photograph 4.2.
half
of
their
original
thick
diameter,
These bands
proved to be simple
and
free
subsequent
trouble
in
all
(see Chapters 5 and 6).
48
seal
0.56
They could be
Photograph 4.3.
were
and
see
to install
design
testing
The
buckling
stability
Rogers' analysis. 1
the
using
load (ib/in),
R is the band
E is the modulus of elasticity (30 x 106 psi for
steel) and B is
the band width
B = 0.5
0.030 in.
checked
EB
radius (in.),
in.,
was
] 1/3
Here W is the gasket compressive
2.75
bands
The required band thickness, t (in.), was.
3
[4R
t=
of
(in.).
For W = 5 lb/in, R =
the required band thickness is t =
in.,
The prototype bands
had a thickness of
t = 0.025
in. and had very large slots cut in them, greatly reducing the
moment
the
inertia
of
subsequent
of the band cross-section.
testing
the
bands
Yet in all
of
never collapsed,
even when
deliberate attempts were made to buckle the bands.
The most
likely explanation for this discrepancy was that the band was
constrained when
ginal
it was in place.
The analysis
in the ori-
reference was based on a curved beam loaded by a con-
stant
radial
loading
of
the
analysis
leads
The
not constrained.
This beam was
load.
to a buckling
failure
of
the
beam at much lower loads.
A property of the mechanical ratchet retaining band which
had
to
be
checked was
its
ability
to
produce an
acceptably
uniform compressive load around the pipe circumference.
was checked using
a 6 in.
This
diameter plastic pipe section.
A
ring of silicone sponge (0.25 in.
thick by 0.56 in. wide) was
the
A prototype retaining band
inserted
into
pipe section.
was used to compress it against the pipe wall.
The
pipe
distribution
circumference
of
was
the
compressive
measured
at
stress
several
around
the
The
locations.
strain of the sponge was converted to stress using the stressstrain curve in Appendix A.
4.8
for
values of
retaining
band circumferential
exten-
The desired stress level of 5 psi was easily achievable
sion.
with
two
The results are plotted in Figure
0.4
in.
extension.
The
large
fluctuation
between
two
adjacent stations was because the latch was between those stations.
The large amount of friction between the band and the
sponge meant
that
there was
little,
the band and the sponge except near
sliding precluded uniform
if any,
sliding
the latch.
load distribution.
between
The lack
This
of
was cured
by attaching small, axially aligned, metal strips to the inner
surface of
the subsequent seal prototypes, on which the bands
could easily slide.
4.4.3 Rejected alternatives
A possibility which was considered was a continuous steel
tape with compound curvature, see Figure 4.9.
by
inspired
deployed
from
allowing
it
measuring
steel
a
collapsed
It
tapes.
position
to pop into place.
by
Only
that
such
a design
did
not
have
would
simply
been
releasing
it,
low forces would be
required to handle and release such a band.
were
This design was
Its disadvantages
accomodate
varying
pipe
diameters and it would have required a substantial development
effort.
An
internal retaining ring was one of the retaining band
devices which was rejected.
An analysis by Timoshenko for a
ring
and
with
constant
curvature
uniform
radial
the exterior was used for a parametric study.8
found in Appendix C.
pressure
on
Details can be
The bulk of the analysis was done at the
high compressive stresses expected with the baseline mechanical
seal.
A typical plot
of ring pressure
ring radius is shown in Figure 4.10.
an
end
view
of
cross-sectional
such
a
height.
retaining
The
The figure also contains
ring,
major
as a function of
showing
problems
the
with
variable
retaining
rings were
that they had high section heights, several would
be
for
needed
distribution,
much
every
and
smaller than
joint
to
provide
the
they could not be compressed
the pipe.
The general
desired
load
to a diameter
conclusion
of this
analysis is that bending is an inefficient way to generate the
necessary gasket load.
A hinged retaining ring was also considered, see Figure
4.11.
Each ring would have 2 hinges and a ratchet.
allowed the ring to collapse into a smaller package.
This
Multiple
-
"-"---
-------
I
wlii
i'-
'
It was put aside because of
rings would have been required.
excessive stiffness and complexity of installation when
compared to a thin band with a mechanical ratchet.
Consideration had also been given to "garter springs",
They are normally used as part of an
see Figure 4.12.
external shaft seal where they are in tension and easy to
For use with an internal mechanical seal they would
handle.
Long springs are very unstable in combe in compression.
pression.
An attempt was made to install a long garter
spring, made from smaller springs, in a pipe section.
This
was unsuccessful because the spring was extremely difficult to
handle.
Based on the judgement that this problem would persist, garter springs were dropped from further consideration.
Table 4.1
: Summary of STR I Test Results.
Gasket
Time from
Material
Start of Test
Silicone sponge
Silicone sponge/RTV
Leak Rate
0.7
ft
3
/hr
24 hr cure
0.0045 ft 3 /hr
10 days
0.043 ft 3/hr
1:00
1.64 ft3/hr
(no "gas" pressure)
Type A asphalt
(no "gas" pressure)
Type B asphalt
(no "gas" pressure)
Type B asphalt
(6 inwg
"gas" pressure)
Type C asphalt
(6 inwg "gas" pressure)
Type D asphalt
(6 inwg "gas" pressure)
24:00
0.073 ft3/hr
96:00
0.021 ft3/hr
288:05
0.0077 ft 3/hr
0:07
3
0.0048 ft /hr
70:00
0.96 ft3/hr
0:03
3
0.75 ft /hr
24:00
0.0019 ft 3/hr
42:00
0.00032 ft 3/hr
0:05
0.0047 ft 3/hr
26:00
none detected
Notes:
1) All leak rates were taken at 6 inwg "gas" pressure and 5
psi gasket material compressive stress.
2) Whether or not the gasket material was subjected to a
continuous "gas" pressure of 6 inwg before and between
leak measurements is noted in the gasket material
column.
52
b-"Forward
Inflatable ring
to lift skirt
Pipe
Note: Suspension system is hidden behind the belt
drive housing in this view. A shaft drive
would be necessary to deliver power to the
gear box from the rest of the mechanism.
Figure 4.1 : Hypothetical Wire Wheel Cleaning
Mechanism.
SThreaded
Rod
F7TH
Sealing --
4-
Endplate
--
Window
Plate
Gt
Gasket Material
*
"Gas "
-
Piston
Pressure
Cavity
"Gas "
Pressure
Port
High
Pressure--
Port
Diaphragm
£7I)s
Grooves
S
Clamping Ring
Pipe
Figure 4.2 : Cross-Section of STR I Test Section.
_
1
IIIIII
~'^- IIIIIY
YIIIIIII
--
--
I~
To test
section
Barrel
Water
bath for
temperature
control
Water
level
Pressurizingtube
Sight tube
for water
tank
-
Water
level
-
Water
tank
Figure 4.3 : Water Tank Leak Measurement System.
S
Pressure gauge
To test section
Valve
5 psi
air
supply
#1
SValve #2
To water tank system
Vent to
atmosphere
Figure 4.4 : Schematic of Constant Pressure
"Gas" System.
55
3.0
2.5
2.0
SSponge
aQ 1.5
MSponge/RTV
1.0
0.5
0,0
0
2
4
6
8
10
Gasket Material Compressive Stress [lb/in 2]
Figure 4.5 : Leak Rates of Sponge and Sponge/RTV
Gasket Materials (STR I).
10 r
N
'a 0.1
0)
'a
.0
'a
0)
0
0.01
0%
0.001
10
100
Time from Start [hours]
Figure 4.6 : Leak Rate Decrease for Type B Asphalt
Seal, First Test, STR I.
1000
lK
a) Mechanical ratchet.
Sadhesive
b) Adhesive lap joint.
c)
Spring loaded band.
Figure 4.7 : Joining Methods for Retaining Bands.
0.50 in.
Extension
$'4
0
0.30 in. Extension
U
C)
u)
1
2
4
Station Number
3
5
6
Figure 4.8 : Compressive Stress Distribution in a
Sponge Gasket Material Created by the Prototype
Retaining Band.
aCross-section
Figure 4.9 : Steel Tape Retaining Band Concept.
50
40
(N
r-4
30
ho = 0.150 in.
$4
20
h o = 0.125 in.
'-4
.a
10
3.5
3.6
3.7
3.8
Outside Diameter of Ring [in.]
Figure 4.10 : Retaining Ring Applied Pressure.
3.9
Figure 4.11 : Hinged Retaining Ring Concept.
Garter
spring
Seal
Figure 4.12 : Garter Spring Retaining Band Concept.
62
j__ __
_
_1__1
Photograph 4.1
Photograph 4.2
: STR I Test Section.
: Prototype Retaining Bands.
__ _
Photograph 4.3 :Contracted Prototype Retaining Bands.
CHAPTER 5
INTERNAL MECHANICAL SEAL PROTOTYPES
The results of the tests with STR I had clearly shown the
advantages of using a
required compressive
sealant, was shown
reduce
viscous
tainment
which
till
was
sealant
stresses.
to work,
flow.
with
Soft
leak
I
require
not
containment
the
cure
the
noncuring
only require
However,
will
rates and
asphalt, a
sealants will
cured.
STR
lower
but would
Curing
they have
used
to
to
con-
silicone RTV
in
a
gas
main.
Research was done to find a suitable curing sealant.
While
ials
and
tests.
STR
I had been adequate
sealants,
A
it was
for
testing gasket mater-
clearly not
suitable
new test apparatus was built
for prototype
to simulate a gas main
so that curing and noncuring seal concepts could be evaluated.
The results from the tests using this apparatus are presented.
5.1 CHOICE OF CURING SEALANT
Silicone RTV
is
a
1 part
sealant which
vapor in the air to catalyse the
natural
gas
main,
on water
vulcanization process.
is almost completely dry,
referred to as RTV) will not cure
gas
relies
silicone RTV
in a gas main.
silicone would need a
catalyst
Since
(hereafter
To cure in a
other
than water
vapor to achieve vulcanization.10
Dr.
sulted
Pluddemann
on
silicones
this
silicones,
would
be
They
and
use
a
the
silicones
survive
Some
best.
for
of
both
separate
Dow Corning
needed
Brady
gas main.
probably work
vulcanizing
will
cure
of a
which
mendations.
Mr.
matter.
would
environment
and
has
Dow
felt
for
a
of Dow
catalyst
They
made
to
that
long
insure a
were
in
Corning's
for
no
con-
vulcanizing
time
the
2 part
vulcanization,
specific
done proprietary
pipelines.10,11
in this area
Corning
recom-
research on
Further
50 year life
research
for the
silicone selected.
Based on this
information, Dow Corning 3112 RTV Silicone
Rubber was chosen as having the typical properties of a 2 part
vulcanizing
silicone.
encapsulant.
Four
This
product
catalysts
are
is
normally used
available
to
as
adjust
an
the
working time from 1 minute to 80 minutes.
The standard S
catalyst gives a working
Working time is
defined
as
the
time,
time of 45 minutes.
after
catalyst
addition,
silicone rubber needs to triple its viscosity.
which
the
See Appendix A
for further details.
hand mixing worked
While
appropriate method
well
in
the
laboratory,
not
an
for
the automatic mixing of silicone elastomers
less mixer.
contains
for field use.
A motionless mixer
internal
vortex
is a motion-
is a section of tubing which
generators.
less than 0.5
The
in.
vortices
promote
Sizes
in diameter, which will
Motionless mixers will
inside of a main.12
is
A standard method
extensive mixing in the fluid forced through the tube.
are available,
it
fit
provide a simple
means of mixing a silicone sealant inside a gas main, if this
is found to be necessary or desirable in Phase III.
5.2 SEAL TEST RIG II
The STR I test section was clearly limited in its ability
to simulate the conditions in a 6 inch main.
