American Petroleum Institute
Subcommittee on Pressure Relieving Systems
Task Force on RP 520
Spring 2008 Meeting Minutes – New Orleans, LA
April 15, 2008
I. Introduction and registration of attendance.
A registration was taken and introductions made. A handout consisting of the proposed
agenda, minutes of the previous meeting, five inquiries and documents related to workin-progress, and an action item list was distributed.
II. Appointment of a secretary
Don Griglack was appointed secretary for the meeting.
III. Approve the minutes of Fall 2007 meeting.
A request was made to add “San Antonio, TX” to the header of the Fall 2007 minutes.
The minutes were then approved as edited.
IV. Review of inquiries.
There was some discussion on the inquiry process related to the use of contractors and
manufacturers (non-users) when discussing and finalizing responses to inquiries. API
requires a balloting process to approve formal inquiry responses if non-users are
involved in the discussion. Since it was determined that the input from these groups is
critical, the task force decided to utilize the API balloting process to finalize all inquiry
responses developed by the task force.
There were five inquiries to be reviewed, including two that had been previously
discussed but for which no interpretation had been issued.
1. Inquiry 520p1-I-02/07 from Worley-Parsons.
The inquiry addresses a clarification of Cp/Cv guidance referenced in inquiry
520-I-05/03 regarding use of ideal gas versus real gas values. The response that
was agreed to by the task force is:
The Cp/Cv (k value) used in the equations presented in RP520 Part 1 is based
on the ideal gas and not the real gas value at the relieving conditions. Note that
some simulator software packages provide an estimate of the “real” gas specific
heat ratio. Caution should be exercised, as the real gas specific heat ratio is not
a good estimate for the isentropic expansion coefficient and its use is
inappropriate in the vapor sizing equations provided in RP520.
2. Inquiry 520p1-I-03/07 from Toyo Engineering
The inquiry addresses valve selection based on the vendor’s calculation. The
response that was agreed to by the task force is:
The inquiry addresses the instance when a vendor’s calculations results in a
smaller pressure relief valve than is required using the preliminary sizing
criteria outlined in API RP520 Part 1. Selecting a smaller valve based on the
vendor’s actual orifice area and rated coefficient of discharge is appropriate.
An Action Item was added to prepare a change to the text of the RP to reduce
confusion regarding API versus actual orifice areas and discharge coefficients.
Denis DeMichael accepted this action.
3. Inquiry 520p1-I-04/07 from Jacobs Engineering
The inquiry addresses the reference conditions used for certain equations and
differences between USC units and SI units. The response agreed to by the task
force is:
The units presented in paragraphs 3.6.2.1.1 of the 7th edition of API RP 520 Part
1 for the vapor volumetric flowrate, V, represent reference conditions.
Reference conditions in US customary units are called standard conditions and
are at 60 oF and 14.7 psia. The reference conditions used for SI units in these
equations are called normal conditions and are at 0 oC and 101.325 kPaa.
An Action Item was added to prepare a change to the text of the RP to clarify
the issue of ‘standard’ and ‘normal’ conditions in equations 3.3 and 3.4.
4. Inquiry 520p2-I-01/07 from Per Helgesen
The inquiry addresses the use of a pressure relief device as a isolation valve.
The response agreed to by the task force is:
A pressure relief device shall not be used as a block valve to provide positive
isolation. API RP520 Part 2 does not provide guidance related to what
maintenance activities can be safely conducted on either the upstream or
downstream side of a closed pressure relief valve.
5. Inquiry 520p2-I-01/08 from ConocoPhillips.
The inquiry concerned the isolation of installed spare relief valves when not in
service. The response agreed to by the task force is:
Yes, the intent of paragraph 6.3.3 of API RP 520 Part 2 is to isolate the spare
PRV so that it is not exposed to process conditions.
An Action Item was added to propose a change of the text of paragraph 6.3.3 of
Part 2 to clarify the intent to have the spare PRV isolated when not in service.
Maybe a definition of spare valve or changing the word ‘additional’ to ‘spare.
Tom Bevilacqua accepted this action with assistance from Mike Porter, Don
Eure and Jude Golla.
V. Status of API RP 520 Part 1
An action item was added to check equation D.6 in Appendix D for a potential error
raised by Ron Darby. Bill Ciolek, Aubrey Shakelford and Freeman Self will
investigate.
