GRI-91/0283
.... '~.~-
Topical Report
I
Guidelines for Pipelines Crossing Railroads
Prepared by:
School of Civil and Environmental Engineering
Cornell University
Ithaca, NY 14850-3501
REPRODUCED BY
us. DEPARTMENT OF COMMERCE
Gas Research Institute
NATIONAL TECHNICAL INFORMATION SERVICE
SPRINGFIELD, VA 22161
Transport and Storage Research Department
December 1991
PB93-126985
GUIDELINES FOR PIPELINES CROSSING RAILROADS
TOPICAL REPORT
June, 1988 - December, 1991
Prepared by
Principal Investigators
H. E. Stewart
T. D. O'Rourke
A. R. Ingraffea
Coauthors
A. Barry
M. T. Behn
C. W. Crossley
S. L. EI-Gharbawy
School of Civil and Environmental Engineering
Cornell University
Ithaca, NY 14853-3501
Report No. GRI-91/0283
for
GAS RESEARCH INSTITUTE
Contract No. 5091-271-2273
GRI Project Manager
Kenneth B. Burnham
December, 1991
GRI DISCLAIMER
LEGAL NOTICE
This report was prepared by Cornell University as an account of
work sponsored by the Gas Research Institute (GRI). Neither GRI, members of GRI,
nor any person acting on behalf of either:
a.
Makes any warranty or representation, express or implied, with respect to
the accuracy, completeness, or usefulness of the information contained in
this report, or that the use of any apparatus, method, or process disclosed
in this report may not infringe privately owned rights; or
b.
Assumes any liability with respect to the use of, or for damages resulting
from the use of, any information, apparatus, method, or process disclosed
in this report.
S02n-l01
11. REPORT NO.
REPORT DOCUMENTATION
PAGE
1
GRI-91/0283
4. Title end Subtitle
L R.port o.te
Guidelines for Pipelines Crossing Railroads
7. Author(s)
PB93-1269f5
1'-
Topical Report
H.E. Stewart, T.D. O'Rourke, A.R. Ingraffea, A. Barry,
M l' Rehn C.W Cro!';!';lev and S.L. El-Gharbawv
December 1991
..
.. "'''ormin. Or.enintion Rapt. No.
9. Petform1na O.... niz.tlon Name .nd Add,esa
10. ProlectlTask/Work Unit No.
School of Civil and Environmental Engineering
Cornell University
Ithaca, NY 14853-3501
u.
eomractCC) or G,ant(G) No.
CC)
5091-271-2273
(G)
12. Sponsorl". O.... "lzation
N.~
11 Type of Report & Period Covered
.nd Addr...
Topical Report
(June 1988-Dec. 1991)
Gas Research Institute
8600 West Bryn Mawr Avenue
Chicago, IL 60631
1•.
15. SuPPlement.ry Not ••
16. Abstract CLlmlt: 200 words)
The guidelines in this report were developed from a comprehensive analytical methodology
to assess the three-dimensional stress state imposed in pipelines at railroad and highway
crossings, as well as the validation of the analytical models by full-scale field experiments. The result is a design procedure so that uncased pipelines can be installed safely
and reliably with respect to the stress environment at transportation crossings. The guidelines apply to steel pipelines for natural gas transmission and distribution systems, normally installed with auger boring and pipe jacking construction methods.
This report represents -a summary of the design procedure for uncased railroad crossings.
All of the necessary design curves are given, along with example calculations. A similar
document has been prepared for the design of uncased highway crossings (Report No. GRI-91/
0284, -'Guidelines for Pipelines Crossing Highwaysil). A complete technical summary of the
research used to develop the design procedures is given in Report No. GRI-9l/0285, "Technical
Summary and Database for Guidelines for Pipelines Crossing Railroads and Highways."
The benefits of a more accurate and comprehensive stress analysis procedure affect virtually all aspects of pipeline design. Technology transfer plans have been initiated by GRI
to aid in the implementation of these design procedures within the gas industry."
17. Document A"alysls
a. OHcnptors
Analytical models, Crossings, Design, Pipelines, Railroads, Soil-structure interaction,
Stress analysis
II. ldentlfiers/Open·Ended T.rms
c. COSATI field/Group
I.. Av.lI.bllity
St.t.~nt
,.. lecurtty Clns (Thl. Report)
Unclassified
Unrestricted
20. lec:urtty C.... (This .....)
21. No. of P•• n
65
22. Price
Unclassified
(Sa. ANSI-Z39.18)
See '".tructio". on II ........
Of'TIONAl fO"" 272 (4-77.
CFormerly NTlS-3S)
Depertment of Commerce
RESEARCH SUMMARY
Title
Guidelines for Pipelines Crossing Railroads
Contractor
Cornell University
Principal
Investigators
A. R. Ingraffea, T. D. O'Rourke, and H. E. Stewart
Report Period
June 1988 - December 1991
Objectives
The overall goals of the research were to develop a comprehensive methodology to assess the three-dimensional stress state
imposed in pipelines at railroad and highway crossings, to
validate the analytical models by full- scale field experiments
at actual crossings, and to establish a design procedure so
that uncased pipelines can be installed safely and reliably
with respect to the stress environment at transportation
crossings. The five principal objectives of this report are
to:
Technical
Perspective
1.
Present detailed results of analytical modeling used to
develop design curves, and to explain underlying assumptions inherent to the design curves.
2.
Present a methodology that can be used to analyze stresses in uncased carrier pipes crossing beneath railroads
and highways.
3.
Present the results of full-scale field experiments on
uncased pipelines installed by auger boring techniques
beneath a railroad.
4.
Present comparisons between current design practice and
the newly devised analytical methods used to model the
stresses in buried pipelines.
5.
Compare the results of site-specific numerical modeling
with the results from the field experiments for the purpose of validating the proposed design methodology.
Railroad and highway authorities sometimes require that natural
gas pipelines be encased at locations where they cross rightsof-way. This practice is followed because of a perceived improvement in the structural integrity of the casing-gas piping
system. Many gas companies, however, believe that reasonable
alternatives to encasements can be developed if adequate methods are available to analyze the stresses imposed on the uncased carrier. Considerable savings and improved safety would
be realized if gas transmission and distribution companies
could pursue alternative measures. Moreover, difficulties with
corrosion would be obviated by removal of the carrier from the
casing, since the presence of a casing may expose the carrier
to atmospheric corrosion, along with reducing the effectiveness
of any cathodic protection system.
When the carrier is installed without a casing, it is exposed
to three-dimensional stresses generated by traffic loads and
impacts, soil weight, and internal pressure. To evaluate the
effects of these loadings in a realistic manner, it is necessary to have a comprehensive design methodology which addresses
the three-dimensional stress state and properly accounts for
soil-pipeline interaction. Such a methodology is required to
show that uncased pipelines, when properly designed, will perform safely and reliably in response to the repetitive loading
environment of railroad and highway crossings.
Technical
Approach
The technical approach used for this study consisted of closedform analytical model evaluation for dead load stresses, threedimensional finite element analyses for live load stresses,
and full-scale field experimentation to substantiate the analytical models. Two high-pressure pipelines were fabricated
and instrumented to measure field response. The pipelines were
installed using auger boring methods beneath an experimental
railroad at the Transportation Test Center. Field data were
collected for over two years for a variety of test conditions.
A database of actual field performance of uncased pipelines
was generated and used to calibrate analytical models. Following model verification, design curves were developed to cover
the range of pipeline geometries normally encountered at most
pipeline crossings. Recognizing the need to account for the
combined three-dimensional stresses in the uncased pipeline
and the effect of cyclic loading on welds, design methods were
developed to evaluate pipe stresses according to yield and
fatigue criteria.
Results
The results of the study are embodied in a concise set of design guidelines that can be used to evaluate stresses in uncased pipelines which cross beneath railroads and highways,
and normally installed using auger boring methods. The design
methodology, referred to as the Cornell/GRI Guidelines, is
derived from analytical models developed specifically for these
types of conditions. Analytical models and design curves are
developed for I) circumferential stresses due to soil loads
from auger bored construction, 2) circumferential stresses due
to live railroad and highway loadings, and 3) longitudinal
stresses due to live railroad and highway loadings. The Cornell/GRT Guidelines recommend three additional design checks
for uncased gas pipelines, in addition to satisfying federal
regulations. The first relates to pipe yield, and is evaluated
by comparing combined circumferential, longi tudinal, and radial
stresses against a factored specified minimum yield strength.
The second and third additional criteria deal with fatigue of
the girth and longitudinal welds. These checks are evaluated
by comparing cyclic live load stresses in the uncased carrier
to factored fatigue endurance limits for pipeline welds. The
design methodology is founded on the results of fully threedimensional numerical modeling. To substantiate the analytical
approach, field experiments were conducted on two pipelines
installed by auger boring beneath a railroad. The results of
site-specific numerical modeling agreed favorably with the
field experimental measurements. Furthermore, comparisons made
between field measurements, stresses predicted using the Cornell/GRI Guidelines, and current design practice indicate that
stresses can be predicted more accurately using the recommended
procedures than by using currently adopted methods. In addition to previous research conclusions that thicker wall pipe
and greater depths of installation are feasible alternatives
to casings, the design recommendations put forward in this
report can be used to develop optimal designs for a range of
pipe wall thickness and depth combinations at both railroad
and highway crossings.
Project
Implications
This report is associated with a project that has resulted in
a comprehensive design methodology for gas pipelines crossing
railroads and highways.
The methodology is applicable for
steel transmission and distribution piping, and has been reviewed by gas, railroad, and highway industry participants.
Computer software, suitable for PC applications, has been developed for applying the methodology in an interactive graphics
environment.
As part of GRI' s enhanced technology transfer activities, seminars for instruction in these state-of-the-art design practices have been organized, and represent a major technology
transfer component of the work. Case studies have been undertaken wi th gas companies to illustrate the application and cost
savings potential associated with these advanced design practices.
The technical effort on this work has ended. However, GRI is
providing through Cornell University technical input to various
organizations as they incorporate this new technology into
their standards. Two such groups are: 1) the American Railway
Engineering Association as part of their effort to provide an
option for an uncased crossing in new construction, and 2) the
American Petroleum Institute in the revision of API RP 1102,
Recommended Practice for Steel Pipelines Crossing Railroads
and Highways.
In addition, GRI is considering additional work that would
allow adaptation of this methodology for new and emerging
trenchless construction techniques.
