MEETING MINUTES
API RP 520 TASK FORCE
FALL 2009 MEETING
DALLAS, TEXAS
Date: November 10, 2009
Time: 8:00A – 4:45P
.
1. Chairman P. Henry called the meeting to order at 8AM, asked for introductions
and sent around the meeting sign up sheet. There were 40 attendees at the
meeting.
2.
A plaque recognizing the many contributions of A. Shackelford was presented by
Steve Crimaudo.
3.
Paulette Saunders was appointed secretary to record meeting minutes.
4.
The meeting minutes from the Spring 2009 Denver, CO 520 task force meeting
were reviewed. A motion was made to approve the minutes. This motion was
seconded and it was voted as approved with only minor edits.
5.
No new inquiries.
6.
The following inquiries were discussed:
a.
Discussed the balloting on the inquiry from 520p1-I-02/08 from Shell
regarding taking into account inlet pressure loss when sizing a pressure
relief valve and when determining the maximum built-up back pressure
for conventional pressure relief valves. Regarding the sizing portion of
the inquiry the group is in agreement that it is common practice to not
take into account losses of 3% or less in the sizing calculations.
A
negative response to the balloting was received based on the fact that the
language in the proposed response included guidance that is not in the
current version of the document. There was discussion on whether it is
appropriate to use the response to an inquiry to document and publish
intended upcoming changes to the document. Although, there is no text
specifically discussing the topic, the example problems in API 520 Part 1
clearly do not include any reduction in the pressure at the inlet to the
valve based on the inlet pressure loss. A vote was taken to send out the
response as written without modification. (Action P. Henry to send out
the response.)
b. 520p1-I-01/09 from Tanker Pacific Management regarding the reduction
in ASME hydrostatic pressure.
 1st Part: Should the hydrotest pressure that is used to determine the
permissible high pressure/low pressure ratio for tube rupture and
other remote contingencies take into account the corrosion
allowance. API 521 Section 3.21 recognizes the correction for
hydrotest pressure for temperature only. ASME VIII, Division 1,
Appendix M recognizes corrections to hydrotest pressure for both
temperature and corrosion allowance. Response: “Yes, the
language in the document will be reconsidered.” (Action item: R.
Danzy and P Henry will consider changes to the definition to the
corrected hydrotest pressure as part of an action item assigned by
the 521 task force.)
 2nd Part: Is API going to revise Figure 1 based on reduced
hydrotest pressures in the ASME code. Response: “No, the
allowable overpressure is based on the construction code”. (Action
P. Henry to draft response with clarification.).
 3rd Part: Is API considering adding clarifications on this. (Action
item: P. Henry to prepare draft response “No” without
clarification.)
c.
7.
Reviewed the proposed rewrite of the questions from Middough, prepared
by A. Shackelford, on using ideal versus real gas properties to size a
pressure relief valve into formal inquiry format. This is not a formal
inquiry, however, the intent based on agreement at the Spring 2009
meeting was to issue this as a formal inquiry in order to get the
information into the public record. Discussion was held whether or not
this should be a converted to a formal technical inquiry or held to
incorporate into the document for the next version. There was agreement
that the response provides good background and information. A vote was
taken and it was decided not to issue this as an official inquiry with the
response. The response prepared may be used to modify Appendix B in
the future, see Attachment 1 to these minutes. (Action: P. Henry to send
out the response as a separate e-mail and as attachment to the minutes for
use of the committee members.)
API RP 520 part II Work in Progress
a. P. Henry announced his goal to have a draft of API 520 Part II out for
ballot before the end of the year. P Henry briefly reviewed major changes
in the current draft.
b. Discussion on changes to section 5.3 on whether superimposed back
pressure should be excluded from consideration on relief valves in
thermal service with heat input from ambient or solar radiation. A new
section 5.3.2 on thermal relief valves was added to expand the discussion
on back pressure. This will mimic the changes made to 4.2.3 (Action P.
Henry to prepare draft of new section for outlet pressure drop on thermal
expansion (solar) valves.)
c. Question on 4.2.3: should this section be expanded to eliminate the need
to evaluate inlet piping pressure drop analysis for any case where the
relief capacity exceeds the required thermal expansion relief rate by a
factor > 10? Some installations with just solar do require almost the full
capacity of a nominal valve. Examples of installations where the
exception should not be used were added.
d. Reviewed new Section 6.3 on isolation valves (combining old sections
6.31 and 6.32, prepared by C. Kraus). The change removed a lot of
redundancy on inlet and outlet block valves. Explanation added to
describe why butterfly and globe valves should not be used. Concern
about restricting the use of high performance butterfly valves in header
systems prompted the inclusion of language to allow their use in these
limited situations. Discussion occurred on whether or not the outlet
piping or block valves should have the same nominal pipe size as the
outlet of the PRV as inferred by the section on butterfly and globe style
valves. Captured edits to this section.
e. Revisions to the section on spare relief devices will be postponed until the
next release of this document. (T. Bevilacqua will provide language for
spare vales for the next revision of this document.)
f. Some valves of larger sizes will have choked flow at the outlet flange. It
was suggested that one solution would be to have manufacturer’s provide
a 4P8 (and 6R14) valve to eliminate problems with choking flow at the
RV outlet flange. This suggestion did not result in any action items.