This was recti-
fied by building a new test section which could use
sections
from 6 inch gas mains.
5.2.1 Description of apparatus
A
cross-section
section
also.
Seal
seal
is
The
new
prototypes
could
prototype
place,
water
shown
of
the Seal
in Figure
test
section
similar
now be
tested
retaining
had
the
II
important
baseline
internal
to
5.2
features.
mechanical
diameter pipe.
clamp the
the retaining cuffs of
the
test
5.1 and
several
in a 6 in.
system and
(STR II)
see Photographs
bands were used
thus compressing
tank measuring
to
5.1,
Test Rig
The
seal
in
the seal. The
constant pressure
system
of STR I were retained.
A flexible skirt was used to seal off the "gas" pressure
cavity.
Air at 6 inwg inside the "gas" pressure cavity was
used to simulate the natural gas in a main which would be
trying to leak past a joint seal.
The skirt was cut from a
large
Bellofram diaphragm
(model no. 4-550-337-FAJ)
of
neoprene coated fabric.
Since the skirt had originally been
cylindrical, triangular cuts had to be made to allow one end
to be clamped in the smaller sealing plate without overlapping
sections of the skirt.
The cuts were carefully sealed with
RTV. During every subsequent test the skirt was checked for
leaks with a liquid leak detector, Snoop.
The interface between the skirt and the seal under test
was a potential leak site.
The retaining band was used to
press the skirt into the top of the seal.
Liberal use was
made of RTV. This area was always checked with Snoop for
leaks.
The end plate was machined from aluminum. The plexiglass
window was sealed in place with RTV.
RTV was also used to
seal the endplate to the pipe section.
The clamps held the
plate in place till the RTV had cured.
5.2.2 Pipe section characteristics
All of the pipe sections used for the STR II tests were
taken from one half of a 5 foot long pipe section, which
contained a joint in the middle, that had been removed from
Con Edison's system.
A brittle brown scale coated the pipe
interior. The scale was thickest on the bottom, and much
thinner on the sides and top.
The size of the scale was
estimated by comparing it with several small painted glass
spheres which were 1, 3 and 5 millimeters (mm) in diameter.
At the bottom, the scale had a maximum height of about 3 mm
(0.12 in.), see Photograph 5.3.
The average height of the
scale was about a third of that.
On the sides and top, the
maximum height was about 1 mm (0.04 in.), see Photograph 5.4.
This scale was typical of Con Edison's system. 2
67
5.3 INJECTED SILICONE SEALS
felt that the sealing ability of a seal using
It was
silicone would be improved if more than a thin layer could be
used.
Consequently
cavity
into
the
which
silicone
sealant
seal prototype was
could
be
injected.
expected to provide plenty of sealant
given
This
a
was
to fill the surface
irregularities.
5.3.1 Seal geometry and fabrication
The Type 1 injected silicone seal which was used for the
STR II
tests
is shown
in cross-section in Figure 5.2a.
prototypes were made.
The retaining cuffs were made from the
same silicone sponge used earlier, see Appendix A.
0.25
in.
in. high by 0.6
thick
(1/32"),
Two
in. wide.
2.0
They were
The silicone sheet was 0.031
in. wide, and had a hardness of 30
durometer, see Appendix A.
It should be noted that Figure 5.2
is to scale in the axial direction, while the scale is doubled
in the radial direction for clarity.
The
were
first
made
2.0 in.
seal
from steel
long, 0.5
prototype
used
reinforcing
feeler gauge stock.
in. wide, and 0.030
strips which
These strips were
in.
thick.
The
second
seal prototype used 2024 aluminum for the reinforcing strips.
They were 2.0 in. long, 0.25 in. wide, and 0.020 in.
thick.
A beam bending analysis was done to determine the sealant
cavity
pressure
fail. 13
that
would
cause
reinforcing
strips
to
A strip was assumed to be a beam with fixed ends and
a uniform load distribution.
80%
the
of
the
neglected.
seal
The strips were assumed to cover
circumference.
The
silicone
sheet
was
A typical yield stress of 14.5 X 103 psi for the
2024 aluminum was used.
For a sealant cavity pressure of 10
psi and a beam length of 1 in. (the distance between retaining
bands)
the
yielding.
section
The
0.020
height
in.
had
thick
to
be
0.021
aluminum
in.
to
reinforcing
avoid
strips
were felt to be adequate since the sealant cavity pressure was
not
anticipated
to reach
10
psi.
An
advantage of
the thin
aluminum strips was that their deflection would provide a
visual
indicator
of
the
sealant
cavity
pressure.
The
deflection would also provide a reserve of pressurized sealant
to offset slight flow during curing.
An
injection
block
aluminum and a grease
was
fabricated
nipple,
see
Figure
from
a
piece
of
5.3 and Photograph
5.2.
The aluminum block was screwed to a piece of feeler gage
reinforcing strip. The grease nipple (for the grease gun used
to inject the silicone sealant) was screwed into the block. A
hole through the block and silicone sheet allowed the sealant
to be injected into the sealant cavity.
The seal was installed so that the injection block was at the bottom of the
pipe.
The seal prototypes were hand fabricated in a 6 in. diameter plastic pipe section.
The retaining cuffs were cut to
length in the pipe.
The ends were bonded together with RTV
and allowed to cure.
bonded to
The silicone sheet was
the silicone sponge
cut to size and
retaining cuffs.
The axial
reinforcing strips and injection block were then bonded to the
sheet with RTV.
A V-groove for the vent, at the top of the seal, was cut
and a small aluminum channel was bonded into it to provide a
flow restriction while preventing collapse of the vent by the
compressive load exerted by the retaining bands.
5.3.2 Test procedure
The pipe section for the test was cut using a cutoff saw.
Care was taken to preserve the pipe scale as the saw blade
typically knocked off the scale next to the cut.
The pipe
section was prepared by sealing and clamping
place. The pipe interior was not cleaned.
The
section.
fabricated
seal
was
popped
The skirt was coated with RTV.
bands were clamped into place.
snap
0.4
from a snug fit.
place
in
pipe
The two retaining
The bands were extended
From Figure 4.8 this
produce at least 5 psi compressive stress in
69
the
This was done using a pair of
ring pliers with offset pins.
in.
into
the endplate in
is seen to
the silicone
The RTV was allowed to cure.
sponge retaining cuffs.
The continuous pressure
system was connected and 6 inwg
"gas" pressure was applied to the "gas" pressure cavity.
The
3112 silicone was hand mixed using a 10:1 ratio of silicone to
type S catalyst for a working time of 45 minutes.
It was then
loaded into the grease gun. During injection of
the silicone
into
the sealant
that
it
silicone
cavity,
remained
at
the
6
"gas"
inwg.
sealant was seen
pressure was adjusted
Injection
to be
coming
was
from the
so
halted
when
vent.
The
grease gun was quickly cleaned up for later use.
The
leak
constant
rate
test
pressure
was
started
system.
The
by disconnecting
leak
rate
could
then
the
be
measured with the water tank system by the method described in
section 4.3.2.
inwg
"gas"
The leak tests were always conducted at 6
pressure.
After
the leak
test the continuous
pressure system was reconnected so as to provide a constant 6
inwg "gas" pressure till the next leak test.
5.3.3 Test results
The
insertion
trouble free.
slightly
edly,
Seal
#1
into
the
pipe
section was
The wide steel reinforcing strips made the seal
stiff
fashion.
of
in
bending.
The width of the
Deformation was
in
a segmented
reinforcing strips, not unexpect-
caused the compressive stress in
the retaining cuff
to
vary across the width of the strip after the seal was clamped
into place.
The average retaining cuff compressive stress was
about 5 psi.
The
retaining cuffs conformed very well
to the
pipe surface irregularities, crushing much of the scale.
steel
reinforcing
strips
did' not
deflect
visibly
The
during
injection.
A question which needed to be answered was whether or not
the
"gas"
pressure
would
create
leak
paths
in
the
silicone
after injection, but before the silicone had had a chance
cure.
Accordingly, Seal #1
the silicone
injection
was tested twice.
had ended,
the
leak
be 0.0059 ft 3/hr at 6 inwg "gas" pressure.
70
to
One hour after
rate was found
to
The seal had been
subjected to continuous
"gas" pressure from before injection
till just before the leak test. The continuous "gas" pressure
was reapplied after the leak test.
The next day (28 hours
after injection) the leak rate was found to be 0.0055 ft 3 /hr
at 6 inwg
"gas" pressure.
The silicone was
before this second leak test.
not affected
fully cured well
The "gas" pressure had clearly
the seal while the silicone was
the quality of
curing.
The
seepage
seal
was
inspected after
had occurred
out from
the
leak
tests.
Some
under
the retaining cuffs,
similar to Photograph 5.2, most of it near the bottom of the
seal where the crushed, rougher scale had left slightly larger
unplugged leak paths.
The silicone in the sealant cavity had
molded
very well
to
the scale
on
the pipe wall,
similar to
Photograph 5.5.
The sponge retaining cuffs had also deformed
around a few small burrs.
The
proved
narrower reinforcing strips
the
flexibility
of
the
seal.
of
Seal
#2 greatly
Insertion
was
im-
trouble
free.
The stress distribution under each strip was more
uniform.
The seal now deformed in a much more continuous
manner. The retaining cuffs again crushed the pipe scale and
conformed
to
the
pipe
surface.
The
reinforcing
strips
deformed slightly near the end of the silicone injection, the
deformation was in the bottom half of the seal. Seepage after
injection allowed the strips to flatten back out.
One
the
in-wg
hour after
leak rate
of Seal
"gas" pressure.
before
the
reapplied.
flow rate of
Figure 4.4,
the silicone
test.
#2 was
The
sealant
found
had
been
to be 0.014
ft
injected,
3
at 6
"gas" pressure had been maintained
After the
test,
The next day, after
the
"gas" pressure was
the silicone had cured,
"gas" vented to the atmosphere by Valve
was the same,
/hr
indicating
were created while the sealant cured.
again.
that no
the
#2, see
new leak paths
The seal was not tested
Post-test inspection again turned up seepage, see Photograph 5.2, mostly at the bottom of the pipe. The silicone had
71
also molded well to the pipe scale, see Photograph 5.5.
The
test results are summarized in Table 5.1,
and docu-
mented in Appendix D.
5.4 ASPHALT SEALS
To provide a solid basis for comparing the effectiveness
of asphalt as a sealant to injected silicone it was necessary
to test the asphalt in a similar seal geometry.
Because the
injection of hot asphalt into a sealant cavity would have been
difficult,
the
asphalt
was
applied
at
room
temperature.
Asphalt-impregnated fiberglass was placed into a sealant cavity before the seal was
ably
different
silicone,
from
it was an
installed.
the
While
procedure
this was consider-
used
for
option which needed
the
to be
injected
tested
for
applicability in a gas main.
5.4.1 Seal geometry and fabrication
The
The
same asphalt seal was used for two different tests.
seal
silicone
cross-section
retaining
silicone).
The
is
cuffs
cuffs had
shown
were
in
Figure
used
a hardness
5.2b.
Solid
from
(molded
3112
of about 60 durometer.
The considerably harder material, compared to sponge, was used
to
the
investigate
sealing ability.
about 0.5
influence
of
cuff
retaining
hardness
on
The retaining cuffs were 0.20 in. high and
in. wide near the silicone sheet.
The silicone
sheet between the retaining cuffs was the same material used
for the injected silicone seal,
it was
2.0 in. wide.
aluminum reinforcing strips were exactly like
the earlier injected silicone seal
tests.
ratchet retaining bands were used.
The
those used
for
The mechanical
There was no vent nor
injection block.
Both
performed
asphalt
tests
used
the best in the
the
Type
D
STR I tests,
asphalt, which
had
to impregnate the
fiberglass.