GRI Project Manager
K. B. Burnham
Senior Project Manager
TABLE OF CONTENTS
Research Summary
Table of Contents ...................................................... .
i
List of Tables ......................................................... .
iv
List of Figures ........................................................ .
v
List of Symbols ........................................................ .
vi
List of Equations ...................................................... .
viii
Section
Page
1
1.1
1.2
1.3
2
3
1
SCOPE
General
Type of Pipeline
Provisions for Public Safety
1
1
1
DIMENSIONS AND DEFINITIONS
2
2.1
2.2
Dimensions
Definitions
2
2
2.2.1
2.2.2
2.2.3
2.2.4
2.2.5
2.2.6
2.2.7
2.2.8
2.2.9
2.2.10
2.2.11
2.2.12
2.2.13
2.2.14
2
2
2
2
3
3
3
Carrier Pipe
Cased Pipeline or Pipe
Casing
Distribution Line
Girth Weld
Longitudinal Weld
Maximum Allowable Operating Pressure (MAOP)
Percussive Mo1ing
Pipe Jacking with Auger Borer
Railroad
Specified Minimum Yield Strength (SMYS)
Transmission Line
Trench1ess Construction
Uncased Pipeline or Pipe
4
4
4
4
4
4
5
DESIGN
6
3.1
Type of Crossing
6
3.1.1
3.1. 2
6
6
3.2
Cased Crossings
Uncased Crossings
Loads
8
-i-
Section
3.2.1
3.2.2
3.3
3.5
4
9
3.2.1.1
3.2.1.2
9
9
Earth Load
Raiiroad Live Load
Internal Load
9
Stresses
10
3.3.1
Stresses Due to External Loads
10
3.3.1.1
3.3.1.2
10
12
3.3.2
3.4
External Loads
Stresses Due to Earth Load
Stresses Due to Railroad Live Load
Stresses Due to Internal Load
14
Limits of Calculated Stresses
14
3.4.1
3.4.2
Check for Allowable Stresses
Check for Fatigue
16
19
3.4.2.1
3.4.2.2
22
Girth Weld
Longitudinal Weld
Example Problems
20
24
INSTALLATION
25
4.1
4.2
Type of Construction
General
25
25
4.2.1
4.2.2
4.2.3
4.2.4
4.2.5
25
25
4.3
Uncased Crossings
4.3.1
4.3.2
4.3.3
4.4
Excavation
Auger Boring
Backfilling
Welding
Pressure Testing
26
26
26
26
Orientation of Longitudinal Welds at Railroad
Crossil)gs
Location of Girth Welds
Protective Coatings
27
27
27
Cased Crossings
27
4.4.1
4.4.2
4.4.3
27
28
28
Insulators
End Seals
Corrosion Control
-ii-
Section
Page
REFERENCES
29
APPENDIX A
30
APPENDIX B
35
-iii-
LIST OF TABLES
3.1
Recommended Factors of Safety Used with Seff' SFG' and SFL
for Various Class Locations
20
Fatigue Endurance Limits, SFL and SFG' for Various Steel
Grades
21
A.I
Typical Values for Modulus of Soil Reaction, E'
30
A.2
Typical Values for Resilient Modulus, Er
30
A.3
Class Locations
31
A.4
Design Factor, F, for Uncased Steel Pipeline Crossings
31
A.S
Longitudinal Joint Factor, E, for Steel Pipe
32
A.6
Temperature Derating Factor, T, for Steel Pipe
33
A.7
Specified Minimum Yield Strengths for Various Steel Grades
33
A.8
Typical Steel Properties
34
3.2
-iv-
LIST OF FIGURES
Figure
2.1
Cross-Section of Typical Uncased Crossings of Railroads
3
2.2
Cross-Section of Typical Cased Crossings of Railroads
3
3.1
Flow Diagram of Design Procedure for Uncased Crossings of
Railroads
7
3.2
Stiffness Factor for Earth Load Circumferential Stress, KHe
11
3.3
Burial Factor for Earth Load Circumferential Stress, Be
11
3.4
Excavation Factor for Earth Load Circumferential Stress, Ee
13
3.5
Recommended Impact Factor versus Depth
13
3.6
Railroad Stiffness Factor for Cyclic Circumferential Stress,
KHr
15
Railroad Geometry Factor for Cyclic Circumferential Stress,
GHr
15
Railroad Double Track Factor for Cyclic Circumferential
Stress, NH
16
3.9
Railroad Stiffness Factor for Cyclic Longitudinal Stress, KLr
17
3.10
Railroad Geometry Factor for Cyclic Longitudinal Stress, GLr
17
3.11
Railroad Double Track Factor for Cyclic Longitudinal Stress,
NL
18
Longitudinal Stress Reduction Factors, RF
23
3.7
3.8
3.12
-v-
LIST OF SYMBOLS
bored diameter of crossing
- burial factor for circumferential stress from earth load
- external diameter of pipe
- longitudinal joint factor
E'
- modulus of soil reaction
Ee
- excavation factor for circumferential stress from earth load
Er
- resilient modulus of soil
Es
- Young's modulus of steel
F
- land use and building class location factor
Fi
- impact factor
FS
- factor of safety
GHr
- geometry factor for cyclic circumferential stress from rail load
GLr
- geometry factor for cyclic longitudinal stress from rail load
H
depth to top of pipe
KHe
- stiffness factor for circumferential stress from earth load
KHr
- stiffness factor for cyclic circumferential stress from rail load
KLr
- stiffness factor for cyclic longitudinal stress from rail load
~
- distance of girth weld from centerline of track
MAOP
- maximum allowable operating pressure
NH
- double track factor for cyclic circumferential stress
NL
- double track factor for cyclic longitudinal stress
Nt
- number of tracks at railroad crossing
p
- internal pipe pressure
RF
- longitudinal stress reduction factor for fatigue
Seff
- total effective stress
SFG
- fatigue endurance limit of girth weld
-vi-
SFL
- fatigue endurance limit of longitudinal weld
SHe
- circumferential stress from earth load
SHi
- circumferential stress from internal pressure
Sl,S2,S3
stresses in pipe; Sl
maximum circumferential stress; S2 - maximum
longitudinal stress; S3 = maximum radial stress
SMYS
- specified minimum yield strength
T
- temperature derating factor
~
- pipe wall thickness
w
- applied design surface pressure
0T
coefficient of thermal expansion
1
- unit weight of soil
6S H
- cyclic circumferential stress
6S Hr
- cyclic circumferential stress from rail load
6SL
- cyclic longitudinal stress
6SLr
- cyclic longitudinal stress from rail load
vs
-
Poisson's ratio of steel
-vii-
LIST OF EQUATIONS
Earth Load
(3.1)
Live Load
Fi - 1. 75 for H
Fi
~
~
(3.2a)
5 ft (1.5 m)
1. 75 - 0.03(H - 5) for H (ft) > 5 ft
(3.2b)
[Fi - 1. 75 - O.l(H - 1. 5) for H (m) > 1. 5 m]
F·1.
=
1.0 for H
~
30 ft (9.1 m)
(3.2c)
(3.3)
(3.4)
Internal Load
(3.5)
[SHi(Bar1ow) - pD/2tw]
~
F'E'T'SMYS
(3.6)
Limits of Calculated Stresses
(3.7)
(3.8)
S3
- -p
=
-
(3.9)
MAOP
-viii-
(3.10)
(3.11)
Seff ::; SMYS/FS
(3.12)
(3.l3)
(3.14)
(3.15)
(3.16)
-ix-
SECTION 1
SCOPE
1.1
GENERAL
These Guidelines apply to the design and construction of new natural gas
pipelines under existing railroads, normally installed using auger boring and
pipe jacking construction methods.
The provisions in this document were devel-
oped to protect overlying rail facilities, as well as to provide for safe installation and operation of the pipeline.
1.2
TYPE OF PIPELINE
The Guidelines apply to steel pipelines used for natural gas transmission
and distribution systems.
1.3
PROVISIONS FOR PUBLIC SAFETY
The Guidelines give primary emphasis to public safety.
The applicable
regulations of federal, state, municipal, and regulatory institutions having
jurisdiction over the facility to be crossed should be observed during the design
and construction of the pipeline.
The Code of Federal Regulations, Title 49,
Part 192 [Office of the Federal Register, 1990] sets minimum standards with
respect to natural gas pipelines.
To reflect the institutions which developed the methodology described herein, the Guidelines for Pipelines Crossing Railroads are referred to throughout
this publication as the Corne11/GRI Guidelines.
This name is taken as the formal
name for the Guidelines, suitable for reference in communications and future published work.
-1-
SECTION 2
DIMENSIONS AND DEFINITIONS
2.1
DIMENSIONS
Figures 2.1 and 2.2 show cross-sections of uncased and cased pipelines,
respectively, at railroad crossings.
Minimum depths of cover for railroads are
defined from top of pipe to the bottom of rail, ground surface, or drainage
ditch.
The American Railway Engineering Association (AREA) [AREA, 1991] speci-
fies a minimal cover for casing pipe of 5.5 ft (1.7 m) beneath rail, except that
under secondary and industrial tracks, it may be 4.5 ft (1.4 m).
At drainage
ditches, minimum covers for railroads are specified typically as 3 ft (0.9 m)
[AREA, 1991]. At all other locations within railroad rights-of-way where casings
are not directly beneath the track, the minimum cover is specified typically at
3 ft (0.9 m) below the ground surface or drainage ditch [AREA, 1991].
Railroad
authorities frequently specify minimum distances for casings to extend beyond
the centerline of track, ditch line, and toe of slope.
As recommended under
Section 1.3, the designer should consult with an authorized agent of the appropriate railroad authority to establish minimum cover requirements for the crossing.
2.2
DEFINITIONS
The following definitions apply to these Guidelines:
2.2.1
CARRIER PIPE
Steel pipe for transporting natural gas.
2.2.2
CASED PIPELINE OR PIPE
A carrier pipe inside a casing which crosses beneath a railroad.
2.2.3
CASING
Conduit through which the carrier pipe may be placed.
2.2.4
DISTRIBUTION LINE
A pipeline other than a gathering or transmission line, as defined by the
-2-
-3-
Railroad \
Minimum depth
be low d itch
t.
£Drainage ditch
,-"""",~~"""¢,**,..,...,4.
Uncased carrier pipe
Minimum depth below ground
Figure 2.1.
roil
!
Cross-Section of Typical Uncased Crossings of Railroads
ROilrOOd\
f
Minimum depth
below bottom of roil
ditch
'Vent
Figure 2.2.
Cross-Section of Typical Cased Crossings of Railroads
Code of Federal Regulations [Office of the Federal Register, 1990].
2.2.5
GIRTH WELD
A full circular weld which joins two adjacent sections of pipe.
2.2.6
LONGITUDINAL WELD
Weld running lengthwise along the pipe made during fabrication of the pipe.
2.2.7
MAXIMUM ALLOWABLE OPERATING PRESSURE (MAOP)
Maximum pressure at which a pipeline or segment of a pipeline may be oper-
ated.