Phil Henry noted that API staff have had the approved revision to API RP 520 Part 1
for nine months now and the task force has not yet received galley proofs for review.
VI. API RP 520 Part 2 Work in Progress
1. Vent Stack Angling – C. Eskridge
Chip discussed his research on the effects of angled cut of vertical tail pieces. He
listed several possible effects that could be seen from the angled cut, but indicated
that not all were significant. His recommendation was that the effects on nozzle
loads, vapor dispersion and exit losses should be addressed in Part 2, while the
remainder could be neglected.
An Action Item was added for Chip to draft proposed text to address the issues with
angled cut tail pieces for review at the fall meeting. Bill Ciolek agreed to review.
2. Proposed re-write of 4.2.2 for calculation of inlet losses – A. Shackelford
Aubrey provided background regarding the proposed changes to this section of the
document and an overview of the changes themselves, without a detailed review of
the actual text. After some discussion, a sub-group was formed to conduct detailed
review of the proposed changes with a goal of providing a proposal back to the full
task force for the fall meeting.
The sub-group consists of, in addition to Aubry, Denis DeMichael, Mike Porter,
Tom Bevilacqua, Ed Zamejc, Mohammad Ali, Hari Attal, Becky Thomas, Phil
Henry, Chris Buxton, Barry Weber and Freeman Self.
An Action Item was added for Aubry Shackelford to schedule a teleconference
during the early summer to begin this review.
3. Relief Valve Bellows Vent Location – R. Danzy
Roger Danzy discussed the idea of venting the bonnet of the balanced bellows PSV
to a location that could become pressurized (i.e., to a flare header) and the issues of
how to address the changes in bonnet pressure that could result. Roger proposed
language cautioning users about bonnet pressure and the effects on set pressure.
The task force generally agreed that venting the bonnet to a location that might
become pressurized was not a good idea and should not be addressed in Part 2.
4. Balanced Bellows Venting Options – R. McMican
Bob McMican presented additional information, in the form of the current
ExxonMobil standard for venting of balanced bellows valves that accompanies the
figures that he presented at the previous meeting. Using this information as an
example of what one user is doing a sub-group was formed to propose language to
the task force for consideration at the fall 2008 meeting. The sub-group consists of
Carlene Fontenot, Denis DeMichael, Mohammad Ali, Roger Danzy, and Tony
Price.
An Action Item was added for Carlene Fontenot to propose language for the safe
venting of balanced bellows relief valves and language to address the reasons for
venting the bonnet of balanced bellows relief valves to a location free of
backpressure.
5. Precautions for Rupture Disk Installations – S. Palmer and K. Roth
No report. S. Palmer, G. Hernandez and J. Golla will provide information at the
next meeting.
VII Old Business
1. Review of Action Item List
2002-02: A reference to B31.3 to be added by P. Henry as a note
A new Action Item was created to look at the reaction force equation for use of the
proper temperature.
2004-07: C. Eskridge to propose language for the necessary caution statement.
2005-05: D. DeMichael to lead on resolution with assistance from A. West.
2005-04: Include this in the work of A. Shakleford’s sub-group on inlet pressure
loss.
2002-01: T. Bevilacqua to address at the fall meeting.
2005-06: D. DeMichael to propose language for this caution regarding liquid
discharge into an initially empty vertical discharge line.
2005-07: In progress
2006-03: P. Henry to add caution regarding freezing.
2007-02: Include this in the work of A. Shakleford’s sub-group on inlet pressure
loss.
2007-04: P. Henry may present the results of his gap analysis at the fall meeting.
2007-13: P. Henry to address
2007-14: P. Henry to address
2007-09: G. Hernandez to address this item with assistance from J. Richardson.
2. P. Henry will add the latest draft of of RP 520 Part II to the drop box and send a note
to task force members letting them know it is available.
VIII New Business
1. ISO 4126 and TC-185 Tom Bevilacqua
ISO 4126 is the ISO counterpart to API RP 520 and was developed in Europe
without significant participation by American industry or API. Indeed parts of ISO
4126 were developed by CEN and didn’t have any ISO input.
TC-185 that will continue to work on ISO 4126 Part 10 dealing with two-phase
flow, and will be re-opening Parts 1 (Spring Operated Valves), 4 (Pilot Operated
Valves), 5 (Controlled Safety Pressure Relief Systems - CSPRS) and 7 (Common
Data) for review and revision. The devices described in Part 5 are not commonly
used in the US, and very little interest is expected from US users.