However, the tests used different fiberglass
reinforcing.
Test
#1 used a 1.0
in. wide by 0.20
strip of the denser fiberglass mat (8.3 lb/ft3).
in.
thick
Test #2 used
two long strips, 1.0 in. wide, of woven fiberglass cloth,
Appendix A. This was done to investigate an alternative
the stiff fiberglass mat material which had been used up
then.
It should be noted that the mat for Test #1 had
extra layer of pure asphalt on one side.
see
to
to
an
A potential problem which was raised during discussions
on asphalt as a sealant was excessive flow.
Asphalt is a
visco-elastic material.
At low stress levels it can behave
like an elastic material, by elastically deforming while under
stress.
At some higher stress level, which depends on
temperature and asphalt grade, the asphalt will deform like a
viscous fluid by flowing to relieve the stress.
Given that
stress levels of several psi were anticipated on the asphalt,
a means beyond using retaining cuffs needed to be found to
reduce the asphalt flow which was expected (the asphalt in the
STR I tests had experienced too much viscous flow).
The best means of stopping viscous flow through an
interface is to physically block the leak paths. Small, solid
spheres mixed into a fluid would be convected to the leak
paths by the flow.
If the spheres were not too small, they
would plug up the entrances or passages of a leak path. This
would lower the flow rate of the fluid and raise the pressure
level which would be required to force the fluid down the
plugged leak paths.
A mixture of aluminum spheres, 0.025 in. in diameter, and
Type D asphalt was made.
To test the effectiveness of the
spheres in plugging leak paths, a cylinder with a long, thin
slot (0.5 in. by 0.015 in.) was used.
Asphalt inside the
cylinder could be pressurized by a piston loaded with weights.
The flow of pure asphalt was compared to a mixture of asphalt
and aluminum spheres.
The aluminum spheres were very
effective in reducing the flow of asphalt, producing nearly a
10 fold reduction in the flow of asphalt out of the slot.
For maximum effectiveness,
the mixture of aluminum
spheres and asphalt was placed on the edges of the impregnated
fiberglass. This is shown in Figure 5.2b and Photograph 5.6.
The
around
impregnated
the
seal
nated strip
mat
cavity.
for Test
#2
for
Test
#1
The
ends
were butted.
was
wrapped
was wrapped several
only
The
times
once
impreg-
around
the
seal cavity.
The
seal
was
hand
fabricated
and
bonded
together
with
diameter pipe, see section 5.3.1.
RTV in a 6 in.
5.4.2 Test procedure
tests were prepared
The pipe sections for the
manner as
those
for
the
injected
silicone
the
mat was kneaded prior
in the same
tests,
see
section
5.3.2.
For Test
loosen
#1
it up.
was
put
on
on
the outside of
one
side.
wrapped around
into the mat.
the mat, a
After
the
seal and
the
worked together.
then
to
A high asphalt temperature was necessary to get
good penetration of the asphalt
no asphalt
to impregnation
cut
this left
layer of pure asphalt
strip
to
Since
had
cooled,
length.
it was
ends were
The
The aluminum spheres and asphalt mixture was
applied to the edges
of the mat.
The seal was now ready
for installation.
For
asphalt
on the
Test
#2
the
temperature,
fiberglass.
removed
and
aluminum
the
spheres
strips
which
were
resulted
impregnated
in
a
thick
at
a
lower
asphalt
layer
After cooling, the unimpregnated ends were
strips wrapped
and
asphalt
around
mixture
the
was
seal
then
cavity.
The
applied.
The
seal was ready for installation, see Photograph 5.6.
The
seals
section.
The
clamped
into
was
measured
applied
6
were
deformed
to
be
installed
skirt was coated with RTV and
place
with
the
immediately.
inwg
"gas"
the
retaining bands.
The
pressure
continuous
whenever
leak
in
the
seal was
The
leak
pressure
tests
test
then
rate
system
were
not
being run.
5.4.3 Test results
During
stiffness
Test
and
#1
the
tackiness
seal
of
was
hard
the asphalt
to
install
mat.
Some
due
to
the
effort was
needed to keep the ends of the mat together. The seal had to
be pushed into place a bit because the seal was a bit larger
in circumference than the pipe was (this is more desirable
than a gap) and the mat did not readily shrink in circumference. The room temperature was about 80 degrees F.
There was too much asphalt in the sealant cavity.
This
led to large deflections of the reinforcing strips and poor
contact between the retaining cuffs and the pipe.
Because
asphalt is incompressible, the retaining bands could not be
extended more than 0.2 in.
Most of the deflection that
occurred was to push the retaining cuffs around the sealant
cavity.
The solid silicone retaining cuff did not conform to
the pipe.
Problems were encountered in sealing the skirt. Several
days were required to achieve a good seal at the skirt. After
167 hours the leak rate was 0.022 ft 3/hr at 6 inwg "gas"
pressure.
This was the first good measurement, the test was
terminated.
Some seepage of the aluminum spheres and asphalt mixture
from under the retaining cuffs occurred immediately after
installation, similar to Photograph 5.7.
After several hours
the flow ceased. The flow led to a noticable drop in the
compressive load on the retaining bands. Disassembly revealed
that aluminum spheres had been trapped under the retaining
cuff, some were still inside the completely filled sealant
cavity.
For Test #2 the seal was refurbished before it was used.
The seal was a little
easier to install
due to the lower
bending stiffness. Less effort was also required to push the
seal flush against the pipe. The room temperature was 80
degrees F.
Problems were encountered in getting good contact between
the pipe and retaining cuffs. The mixture of aluminum spheres
and asphalt resulted in 2 small ridges running around the seal
at the edges of the sealant cavity, see Photograph 5.6.
The
retaining bands bent the seal around these two ridges.
75
Retaining
band extension
was only about 0.2
in.
The
solid
silicone retaining cuffs did not conform to the pipe.
Problems were again encountered with
The best
seal which could
leakage at the skirt.
ft
3
/hr
at 6
inwg
sealing the
skirt.
be achieved had a small amount of
After 119 hours the leak rate was 0.043
"gas"
pressure.
The
test
was
terminated
2
days later after the skirt leakage had increased.
Some flow of the aluminum spheres and asphalt mixture out
from under the retaining cuffs occurred again for a few hours
after installation, see Photograph 5.7.
The flow again led to
a noticable drop in the compressive load on
bands.
Disassembly
revealed
aluminum
the retaining
spheres
retaining cuffs and inside the sealant cavity.
pocket, 3 in.
the
sealant
under
the
A shallow air
long by 0.75 in. wide, was found at the top of
cavity next
to
the silicone
sheet
of
the
seal.
Not enough asphalt had been put into the sealant cavity.
The
test
results
are
summarized
in
Table
5.1
and
documented in Appendix D.
5.5 DISCUSSION OF STR II RESULTS
The
leak
injected
silicone
seals
rates of 0.006 and 0.014
performed
ft 3 /hr
very well.
The
compared favorably with
typical joint leak rates of 0.25 ft3/hr.
The use of a sealant
cavity allowed plenty of silicone to be available to fill
surface
irregularities.
The
flexible
aluminum
the
reinforcing
strips provided pressure that continued to force the silicone
into the scale even after injection.
The compliant retaining
cuffs performed as expected by crushing and conforming
to the
pipe scale.
The
asphalt seals did not perform as well.
rates of 0.022
use
of
sealant.
and 0.043
a sealant cavity
But,
the stiff
ft 3 /hr
The leak
were not as acceptable.
had provided
a useful
retaining cuffs
reservoir
The
of
did not allow full
advantage to be taken of the available asphalt since the cuffs
did not
conform to
the pipe surface
the leak paths through the scale.
76
to minimize
the size
of
the
sealing
test
section was used
this chapter
test results in
(the
time
each
the skirt worsened
problems with
The
The
are presented in the order in which they were done).
It
minimum measured leak rate got higher with each test.
should be pointed out that any leakage at the skirt would be
measured by the leak test. Therefore, it is entirely possible
the actual
that
smaller than the measured leak rate.
For the asphalt Test #2,
There may have been leakage for each
this actually happened.
(getting worse with
test
interface was
leak rate at the seal-pipe
each
subsequent
seal
This
test).
the asphalt
factor must be considered when the leak rates of
seals are compared to those of the injected silicone seals.
A feature of the asphalt seal prototype which degraded
sealing performance was the prefilled sealant cavity.
Injection into a sealant cavity after seal installation allows
the
retaining cuffs
the
the pipe scale,
to crush and conform to
establishing a mechanical support of the retaining band load.
With prefilling, the sealant is being forced out from under
the cuffs are trying to crush the
the cuffs at the same time
scale.
This
support
of
least
produces, at
the
retaining
with subsequent flow.
band
fluid
partially, a
load
which
be
can
pressure
dissipated
This sealing problem is exascerbated by
the need to slightly overfill the sealant cavity to achieve a
seal.
problem
Another
prefilled
with
sealant
cavities
estimating how much sealant to place in the cavity.
uncleaned
will
joints
require
will
varying
have
slightly different quantities of
achieve a seal.
cuffs.
Different
scale,
which
sealant
to
Too much sealant will result in small to
nonexistant contact pressure between
the pipe.
of
amounts
is
the retaining cuffs and
This will lead to excessive asphalt flow under the
The
flow will lead
to a reduction
in compressive
stress on the asphalt, because the rigid retaining bands used
cannot expand to continue to apply compressive stress when
high sealant flow occurs.
to
continue
blocking the
The sealant will
then be less able
leak paths against
"gas" pressure.
Too
little sealant
pockets.
the sealant
in
cavity will
The resulting low compressive stress on the sealant
the leak paths
will not be able to force the sealant into
seal
result in air
them up.
either.
to
The seal will probably leak as a result of
It should be noted that Test #1 was overfilled while
Test #2 was underfilled.
It
should
be
pointed
out
that
the
problems
which were
experienced with the asphalt seal will be typical of any seal
which
uses a prefilled sealant
sealant
is curing
harder
to
make
Transportation
may
have
cavity.
or non-curing will
a
seal
for
the
of a prefilled
Sealant
reasons
quantities
it will
outlined
the
inside
have
to
of a
be
controlled to avoid the problems mentioned above.
be
above.
to avoid contaminating
will
the
or not
not matter,
seal down
to be carefully done
sealant.
Whether
main
the
carefully
While these
problems are not insurmountable, they do not exist for a seal
which uses an injected sealant.
The
with
performance
two
changes
of
to
the
asphalt
the seal
design.
cuffs should be more compliant.
injected
into the
the pipe.
seal
after
The asphalt would
(temperature
control would
seal).
aluminum
The
seals
could
First,
be
the
improved
retaining
Second, the asphalt should be
the
seal
has been clamped
into
have to be heated to allow this
to
be critical
spheres
could
be
the success
mixed
of
the
in with
the
asphalt.
The
aged
the
asphalt
fault
test results
injected silicone
further development of
seal
of
for the
the
did
not perform as
seal,
not
the
this
well,
seal
concept.
this
sealant.
was
encour-
While the
largely the
Asphalt works as
sealant, but it will require hot injection.
The asphalt will
also be much more sensitive to temperature than silicone.
these
reasons,
asphalt
is
felt
to
be
an
a
ideal
For
fallback
solution if unanticipated chemical problems should arise with
the use of a silicone sealant.
---- '--
--
I
M IIII
41110
1,1I,I
,
,I
I
1
III
Y I1
Table 5.1 : Summary of STR II Test Results.
Time from
Seal1
Start of Test
Leak Rate
Type 1 silicone
Seal #1
Seal #2
2:15
0.0059 ft 3 /hr
28:20
0.0055 ft 3 /hr
1:00
0.014 ft 3 /hr
Asphalt
Test #1
(mat)
167:40
0.022 ft 3 /hr
Test #1
(tape)
119:10
0.043 ft3/hr
Notes:
1) All leak rates were at 6 inwg "gas" pressure.