-4-
2.2.8
PERCUSSIVE MOLING
Construction method in which a percussive moling device is used to advance
a hole as sections of pipe are jacked simultaneously into place behind the advancing instrument.
2.2.9
PIPE JACKING WITH AUGER BORER
Construction method for pipeline crossings in which the excavation is per-
formed by a continuous flight auger as sections of pipe are welded together and
then jacked simultaneously behind the front of the advancing auger.
2.2.10
RAILROAD
Rails fixed to ties laid on a roadbed that provide a track for rolling stock
drawn by locomotives or propelled by self-contained motors.
2.2.11
SPECIFIED MINIMUM YIELD STRENGTH (SMYS)
a) For steel pipe manufactured in accordance with a listed specification,
the yield strength specified as a minimum in that specification; or b) for steel
pipe manufactured in accordance with an unknown or unlisted specification, the
yield strength determined in accordance with the Code of Federal Regulations,
Title 49, Part 192 [Office of the Federal Register, 1990].
2.2.12
TRANSMISSION LINE
Pipeline, other than a gathering line, that:
a) transports gas from a
gathering line or storage facility to a distribution center or storage facility;
b) operates at a circumferential (hoop) stress of 20 percent or more of SMYS;
or c) transports gas within a storage field.
The definition here is identical
to that in the Code of Federal Regulations [Office of the Federal Register,
1990].
2.2.13
TRENCHLESS CONSTRUCTION
Any construction method for installing pipelines by subsurface excavation
without the use of open trenching.
-5-
2.2.14
UNCASED PIPELINE OR PIPE
A carrier pipe without a casing which crosses beneath a railroad.
SECTION 3
DESIGN
3.1
TYPE OF CROSSING
The decision to use an uncased or cased crossing must be predicated on care-
ful consideration of the stresses imposed on uncased pipelines, as well as the
potential difficulties associated with the corrosion protection of cased pipelines.
These Guidelines focus specifically on the design of the uncased carrier
to accommodate safely the stresses and deformations imposed at railroad crossings.
The designer should be aware that the presence of a casing may affect the
cathodic protection system, as explained in Section 4.5.3.
3.1.1
CASED CROSSINGS
Design procedures for casings beneath railroad crossings have been estab-
lished and used in practice for many years.
The relevant specifications for
selecting minimal wall thickness for casings under railroads are given by the
American Railway Engineering Association (AREA) [AREA, 1991].
Design practices
suitable for casings beneath railroads are provided by the American Society of
Civil Engineers (ASeE) [Committee on Pipeline Crossings of Railroads and Highways, 1964], the American Society of Mechanical Engineers (ASME) [ASME, 1989],
and the American Petroleum Institute (API) [API, 1981].
It is recommended that
casings for railroads be selected according to the minimal wall thicknesses as
given by AREA [AREA, 1991].
3.1.2
UNCASED CROSSINGS
To ensure safe operation, the stresses affecting the uncased pipeline must
be accounted for comprehensively, including both circumferential and longitudinal stresses.
3.1.
The recommended design procedure is shown schematically in Figure
It consists of the following steps:
a)
Begin with the wall thickness for the pipeline of given diameter
approaching the crossing. Determine the pipe, soil, construction,
and operational characteristics.
b)
Use the Barlow formula to calculate the circumferential stress due
to internal pressure, SHi(Bar1ow).
Check SHi(Bar10w) against F'E'T'SMYS
-6-
-7-
Begin
Pipe, Operational,
Installation, and
Site Characteristics
External Load
• •
Internal Load
Railroad Live Load
Earth Load
Calculate the Circumferential
Stress Due to Internal Pressure,
Using the Barlow Formula,
SHi (Barlow) : Eq. 3.6
Calculate,
w Section 3.3.1.2
Fi Eq. 3.2 or Figure 3.5
,
t
Calculate Circumferential
Stress Due to Earth Load
SHe: Eq. 3.1
Figures 3.2, 3.3,3.4
Calculate Cyclic Circumferential
Stress Due to Live Load,
6S H : Eq.3.3
Figures 3.6, 3.7, 3.8
SHi (Barlow)
Calculate Cyclic Longitudinal
Stress Due to Live Load,
6S L : Eq. 3.4
Figures 3.9,3.10, 3.11
~F'E'T'SMYS ~
Calculate the Circumferential
Stress Due to Internal Pressure,
SHi : Eq.3.5
•
Calculate the Principal Stresses,
5 1 ,5 2 ,5 3 Eqs. 3.7, 3.8,3.9
Calculate Effective Stress,
Seff: Eq. 3.10
Fails Seff Check
Fails Fatigue Check
•
Check for Allowable Seft
Table 3.1
Eq. 3."
Check for Fatigue in Girth Weld:
Tables 3.1, 3.2
Eq. 3.13 or 3.14
Check for Fatigue in
Longitudinal Weld:
Tables 3.1, 3.2
Eq. 3.15 or 3.16
•
•
•
Satisfactory Design
Optimal Design
?
I
No
Design Complete
Figure 3.1.
Flow Diagram of Design Procedure for Uncased Crossings of Railroads
-8-
c)
Calculate the circumferential stress due to earth load, SHe'
d)
Choose the external live load, w, and the appropriate impact factor,
Fi'
e)
Calculate the cyclic circumferential stress,
longitudinal stress, ~SL' due to live load.
f)
Calculate the circumferential stress due to internal pressure, SHi'
g)
Check effective stress, Seff'
~SH'
and the cyclic
Calculate the principal stresses, Sl' in the circumferential direction, S2 in the longitudinal direction, and
S3 in the radial direction.
Calculate the effective stress, Seff'
Check by comparing Seff against the allowable stress,
SMYS/FS.
h)
Check welds for fatigue.
Check girth weld fatigue by comparing
girth weld fatigue limit, SFG/FS.
~SL
against the
Check longitudinal weld fatigue by comparing ~SH against
the longitudinal weld fatigue limit, SFLlFS.
i)
If any check fails, modify the design conditions in Step a) appropriately and repeat Steps b) through h).
Recommended methods for performing Steps b) through h), above, are described in
Sections 3.2 through 3.4.
3.2
LOADS
A carrier pipe at an uncased crossing will be subjected to both internal
load from gas pressurization, and external loads from earth forces (dead load)
and train traffic (live load).
load.
An impact factor should be applied to the live
Recommended methods for calculating these loads and impact factors are
described in the following subsections.
Other loads may be present as a result of temperature fluctuations caused
by changes in season, longitudinal tension due to end effects, unusual surface
loads associated with specialized equipment, and ground deformations arising
from various sources such as shrinking and swelling soils, frost heave, local
instability, nearby blasting, and undermining by adjacent excavations.
Pipe
-9-
stresses induced by temperature fluctuations are treated explicitly in these
Guidelines.
All other loads are a result of special conditions.
Loads of this
nature must be evaluated on a site-specific basis, and therefore are outside the
scope of these Guidelines, which generally are focused on the railroad environment.
Ingraffea, et al. (1991) describe how pipeline stresses can be influenced
by longitudinal bends and tees in the vicinity of the crossing, and give equations to evaluate such effects.
3.2.1
EXTERNAL LOADS
3.2.1.1
Earth Load
The earth load is the force resulting from the weight of the overlying
soil that is conveyed to the top of pipe, calculated according to the procedures
widely adopted in practice for ditch conduits [Marston, 1930].
Such procedures
have been used in pipeline design for many years, and have been embodied in specifications proposed by various professional organizations [e.g., AREA, 1991;
ASME, 1986; Committee on Pipeline Crossings of Railroads and Highways, 1964;
API, 1981].
3.2.1.2
Railroad Live Load
It is assumed that the pipeline is subjected to the load from a single
train, as would be applied on either track shown in Figure 2.1.
For simultane-
ous loading of both tracks, stress increment factors for the cyclic longitudinal
and cyclic circumferential stress are used.
The crossing is assumed to be ori-
ented at 90 degrees with respect to the railroad, and is an embankment-type
crossing, as illustrated in Figure 2.1.
This type of orientation generally is
preferred with respect to new pipeline construction, and is likely to result in
pipeline stresses larger than those associated with pipelines crossing at
oblique angles to the railway.
3.2.2
INTERNAL LOAD
The internal load is produced by gas pressure, p.
operating pressure, MAOP, should be used in the design.
The maximum allowable
-10-
3.3
3.3.1
STRESSES
STRESSES DUE TO EXTERNAL LOADS
External loading on the carrier pipe will produce both circumferential
and longitudinal stresses.
Recommended procedures for calculating each compo-
nent of these stresses follow.
For purposes of design, it is assumed that all
external loads are conveyed vertically across a 90 degree arc centered on the
pipe crown, and resisted by a vertical reaction distributed across a 90 degree
arc centered on the pipe invert.
3.3.1.1
Stresses Due to Earth Load
The circumferential stress at the pipeline invert caused by earth load,
SHe (psi or kPa) , is determined as follows:
(3.1)
in which KHe
Be
stiffness factor for circumferential stress from earth load,
burial factor for earth load
~
excavation factor for earth load,
soil unit weight (lb/in. 3 or kN/m 3 ) , and
D
pipe outside diameter (in. or m).
Ee
It is recommended that ~ be taken as 120 Ib/ft 3 (18.9 kN/m 3 ) [equivalent
to 0.069 lb/in. 3 ] , unless a higher value is justified on the basis of field or
laboratory data.
The earth load stiffness factor, KHe , accounts for the interaction between
the soil and pipe, and depends on the pipe wall thickness to diameter ratio,
tw/D, and modulus of soil reaction, E'.
ous E', as a function of tw/D.
Figure 3.2 shows KHe , plotted for variValues of E' appropriate for auger borer con-
struction may range from 0.2 to 2.0 ksi (1.4 to 13.8 MPa).
It is recommended
that E' be chosen as 0.5 ksi (3.4 MPa) , unless a higher value is judged more
appropriate by the designer.
Table A.l in Appendix A gives typical values for
E'.
The burial factor, Be' is presented as a function of the ratio of pipe
depth to bored diameter, H/Bd' for various soil conditions in Figure 3.3.
If
the bored diameter is unknown or uncertain at the time of design, it is recommended that Bd be taken as 1.1 D.
-11-
.s::;
~
~
12000~~~--~-T--r-~~~~~--~-r--~~~--~~
tfl:r:
:x:::
"'0 ~
~I/'I
01/'1
co~
~
Q)
E" ksi (MPo)
in
8000
0.2 (1.4)
0.5 (3.4)
C":;)0
<l~
~
1.0 (6.9)
-§
Q)
.E~
~
2.0 (13.8)
4000
uu
If .:
U
~"'O
c: 0
Q) 0
~.-J
0
c.n
l __~-l__~~L-~
__~::::J:::~:r::~~==~==±=~==J
0.02
0.04
0.06
0.08
0
Wall Thickness to Diameter Ratio, tw I D
Figure 3.2.