There are no reports or evidence that could be quoted where valves did
not operate as intended due to excessive body bowl pressure build-up.
However, it is not possible to flow test these larger valves. (2J3, 3L4,
4P6, 6R8, 8T10) Testing has been accomplished showing instability at
outlet area to inlet area ratios </= 5.5. This data was developed by
placing orifice plate on the outlet of the valve which may have led to
inaccuracies. The group agreed to add cautions related to this topic to the
next version of 520 Part 1 (P. Henry action item).
g. F. Self presented considerations and requirements to allow relaxation of
the 3% inlet pressure drop rule. F. Self’s basic premise was that in some
situations, relaxation of the 3% rule is acceptable if the accumulated
pressure in the protected equipment is taken into consideration. Lively
debate resulted due to the fact that many in the task force felt that
instability occurs during the transient period immediately after valve
opening and only under steady state flow after the valve fully opens does
the accumulated pressure at the inlet provide any benefit to stability. No
decision was reached.
Meeting was adjourned at 4:00 pm
Attachment 1
520p1-I-02/09
Isentropic Nozzle Flux Equation
Middough
Following is the proposed response to the TI 520p1-I-02/09 submitted to the API RP 520
Task Force by Nancy Benkalowycz of Middough:
The solution of the isentropic nozzle flux equation requires the pressure and specific
volume of the fluid as it enters into the nozzle, and relationship between these two
variables as the fluid is reduced in pressure in a reversible and adiabatic (constant
entropy) fashion. For the purposes of the questions below, the isentropic relationship
n
between the pressure and specific volume referred to as Pv^n is P  v n  P0  v0 , unless
otherwise noted, where P is the pressure, v is the specific volume, n is the isentropic
expansion coefficient, and 0 represents the conditions at the inlet to the nozzle.
1. If one has a relationship for the isentropic P-v behavior of a fluid that can be
described by Pv^n where n is a constant value, does the equation shown in B.10
represent the analytical solution of the nozzle flux equation for that fluid behavior?
Yes.
2. Does the isentropic P-v behavior of real gases always follow the Pv^n relationship?
No.
3. If the fluid does not follow the Pv^n relationship can the general nozzle flux equation
as shown in B.1.1.3 be used as it is applicable regardless of the fluid non-ideality as
indicated in B.1.1.4? Yes
4. Based on the calculations performed as part of the development of Appendix B and
published in the article referenced in [B.5.3], was the general thermodynamic region
where the isentropic behavior of gases was found not to follow the relationship of
Pv^n limited to the area near the thermodynamic critical point where the ratio of the
inlet pressure to the thermodynamic critical pressure is between 0.8 and 2? Yes.
5. Based on the calculations performed as part of the development of Appendix B and
published in the article referenced in [B.5.3], the fluids for evaluation were
specifically chosen as a detailed IUPAC thermodynamic model was available for
those fluids based on extensive thermodynamic data which was needed to perform the
numerical integration of the isentropic mass flux equation. These fluids included nbutane, propane, methanol, ethylene, water, nitrogen, and argon. Is the qualification
in B.3.5.2. for “low molecular weight” based solely on the fact that the calculations
comparing numerical integration using the detailed thermodynamic models were
limited to the fluids chosen and not because of any known limitations for higher
molecular weight fluids? Yes.