2) All seals were subjected to 6 inwg "gas" pressure
continuously.
79
"Gas"
Pressure
Port
Retaining
Cuffs of Seal
Window
Figure 5.1 : Cross-Section of STR II
Test Section.
--- ---- ---
--
11111
Sealant
Cavity
Retaining
Bands
Reinforcing
Strips
Z
Sheet
"
. .;::
. .
Pipe
'
Sponge
Retain
ing
-Cuffs
Radial
Direction
a) Type 1 Injected Silicone Seal.
Axial Direction
-Sealant
Cavity
Retaining
Band s
Reinforcing
Strips
I1
Sheet
,C
\
\~
~
\
\\
\
\'il
Solid
Retaining
Cuffs
Pipe
Aluminum spheres
and asphalt mix
b) Asphalt Seal.
Figure 5.2 : Seal Prototypes Tested in
STR II.
Note: The drawings are to scale in the axial direction.
In the radial direction the scale was doubled for clarity.
Axial View of Seal
Figure 5.3 : End View of Type 1 Injected Silicone Seal.
82
T
4
Photograph 5.1
Photograph 5.1
: STR II
Test Section and Apparatus.
STR 'II Test Section and Apparatus.
Photograph 5.2 : STR II Test Section, Type 1 Injected
Silicone Seal, Seal #2.
OIL-
mm
---
-------
H-
0
(D
N
()
tn
0(1
(D
H-l
cD
In
-c
0
0
rt
O
----
_
-
-,
r
(l
0I-,.
'
0
0
rt
U-.
-
,.
__,,
h
I*r~C~e
~e~s
7
Photograph 5.5 : Removed Type 1 Injected Silicone Seal
Showing Molding Ability of the Sealant, STR II,
Seal 42.
Photograph 5.6
: Asphalt Seal,
..
.,
Test =2.
r'
Photograph 5.7
Test #2.
: Seepage From Asphalt Seal,
86
STR II,
--
--
-
________________________il
IE
I
I*
CHAPTER 6
INJECTED SILICONE SEAL JOINT TESTS
The results of STR II were encouraging, especially the
injected silicone seal tests.
To really prove the sealing
ability of an injected silicone seal, it needed to be tested
in
a
real joint under controlled laboratory conditions.
Discussions of the problems involved in sealing field
joints led to the development of two seal concepts based on
the configuration tested with STR II.
To accomodate some of
the
uncertainties in sealing pipe joints, each concept
addressed a slightly different set of priorities.
The joint
tests were done to clarify the design choices involved.
The need to use injection with an asphalt seal, which had
been demonstrated by the results of STR II, would have required substantial further development to implement correctly.
Consequently, the decision was made to only proceed with
silicone for the joint tests. However, the ability of asphalt
to survive in a natural gas main makes it an ideal fallback
solution should unexpected problems arise with the silicone
sealants.
6.1 SEAL GEOMETRIES
The first seal to be tested in a joint was the Type 1
injected silicone seal, see Figure 6.1a. The seal design and
materials were unchanged from the STR II tests. This seal was
intended to be installed with the sealant cavity spanning the
joint recess. The intention was to fill as much of the joint
recess with sealant as possible.
The sealant would then
function as a labyrinth seal, forcing any leak paths to be as
long as possible.
The grease nipple was installed on an
extension to the injection block to allow the silicone to be
injected from outside the test section. Three vents were used
at the top of the seal instead of one. The seal was hand
fabricated, see section 5.3.1 for details.
87
The
other
seal
configuration
which
was
tested
Type 2 injected silicone seal, see Figure 6.1b.
connected by an
essentially two Type 1 seals
bridge spans
bridge.
The
injected
directly into
design
is
to
joint recess.
the
minimize problems
risk of blowing out the
the
injection.
joint recess,
the
related
is
goal
of
not
this
flexure and
during sealant
The sealant cavities were separate, each one was
served by its own injection block
Three
is
elastomeric
joint
joint packing
the
This seal
silicone
The
to
was
vents
at
bridge was
the
0.87
top
in.
of
wide,
the
(extensions were used).
seal served
the whole
each cavity.
seal was 4.5
in.
The
wide.
The
The other seal dimensions can be found from Figure 6.1b.
minor differences
in
compared
to
the Type
ficant.
The seal was
retaining cuff and
1 seal
were not
sealant cavity width
expected
to be
signi-
hand fabricated by the same methods as
the Type 1 seal.
6.2 TEST JOINTS
The joints which were used became
the
test sections.
This joint test section replaced the STR II test section.
The
rest
and
of
the
leak
measurement
apparatus,
the
water
tank
constant "gas" pressure systems, was not changed.
The joint used for the Type 1 seal test was a field joint
removed
from Con
Edison's
system,
see
Photograph
6.1.
The
scale on the pipe interior was the same as the scale described
in
section 5.2.2, see Photograph 6.2.
not cleaned for the test.
leak,
The pipe interior was
Since the joint as received did not
it was made to leak by removing the external mechanical
clamp and drilling holes
through
the
lead packing
joint, yielding a leak rate of 2.0 ft 3 /hr.
into a closed test section
of
the
The joint was made
by bonding a plexiglass window
to
the Type
by
each end.
The
"joint"
used
for
2 seal
test
was made
cutting a section of pipe in half, see Photograph 6.3.
Since
the joint recess would not be filled with sealant, the lack of
an actual
joint recess would not affect
88
the results.
The
scale on the pipe interior was not quite as rough as the above
joint, see Photograph 6.4, even though they came from the same
pipe section.
The pipe interior was not cleaned.
Plexiglass
windows were again used to create a closed test section.
6.3 TYPE 1 INJECTED SILICONE SEAL TEST
Because
similar
the
test procedures
for
to the procedures used for STR
this
II,
test were
very
they will not be
mentioned in detail here.
The seal was installed and clamped with no problems.
bands were tightened 0.4 in.,
pipe scale.
ft3/hr
crushing and conforming to the
The second plexiglass window was bonded into
place with RTV.
2.1
at
Prior to injection
6
inwg
"gas"
the seal with
the
the usual
the
joint
pressure.
sealant was prepared as usual.
out of
The
The
leak rate was
3112
silicone
The sealant was injected into
6 inwg "gas" pressure trying
test section.
There was
to leak
some deformation of
the
aluminum reinforcing strips at the bottom of the seal near the
end of injection.
The strips flattened out with the seepage
which occurred after injection.
One
hour after injection a leak test was run.
could be detected.
No
leak
The test section was left connected to the
water tank for 11 days.
During this
time
the
"gas" pressure
in the joint rose to 8 inwg and remained steady.
No leakage
was detected during this entire time.
Inspection of the seal reveale-I minor seepage of silicone
out
from under
seepage was
the retaining cuffs,
evident
joint was sectioned
in
recess,
holes
the
of
lead packing.
No
The
extent of silicone flow
The silicone h~?
the bottom and side
Photograph 6.6.
irn
to determine the
into the joint recess.
joint
the
see Photograph 6.5.
completely filled the
the
joint are
shown
in
The results are summarized in Table 6.1 (see
Appendix D for documentation).
89
6.4 TYPE 2 INJECTED SILICONE SEAL TEST
The
seal
was
were
used) with
in.,
causing
usual.
The
Prior
inwg
as
to
installed and
no
the
problems.
retaining cuffs
injection
the
"gas" pressure.
usual
6 inwg
"gas"
The
(4 retaining bands
bands
were
to conform
window was
leak
joint
tightened
to the
bonded
rate was
scale as
into
place.
ft3/hr
2.2
0.4
at
6
The 3112 silicone sealant was prepared
sealant was
The
section.
The
second plexiglass
usual.
clamped
injected
pressure
aluminum
trying
into
to
reinforcing
seal
the
leak out
strips
of
with
the
the test
deflected
and
flattened as usual.
One hour after injection a leak test was run.
was
detected.
water
tank
resulted
for
in a
pressure.
The
test section was left connected
2 days.
leak
To test
A leak
rate
of
test over
0.000038
the effects
of
change
raised
in
the
the leak rate,
leak
rate
to
as
the next
ft3/hr at
hours
6 inwg
"gas"
the
test
The compression caused
expected.
The stretching
ft3/hr
at
minor
seepage
0.00019
to the
25
"joint" flexure,
section was compressed and stretched.
no
No leakage
6
inwg
"gas"
pressure.
Inspection
under
seeped
the
revealed the usual
retaining
into
the
cuffs,
"joint
see Photograph
recess",
results are summarized
in
see
Table 6.1,
of silicone
6.7.
Some
Photograph
6.8.
had
The
see Appendix D for docu-
mentation.
6.5 DISCUSSION
The measured leak
configurations
clearly
rates
from both of
demonstrated
that
the
tested
injected
seal
silicone
seals will seal an uncleaned gas main joint.
An
analysis was
done
to determine
the
magnitude
of any
possible leakage that would have resulted from permiability of
the bridge
in the Type 2 seal.
The flow rate through a mem-
brane, Q (cm3/min), can be found from the following. 1 4
Q = P (p)AA
e
t
Where P
is the permiability constant (7.9 X 10 - 6 cm3mm/min
2
e
cm
mmHg) for silicone sheet, p is the pressure difference
across the membrane (6 inwg = 11 mmHg), A is the area of the
membrane
(102 cm 2),
and
t is
the
thickness
of
the membrane
(0.031 in. = 0.79 mm).
This resulted in a predicted leak rate
of 0.000028 ft3/hr due to permiability.
The leakage of the
Type 2 seal was therefore felt to be due to the permiability
of the silicone sheet bridge.
Leakage due to bridge permiability will be even less in
any implemented seal design.
Silicone was not recommended as
a bridge material, fluorocarbon is the elastomer to use. This
will
other
lower
leakage because the permiability constant
rubbers,
including
tude lower than it is for
Joint
flexure
fluorocarbon,
is
for all
an order of magni-
silicone. 1 4
resulting from either ground vibration
or
thermal stresses and its effects on the two injected silicone
seal types needs further investigation.
The Type 2 seal will
be the least affected of the two seals because of the flexible
bridge.
The
Type 1 seal
may have
more
problems with
joint
flexure.
Comments from Con Edison personnel indicated that the low
injection pressures which were used for the Type 1 seal, less
than 10 psi, will not cause the joint packing to be blown out
of the joint.2
This leaves joint flexure as the major problem
of the Type 1 seal concept.
91
Table 6.1
: Summary of Joint Test Results.
Time from
Seal
Injection
Leak Rate
Type 1 silicone
0:50
none detected
to 11 days
none detected
Type 2 silicone
0:15
none detected
75:15
0.000038 ft 3 /hr
(compressed)
120:00
0.000038 ft 3 /hr
(stretched)
191:00
0.00019 ft 3 /hr
Notes:
1) All leak rates were at 6 inwg "gas" pressure.
2) All seals were subjected to 6 inwg "gas" pressure
continuously.
Retaining
Bands
Reinforcing
Strips
Sheet
- Sponge
Retaining
Cuffs
Pipe
Joint -
Recess
(Filled)
a) Type 1 Injected Silicone Seal.
Radial
Direction
Axial Direction
Retaining
Bands
Bridge
Reinforcing
Strips
Sheet -P
.
.... ...
J/J
5/=
Pipe
Sealant
Cavity
Joint
Recess
(Unfilled)
Sealant Cavity
Sponge
Retaining
Cuffs
b) Type 2 Injected Silicone Seal.
Figure 6.1 : Injected Silicone Seal Prototypes
Tested in Field Joints.
Note: The drawings are to scale in the axial direction.