-
Stiffness Factor for Earth Load Circumferential Stress, KHe
.s::;
~
~
~co
"Cui
Q)I/'I
o~
coin
10
.
~o
g':+:
<l ~
..
..
..
Q)
Soil
Type
E
:;)
A
Loose to medium dense
sands and grovels i
soft cloys and silts
B
Dense to very dense
sands and grovels;
medium to very stiff
cloys and silts
0-
-
!2
l:
u·oU
u:."C
_
0
05
.
o 0
'':;: .-J
:;)
CD
Description
Depth to Bored Diameter. Ratio, HIBd
Figure 3.3.
Burial Factor for Earth Load Circumferential Stress, Be
-12-
The excavation factor, Ee , is presented as a function of the ratio of bored
diameter to pipe diameter, Bd/D, in Figure 3.4. If the bored diameter is unknown or uncertain at the time of design, Ee should be assumed equal to one.
3.3.1.2
Stresses Due to Railroad Live Load
Surface Live Loads
The live, external rail load is the vehicular load, w, applied at the surface of the crossing.
It is recommended that Cooper E-80 loading of w - 13.9
psi (96 kPa) be used.
This is the load resulting from the uniform distribution
of four 80-kip (356-kN) axles over a 20-ft by 8-ft (6.l-m by 2.4-m) area.
Impact Factor.
It is recommended that the live load be increased by an
impact factor, Fi , which is a function of the depth of burial, H, of the carrier
pipeline at the crossing. The impact factor for railroad crossings, as shown
in graphical form in Figure 3.5, is:
Fi - 1.75 for H
~
5 ft (1.5 m)
Fi - 1.75 - O.03(H - 5) for H (ft) > 5 ft
[Fi
=
~
30 ft (9.1 m)
Railroad Cyclic Stresses.
~SHr
(3.2b)
1.75 - O.l(H - 1.5) for H (m) > 1.5 m]
Fi - 1.0 for H
load,
(3.2a)
(3.2c)
The cyclic circumferential stress due to rail
(psi or kPa) , may be calculated from:
(3.3)
in which KHr - railroad stiffness factor for cyclic circumferential stress,
GHr - railroad geometry factor for cyclic circumferential stress,
NH - railroad single or double track factor for cyclic circumferential
stress,
Fi
- impact factor, and
w
- applied design surface pressure (psi or kPa).
The railroad stiffness factor, KHr , is presented as a function of the pipe
wall thickness to diameter ratio, tw/D, and soil resilient modulus, Er , in Figure 3.6. Table A.2 in Appendix A gives typical values for Er .
The railroad geometry factor, GHr' is presented as a function of pipe
-13-
1.4~-----------------------------------------------------~
-
.s::.
o
W
~
G)
-0 W
o
en
<n
~
U5
~
1.3
CD ~
C1>
C1' ::::J 0
1.2
<1:';::
~
c
C1>
.E n;
~
o
1.1
E
::::J
'0 ~
~ U
1.0
C"'O
0
o
:;::
~
o
0
-' 0.9
<..>
)(
W
0.8~----~------~------~----~------~----~
1.00
1.05
1.10
1.15
1.20
1.25
1.30
Ratio of Bored Diameter to Pipe Diameter, Bd 10
Figure 3.4.
Excavation Factor for Earth Load Circumferential Stress, Ee
Impact Factor, Fj
1.00
o
1.25
1.50
1.75
2.00
o
5
2
--
4
:c
E
-
.t::
~
G)
0
6
8
Figure 3.5.
Recommended Impact Factor versus Depth
-14-
diameter, D, and depth of burial, H, in Figure 3.7.
The single track factor for cyclic circumferential stress is NH
=
1.00.
The NH factor for double track is shown in Figure 3.B.
The cyclic longitudinal stress due to rail load,
~SLr
(psi or kPa) , may be
calculated from:
(3.4)
in which KLr
=
railroad stiffness factor for cyclic longitudinal stress,
GLr
railroad geometry factor for cyclic longitudinal stress,
NL
railroad single or double track factor for cyclic longitudinal
stress,
Fi
- impact factor, and
w
=
applied design surface pressure (psi or kPa).
The railroad stiffness factor, KLr , is presented as a function of
Er in Figure 3.9.
~/D
and
The railroad geometry factor, GLr , is presented as a function of D and H
in Figure 3.10.
The single track factor for cyclic longitudinal stress is NL
=
1.00.
The
NL factor for double track is shown in Figure 3.11.
3.3.2
STRESSES DUE TO INTERNAL LOAD
The circumferential stress due to internal pressure, SHi (psi or kPa) , may
be calculated from:
p(D in which p
D
~)/2~
(3.5)
internal gas pressure, taken as the maximum allowable operating
pressure, MAOP (psi or kPa) ,
pipe outside diameter (in. or mm), and
wall thickness (in. or mm).
3.4
LIMITS OF CALCULATED STRESSES
The stresses calculated in Section 3.3 may not exceed certain allowable
values.
The allowab1es for controlling yielding and fatigue in the pipeline are
described in the following subsections.
-15-
500
.~
...
:r: 400
U
>-
U
-~
0
~
0
(.)
0
LL..
VI
VI
c
5 (34)
10 (69)
~
VI
VI
(1)
300
~
(/)
0
C
200
-- Q)
E r' ksi (MPa)
~
Q)
~
Q)
E
( /)
-,;::)
0
0~
~
(.)
~
100
U
'0
0:::
0
0
0.02
0.04
0.06
Wall Thickness to Diameter Ratio,
Figure 3.6.
0.08
tw / D
Railroad Stiffness Factor for Cyclic Circumferential Stress, KHr
(mm)
Railroad
.~
... 1.00
u>- (!):r:
(.)
~
oS
~
VI
VI
-~
0
v
if
-
(1)
~
(/)
0.75
0
>--=
~
c
(1)
H, ft (m)
6 (1.8)
10 (3.0)
14 (4.3)
(1)
~
E
(1)
(1)
E
0.50
0(!)
-,;::)
0
e
~
v
~
U 0.25
'0
0:::
0
0
36
42
Diameter, 0 (in.)
Figure 3.7.
Railroad Geometry Factor for Cyclic Circumferential Stress, GHr
-16-
(mm)
1000
0
2.0
0
U
H, ft(m)
14 (4.3)
10 (3.0)
6(1.8)
u>.
..
..-
.E z
:x:
~
..
tf en
en
0
C1>
0
1.5
( /)
.:It!
0
0
t!::
0
:.;:::
c:
C1>
_C1> ..
C1>
J:;J-
E
..
:l
0
o
-0
0
0
1.0
:l
0
U
~
'0
a:::
0.5
Figure 3.8.
3.4.1
0
6
12
24
18
30
Diameter, D (in.)
36
42
Railroad Double Track Factor for Cyclic Circumferential Stress, NH
CHECK FOR ALLOWABLE STRESSES
Two checks for the allowable stress are required.
The first is specified
by the Code of Federal Regulations, Title 49, Part 192 [Office of the Federal
Register, 1990] as referenced in Paragraph 192.105.
The circumferential stress
due to internal pressurization, as calculated using the Barlow formula, SHi(Barlow) (psi or kPa) , must be less than the factored specified minimum yield
strength.
This check is given by:
[SHi(Barlow) in which p
pD/2~] ~
F'E'T'SMYS
(3.6)
- internal gas pressure, taken as the maximum allowable operating
pressure, MAOP (psi or kPa) ,
D
- pipe outside diameter (in. or mm),
~
- wall thickness (in. or mm),
F
- building class location design factor,
E
- longitudinal joint factor,
-17-
Railroad
500
400
~
o
-
en
(1)
-Lf-
300
-
200
~
o
~
(,)(/)
o
en
C
en .-
(1)"0
_C
:a0'
.-
.- C
0
(/)-1
"0
o
e
100
'0
0:::
o~~~
o
__~~__~~~__~~__~~~~~~__~~
0.02
0.08
Wall Thickness to Diameter Ratio, twlD
Figure 3.9.
Railroad Stiffness Factor for Cyclic Longitudinal Stress, KLr
(mm)
2.5
0~~~~~~~~-r~~~,-8~OrO~,-_I~OrOO~
Railroad
.~
~
U
..
-l
<.!)
2.0
~
.$2
~
VI
VI
- e-n
-~
(1)
0
~
1.5
( ,)
If
"0
>- C
:0
( 1)
::I
E .&
~
0
(1)
<.!)
"0
o
e
1.0
H, ft (m)
6 (1.8)
10 (3.0)
14 (4.3)
C
0
...J
0.5
'0
0:::
Diameter, 0 (in.)
Figure 3.10.
Railroad Geometry Factor for Cyclic Longitudinal Stress, GLr
-18-
(mm)
0
2.0
0
0
>-
H, f1(m)
14 (4.3)
IO{3.0)
6 (1.8)
u
-- .
~
0
~
0
0
...J
z
0
-
.=
0
.~
&'
1.5
en
en
Q.)
~
..:.: c.n
0
Q.)
-
"'0
::;)
:c .& 1.0
::;)
0
0
c:
.3
"'0
0
e
·0
a:
0.5
0
Figure 3.11.
6
12
24
18
30
Diameter, D (in.)
36
42
Railroad Double Track Factor for Cyclic Longitudinal Stress, NL
T
- temperature derating factor, and
SMYS - specified minimum yield strength (psi or kPa).
Tables A.3 and A.4 in Appendix A give descriptions of the class locations,
and F values for various kinds of thoroughfares as dependent on class location,
respectively.
Tables A.S and A.6 in Appendix A give the longitudinal joint fac-
tors, E, for steel pipe, and temperature derating factors, T, respectively.
Table A.7 in Appendix A lists typical values of SMYS for various steel grades.
The second check for the allowable stress is accomplished by comparing the
total effective stress, Seff (psi or kPa) , against the specified minimum yield
strength divided by a factor of safety.
Principal stresses, Sl' S2' and S3 (psi
or kPa) , are used to calculate Seff.
The principal stresses are calculated
from:
(3.7)
in which
~SH
-
~SHr
(psi or kPa) for railroads.
-19-
(3.8)
in which
~SL
-
~SLr
Es
- Young's modulus of steel (psi or kPa) ,
oT
T1
coefficient of thermal expansion of steel (per degree F or per
degree C),
~emperature
-
T2
vs
(psi or kPa) for railroads
at time of installation, (degrees F or degrees C),
maximum or minimum operating temperature, (degrees F or degrees
C), and
- Poisson's ratio of steel.