6. If the isentropic expansion coefficient in the Pv^n relationship is constant, can the
value for n be calculated based on the properties of the fluid at the inlet, specifically
v  P  C p
as indicated in B.3.1.2? Yes
n     
P  v T Cv
7. Can the isentropic expansion coefficient in the Pv^n relationship also be calculated by
flashing the fluid isentropically from the inlet conditions to a lower pressure, the
choking pressure being an appropriate value to use as that lower pressure, and solving
for the value of n based on the pressure and specific volume at both points as implied
by the validity of the Pv^n relationship described in B.3.1.1.? Yes
8. If the fluid is an ideal gas where the compressibility factor Z is equal to 1, can one
P
 P 
show that     and that the value for the isentropic expansion coefficient
v
 v T
shown in question 5 is equal to the ideal gas specific heat ratio, i.e. n 
C *p
Cv*
is used to represent the ideal gas constraint as described in B.3.2.2.? Yes
where *
9. Since most gases do not have a compressibility factor equivalent to one, the
committee attempted to develop reasonable guidance for when the use of the ideal gas
specific heat ratio as an estimate of the isentropic expansion coefficient for use in the
Pv^n equation while still using the actual gas specific volume at the inlet (as is
customarily done) did not result in errors more than 5% between the mass flux
calculated using the ideal gas specific heat ratio as opposed to the isentropic
expansion coefficient for the fluids evaluated. Is this the basis for the criterion
indicated in B.3.5.2.? Yes
10. If the ideal gas specific heat ratio is used as an estimate for the isentropic expansion
coefficient and the compressibility of the gas is forced to a value of 1 for use in
calculating the density of the gas, did the comparison of the calculations using this
constraint for the fluids selected find that the determination of the mass flux is
relatively conservative with respect to the sizing of the relief valve effective discharge
area as indicated in B.3.5.1.? Yes
Attachment 2 – Outstanding Action Item List 11/24/2009
Item #
Description
2002-01
Include more details in Part 2 on pilot
sense line purging techniques
Responsible
T. Bevilacqua
C. Buxton
R. Danzy
Date
10/02
Comp.
Y/N
No
Status
Left over item that did not make into
Part 2, 5th Edition. Tom to provide
cautionary sentence or two to add to Part
2.
In Denver (04/2009), C. Buxton and R.
Danzy volunteered to draft up wording
on pilot purge techniques.
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
2005-05
What rated capacity should be used
for inlet DP calc for an uncertified
valve in liquid service? Modification
needed to 520 Part 2?
2005-07
Any built-up back pressure limitations
on open bonnet PRVs? Clarification
needed to Part 2?
Clarify issues regarding 3% rule
downstream of pressure regulator or
where the PRV is located far away
from source of pressure
2006-06
Unassigned
Proposed wording provided 10/30/09,
review in Dallas
No progress to date
07/04
04/08
N
07/05
No
The 0.6 Kp is a conservative sizing
criteria, that results in a very large valve.
What will the relieve valve pass?
D. DeMichael
07/05
N
A. Shackelford
F. Self
R. Thomas
05/06
N
Ask MFGs. Is there any built-up back
pressure limitations on a Section I valve
in Section VIII service.
Heuristic approach submitted by
Shackelford to be reviewed 4/08 in New
Orleans.
(04/2008) C.
Eskridge to add
cautionary
statement to Part
2
D. DeMichael
with review by
A. West
Separate meeting held in Houston to
discuss further was August 2008.
(2005-04) Resolve once and for all
issues related to using rated versus
required flow for inlet pipe sizing,
need for next revision of Part 2
Review proposed revision 11/2008 in
LA.
In Denver (04/2009), F. Self volunteered
to provide more guidance related to the
“engineering analysis” required when
exceeding the 3% rule. R. Thomas
agreed to provide assistance.
2006-07
Research 45 degree cut on vent pipe
outlet and provide recommendations
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
Perform gap analysis of ISO-4126 and
API 520 Parts 1 and Part 2
o Shackelford – Provide
summary of potential scope
of this effort
2007-04
C. Eskridge
B. Ciolek to
review
P. Henry
05/06
N
Eskridge provided some background in
Seattle 4/2007, needs to be written up.
05/06
N
Did not make into 8th edition. Left over
for 9th edition.
A. Shackelford
P. Henry
4/07
No
P. Henry will highlight ISO 4126 parts 7
and 9 these differences to the group in a
presentation in Dallas. G. Hernandez
will highlight differences between ISO
4126 part 6 and API 520.
Item #
Description
P. Henry – Perform gap
analysis on Part 9,
“Installation”
Address a possible waiver of API
copyright on the data sheets and the
data sheet explanatory text, as was
done for STD 537
Review the different options for
bellow vent arrangements and provide
a recommendation to the task force.
Responsible
Date
Comp.
Y/N
Status
o
2007-06
2007-10
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
P. Henry
4/07
N
Roland Goodman was contacted and he
stated that this should be no problem to
include in the 8th edition.
D. Eure
D. DeMichael
B. McMican
M. Ali
C. Fontenot
R. Danzy
T. Price
C. Brooke
C. Buxton
L. McDaniel
K. Roth
S. Palmer
C. Brooke
D. DeMichael
J. Golla
G. Hernandez
D. Miller
9/07
No
B. McMican provided figures to
consider. Team created to provide text
for 520 Part 2.
D. Eure volunteered to lead this effort in
Denver (04/2009).
9/07
No
The recommendations are to be
reviewed by Dean Miller, Chester
Brooke, & Denis DeMichael. Also
volunteering review in April 2008
meeting were J. Golla and G.