In the radial direction the scale was doubled for clarity.
7
Photograph 6.1
Photograph 6.2
I
: Joint for Type 1 Seal Test.
: Pipe Scale for Type 1 Seal Test.
--;----------
r__-- oe
-- -C---- -rr
_~Ei-is
t
Photograph 6.3
: Joint for Type 2 Seal Test.
I
Photograph 6.4
: Pipe Scale for Type 2 Seal Test.
~;_h~L~L~--LCi ---1L~-~3111111)~
r
~--S;ilP
C-~
Photograph 6.5
Photograph 6
by Type
: Seepage From
: Section Show Injected Silicc..
cype
1 Joint Test.
-t
R-ecess Filling
A
- L--_ _--il-;--F
i
_r_ _..- _._~_LL
EIIIIL*LIYII~
lc
~L~-~irC
Photograph
6.7
: Seepage From Type 2 Joint Test.
Photograph 6.8 : Seepage Into Recess by Type 2
Injected Silicone Seal.
CHAPTER 7
SEAL DEPLOYMENT
Throughout
author,
the
seal
development
deployment
was
work
an
which
issue
proposed
seal
was
done
which
by
was
concept
the
always
considered.
Obviously any
deployable.
Considerations of deployment influenced the seal
development which was being done in parallel.
had
to be
The discussion
of seal deployment which follows will be in general terms.
There are a number of seal design features which must be
considered in
research related to seal deployment.
The most
desirable seal features are as follows.
1) Simplicity of seal design, preferably one-piece.
2) Small and convienient packaging of the seal.
3) Seal should be flexible.
4) Minimize obstructions to gas flow.
5) Mechanism to deploy seal is as simple as possible.
6) Seal concept must allow the installation mechanism to
be loaded with a reasonable number of seals to avoid
multiple entries and traverses of the pipe.
How well these design features are
whether
or
not
a given
seal
implemented will determine
concept
can
be
reliably
and
economically deployed.
The
need
before.
for
simplicity of
seal
design has
Because multiple-piece seals will
been
stated
require a more
complex installation mechanism than a one-piece seal,
latter
is
the preferable
seal
to hold
the
costs down and improve
reliability.
The size of the seal package before it
is deployed will
determine whether or not the seal can be transported down the
gas
main.
Seal
packages which
pipe interior will not
pipe.
are
barely
smaller
than
the
negotiate anything except straight
Thus a smaller seal package provides an opportunity to
send the installation mechanism as far away from the pipe main
access as possible.
This should lower
the cost of the
joint
--
-
-
-
--
...
..
9 OMINIIM
l"
hW YMi
mil IW3h
repair.
Seal flexibility allows the seal to be deformed into a
package that is conducive to transportation and deployment.
Seals which are stiff in bending limit the options available
to the designer.
The flow obstruction of the seal package should be
minimized.
Excessive pressure drop across the mandrel could
lead to disruption of customer service.
If high localized
flow velocities are created, they could entrain dust from the
pipe scale into the gas flow.
This is undesirable.
In
addition, a seal which is a large flow restriction will also
reduce the space that the installation mechanism can occupy.
Some seal packages require a complex set of motions for
installation. Thus the installation mechanism will have to be
more sophisticated.
Complexity will reduce reliability and
raise cost.
The seal package affects the number of seals that a
mechanism can deploy.
For an internal mechanical seal to be
financially viable, a mechanism would probably need to install
several seals before returning to the pipe access.
In
addition, the seal package will determine how the seal is
loaded into the mechanism.
A configuration must be found
which will allow for easy reloading.
There are four seal packages which cover the majority of
design options available. These are shown in a schematic form
(end view) in Figure 7.1.
It was on these seal packages that
the bulk of the conceptualizing was done.
Package #1 is shown in Figure 7.1a.
This would be a one
piece seal (retaining bands attached) that would be radially
expanded into position. This would require that the elastomeric parts of the seal be stretched circumferentially to
deploy the seal.
The resulting creep of the elastomeric
components due to the tensile stress is undesirable.
Such a
seal
package
will
also
have
difficulties
in
negotiating
obstructions in the main since it will have to be quite large
to reduce the installed tensile stress in the elastomeric
99
components.
Figure 7.1b is of Package #2.
The Type 1 silicone seal
can be deformed into this shape, see Photograph 7.1.
If the
retaining bands can be made thin enough, this could also be a
one-piece seal.
This seal is deployed by raising the inner
portion of the collapsed "U" to the top of the pipe. The seal
is not stretched into position. This shape was used to insert
the seal prototypes into the pipe sections. The seals usually
were released so that they popped into place.
This package
can be easily narrowed (make the "U" taller) to improve the
negotiation of obstacles.
Package #3 is shown in Figure 7.1c. This could also be a
one-piece seal if the retaining band can be wound to half its
installed radius, which was possible with the prototype
retaining bands. This package would be deployed by expanding
the retaining band, forcing the seal to conform to the pipe.
This seal would not be stretched into place.
This package
fills a large amount of the pipe cross-section. The room
available
for the mechanism is
therefore
reduced, which may
complicate the design problem.
Storage of seals in the
mechanism will be a problem because of the large volume which
the seal will occupy.
Package #4 is shown in Figure 7.1d. The Type 1 silicone
seal can be deformed into this shape, see Photograph 7.2.
This is a one-piece seal package, the retaining bands would be
doubled up in the circular loop.
It would be deployed by
releasing the flap and then expanding the retaining bands.
The seal would not be stretched into place. This package uses
a modest amount of the pipe cross-section. Seal storage will
require the mechanism to fit inside the circular loop of the
seal package.
This package can be made small enough to
negotiate obstructions.
The two most promising seal packages are #2 and #4. Both
of them take advantage of the inherent flexibility of an elastomeric seal to provide for a simple deployment motion and to
minimize the volume occupied by the seal. Further development
100
--
--
-
--
--
-
--
IIi
'-m
work should be focused on these two packages.
Research was conducted by Mark Shelley which led to the
development of a simple mechanism to deploy the seal from the
configuration of Package #4.
&
101
Pipe
a) Package #1
b) Package #2
c) Package #3
d) Package #4
Pipe
Figure 7.1 : Seal Packages for Deployment.
Note: The seal centerline is the heavy line inside
the pipe.
102
1
--
-
-- -
;
------
~-"-L~ZS
Photograph 7.1
Shape.
: Type 1 Silicone Seal in Package #2
~ Sls~~
Photograph 7.2 : Type 1 Silicone Seal in Package #4
Shape.
103
CHAPTER 8
CONCLUSIONS AND RECOMMENDATIONS
The major conclusions which
deal primarily with
resulted from
this
research
the design features which an internal
mechanical seal design will need to successfully seal
pressure
cast iron natural
gas distribution
mains.
low
They are
as ollows.
Cleaning
eliminated.
of
the
pipe
interior
must
be
or
Debris removal should be limited to pushing thick
scale in the immediate vicinity of the pipe
way.
minimized
joint out of the
The seal and installation mechanism must be designed to
operate with
this goal
in mind.
Any cleaning which
is done
will pose complex sealing and mechanism problems.
A sealant
provided by
adhere to
curing,
should be
the
seal
the pipe interior.
greatly
lowers
Vulcanizing
curing sealant.
but
the
eliminates the
the
needed to achieve a seal.
be
used,
mechanical support
need
for the sealant
to
The sealant, curing or nonrequired
compressive
stresses
This simplifies the seal design.
2 part
silicone
is
the
best choice
for a
Asphalt is a non-curing sealant which should
treated as as alternate solution if problems should arise
with the silicone.
The sealant should be
after
the
seal
has
been
injected
clamped
into
into a sealant
place.
cavity
The
retaining
cuffs of the seal will then rest on a mechanical
support,
minimizing problems with sealant flow.
The
retaining cuffs
of
the
seal
should
be
compliant
conform to the irregularities of the pipe surface.
to
This will
reduce the size of any potential leak paths.
The seal should be flexible
in
bending to allow the seal
to be deformed for transport and deployment.
The
retaining
mechanical ratchet.
band
should
be
of
thin
This will allow the seal
steel
with
a
to be one-piece
design since the retaining band could deform with the rest of
the
seal.
The
ratchet
will
provide
104
easy
adjustability
for
~II~____I
_
^IIMINI
variations in pipe circumference.
Flexible axial reinforcing strips should be incorporated
into the seal to provide a reservoir of pressurized sealant to
compensate for slight sealant flow after injection.
At least one vent near the top of the seal should be used
to ensure that the sealant cavity is completely filled during
injection.
The Type 1 and Type 2 injected silicone seal concepts
incorporate all of these design features.
The joint tests
proved that these two seal concepts will seal uncleaned pipe
joints covered with moderate pipe scale.
These two seal
concepts should be used as the basis for further development
in Phase III..
Further seal development needs to be concentrated in
several areas. These recommendations are as follows.
Further study is needed on silicone sealants.
A 50 year
life in a natural gas main must be demonstrated. The catalyst
must be shown to function properly.
Satisfactory mixing of
the silicone sealant must be demonstrated, complete mixing may
not be necessary.
Different catalysts, giving varying cure
times, should be investigated to determine which one will
allow the simplest implementation.
Viscosity of the uncured
sealant, which affects sealant flow before curing, should be
optimized.
If asphalt is used as a sealant, then further work should
be done to document its longterm behavior in a gas main. The
final asphalt grade which is selected will have to be a
compromise between flowing ability and hardness (for high
temperature capability).
The effects of vibration and thermal cycling on the
sealing ability of the Type 1 and Type 2 silicone seals must
be studied.
If the Type 1 seal is adversely affected, then
the final seal design will have to incorporate. the elastomeric
bridge of the Type 2 seal to minimize damage due to joint
movement. Because the scale of the pipe is not removed prior
to seal installation, there exists the possibility that leak
105
paths will open up under the scale due
to vibration, this
needs to be studied as well.
The
feastures
final
as
seal
design,
possible,
cooperation with
incorporating
should
industry.
This
be
done
as
many
in
Phase
design will
then
desirable
III
in
drive
the
design of the installation mechanism.
S
106
----
----
--
-oil
APPENDIX A
MATERIALS USED FOR SEAL DEVELOPMENT
Asphalts
Type A
: ASTM Type II.
Type B
: Ox Flux.
Type C
:
Type D
: AC-10, kin. viscosity =
Em Flux.
Note : Types B,
1100 centistrokes
(225 F).
C, and D were obtained courtesy of Bob
Dennis, Exxon, from their Everett, MA, refinery.
Fiberglasses
:
Thin Mat
Thick Mat
Cloth
:
: Stiff yellow insulation,
Boatex Fiberglass Co.,
Reinforcing
Steel
Flexible yellow insulation, 2.9
lb/ft 3
8.3 lb/ft 3
style 7500, finish volan.
Strips
: Made from Starrett Feeler Stock, 0.030 in.
Aluminum
:
2024 sheet, 0.020
in.
thick.
thick.
Retaining Bands
Made from Ideal Co. Hy Gear Stainless Steel Hose Clamp,
9/16 in. wide, 0.025
in. thick.
Silicones
RTV
: General Electric RTV Silicone Rubber, RTV 108.
Sponge : COHRlastic Silicone Sponge Rubber, R10470
Medium.
A stress-strain curve for this sample was
obtained, it is shown
in Figure A.1.
Solid Sheet : COHRlastic Silicone Solid Rubber, 300.
Has a hardness
Silicone Sealant
of 30 durometer, was 1/32
in.
: Dow Corning 3112 RTV Silicone Rubber.
Used S catalyst
in
standard
10:1
ratio.
Working
time is 45 minutes, pot life 3 hours, and cure time
6 hours
thick.
(all at 25 C).
It has a cured
60 durometer.
107
hardness of
30
25
20
15
10 .