Table A.8 in Appendix A gives typical values for Es ' v s ' and oT'
S3
- -p
=
-
(3.9)
MAOP
It should be noted that the Poisson effects from SHe and SHi are reflected
in S2 as vs(SHe + SHi)'
The Poisson effect of
sented in the equation for Sl'
The values of
~SL
~SH
on Sl is not directly repreand
~SL
in these Guidelines
were derived from finite element analyses and therefore already embody the
appropriate Poisson effects.
The total effective stress, Seff (psi or kPa) , may be calculated from:
(3.10)
The check against yielding of the pipeline may be accomplished by assuring
that the total effective stress is less than the factored specified minimum
yield strength, using the following equation:
Seff ::;; SMYS/FS
(3.11)
in which SMYS = specified minimum yield strength (psi or kPa) , and
FS
- factor of safety.
Table 3.1 gives recommended factors of safety for various class locations.
The designer may use values other than those given in Table 3.1, and is not constrained to use the same factor of safety for all of the additional design
checks.
3.4.2
CHECK FOR FATIGUE
The check for fatigue is accomplished by comparing a stress component nor-
mal to a weld in the pipeline against an allowable value of this stress,
-20-
Table 3.1.
Recommended Factors of Safety Used with Seff' SFG' and SFL for
Various Class Locations
Class Location
Factor of Safety, FS
1.4
1.6
1.8
2.0
1
2
3
4
referred to as a fatigue endurance limit.
These limits have been determined
from S-N data [Celant, et al., 1983; DIN, 1989] and the minimum ultimate tensile
strengths of commonly used pipe steel [API, 1991].
3.4.2.1
Girth Weld
The cyclic stress that must be checked for potential fatigue in a girth
weld located beneath a railroad crossing is the longitudinal stress due to live
load.
The design check is accomplished by assuring that the live load cyclic
longitudinal stress is less than the factored fatigue endurance limit.
The
fatigue endurance limit of girth welds is taken as 12,000 psi (82,740 kPa), as
shown in Table 3.2 for all steel grades and weld types.
The general form of the design check against girth weld fatigue is given
by:
(3.12)
in which
~SL
-
~SLr
(psi or kPa) for railroads,
SFG - fatigue endurance limit of girth weld - 12,000 psi (82,740 kPa),
and
FS
factor of safety.
Equation 3.12 is the general form of the girth weld fatigue check.
the value of
~SL
Since
is influenced by whether single or double track crossings were
selected, this must be accounted for in the fatigue checks. The fatigue endurance limits are based on 2 x 10 6 load cycles.
It is overly conservative to
assume that all of the applied load cycles will be those generated by
-21-
Table 3.2.
Fatigue Endurance Limits, SFG and SFL' for Various Steel Grades
SFL (psi)
Steel
Grade
SMYS
(psi)
A25
A
25000
30000
35000
42000
46000
52000
56000
60000
65000
70000
80000
B
X42
X46
X52
X56
X60
X65
X70
X80
Minimum Ultimate
Tensile Strength
(psi)
SFG (psi)
All Welds
Seamless
and ERW
SAW
12000
12000
12000
12000
12000
12000
12000
12000
12000
12000
12000
21000
21000
21000
21000
21000
21000
23000
23000
23000
25000
27000
12000
12000
12000
12000
12000
12000
12000
12000
12000
13000
14000
45000
48000
60000
60000
63000
66000
71000
75000
77000
82000
90000
1 psi - 6.89 kPa
simultaneous loading of both tracks, with the train wheel sets always in phase
directly above the crossing.
Therefore, the cyclic longitudinal stress used in
the girth weld fatigue check at railroad crossings is based on the live load
stress from a single track loading situation.
The resulting equation is given
by:
(3.13)
in which
~SLr
- cyclic longitudinal stress determined from Equation 3.4 (psi or
kPa) ,
NL
= single or double track factor used in Equation 3.4 (Note: NL =
1.00 for single track crossings),
SFG - fatigue endurance limit of girth weld - 12,000 psi (82,740 kPa),
and
FS
- factor of safety.
Equation 3.13 is applicable to railroad crossings in which a girth weld is
located at a distance,
track.
Le,
less than 5 ft (1.5 m) from the centerline of the
For other locations of a girth weld, Equation 3.13 is replaced by:
(3.14)
-22-
in which RF - longitudinal stress reduction factor for fatigue.
RF is obtained from Figure 3.12.
Figure 3.l2a is for values of
or equal to 5 ft (1.5 m), but less than 10 ft (3.0 m).
ues of
Lc
Lc
greater than
Figure 3.l2b is for val-
greater than or equal to 10 ft (3.0 m).
3.4.2.2
Longitudinal Weld
The cyclic stress which must be checked for potential fatigue in a longitudinal weld located beneath a railroad crossing is the circumferential stress
due to live load.
The check may be accomplished by assuring that the live load
cyclic circumferential stress is less than the factored fatigue endurance limit.
The fatigue endurance limit of longitudinal welds, SFL' is dependent on the
type of weld and the minimum ultimate tensile yield strength.
Table 3.2 gives
the fatigue endurance limits for ERW and SAW longitudinal welds made in various
grade steels.
For SMYS values intermediate to those listed in Table 3.2, the
fatigue endurance limits for the closest SMYS listed that is lower than the particular intermediate value should be used.
For example, if the SMYS was 54,000
psi (372 MPa) , the fatigue endurance limits for X52 grade steel would be used.
The general form of the design check against longitudinal weld fatigue is
given by:
(3.15)
in which
~SH
-
~SHr
SFL
~
fatigue endurance limit of longitudinal weld obtained from Table
3.2 (psi or kPa) , and
FS
- factor of safety.
(psi or kPa) for railroads,
Equation 3.15 is the general form of the longitudinal weld fatigue check.
As described previously in the section dealing with girth weld fatigue at railroad crossings, it is overly conservative to use double track cyclic stresses
for fatigue purposes.
Therefore, the cyclic circumferential stress used in the
longitudinal weld fatigue check at railroad crossings is the live load stress
from a single track loading situation.
The resulting equation is given by:
(3.16)
in which
~SHr
- cyclic circumferential stress determined from Equation 3.3 (psi
or kPa) ,
NH
- single or double track factor used in Equation 3.3 (Note: NH -
-23-
D (mm)
LL.
a::
..:-
-
I. 0
or--"-"T-"""T"--r--"T"'----,r----r-"""T"-.,--,.--,.--,
200
400
800
600
1000
o
( .)
H=14ft (4.3m)
~
c:
~
H=IOft(3.0m}
(.)
:::)
-0
&
0.5
H=6ft(1.8m}
5ft (1.5m) ~ LG < IOft(3.0m)
(/)
(/)
~
U5
LG= Distance from
railroad centerline
to nearest girth weld
o
.5
-
-0
:::)
.&
c:
o
6
....J
12
18
24
30
36
42
Pipe Diameter, D (in.)
a) For
Lc
Greater Than or Equal to 5 ft (1.5 m) but Less Than 10 ft (3.0 m)
D (mm)
LL.
a::
..:-
200
0
1.0
400
600
0
800
1000
lOft (3.0m) ~ LG
( .)
~
c:
0
~
(.)
:::)
-0
Q)
a::
H = 14 f t (4. 3 m)
0.5
(/)
H = 10ft {3.0m}
(/)
Q)
~
H=6ft (1.8m)
(/)
0
c:
~
:::)
'c;,
c:
0
....J
0
0
6
12
18
24
30
36
42
Pipe Diameter, 0 (in.)
b) For
Lc
Figure 3.12.
Greater Than or Equal to 10 ft (3.0 m)
Longitudinal Stress Reduction Factors, RF
-24-
1.00 for single track crossings),
SFL
FS
3.5
fatigue endurance limit of longitudinal weld obtained from Table
3.2 (psi or kPa), and
factor of safety.
EXAMPLE PROBLEMS
Example problems demonstrating the application of the design procedure for
gas transmission and distribution pipelines at railroads are provided in Appendix B.
SECTION 4
INSTALLATION
4.1
TYPE OF CONSTRUCTION
Pipe jacking with an auger borer is the predominant means of pipeline
installation beneath railroads in U. S. practice.
Percussive moling also is used,
but is restricted to small pipelines, typically less than 6 in. (150 mm) in
diameter.
For trenchless construction techniques which excavate an oversized
hole relative to the size of the pipe, the diameter of the bored hole, Bd , needs
to be known or specified before construction.
By means of Figure 3.4, the
designer can account for the influence of the bored hole diameter, Bd , on the
earth load transmitted to the pipe. When the auger is adjusted to excavate a
hole equal in size to the pipe, or when percussive moling or a similar insertion
method is used, the designer should assume that the bored diameter is equal to
the pipe diameter, Bd - D.
4.2
GENERAL
The following considerations apply to pipeline installation, irrespective
of uncased or cased crossings.
4.2.1
EXCAVATION
The pipe is jacked from an excavation, referred to as a launching pit, into
an excavation, referred to as a receiving pit.
Both the launching and receiving
pits are excavated and supported so as to ensure safety of construction personnel
and to protect the adjacent railroad.
4.2.2
AUGER BORING
Auger boring for a pipeline crossing often is performed with an auger that
is a fraction of an inch to as much as 2 in. (51 mm) larger in diameter than the
pipe, under circumstances in which the auger is advanced in front of the casing.
Modifications of the method, such as reducing the auger size and fitting the pipe
or casing with stops to prevent the auger from leading the pipe, can substantially reduce the overexcavation. Reduction in the amount of overexcavation will
decrease the chances of disturbing the surrounding soil and overlying facility,
-25-
-26-
and can diminish the amount of earth load imposed on the pipe.
It should be
recognized, however, that reductions in overcutting generally will increase frictional and adhesive resistance to the advance of the pipe.
It may be necessary,
therefore, to require track-mounted equipment in the launching pit, with a suitable end bearing wall so that adequate jacking forces can be mobilized.
For long
or sensitive crossings, the use of bentonite slurry to lubricate the jacked pipe
may be helpful.
4.2.3
BACKFILLING
Careful placement and compaction of backfill in the launching and reception
pits help reduce the settlement of the carrier pipe adjacent to the crossing.
This, in turn, decreases the bending stress in the carrier where it enters the
backfilled launching and reception pits.
Good backfilling practice includes,
but is not limited to, removal of remolded and disturbed soil from the bedding
of the carrier pipe, and placement of fill compacted in sufficiently small lifts
to achieve a dense bedding for the carrier.
Sand bags, bags of cement, and con-
crete blocks can provide supplemental support for the carrier adjacent to the
crossing, as long as adequate cushioning is provided to pad their contact with
the carrier.