The TC is requesting people from within API to volunteer to be nominated as US
technical experts who will participate in the process of review and revision of the
documents with their international counterparts. There are also opportunities for
people who would like to chair one of the working groups.
There has also been discussion within TC-185 of developing a new section
regarding performance testing of relief devices. Since the original development of
ISO 4126 was heavily influenced by device manufacturers, user and consultant
participation in this revision process is strongly encouraged. Please contact Tom or
Alan West with questions or to volunteer.
Item #
Description
2002-01
Include more details in
Part 2 on pilot sense line
purging techniques
Add discussion to Part 2
on reaction forces for
steam valves, perhaps
utilizing B31.1 Appendix
II as a source.
Need to add constants for
equations in Part 2 par.
2.4.1.2
T. Bevilacqua
10/02
Unassigned
10/02
Bill Ciolek
10/02
No
2002-06
Add a better installation
drawing for a closed
system RD application to
Part 2.
B. McMican
10/02
No
2004-07
Modification needed to
RP520 Part 2, caution
about mechanical loads
from initial rupture disk
flow should be
considered, steady state
flow is based on required
flow, mechanical design
should consider high
transient load
Resolve once and for all
issues related to using
rated versus required flow
for inlet pipe sizing, need
for next revision of Part 2
What rated capacity
should be used for inlet
DP calc for an uncertified
valve in liquid service?
Modification needed to
Unassigned
07/04
N
F. Self, D.
DeMichael
04/05
N
D. DeMichael
07/05
N
2002-02
2002-03
2005-04
2005-05
Responsible
Date
Comp.
Status
Y/N
No
Left over item that did not
make into Part 2, 5th
Edition.
No
Left over item that did not
make into Part 2, 5th
Edition.
Left over item that did not
make into Part 2, 5th
Edition. Bill submitted
draft 9/07 for review in
San Antonio.
Recommendations
provided. P. Henry will
make necessary revisions
to part 2.
Left over item that did not
make into Part 2, 5th
Edition. Figures submitted
by McMican and Ciolek,
review in San Antonio,
9/07. See 2007-11.
No progress to date
P. Henry to ask vendors if
they have data supporting
modulation for liquid
PRVs
Item #
2005-06
2005-07
2006-02
2006-03
2006-05
2006-06
2006-07
Description
520 Part 2?
Do you include liquid
head in discharge line
built-up back pressure
calcs when system is
liquid full? Clarifications
needed in Part 2?
Any built-up back
pressure limitations on
open bonnet PRVs?
Clarification needed to
Part 2?
Final review of Figures in
part 1, check for hatching,
update Figure 2 to include
vent hole
Add the following
cautions to part 2 "It is
important to remember
that the bonnet of a
balanced pressure relief
valve must be vented to
atmosphere at all times."
Add a warning about
potential freezing in
either cold service
including potential for
autorefrigeration or cold
ambient temperatures.
Part 2 Metric units in
Section 4.4.1 need to be
consistant
Responsible
Date
Comp.
Y/N
D. DeMichael
07/05
N
D. DeMichael
07/05
N
Ask MFGs.
P. Henry
02/06
N
Will review when comes
back from API editing of
8th edition.
P. Henry
02/06
N
P. Henry
B. Ciolek
5/06
N
05/06
N
05/06
N
Clarify issues regarding
A. Shackelford
3% rule downstream of
pressure regulator or
where the PRV is located
far away from source of
pressure
Research 45 degree cut on C. Eskridge
vent pipe outlet and
provide recommendations
Status
Bill submitted draft 9/07
for review in San Antonio.
Recommendations
provided. P. Henry will
make necessary revisions
to part 2.
Heuristic approach
submitted by Shackelford
to be reviewed 4/08 in
New Orleans.
Eskridge provided some
background in Seattle
4/2007, needs to be written
Item #
Description
2006-09
Need further guidance in
Part 1 for cases where
valve has liquid and vapor
release cases, need
guidance on sizing
(certified vs. uncertified
equations) and
specification for purchase
How do you handle inlet
line pressure drop
calculations for thermal
relief applications
Perform gap analysis of
ISO-4126 and API 520
Parts 1 and Part 2
o Shackelford –
Provide summary
of potential scope
of this effort
o P. Henry –
Perform gap
analysis on Part 9,
“Installation”
Check with Roland on the
use of “must” 31 times in
Part 1
Address a possible waiver
of API copyright on the
data sheets and the data
sheet explanatory text, as
was done for STD 537
Inquiry 520p1-I-02/2007
2007-02
2007-04
2007-05
2007-06
2007-07
Responsible
Date
Comp.