5
0
0
10
30
20
Strain [%]
40
Figure A.1 : Experimental Stress-Strain Curve of
Silicone Sponge Used for Seal Development.
108
50
I__~
_____I
_
~I_
S111111111
APPENDIX B
RETAINING BAND FORCE DERIVATION
The free-body diagram of the retaining band is.
R
W sin 6
Y
F
The
F
forces must sum to zero in the y direction.
2F =
W sin 9 R de
2F = WR[ -cos
9
] = 2WR
F = WR
109
APPENDIX C
RETAINING RING ANALYSIS
This analysis was done by Timoshenko. 9 A retaining ring
with a circular outer boundary has a
rectangular cross-section of width b and
variable depth h.
We would like to find
h so that the ring produces a uniformly
p
Let
+ d)
(r
unstrained
distributed pressure p around the ring
circumference.
be the outer radius of the ring in an
state
and r
the strained radius.
curvature due to bending is the following.
1
r
1
r +d
The
M = -2pbr
2
cross-section mn due
sin2
2
If we take the following.
bh 3
d
12
r2
we get.
h 3 =P
E
24r
d
4
sin
2
2
The maximum section height is.
h3 = p
0
E
24r 4
d
Rearranging gives.
Eh
24
3
d
r
in
M
EI
The bending moment M at any
uniform pressure, p, is.
Substituting,
change
4
110
- 1
r
1
r + d
to
the
__I
~
I_
^_^____11II
i
Letting D be the free diameter and G the compressed diameter
gives.
3
Eh D- G
p =
G4
Waldes Kohinoor, Inc., manufactures an extensive line of
retaining rings. One of these models, N5000-350, is designed
to have a minimum compressed diameter of 3.5 in.
(ho = 0.289
in., b = 0.109 in.).The table below shows the calculated
pressure for this retaining ring and two hypothetical rings
with much smaller maximum section heights.
Table C.1 : Uniform Radial Pressures for 3 Retaining Rings.
(lb/in )
G in.
3.50
3.55
3.60
3.65
3.70
3.75
3.80
3.85
Maximum Section Height
0.289 in.
0.150 in.
0.125 in.
606
499
403
315
236
165
101
42.5
84.7
69.8
56.3
44.0
33.0
23.1
14.1
5.9
49.0
40.4
32.6
25.5
19.1
13.3
8.2
3.4
The last two columns are plotted in Figure 4.10. Commercially available retaining rings a e clearly not viable
alternatives for retaining bands.
111
APPENDIX D
EXPERIMENTAL DATA
All leak rates were measured at 6 inwg "gas" pressure.
The experimental data is converted by the following:
1 ml/sec = 0.1271 ft 3 /hr
Abbreviations are:
ml
s = seconds, min = minutes, hr = hours,
= milliliters, F = degrees F.
Test Section: STR I
Pipe section: lightly scraped for clearance.
Gasket material: sponge and sponge/silicone.
Continuous "gas" pressure: none.
Room temperature: 74 to 78 F.
Data:Diaphragm
Pressure
Sponge
Sponge/RTV
0 psig
700 ml/35.7 s
6.5 ml/115.3 s
650 ml/33.5
545 ml/26.8
4.5 psig
430 ml/71.3
375 m1/57.4
5.0 psig
5.5 psig
6.0 ml/169.3 s
318 ml/58.9
322 ml/61.7
310 ml/61.1
10 psig
73 ml/58.6 s
72 ml/62.4 s
112
-
- - -^---
I
-illi
--
Test Section: STR I
Pipe section:
lightly scraped for clearance.
Gasket material: Type A asph/fiberglass (2.9 lb/ft 3 ).
Continuous "gas" pressure: none.
Room temperature: 80 F.
Time from
Asphalt/
Pressure
Start
Fiberglass
5.0 psig
10 days
54 ml/159 s
Data:Diaphragm
54 ml/158 s
Test Section: STR I
Pipe section: uncleaned brown scale.
Gasket material: Type B asph./fiberglass (8.3 lb/ft3).
Continuous "gas" pressure: none.
Room temperature: 80 F.
Time from
Asphalt/
Pressure
Start
Fiberglass
5.0 psig
0:05
615 ml/30.2 s
0:30
765 ml/43.0 s
1:00
590 ml/45.6 s
2:00
555 ml/50.8 s
4:05
480 ml/64.1 s
8:10
335 ml/72.0 s
20:00
50 ml/98.6 s
24:00
68.5 ml/119.5
48:00
46.0 ml/151.6
73:00
32.0 ml/182.3
96:00
31.0 ml/184.8
168:00
12.5 ml/266.7
192:10
17.5 ml/183.7
216:05
13.0 ml/212.0
265:05
14.5 ml/214.0
288:05
14.0 ml/230.4
Data:Diaphragm
113
Test Section: STR I
Pipe section: same as previous test.
Gasket material: same as previous test.
Continuous "gas" pressure: 6 inwg.
Room temperature:
80 F.
Time from
Asphalt/
Pressure
Start
Fiberglass
5.0 psig
25:10
580 ml/48 s
43:45
485 ml/36.2 s
Data:Diaphragm
Test Section:
STR I
Pipe section: same as previous test.
Gasket material: same as previous test.
Continuous "gas" pressure: none.
Room temperature: 80 F.
Time from
Asphalt/
Pressure
Start
Fiberglass
5.0 psig
96:00
7 ml/227 s
96:05
100 ml/16 s
Data:Diaphragm
Test Section:
STR I
Pipe section: smooth aluminum, to verify sealing of the
diapragm/gasket material interface by the vacuum
grease.
Gasket material: none.
Continuous "gas" pressure: 6 inwg.
Room temperature: 80 F.
Data:Diaphragm
Time from
Vacuum Grease
Pressure
Start
at Interface
5.0 psig
0:10
1.5 ml/660 s
1:50
2.52 ml/49 min
2:39
7.5 ml/17 hr
114
111IIIIJ
Test Section: STR I
Pipe section: same as earlier Type B test.
Gasket material: Type B asph./fiberglass (8.3 lb/ft 3 ).
Continuous "gas" pressure: 6 inwg.
Room temperature: 80 F.
Data:Diaphragm
Time from
Asphalt/
Pressure
Start
Fiberglass
5.0 psig
0:07
8 ml/210 s
70:00
360 ml/47.9 s
Test Section: STR I
Pipe section: same as earlier Type B test.
Gasket material: Type C asph./fiberglass (8.3 lb/ft3).
Continuous "gas" pressure:
6 inwg.
Room temperature: 80 F.
Data:Diaphragm
Time from
Asphalt/
Pressure
Start
Fiberglass
5.0 psig
0:03
370 ml/62.8 s
24:00
11 ml/720 s
42:00
1.0 ml/390 s
Test Section: STR I
Pipe section: uncleaned light scale.
Gasket material: Type D asph./fiberglass (8.3 lb/ft3).
Extra layer of pure asphalt on outside.
Continuous "gas" pressure: 6 inwg.
Room temperature: 79 F.
Data:Diaphragm
Time from
Asphalt/
Pressure
Start
Fiberglass
5.0 psig
0:05
11 ml/300 s
26:10
0 ml/9 min
115
Note:
All subsequent tests were conducted with a continuous
"gas" pressure of 6 inwg being applied
they were not being leak tested.
test when
Test Section:
STR II
uncleaned with scale.
Pipe section:
Seal:
Room
Type 1 silicone,
temperature:
Data:Time
Seal
Leakage
2:15
9.0 ml/195
28:20
13.0 ml/300 s
STR
s
II
uncleaned with scale.
Type 1 silicone, 3112 silicone, Seal
temperature:
Data:Time
#2.
80 F.
from
Seal
Injection
Leakage
1:10
14.7 ml/131
Test Section:
s
STR II
Pipe section:
Seal:
80 F.
from
Pipe section:
Room
3112 silicone, Seal #1.
Injection
Test Section:
Seal:
to the seals under
uncleaned with scale.
asphalt seal,
Type D asph, extra asphalt layer on
on outside, aluminum spheres and asphalt mixture
used,
fiberglass mat
Room temperature:
Data:Time from
(8.3 lb/ft3),
Test #1.
75 F.
Seal
Injection
Leakage
167:40
23.0 ml/131.6 s
This was the first valid test with no skirt leakage.
116
Tes,t Section: STR II
Pipe section: uncleaned with scale.
Seal: asphalt seal, Type D asph, aluminum spheres and
asphalt mixture used, fiberglass cloth, Test #2.
Room temperature: 80 F.
Data:Time from
Seal
Injection
Leakage
119:10
44.0 ml/130.8 s
This was the first
and only valid test with no
skirt leakage.
Test Section: Joint
Joint: real and uncleaned.
Seal: Type 1 silicone, 3112 silicone.
Room temperature: 80 F.
Data:Time from
Seal
Injection
Leakage
joint only
410 ml/25.7 s
seal installed
600 ml/36.1 s (no sealant)
0:50
none detected
to 11 days
none detected
Test Section: Joint
Joint: simulated and uncleaned.
Seal: Type 2 silicone, 3112 silicone.
$7
$7
Room temperature: 80 F
Data:Time from
Injection
seal installed
$7
A
0:15
75:15
compressed seal
(120:00)
stretched seal
(191:00)
Seal
Leakin625
lI/35. 7 s (no sealant)
none lotec ted
27.5 ml/25 .5 hr
26 ml/24 h r
19 ml/3.5 hr
117
APPENDIX E
PHASE I SUPPLEMENTAL REPORT:
MINIMAL LEAKAGE
RATE REDUCTION DUE TO ETHYLENE GLYCOL FOGGING
A goal
effects
the
determine
conducted at M.I.T. was
I research
of the Phase
rates
leak
on
fogging
glycol
ethylene
of
to
through jute specimens removed from the Con Edison systems.
leakage reduction due to ethylene
In previous tests of jute
some
glycol,
jute and
joint geometries;
using
allow
not
These
an
accurate
crushing
included:
sample
homogeneous
the
into a
not replicate field
which did
sample containers
using
did
methods
the resulting
inserting
then
container;
test
field conditions.
of
simulation
the
of
liquid ethylene glycol
(not a vapor), on
the jute.
The
tests
and
joints
curvature
though),
The
forcing
samples by
the
through
glycol
as
and
was
glycol
nitrogen gas
The
for these
present
glycol
For
conditions.
the
In
Con
Edison
to
the only
flow
to the
jute
be
liquid ethylene glycol.
tests
Is the
the
York
gives
0.64
in
the
field
estimated
54.1
Brooklyn
OF
20%
In New
Union's
60%
1.93 mg/ft 3 .
For complete saturation at 65
vapor
amount of
under
gas
average ambient temperature of
saturation gives
the ethylene
absorbed
system
glycol/ft 3 .
vapor
ethylene glycol
at the
mg
(no
geometries
saturation
City
sample
joint
carrier
the
special
in
delivered
gas containing
nitrogen
Important variable
ethylene
eliminate the above
were
jute
vapor when it was bubbled through
An
to
field
the
forced
ethylene
samples.
they
duplicated
holders
These
designed
lead samples were carefully removed from
installed
holders.
restriction.
M.I.T. were
Jute and
shortcommings.
field
at
nitrogen
carrier
118
OF of
gas,
the ethylene
the
glycol
concentration
was
calculated to
be 4.47 mg/ft 3
saturation at 80
concentration
10
ft3 of
for the test apparatus.
*F gives 9.65 mg/ft
3
.)
mg
nitrogen and glycol
of
for
glycol
nitrogen/ethylene
glycol
To determine the actual
In the test rig, measurements were made by passing
vapors
(only one pass
bubbler) through an absorption column.