Support materials subject to biological attack, such as wooden
blocking, may decompose and increase the chance of local corrosion.
4.2.4
WELDING
Carrier pipe at railroad crossings must be welded in compliance with the
Code of Federal Regulations, Title 49, Part 192 [Office of the Federal Register,
1990} .
4.2.5
PRESSURE TESTING
Pressure testing procedures are described by professional societies, such
as AS ME [ASME, 1986; ASME, 1989], and by the Code of Federal Regulations, Title
49, Part 192 [Office of the Federal Register, 1990].
4.3
UNCASED CROSSINGS
The following considerations apply to uncased crossings.
-27-
4.3.1
ORIENTATION OF LONGITUDINAL WELDS AT RAILROAD CROSSINGS
The design checks in these Guidelines against longitudinal weld fatigue are
based on the maximum value of the cyclic circumferential stress, 6SH'
Thus, if
the design check against longitudinal weld fatigue is satisfactory, locating the
weld at any location is acceptable.
However, it may be advantageous to consider
the circumferential orientation of the pipeline welds during construction.
The
optimal location of all longitudinal welds is at the 45, 135, 225, or 315 degree
position, with the crown at the 0 degree position.
For any of these orienta-
tions, Equation 3.3 will predict conservative values of cyclic circumferential
stress.
Accordingly, these optimal weld locations provide an additional margin
of safety against longitudinal weld fatigue.
4.3.2
LOCATION OF GIRTH WELDS
The optimal location of a girth weld at railroad crossings is a distance,
Le.
of at least 10 ft (3.0 m) from the centerline of the track for a single track
crossing.
As indicated in Section 3.4.2, substantial reductions in the value
of applied cyclic longitudinal stress may be obtained in this case.
No reduction
factor should be taken for the fatigue check when evaluating pipelines crossing
beneath two or more adjacent tracks.
4.3.3
PROTECTIVE COATINGS
The selection of a pipeline coating requires consideration of the construc-
tion technique and the abrasion and contact forces associated with pipeline installation.
There are various coatings which are tough and exhibit good resis-
tance to surface stress, moisture adsorption, and cathodic disbondment.
Coatings
suitable for uncased crossings include thermosetting resin epoxies, polyethylene
and po1yo1efin coatings, and reinforced concrete jackets, which may be beneficial
in soils containing cobbles and boulders.
4.4
CASED CROSSINGS
The following considerations apply to cased crossings.
4.4.1
INSULATORS
Insulators electrically isolate
the carrier pipe from the
casing by
-28providing a circular enclosure which prevents direct contact between the two.
Electrically inert materials, such as high density polyethylene and fiberglass,
are preferred.
Horizontal spacing of 10 ft (3.0 m) or less between insulators
is adequate to prevent casing-carrier contact under normal conditions of installation.
4.4.2
END SEALS
The casing usually is fitted with end seals to reduce the intrusion of water
and fines from the surrounding soil.
It should be recognized that a water-tight
seal is not possible under all field conditions, and that some water infiltration
should be anticipated.
4.4.3
CORROSION CONTROL
Casings may reduce or eliminate the effectiveness of cathodic protection.
A cased carrier pipe can be exposed to atmospheric corrosion as a result of
circulation of air and moisture through vents attached to the casing.
The
introduction of a casing creates a more complicated electrical system than
normally would prevail for uncased crossings, so there may be difficulties in
securing and interpreting corrosion control measurements at cased crossings.
REFERENCES
American Petroleum Institute, "Recommended Practice for Liquid Petroleum Pipelines Crossing Railroads and Highways," API Recommended Practice 1102, 5th
Ed., Washington, D.C., Nov. 1981, 19 p.
American Petroleum Institute, "Standard for Welding Pipelines and Related Facilities," API Recommended Practice 1104, 17th Ed., Washington, D.C., 1988,
51 p.
American Petroleum Institute, "Specification for Line Pipe," API Specification
5L (Spec 5L), 39th Ed., Washington, D.C., 1991, 93 p.
American Railway Engineering Association, Manual for Railway Engineering, Chapter
1, "Roadway and Ballast," AREA, Washington, D.C., 1991, pp. 1-5-1 - 1-511.
American Society of Mechanical Engineers, "ASME Guide for Gas Transmission and
Distribution Piping Systems - 1986," 6th Ed., ASME, New York, NY, May
1986, 325 p.
American Society of Mechanical Engineers, "Gas Transmission and Distribution Piping Systems," ANSI/ASME B31.8-l989, ASME, New York, NY, Feb. 1989.
Celant, M., A. Cigada, G. Re, D. Sinigaglia, and S. Venzi, "Fatigue Characteristics for Probabilistic Design of Submarine Vessels," Corrosion Science,
Vol. 23, No.6, 1983, pp. 621-636.
Committee on Pipeline Crossings of Railroads and Highways," Interim Specifications for the Design of Pipeline Crossings of Railroads and Highways,"
Journal of the Pipeline Division, ASCE, New York, NY, Jan. 1964.
DIN 2413, "Berechnung der Wanddicke von Stahlrohren gegen Innendruck," April
1989, 21 p.
Ingraffea, A. R., T. D. O'Rourke, H. E. Stewart, M. T. Behn, A. Barry, C. W.
Crossley, and S. L. El-Gharbawy, "Technical Summary and Database for Guidelines for Pipelines Crossing Railroads and Highways," Report GRI-9l/0285,
Gas Research Institute, Chicago, IL, Dec. 1991.
Marston, A. "The Theory of External Loads on Closed Conduits in Light of Latest
Experiments," Proceedings, Highway Research Board, Vol. 9, 1930, pp. 138170.
Office of the Federal Register, "Transportation of Natural and Other Gas by Pipelines: Minimum Federal Safety Standards," Code of Federal Regulations,
Title 49, Part 192, General Services Administration, National Archives and
Records Service, Washington, D.C., Nov. 1990, pp. 578-633.
Stewart, H. E., T. D. O'Rourke, A. R. Ingraffea, A. Barry, M. T. Behn, C. W.
Crossley, and S. L. E1-Gharbawy, "Guidelines for Pipelines Crossing Highways," Report GRI-9l/0284, Gas Research Institute, Chicago, IL, Dec. 1991.
-29-
APPENDIX A
This appendix contains tables and figures on material properties and design"
values that give supplemental information to that contained in the body of these
Guidelines.
A.1
TABLES OF TYPICAL VALUES
Table A.1.
Typical Values for Modulus of Soil Reaction, E'
Soil Description
E', ksi (MPa)
Soft to medium clays and silts with
high plasticities
0.2 (1.4)
Soft to medium clays and silts with
low to medium plasticities; Loose
sands and gravels
0.5 (3.4)
Stiff to very stiff clays and silts;
Medium dense sands and gravels
1.0 (6.9)
Dense to very dense sands and gravels
2.0 (13.8)
Table A.2.
Typical Values for Resilient Modulus, Er
Soil Description
Soft to medium clays and silts
Er , ksi (MPa)
5 (34)
Stiff to very stiff clays and silts;
Loose to medium dense sands and gravels
10 (69)
Dense to very dense sands and gravels
20 (138)
-30-
-31-
Table A.3.
Class Locations [Office of the Federal Register, 1990]
Class Location
Description
1
Any class location unit that has 10 or less buildings
intended for human occupancy
2
Any class location unit that has more than 10 but less
than 46 buildings intended for human occupancy
3
a) Any class location unit that has 46 or more buildings
intended for human occupancy; or
b) An area where the pipeline lies within 100 yards (91 m)
of either a building or a small, well-defined outside
area (such as a playground, recreation area, outdoor
theater, or other place of public assembly) that is
occupied by 20 or more persons on at least 5 days a
week for 10 weeks in any l2-month period. (The days
and weeks need not be consecutive)
4
Any class location unit where buildings with four or more
stories are prevalent
The class location unit is an area that extends 220 yards (200 m) on either
side of the centerline of a continuous l-mile (1.6-km) length of pipeline
Table A.4.
Design Factor, F, for Uncased Steel Pipeline Crossings [ASME, 1986]
Class Location
Kind of Thoroughfare
1
2
3
4
Privately owned roads
0.72
0.60
0.50
0.40
Unimproved public roads
0.60
0.60
0.50
0.40
Hard surfaced roads,
highways, public streets,
and railroads
0.60
0.50
0.50
0.40
-32-
Table A.5.
Longitudinal Joint Factor, E, for Steel Pipe [ASME, 1986]
Specification
ASTM A 53
ASTM
ASTM
ASTM
ASTM
ASTM
ASTM
A
A
A
A
A
A
106
134
135
139
211
333
ASTM A
ASTM A
ASTM A
ASTM A
API 5L
381
671
672
691
API 5LX
API 5LS
Other
Other
Pipe Class a
Longitudinal
Joint Factor (E)
Seamless
Electric resistance welded
Furnace butt welded
Seamless
Electric fusion arc welded
Electric resistance welded
Electric fusion arc welded
Spiral welded steel pipe
Seamless
Electric resistance welded
Double submerged arc welded
Electric-fusion-welded
Electric-fusion-welded
Electric-fusion-welded
Seamless
Electric resistance welded
Electric flash welded
Submerged arc welded
Furnace butt welded
Seamless
Electric resistance welded
Electric flash welded
Submerged arc welded
Electric resistance welded
Submerged arc welded
Pipe over 4 in. (102 rnrn)
Pipe 4 in. (102 rnrn) or less
1.00
1.00
.60
1.00
.80
1.00
.80
.80
1.00
1. 00
1. 00
1.00
1. 00
1.00
1.00
1.00
1.00
1.00
.60
1.00
1.00
1.00
1.00
1.00
1.00
.80
.60
a - If the type of longitudinal joint can not be determined, the
joint factor to be used must not exceed that designated for
"Other"
-33-
Table A.6.
Temperature Derating Factor, T, for Steel Pipe [Office of the
Federal Register, 1990]
Gas Temperature a
250°F
300°F
350°F
400°F
450°F
T
or less (121°C or less)
(149°C)
(177°C)
(204°C)
(232°C)
1.000
0.967
0.933
0.900
0.867
a - for intermediate temperatures, the
derating factor is determined by
interpolation
Table A.7.