Y/N
P. Henry
05/06
N
D. DeMichael
P. Henry
07/07
No
A. Shackleford
P. Henry
4/07
No
P. Henry
4/07
No
P. Henry
4/07
No
P. Henry
4-07
No
Status
up
Did not make into 8th
edition. Left over for 9th
edition.
See 2007-14.
Roland Goodman advised
that is was best to change
"must" to "shall" where it
makes sense. "Must"
should not be used as an
alternative to "shall" since
it denotes an
external regulatory
requirement while "shall"
denotes a requirement in
the standard. He thinks
these changes could be
made without requiring a
re-ballot
Roland Goodman was
contacted and he stated
that this should be no
problem to include in the
8th edition.
Phil Henry will draft a
Item #
2007-08
2007-09
2007-10
Description
Responsible
from WorleyParsons
related to use of real gas
specific heat capacity
ratio versus the ideal
value.
C. Brooke
D. DeMichael
B. Ciolek
T. Bevilacqua.
Inquiry 520p1-I-03/2007
from TOYO Engineering
related to selection of a
smaller valve based on
actual vendor orifice area
and certified coefficient
of discharge.
Final Review of API 520
Part 1 prior to publication
P. Henry
C. Buxton
F. Self
Dr. Lai
D. DeMichael
T. Bevilacqua
B. Webber
P. Henry
C. Eskridge
C. Fontenot
C. Plants
T. Bevilacqua
D. Eure
J. Stokes
M. Porter
A. West
Dr. Lai
D. Griglack
S. Palmer
B. Ciolek
D. DeMichael
C. Buxton
F. Self
B. Webber
A. Shackleford
E. Zamejc
D. Cobb
J. Golla
G. Hernandez
C. Brooke
D. DeMichael
B. McMican
M. Ali
Review the different
options for bellow vent
arrangements and provide
a recommendation to the
task force.
Date
Comp.
Y/N
Status
response based on text
from the 520-I-05/03
response, cautioning that
use of the real gas value is
not appropriate. The draft
response will be reviewed
by several task force
members.
Phil Henry will draft a
response for this inquiry
which will be reviewed by
several task force
members.
4-07
No
9/07
No
Assignments for review
passed out at the fall 2007
meeting. Phil Henry will
distribute the original draft
document sent to API and
the final version returned
from API to the teams
when available. The
turnaround for consistency
and editorial reviews is one
month after sending the
documents to the teams. P.
Henry will also provide an
Excel spreadsheet to
reviewers to use for their
comments.
9/07
No
Mohammad Ali will
provide additional user
guidance to the team.
McMican submitted
several drawings for draft
of 6th edition. Reviewed in
San Antonio. Additional
Item #
Description
2007-11
Review the precautions
related to RD installations
included in API RP 520
Part 1 & 2 to determine
they are adequately
addressed and to
determine what drawings
are necessary to illustrate
the installation
precautions
Consider a title change
for API 520 Part 1 so not
only refineries are
referenced but to include
chemical plants.
Add precaution that
addresses discharges of
two-phase releases to
atmosphere in API 520
Part II section 4.4.1.2.
Add discussion to Part 2
related to inlet and outlet
piping pressure drop
calculations for thermal
relief valves.
Inquiry 520p1-I-04/2007
from Jacobs related to
units and conversions for
paragraph 3.6.2.1.1
definition of V
Inquiry 520p2-I-07 from
Per Helgesen of Norway
related to use of a PRV as
a block valve
Inquiry 520p2-I-08 from
ConocoPhillips related to
sparing of PRVs
Appendix D Equation D.6
correction as stated by
Ron Darby
2007-12
2007-13
2007-14
2007-15
2007-16
2008-01
2008-02
Responsible
Date
Comp.
Y/N
G. Hernandez
S. Palmer
9/07
No
P. Henry
9/07
No
P. Henry
9/07
No
P. Henry
9/07
No
P. Henry
3/08
No
P. Henry
3/08
No
P. Henry
4/08
No
Unassigned
4/08
No
Status
text supplied in Spring 07.
The recommendations are
to be reviewed by Dean
Miller, Chester Brooke, &
Denis DeMichael