89
(Complete
an
glycol
average
mixture
concentration much closer
through the
Two tests yielded 118 and
of
10.35
apparently
mg/ft
3
The
stabilized
at
a
to the saturation conditions at
80 *F than at 65 *F.
In comparison to
Con Edison's
temperature
(assumed to be 54.10F),
exposed
glycol
to
concentrations
20%
saturation at ambient
the test jute specimens were
between
7
(4.47/0.64),
and
16
(10.35/0.64), times greater than the estimated field conditions.
The
test program at M.I.T. used
and 9 as test specimens.
11
samples,
The two control
had pure nitrogen gas passed through
samples (no.
them.
had nitrogen
passed through them.
E of the Phase
2 and
The nine test
gas containing ethylene glycol
The test appara+us
I report.
12),
If further drying out-
of the jute occurred, these leak rates would rise.
specimens
2 as controls
vapors
is described in Appendix
Leakage meas,fements were taken weekly
using 6 Inches of water pressure drop dcross the specimens.
The average normalized
leak
(relative 'o
rate of the 9 test specimens
average leak reduction after 280 days
for the decay
10%, Is
also
is about 45 days.
plotted.
The
large
"
'Is Initial
i'own
was
14%.
Figure
1.
scater
in
The
The time constant
The s anddrd deviation of
evident from Figure 2, where the normalized
119
in
leak rate),
the
data
about
points
leak rates of
is
some of
the
specimens
test
to
normalized
the
days while
In Table
specimens
( 270
ref.
was
54
Phase
about
British
long
In
of
using
twice
Gas
obtainable at
plug
small
as
long
the
leak
In
rate
leak
for
specimens
280
individual
rates
for the
leak
jute
in
The
as
the
showed
Gollob
Analytic
reduction after 9 months
cylindrical
time
MIT
containers
constant
test.
much
Services
of
Tests
higher
the
(see
decrease
conducted
reductions
with
by
very
but are not as relevant give the differences
the
be
jute.
noted
the end
leaks
average
a 17%
Corporation
should
by
crushed
time constants,
It
conducted
I report).
the condition of
leak rates
The mean normalized
tests
Edison showed
days),
its
not
were
In Table 2.
are
In comparison,
for Con
1.
The
rates
control
the
Number 2 doubled
12 stayed the same.
specimens are
leak
The
because
controls
so differently.
responded
9 test
plotted.
are
of
that
the
the test.
that occurred
specimen
Silicone
in the
weights
sealant
specimens
were
was
during
not
used
to
the test,
Invalidating any weight gain measurements.
In conclusion,
reduction
of
14%
with
exponential
decay.
not
the
that
provide
it
might
feasibility
leak
is
reductions
the M.I.T.
test
showed
a time constant of
So,
large
ethylene
leak
provide
either
which
glycol
reductions
for
limited
would
other
or
120
average total
days
fogging
for
the
for
Con
occur
in
The
the
apparently
Edison
given
leak
the roughly
will
systems.
non-existant
probably
joints.
45
an
system
economic
the
leaking
modest
field
Mlw
I0
il
1.2 l"
1.0 -
.
4
.
.,.
,e e.
--
*%*
*
* •**
*
.
*,*
.e
•
•
•- *•*
*
*
0.8 1 std. dev.
0.6 -
0.4
9 Samples
0.2
no.
0.0 -
I
I
40
-
1
80
v
120
160
3 - 11
I
'00
I
I
40
TIIE (DAYS)
Figure 1: Mean Normalized Leak Rate Reduction of 9 Test Samples.
121
,s0
1.2,
1.0
0.8
0.6
0.4
Sample 3
o
0.2
S1
11 a
0.0
80
120
200
240
TIME
Figure 2.
Normali:ed Leak Rates for Several Typical
Test Samples.
122
280
-----
---------
---
--
--- --
------
N iliiiiiit
1 IIIlilm
Ii
ii
wMIt,
Table 1: Normalized Leak Rates for All Test Specimens.
Days
Sample 3
Leakage
Normalized
Rate
Leakage
Rate
(cc/min)
1
7
14
21
28
35
42
49
56
63
70
77
85
101
108
115
128
136
143
157
164
171
178
185
192
199
206
219
234
255
280
1367
1255
1071
1071
1087
1056
980
949
949
872
934
859
859
888
836
836
826
848
826
857
857
857
857
848
866
866
857
857
866
857
848
&
Sample 4
Leakage
Normalized
Rate
Leakage
Rate
(cc/min)
1.000
.946
.869
.876
.855
.842
.799
.806
.799
.778
.792
.743
.736
.743
.736
.736
.736
.743
.743
.743
.757
.764
.743
.772
.772
.778
.778
.764
.757
.757
2183
2066
1898
1913
1867
1837
1745
1760
1745
1699
1729
1621
1607
1621
1607
1607
1607
1621
1621
1621
1653
1667
1621
1685
1685
1699
1699
1667
1653
1653
1653
1.000
.918
.783
.783
.795
.772
.717
.694
.694
.638
.683
.628
.628
.650
.612
.612
.604
.620
.604
.627
.627
.627
.627
.620
.634
.634
.627
.627
.634
.627
.620
.757
I
Sample 5
Leakage
Normalized
Rate
Leakage
(cc/min)
Rate
1755
1775
1791
1806
1898
1837
1714
1745
1699
1668
1729
1575
1547
1547
1561
1515
1561
1575
1575
1547
1575
1547
1547
1621
1639
1639
1607
1561
1547
1561
1561
1.000
1.011
1.021
1.029
1.081
1.047
.977
.994
.968
.950
.985
.897
.881
.881
.889
.863
.889
.897
.897
.881
.897
.881
.881
.924
.934
.934
.916
.889
.881
.889
.889
I ________________________________________
123
Table 1: cont'd.
Days
1
7
14
21
28
35
42
49
56
63
70
77
85
101
108
115
128
136
143
157
164
171
178
185
192
199
206
219
234
255
280
Sample 6
Normalized
Leakage
Rate
Leakage
Rate
(cc/min)
2862
2908
2755
2755
2831
2785
2709
2709
2632
2663
2694
2603
2617
2649
2603
2631
2617
2709
2649
2663
2709
2709
2649
2585
2631
2677
2695
2723
2677
2649
2649
Sample 7
1.000
1.016
.963
.963
.989
.973
.947
.947
.920
.930
.941
.910
.914
.926
.910
.919
.914
.947
.926
.930
.947
.947
.926
.903
.919
.935
.942
.951
.935
.926
.926
Sample 8
Leakage
Rate
(cc/min)
Normalized
Leakage
Rate
Leakage
Rate
(cc/min)
Normalized
Leakage
Rate
2143
2219
2234
2112
2189
2097
1990
2051
1944
2005
1990
1896
1869
1837
1823
1823
1892
1837
1.000
1.035
1.042
.986
1.021
.979
.929
.957
.907
.936
.929
.885
.872
.857
.851
.851
.883
.857
.857
3413
3137
3153
3137
3183
3046
2938
2943
3076
2984
2954
2971
2893
3016
2952
2938
2952
2938
2938
2971
2984
2952
2879
2952
2984
2971
2984
2952
2925
2952
2925
1.000
.919
.924
.919
.933
.892
.861
.862
.901
.874
.866
.870
.848
.884
.865
.861
.865
1837
1804
1804
1837
1791
1791
1837
1837
1850
1791
1804
1758
1745
I
.842
.842
.857
.936
.836
.857
.857
.863
.836
.842
.820
.814
I
124
.861
.861
.870
.874
.865
.844
.865
.874
.870
.874
.865
.857
.865
.857
Table 1: cont'd.
Days
1
7
14
21
28
35
42
49
56
63
70
77
85
101
108
115
128
136
143
157
164
171
178
185
192
199
206
219
234
255
280
________
Sample 9
Normalized
Leakage
Leakage
Rate
Rate
(cc/min)
v
1.000
3000
1.031
3092
.964
2893
.949
2847
.979
2938
.939
2816
2755
.918
.934
2801
.913
2740
2755
.918
2724
.908
.918
2755
.892
2677
2741
.914
.883
2649
.898
2695
.908
2723
.908
2723
.908
2723
2755
.918
2814
.938
2787
.929
2723
.908
2755
.918
.914
2741
.923
2769
.934
2801
.944
2833
.938
2814
.918
2755
.908
2723
I
Sample 10
Normalized
Leakage
Rate
Leakage
Rate
(cc/min)
2938
2893
2816
2770
2862
2648
2724
2709
2709
2678
2678
2755
2617
2631
2631
2631
2695
2677
2649
2677
2755
2741
2649
2663
2663
2723
2741
2709
2723
2695
2695
I
1.000
.985
.958
.943
.974
.901
.927
.922
.922
.912
.912
.938
.891
.896
.896
.896
.917
.911
.902
.911
.938
.933
.902
.906
.906
.927
.933
.922
.927
.917
.917
Sample 11
Leakage
Normalized
Rate
Leakage
Rate
(cc/min)
2877
2938
2984
2938
2954
2877
2862
2801
2847
2785
2847
2847
2893
2847
2906
2833
2860
2879
2860
2938
2984
2938
2893
2925
2893
3030
2952
2925
2952
2984
2906
_________________________
125
1.000
1.021
1.037
1.021
1.027
1.000
.995
.974
.990
.968
.990
.990
1.006
.990
1.010
.985
.994
1.001
.994
1.021
1.037
1.021
1.006
1.017
1.006
1.053
1.026
1.017
1.026
1.037
1.010
Table 1: cont'd
DAYS
1
7
14
21
28
35
42
49
56
63
70
77
85
101
108
115
128
136
143
157
164
171
178
185
192
199
206
219
234
255
280
Sample 2
LEAKAGE
NORMALIZED
RATE
LEAKAGE
(CC/MIN)
RATE
DAYS
627
582
627
673
750
704
811
872
826
903
949
1226
964
1102
1102
1070
1088
1102
1102
1102
1134
1180
1134
1180
1148
1180
1194
1272
1253
1286
1272
1 .000
.928
1 .000
1.073
I
7
14
21
28
35
42
1.195
1.123
1 .293
1.391
1.317
1 .440
1 .514
1.955
1 .537
1 .758
1 .758
1 .707
1 .735
1 .758
1 .758
1 .758
1 .809
1.882
1 .809
1.882
1.831
1.882
1 .904
2.029
1.998
2.051
2.029
49
56
63
70
77
85
101
108
115
128
136
143
157
164
171
178
185
192
199
206
219
234
255
280
Note: Samples 2 and 12 are control specimens.
continued drying out.
126
Sample 12
NORMALIZED
LEAKAGE
RATE
LEAKAGE
(cc/MIN)
RATE
3030
2969
2969
3046
2969
2801
2938
2908
2877
2893
2893
3200
2893
2893
2833
2938
2984
2938
2893
3016
2938
3016
2952
2906
2984
3044
3044
3044
3076
3016
2971
They exhibited
1 .000
.980
.980
1 .005
.980
.924
.970
.960
.950
.955
.955
1 .056
.955
.955
.935
.970
.985
.970
.955
.995
.970
.995
.974
.959
.985
1.005
1.005
1.005
1.015
.995
.981
Table 2: Mean Normalized Leak Rates for Specimens 3 - 11.
Day
Mean of Normalized
Leak Rate
%sat
1
7
1.000
.987
.951
.941
. 962
.927
14
:1I
:3
35
.897
49
36
63
70
.899
.890
.388
.890
85
101
108
113
123
136
143
137
164
171
.352
.860
.861
.833
Std. Dev.
0.000
.045
.079
.072
.084
.080
.084
.091
.085
.100
.092
.105
.103
.097
.107
.104
.110
.108
.109
.108
.114
.609
. 53
u's
185
192
199
106
.s-:
.109
.105
.106
.102
.111
.109
.110
.108
.110
155
28019
.10"
Note: Fluctuations in % sauri::- reflect .hanges in the air
-The number which is quoted is
temperature of the lab.
based on Figure 34 orf ;~pedx E.