Specified Minimum Yield Strengths for Various Steel Grades [ASME,
1986]
Type a
Grade
A25
A
B
X42
X46
X52
X56
X60
X65
X70
X80
a -
BW, ERW, S
ERW, GMAW,
ERW, GMAW,
ERW, GMAW,
ERW, GMAW,
ERW, GMAW,
ERW, GMAW,
ERW, GMAW,
ERW, GMAW,
ERW, GMAW,
ERW, GMAW,
BW
ERW
S
GMAW
SAW
=
-
-
SMYS, psi (kPa)
S,
S,
S,
S,
S,
S,
S,
S,
S,
S,
SAW
SAW
SAW
SAW
SAW
SAW
SAW
SAW
SAW
SAW
25,000
30,000
35,000
42,000
46,000
52,000
56,000
60,000
65,000
70,000
80,000
furnace butt weld
electric resistance weld
seamless
gas metal-arc weld (MIG)
submerged arc weld
(172,370)
(206,840)
(241,320)
(289,580)
(317,160)
(358,530)
(386,110)
(413,690)
(448,160)
(482,640)
(551,580)
-34-
Table A.8.
Typical Steel Properties
Property
Typical Range
Young's modulus, Es ' psi (kPa)
28 - 30 x 10 6
(1.9 - 2.1 x 10 8 )
Poisson's ratio,
0.25 - 0.30
Vs
Coefficient of thermal expansion,
QT' per of (per °C)
6 - 7 x 10- 6
(1.6 - 1.9 x 10- 5 )
APPENDIX B
RAILROAD EXAMPLE PROBLEM RR.l
A nominal 2-in. (5l-mm) diameter [actual outside diameter
mm)]
~
distribution pipeline with a wall thickness of 0.172 in.
intended to cross a single track railroad in a Class I location.
constructed of Grade B steel [SMYS
~
2.375 in. (60
(4.4 mm)
is
The pipe is
35,000 psi (241 MPa)], and will carry
natural gas at a maximum allowable operating pressure of 1000 psi (6.9 MPa).
The initial design depth for the pipeline is 6 ft (1.8 m).
The pipeline will
be installed without a casing, using auger boring construction.
eter of the crossing will be 3 in. (76 mm).
mined to be a loose sand.
The bored diam-
The soil at the crossing was deter-
The resilient modulus of the soil at the crossing
was estimated to be 10 ksi (34 MPa).
Using the Guidelines for Pipelines Crossing Railroads, check whether the
design as given is adequate to withstand the applied earth load, railroad live
load, and internal pressure.
Neglect any changes in pipe temperature.
Assume
that, during construction, any girth welds will be located 5 ft (1.5 m) from the
track centerline.
If the pipe design as given is found inadequate, what is the
wall thickness, maintaining all other construction and operational parameters
as given, that is required to meet the design constraints?
-35-
-36-
Page 1 of 5
RAILROAD CROSSING DESIGN
Problem Description:
Railroad Example Problem RR.1
Step a - Initial Design Information
Pipe and Operational Characteristics:
Outside diameter, D
Maximum allowable operating pressure, MAOP
- 2.375 in.
p
1000 psi
Steel grade
- B
35000 psi
Specified minimum yield strength, SMYS
Class location (1, 2, 3, or 4)
- 1
= 0.60
Class location factor, F
Longitudinal joint factor, E
=
Installation temperature, T1
- N/A
= N/A
Maximum or minimum operating temperature, T2
Temperature derating factor, T
Wall thickness,
1.00
- 1. 000
0.172 in.
~
Installation and Site Characteristics:
Depth, H
=
Bored diameter, Bd
6.0 ft
3.0 in.
Soil type
.., Loose sand
Modulus of soil reaction, E'
== 0.5 ksi
Resilient modulus, Er
=
Unit weight, 'Y
- 120 1b/ft 3 = 0.069 1b/in. 3
Type of longitudinal weld
- ERW
Distance of girth weld from track centerline,
Number of tracks (lor 2)
Rail loading
I.e
=
10 ksi
5 ft
- 1
E-80
Other Pipe Steel Properties:
Young's modulus, Es
- 30000 ksi
Poisson's ratio, Vs
- 0.30
Coefficient of thermal expansion, 0T
6.5 x 10- 6 per of
-37-
Page 2 of 5
RAILROAD CROSSING DESIGN
Problem Description:
Railroad Example Problem RR.l
Step b - Check Allowable Barlow Stress
b.l
Equation 3.6 with:
p
1000 psi
D
2.375 in.
~&=
0.172 in.
F
&=
F·E·T·SMYS
0.60
E
l.00
T
l.00
SMYS
SHi(Barlow)
=
&=
6904 psi
21000 psi
35000 psi
SHi(Barlow)
~
F·E·T·SMYS?
Step c - Circumferential Stress Due to Earth Load
c.l
Figure 3.2 with:
E'
c.2
Figure 3.3 with:
KHe - 259
tw/D - 0.072
0.5 ksi
l. 36
H/Bd
=
24.0
Soil type
=
Loose Sand (A)
c.3
Figure 3.4 with:
c.4
Equation 3.1 with:
l. 26
D
2.375 in.
SHe - 76 psi
3
1 - 120 lb/ft - 0.069 lb/in. 3
Step d - Impact Factor, Fi , and Applied Design Surface Pressure, w
d.l
Equation 3.2 or Figure 3.5 with:
d.2
Applied Design Surface Pressure, w
Section 3.3.1.2:
H - 6 ft
Rail Loading - E-80
w .. 13.9 psi
Yes
-38-
RAILROAD CROSSING DESIGN
Page 3 of 5
Problem Description:
Railroad Example Problem RR.l
Step e - Cyclic Stresses, ASHr and ASLr
e.1
e.1.1
Cyclic Circumferential Stress, ASHr
Figure 3.6 with:
- 0.072
~/D
Er
e.1.2
e.1. 3
Figure 3.7 with:
=
D
2.375 in.
H
6 ft
Section 3.3.1.2 and Figure 3.8 with:
Nt
e.1.4
e.2
e.2.1
=
1
Equation 3.3:
ASHr
Cyclic Longitudinal Stress, ASLr
Figure 3.9 with:
~/D ..,
Er
e.2.2
10 ksi
Figure 3.10 with:
=
D
0.072
1512 psi
•
KLr - 181
10 ksi
2.375 in.
GLr
.., 2.03
H - 6 ft
e.2.3
Section 3.3.1.2 and Figure 3.11 with:
Nt .. 1
e.2.4
Equation 3.4:
ASLr - 8785 psi
-39-
Page 4 of 5
RAILROAD CROSSING DESIGN
Problem Description:
Railroad Example Problem RR.l
Step f - Circumferential Stress Due to Internal Pressurization, SHi
Equation 3.5 with:
MAOP
=
1000 psi
P
SHi
=
6404 psi
=
7992 psi
D = 2.375 in.
0.172 in.
Step g - Principal Stresses, Sl, S2' S3
30 x 10 6 psi
6.5 x 10- 6 per of
Es
aT
Tl
g.l
Equation 3.7 with:
N/A
Vs
0.30
76 psi
SHe
Equation 3.8 with:
N/A
T2
.6SHr
g.2
=
=
Sl
1512 psi
SHi
6404 psi
.6S Lr
8785 psi
10729 psi
SHe ... 76 psi
6404 psi
SHi
g.3
Equation 3.9 with:
MAOP
g.4
Effective Stress, Seff
Equation 3.10 with:
=
P
1000 psi
7992 psi
Sl
S2
=
S3
=
-1000 psi
Seff
=
10628 psi
10729 psi
S3 - -1000 psi
g.5
Check Allowable Effective Stress
Table 3.1
Class location - 1
FS - 1.4
SMYS - 35000 psi
Equation 3.10 with:
Seff - 10628 psi
SMYS/FS ... 25000 psi
Seff < SMYS/FS?
Yes
-40-
Page 5 of 5
RAILROAD CROSSING DESIGN
Problem Description:
Railroad Example Problem RR.l
Step h - Check Fatigue
h.l
Girth Welds
Table 3.1
Class location
=
1
FS - 1.4
Table 3.2
h.1.l
If
SFG - 12000 psi
La < 5 ft (1.5 m) use:
Equation 3.13 with:
~SLr­
NL ...
~SLr/NL
=
SFG/ FS h.1.2
If La ~ 5 ft (1. 5 m) use:
Figure 3.12 with:
LG
Equation 3.14 with:
~SLr
NL
RF
h.2
5 ft
8785 psi
=
RF
~SLr/NL
< SFG/ FS ? Yes
1.00
~SLr/NL =
4304 psi
SFG/FS
8571 psi
=
RF ... 0.49
Longitudinal Welds
Table 3.1
Class location - 1
Table 3.2
Equation 3.16 with:
FS - 1.4
SFL - 21000 psi (ERW)
~SHr
- 1512 psi
NH ... 1.00
~SHr/NH
1512 psi
SFLiFS ... 15000 psi
~SHr/NH
< SFLiFS?
Yes
-41-
RAILROAD EXAMPLE PROBLEM RR.2
A 24-in. (6l0-rnm) diameter transmission pipeline with a wall thickness of
0.500 in. (12.7 rnm) is intended to cross a double track railroad in a Class 1
location.
The pipe is constructed of Grade X-42 steel [SMYS - 42,000 psi (290
MPa)] with SAW longitudinal welds, and will carry natural gas at a maximum allowable operating pressure of 1000 psi (6.9 MPa).
pipeline is 6 ft (1.8 m).
The pipeline will be installed without a casing, using
auger boring construction.
(660 mm).
The initial design depth for the
The bored diameter of the crossing will be 26 in.
The soil at the crossing was determined to be a loose sand.
The
resilient modulus of the soil at the crossing was estimated to be 10 ksi (34
MPa).
Using the Guidelines for Pipelines Crossing Railroads, check whether the
design as given is adequate to withstand the applied earth load, railroad live
load, and internal pressure.
Neglect any changes in pipe temperature.
Assume
that, during construction, any girth welds will be located less than 5 ft (1.5
m) from the track centerline.
If the pipe design as given is found inadequate,
what is the wall thickness, maintaining all other construction and operational
parameters as given, that is required to meet the design constraints?
-42-
Page 1 of 9
RAILROAD CROSSING DESIGN
Problem Description:
Railroad Example Problem RR.2
Step a - Initial Design Information
Pipe and Operational Characteristics:
Outside diameter, D
24.0 in.
Maximum allowable operating pressure, MAOP - P
1000 psi
-'X-42
Steel grade
42000 psi
Specified minimum yield strength, SMYS
Class location (1, 2, 3, or 4)
- 1
.. 0.60
Class location factor, F
Longitudinal joint factor, E
1.00
N/A
Installation temperature, Tl
=
Maximum or minimum operating temperature, T2
.., N/A
Temperature derating factor, T
=
1. 000
0.500 in.
Wall thickness, tw
Installation and Site Characteristics:
Depth, H
'" 6.0 ft
Bored diameter, Bd
-=
Soil type
- Loose sand
Modulus of soil reaction, E'
=
Resilient modulus, Er
"" 10 ksi
Unit weight, 'Y
-=
120 lb/ft 3 = 0.069 lb/in. 3
Type of longitudinal weld
-=
SAW
Distance of girth weld from track centerline,
Lc
26.0 in.