127
APPENDIX F
REFERENCES
1)
Rogers, Thomas: "An Evaluation of Joint Repair Methods for
Cast Iron Natural Gas Distribution Mains and the Preliminary Development of an Alternative Joint Seal", S.M.
Thesis, Massachusetts Institute of Technology, April 1983.
2)
Zlokovitz, Robert, Consolidated Edison of New York,
personal comments of 8/13/84.
3)
Zlokovitz, Robert, Consolidated Edison of New York,
personal conversation of 9/83.
4)
Zlokovitz, Robert, Consolidated Edison of New York,
personal conversation of 1/13/84.
5)
Dallas, Daniel B.7 Tool and Manufacturina Engineers
Handbook, McGraw-Hill, New York, NY, 1976, pg. 24-53.
6)
Baumann, Gurt, Mobay Chemical Co.,
of 1/5/84.
7)
Ostrogorsky, Alex, Ph.D. Candidate M.I.T. Mechanical
Engineering, personal conversation of 1/84.
8)
McGarry, Frederick, Professor M.I.T. Materials Science
Department, personal conversation of 6/13/83.
9)
Timoshenko, S.: Strength of Materials, Part II Advanced
Theory and Problems, D. Van Nostrand Co., New York, NY,
1930, pp. 446-447.
10) Pluddemann, Ed, Dow Corning Co.,
6/27/83.
11) Brady, Sam, Dow Corning Co.,
6/27/83.
personal conversation
personal conversation of
personal conversation of
12) Horner, Terry, TAH Industries, Imlaystown, NJ, personal
conversation of 8/7/84.
13) Shigley, J.E.: Mechanical Engineering Design, McGraw-Hill,
New York, NY, 1977, pg. 647.
14) Roth, A.7 Vacuum Sealing Technology, Pergamon Press,
Oxford, England, 1966, pg. 662.
128
-
"
---
----
---
--
--
..
"- YIIIYIUYNv
lll110i * 111
1
llhiili 11l
191
APPENDIX G
DEPLOYMENT MECHANISM
section
This
installation
of
the
of
the
deals
report
main
The
seal.
with
mechanical
obiective
to
was
demonstrate the feasibility of a simple mechanical device
hold the seal as it
the
over a joint.
once positioned
seal
lines, and
travels through gas
to
to expand
on
Some background
seal deployment has already been presented in Chapter 4.
A
general
device.
It would
diameter pipe,
bends.
of
constraint
design
have
inlcuding
to
was
pass
'tees,'
the
small
freely
area
through
branches, and
of
the
six-inch
ninety degree
The device also would have to allow uninterrupted flow
natural
gas.
This
area
cross-sectional
limited
of
the
the
width,
length,
design
Other
device.
and
specifications resulted from previous research.
Research described
conclusion
in preceeding
chapters
led
to
the
that a simple metal band would be the best device
to permanently secure the seal.
preattached
to
compatability
the
of
seal
these
Since
the band should be
easiest
for
installation,
parts was a significant
the
issue during
the design process.
The metal band was much stiffer than the elastomer seal,
so the configuration of the band was considered first.
would
probably
be
coiled
in
a
transportation,
the
circular shape.
This would permit sufficient reduction of the
band's
cross-sectional
found difficult
to manage,
was held at three inches.
folded
in
a
it expands is
other
plastic
causing
spiraling
so
the
minimum
coil
diameter
Therefore the seal would have to be
configuration
diameter circle.
as
without
area
But a band which overlapped itself three times
deformation.
was
band
During
compatible
with
a
three-inch
In addition, the natural motion of the coil
to unwind, with one end stationary and the
So
outward.
the
seal
must
unfold
in
a
compatible manner.
Possible
seal
configurations
have
been
discussed
* Work in Appendix G was performed by Mark Shelley.
19Q
in
Chapter 7, and are shown in Figure G.1.
#1,
attached
to Package
#3,
daisy-shaped
the
to
relative
seal,
stretchable
the
seal,
band would
to Package
or
have
to
slide
This would make
during expansion.
seal
the
the
If a coiled band were
it
Package #2, the
difficult to preattach the seal to the band.
U-shaped seal, does not permit a three-inch diameter circle to
fit
inside
so preattachment
it,
is
not possible.
Package #4
It can be fastened to
is more compatible with a coiled band.
most of the surface of a coiled band, and the lobe of the seal
can
be
taken up as
the coil expands.
Package
#4
is
the seal
configuration which appeared most promising.
Development of a deployment device began by considering
mechanisms
various
determining
their
usefulness
a
in
expand
which
for
simple
deploying
manner,
the
seal.
and
A
combination of pivoting rods mounted on a sliding joint expand
laterally
when
Figure
G.2.
could
expand
against
compressed
Several
the
from
rods
seal,
each
mounted
but
the
end.
This
is
in
this
radially
rods
would
shown
have
in
fashion
to
slide
This device would be relatively
the uncoiling band.
bulky and complex with its many moving parts.
The
expanded
the
metal
band
could
like a coiled rack
pinion
gear
after
be
fitted
and
with
pinion
installation
gear
teeth
system- but
would
be
and
removing
difficult,
and
during expansion the pitch of the gear teeth would change
slightly, causing binding.
A garter
spring
fastened
to
the
band
could
be
used
to
expand the seal, but such a spring would be awkward to release
in a controlled fashion.
A simple retaining ring could expand and secure the band,
except it could no be compressed enough to pass freely through
the pipes without being permanently deformed.
Another possibility was joining an inflatable tube to the
band, but
this would take up too much area
of the pipe cross
section.
Since the natural motion of the band during expansion was
to
uncoil, some sort of rotary device seemed like a possible
130
-- I'-- I
,,
solution.
The first rotary mechanism tested was a simple
hinge, shown in Figure G.3.
of the coiled band,
forced to expand.
Each arm was fastened to one end
and as
the hinge was closed the band was
This simple hinge device failed to provide
a solid base for an expansion mechanism.
rotary
11111
1 1i 61'
expansion
device
was
developed
first
concentric
However, an improved
employing
concentric
cylinders.
A
diagram of
shown
the
in Figure G.4.
cylinder
expander is
A metal band was coiled around both
cylinders, with each end joined to a different cylinder.
the
cylinders were
rotated
relative
to one
could be forced to expand or contract.
another,
When
the band
The device provided an
effective means for controlling the size of a coiled band and
maintaining its roundness.
The drive mechanism, however,
reouired
improvement.
end of the band,
A metal rod was fastened
passed through a hole in
to the inner
the outer cylinder,
and then through a slot in the inner cylinder.
accomplished
rotating
by
the
holding
outer
the
inner
cylinder
by
cylinder
means
of
Expansion was
stationary,
the
Another problem was to develop a simpler method
metal
and
rod.
to grasp and
release
the
device.
Finally, the system had to be automated to operate by
metal
band,
as screws
were
used
on this
initial
remote control.
The
revised
Figures G.5
through G.7.
spur gear was
was
fitted
gear.
concentric cylinder
is shown
internal
The other cylinder
gear which meashed
system provided
an
efficient
with
means
of
power to rotate one cylinder and expand the seal.
rods
were
welded
to
in
A gear motor which drives a small
fastened to one cylinder.
with an
This
expander
the ends
of
the
band, and
the spur
applying
Short metal
slid
into
grooves (somewhat like dovetail joints) which run parallel to
the axis of
the cylinders.
band
be
could
expansion device.
easilu
(See Figure G.8)
attached
to
and
Thus the metal
removed
from
the
In further development the grooves could be
extended along the length of the cylinders
to be carried at one time:
to allow many bands
and the device could be automated
131
to
each band after
expel
new band onto
it
installed, then push a
has been
This would permit several seals
the expander.
to be installed during each trip down the pipe.
The completed expansion device was loaded with a seal and
placed in a transparent piece of six-inch diameter pipe.
The
seal was held perpendicular and tangent to the pipe, and this
set-up
in Figures G.9
is shown
and
expansion
device
inches
diameter
in
diameter pipe.
was
the
to
expansion
seal
one-half
and
a six-inch
in
smoothly until
unfolded
inside
the
the
seal
the walls of the pipe.
pressed firmly and evenly against
that the expansion device be allowed
slightly during
rotate
four
than
entire
The
expansion device was activated,
The only restriction was
to
less
were
prior
When the
uncoiled and
band
seal
through G.12.
deployment
so
taht
the
seal
could
position itself properly in the pipe.
The
concentric cylinder
expander has
effective device to hold a seal
walls
device
of a six-inch
should be
inches in
diameter so
three-inch
diameter
also
be
obtained
cylinders
that the
minimum.
by
protrudes from the seal.
to automatically
the
In furhter research
slightly
less
than
band may be coiled
Further
better
to be an
and deploy it against
diameter pipe.
made of
proven
size
compaction
of
the
three
to
its
reduction
could
the
which
lobe
Also, a system should be developed
feed seals
from
a storage area
and
release
each one after it is expanded.
One alternative approach to seal deployment would be
to
employ the Package #3 seal configuration, and expand it using
several arms which extend radially outward from a central hub.
The
problem of
sliding
relative
to
the
uncoiling
band would
still have to be dealt with, both the radial arms and the seal
would encounter no sliding motion relative to one another.
system such as
to
extend
this,
which
would
require
several
radial
A
arms
in unison, would be relatively complex compared
to
the concentric cylinder expander: but a seal would not have to
undergo any rotation relative to the pipe during expansion
deployed by this method.
132
if
Another deployment method could make use of a surprising
phenomenon:
the resistance to buckling of even a very thin
(less than 0.007 inches thick) steel band when pressed against
the
pipe wall.
band
expanded
cylinder will
to
secure
Experimentation has shown
against
the
inside
of
that a thin metal
a six-inch
diameter
not buckle under stresses which are sufficient
the
seal.
Even
when
irregularities
more
one-eigth inch high are encountered along the pipe wall,
band
maintains its
shape under pressure.
than
the
Since a very thin
band can sustain bends of one-half inch radius or less without
deforming plastically , a band could be preattached to a seal
folded as in Package #2 or perhaps even Package #3. Alternate
methods
of
deployment
could
be
employing a very thin band.
133
developed
for
these
systems
Package
01:
Circular
Package #2:
U-shaped
eias:omer s=_
Package #3:
Daisy-shaped
Package #4:
Delta-shaped
Figure G.1. Possible seal configurations,
134
_eure
G.2.
Figure G.3.
Piv t
and siie
expansion mechanr.s.
Hinge mechanism with expanded Cana.
This band screwed to
inner cylinder.
Metal
Band
Metal
Rod
Inner
Cylinder
r
Uyll
Outer
Cylinder
Figure
G.4.
First concentric cylinder expander.
1
I
Metal
Band
Outer
Cylinder
Rotate CCW
To Contract
Internal
Gear
earX
Motor
Inner
Cylinder
/
z
Spur
Gear
Groove
Bearing
Figure
G.5. Revised concentric cylinder expander
with expanded metal band.
I
Figure
G.6.
Revised
Concen
end v:ew.
Figure
I is
G.7.
ric
Revised concentric
side view.
138
cylinder
exander--
cylinde r expander--
j
Deployment
Mechanism
Band
Metal
Rod
Figure
G.8. Method of fastening metal band
to expansion device.
139
Figure
G.9.
Expansion test rig--ready for deployment.
~b~,~-~4~
~_SS-
riJ
Figure G.10. Expansion test rig--during dep1oyment.
140
Figure G.11.
Figure
Expansion
G.12.
est rig
with fully deployed
Expansion test rig--side view of
fully deployed seal.
141
seal.