0.5 ksi
.. < 5 ft
Number of tracks (lor 2)
2
Rail loading
E-80
Other Pipe Steel Properties:
Young's modulus, Es
=
30000 ksi
Poisson's ratio, Vs
-=
0.30
Coefficient of thermal expansion, QT
6.5 x 10- 6 per of
-43-
Page 2 of 9
RAILROAD CROSSING DESIGN
Problem Description:
Railroad Example Problem RR.2
Step b - Check Allowable Barlow Stress
b.1
Equation 3.6 with:
p
1000 psi
SHi(Bar1ow)
D
24.0 in.
tw=
0.500 in.
=
24000 psi
F·E·T·SMYS - 25200 psi
F - 0.60
E - 1.00
T = 1.00
42000 psi
SMYS
SHi(Bar1ow)
~
F·E·T·SMYS?
=
2745
Step c - Circumferential Stress Due to Earth Load
c.l
Figure 3.2 with:
tw/D
=
KHe
0.021
E' - 0.5 ksi
c.2
Figure 3.3 with:
H/Bd
=
2.8
Be - 0.82
Soil type - Loose Sand (A)
c.3
Figure 3.4 with:
c.4
Equation 3.1 with:
Ee
D
24.0
=
0.97
in.
SHe - 3616 psi
1 - 120 Ib/ft 3 - 0.069 1b/in. 3
Step d - Impact Factor, F i , and Applied Design Surface Pressure, w
d.l
Equation 3.2 or Figure 3.5 with:
d.2
Applied Design Surface Pressure, w
Section 3.3.1.2:
H
=
6 ft
Rail Loading - E-80
w - 13.9 psi
Yes
-44-
Page 3 of 9
RAILROAD CROSSING DESIGN
Problem Description:
Railroad Example Problem RR.2
Step e - Cyclic Stresses,
e.1
e.1.1
~SHr
~SLr
and
Cyclic Circumferential Stress,
Figure 3.6 with:
~SHr
.. 0.021
~/D
KHr - 326
Er - 10 ksi
e.1.2
D .. 24.0 in.
Figure 3.7 with:
H
e.1. 3
=
GHr
==
0.78
6 ft
Section 3.3.1.2 and Figure 3.8 with:
Nt == 2
e.1.4
e.2
e.2.1
Equation 3.3:
~SHr -=
Cyclic Longitudinal Stress,
Figure 3.9 with:
7052 psi
~SLr
~/D - 0.021
Er == 10 ksi
e.2.2
Figure 3.10 with:
D .. 24.0 in.
H
e.2.3
==
GLr .. 0.71
6 ft
Section 3.3.1.2 and Figure 3.11 with:
Nt == 2
e.2.4
Equation 3.4:
~SLr
- 5279 psi
-45-
Page 4 of 9
RAILROAD CROSSING DESIGN
Problem Description:
Railroad Example Problem RR.2
Step f - Circumferential Stress Due to Internal Pressurization, SHi
Equation 3.5 with:
MAOP - P - 1000 psi
D
=
24.0 in.
tw
=
0.500 in.
SHi - 23500 psi
Step g - Principal Stresses, Sl' S2' S3
aT
=
30 x 10 6 psi
6.5 x 10- 6 per of
T1
=
N/A
T2
=
N/A
Es
0.30
Vs
g.l
g.2
SHe
3616 psi
lISHr
7052 psi
SHi
23500 psi
lIS Lr -
5279 psi
SHe
3616 psi
Equation 3.7 with:
Equation 3.8 with:
34168 psi
S2 "" 13414 psi
SHi - 23500 psi
g.3
Equation 3.9 with:
g.4
Effective Stress, Seff
Equation 3.10 with:
g.4
MAOP
1000 psi
-= P
Sl =
34168 psi
S2 -=
13414 psi
S3
-1000 psi
-=
S3 - -1000 psi
Seff
=
30621 psi
FS
-=
1. 4
Check Allowable Effective Stress
Table 3.1
Class location - 1
SMYS - 42000 psi
Equation 3.10 with:
Seff - 30621 psi
SMYS/FS "" 30000 psi
Seff < SMYS/FS ?
No
-46-
Page 5 of 9
RAILROAD CROSSING DESIGN
Problem Description:
Railroad Example Problem RR.2, revised wall thickness
Step a - Initial Design Information
Pipe and Operational Characteristics:
Outside diameter, D
24.0 in.
Maximum allowable operating pressure, MAOP - P
1000 psi
Steel grade
X-42
Specified minimum yield strength, SMYS
42000 psi
Class location (1, 2, 3, or 4)
Class location factor, F
=
1
=
0.60
Longitudinal joint factor, E
., 1.00
Installation temperature, TI
N/A
Maximum or minimum operating temperature, T2
=
N/A
1.000
Temperature derating factor, T
0.525 in.
Wall thickness, tw
Installation and Site Characteristics:
Depth, H
-= 6.0 ft
Bored diameter, Bd
"" 26.0 in.
Loose sand
Soil type
Modulus of soil reaction, E'
=
10 ksi
Resilient modulus, Er
Unit weight,
-=
"y
Type of longitudinal weld
Distance of girth weld from track centerline,
0.5 ksi
120 Ib/ft 3 = 0.069 1b/in. 3
SAW
Lc
=
< 5 ft
Number of tracks (lor 2)
., 2
Rail loading
- E-80
Other Pipe Steel Properties:
Young's modulus, Es
Poisson's ratio, Vs
Coefficient of thermal expansion, 0T
30000 ksi
- 0.30
6.5 x 10- 6 per of
-47-
Page 6 of 9
RAILROAD CROSSING DESIGN
Problem Description:
Railroad Example Problem RR.2, revised wall thickness
Step b - Check Allowable Barlow Stress
b.1
Equation 3.6 with:
p - 1000 psi
D = 24.0 in.
SHi(Bar1ow)
-
22857 psi
t w = 0.525 in.
F
=
F·E·T·SMYS - 25200 psi
0.60
E - 1.00
1.00
T
SMYS
42000 psi
SHi(Barlow)
s:
F·E·T·SMYS ?
=
2532
Step c - Circumferential Stress Due to Earth Load
c.1
Figure 3.2 with:
E'
c.2
Figure 3.3 with:
KHe
0.022
0.5 ksi
H/Bd
=
2.8
Be - 0.82
Soil type = Loose Sand (A)
c.3
Figure 3.4 with:
c.4
Equation 3.1 with:
Step d
-
Bd/D
=
D
1. 08
Ee
=
0.97
24.0 in.
SHe = 3335 psi
3
120 1b/ft - 0.069 1b/in. 3
Impact Factor, Fi' and Applied Design Surface Pressure, w
d.1
Equation 3.2 or Figure 3.5 with:
d.2
Applied Design Surface Pressure, w
Section 3.3.1.2:
H - 6 ft
Rail Loading - E-80
Fi - 1. 72
w - 13.9 psi
Yes
-48-
Page 7 of 9
RAILROAD CROSSING DESIGN
Problem Description:
Railroad Example Problem RR.2, revised wall thickness
Step e - Cyclic Stresses,
e.l
e.l.l
~SHr
~SLr
and
Cyclic Circumferential Stress,
Figure 3.6 with:
~SHr
,.. 0.022
~/D
KHr .. 321
Er - 10 ksi
e.l.2
Figure 3.7 with:
D
24.0 in.
H
6 ft
e.l.3
Section 3.3.1.2 and Figure 3.8 with:
Nt ~ 2
e.l.4
Equation 3.3:
e.2
e.2.l
~SHr
Cyclic Longitudinal Stress,
Figure 3.9 with:
GHr - 0.78
== 6944 psi
~SLr
~/D
.., 0.022
Er .., 10 ksi
e.2.2
Figure 3.10 with:
D
H
e.2.3
24.0 in.
==
GLr .., 0.71
6 ft
Section 3.3.1.2 and Figure 3.11 with:
Nt - 2
e.2.4
Equation 3.4:
~SLr
,.. 5194 psi
-49-
Page 8 of 9
RAILROAD CROSSING DESIGN
Problem Description:
Railroad Example Problem RR.2, revised wall thickness
Step f - Circumferential Stress Due to Internal Pressurization, SHi
Equation 3.5 with:
MAOP
=
P
=
1000 psi
D
=
24.0 in.
==
0.525 in.
tw
SHi
==
22357 psi
Sl
==
32636 psi
S2
=
12902 psi.
Step g - Principal Stresses, Sl' S2, S3
30 x 10 6 psi
6.5 x 10- 6 per of
Es
0T
Tl
=
N/A
T2
=
N/A
/.Is =
g.l
g.2
Equation 3.7 with:
SHe
Equation 3.8 with:
g.3
Equation 3.9 with:
g.4
Effective Stress, Seff
Equation 3.10 with:
0.30
3335 psi
=
lISHr
6944 psi
SHi
22357 psi
lISLr
5194 psi
SHe
3335 psi
SHi
22357 psi
MAOP - P -
Sl
1000 psi
S3 - -1000 psi
32636 psi
Seff - 29275 psi
S2 - 12902 psi
-1000 psi
S3
g.5
Check Allowable Effective Stress
Table 3.1
Class location
=
1
SMYS
==
42000 psi
Equation 3.10 with:
FS
==
1.4
Seff - 29275 psi
SMYS/FS - 30000 psi
Seff < SMYS/FS?
Yes
-50Page 9 of 9
RAILROAD CROSSING DESIGN
Problem Description:
Railroad Example Problem RR.2, revised wall thickness
Step h - Check Fatigue
h.1
Girth Welds
Table 3.1
Class location -= 1
SFG - 12000 psi
Table 3.2
h.1.1
If
I.e
FS .., 1.4
< 5 ft (1. 5 m) use:
Equation 3.13 with:
t.S Lr - 5194 psi
NL = 1.00
t.SLr/N L < SFG/ FS ?
Yes
t.SLr/N L = 5194 psi
8571 psi
SFG/ FS
h.1.2
If
I.e
~
5 ft (1.5 m) use:
Figure 3.12 with:
Equation 3.14 with:
LG
=
t.SLr
=
RF
=
RF t.SLr/N L < SFG/ FS ?
NL =
h.2
RF t.SLr/N L
=
SFG/ FS
=
Longitudinal Welds
Table 3.1
Class location .. 1
Table 3.2
Equation 3.16 with:
t.S Hr "" 6944 psi
NH
t.SHr/NH
-=
1.16
5986 psi
SFVFS - 8571 psi
FS - 1.4
SFL - 12000 psi (SAW)
t.SHr/NH < SFV FS ?
Yes