Hernandez.
S. Palmer and G. Hernandez completed
draft in 10/2008. Sent to reviewers
11/2008.
Revised again 4/09.
Reviewed in Denver (04/2009), S.
Palmer to make minor revision to A.9
and submit to P. Henry
2007-12
2007-14
Consider a title change for API 520
Part 1 so not only refineries are
referenced but to include chemical
plants.
Add discussion to Part 2 related to
inlet and outlet piping pressure drop
calculations for thermal relief valves.
P. Henry
9/07
No
P. Henry
B. Weber
9/07
No
Combine with (2007-02). P. Henry
added text to section 4.0, needs review
by task force.
B. Weber agreed (11/08) to provide a
caution statement related to thermal
relief valves that are also part of other
relieving scenarios.
Inlet piping revision finalized in Denver
(04/2009).
P. Henry added statement about outlet
piping to 5.3, needs review in Dallas.
2008-03
Inappropriate use of expansion
resistance coefficient in built-up back
pressure calculations.
F. Self
L. McDaniel
4/08
No
F. Self supports NO
Joe Leung per B. Otis says NO
Ron Darby per J. Golla says NO
Per L. McDaniel, July 1994
Hydrocarbon Processing: "Improve
Sizing for Relief Systems" by S. M.
Item #
Description
Responsible
Date
Comp.
Y/N
Status
Ranade of Aspen Technology
supports NO
L.McDaniel supports NO
Brad Otis supports NO
J. Golla supports NO
F. Self to provide new wording from
CCPS Effluent book as a starting point
for possible part I revision
2008-05
Prepare a change to the text of the 520
Part 1 to reduce confusion regarding
API versus actual orifice areas and
discharge coefficients
D. DeMichael
A. Shackelford
P. Henry
4/08
No
F. Self provided text on 10/29/09 from
Darby for review in Dallas
DeMichael and Shackelford provided
suggested modifications to paragraph
3.2.6 on 4/15/2008.
P. Henry to incorporate in next revision
of Part 1
2008-06
2008-08
2008-09
2008-10
2008-11
Prepare a change to the text of the 520
Part 1 to clarify the issue of ‘standard’
and ‘normal’ conditions in equations
3.3 and 3.4
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 valve to a location free
of backpressure
Propose that TF520 update Parts 1 and
2 with respect to the flow rate to use
for pressure drop calculations for
modulating relief valves, referencing
ISO 23251 §7.2.2 and 7.3.1.3
Determine whether there is anything
from Clause 7.3.1.2 (removed from
ISO23251) that needs to be included
into API 520 part 2, including two
references, (Cox, and Van Boskirk)
Inquiry 520p1-I-02/08 from Chester
Brooke of Shell related to 3% inlet
loss and PRV sizing
P. Henry
4/08
No
D. Eure
C. Fontenot
4/08
No
Related to Action Item 2007-10.
D. Eure volunteered in Denver
(04/2009) to work this issue.
P. Henry
11/08
No
F. Self
P. Henry
11/08
No
F. Self to forward articles to P. Henry
and comment on applicability.
P. Henry
C. Brooke
F. Self
6/08
No
Response sent to API 11/13/2008.
Recalled since F. Self wants to work it
again.
Finalized response at Denver 04/2009
meeting and sent to API for balloting
4/29/2009. Balloting completed with 1
negative vote, review in Dallas 11/09.
Discussed in Dallas and it was decided
to send out as is. Sent to API
11/24/2009.
2008-12
2008-13
Modify guidance to PRV datasheets
(Line 17) to assist user’s with
determining the temperature to use for
selecting spring materials
Contact Friedl, invite him to speak to
TF 520 at the Spring 2009 mtg in
Denver. Develop a list of questions
that we would like him to cover
related to non-equilibrium two-phase
P. Henry
11/08
No
M. Davies
P. Henry
A. Shackelford
E. Zamejc
T. Bevilaqua
11/08
No
A. Shackelford, E. Zamejc, T.
Bevilacqua and C. Brooke to send P.
Henry questions to ask Friedl. M.
Davies to keep trying a formal invite to
Friedl to attend future API task force
Item #
2008-14
2008-16
2008-17
2008-18
2009-01
2009-02
2009-03
2009-04
2009-05
2009-06
Description
flow
Recommended revision to Part 1.
Replace the last sentence (before the
note) in 3.5.1.2 with: Although the
allowable overpressure differs from
the allowable accumulation by the
pressure drop between the protected
system and the pressure relief device
(when the set pressure is equal to the
maximum allowable working
pressure), this difference is neglected
in PRV sizing and selection when the
inlet pressure drop doesn't exceed that
allowed by API 520 Part 2
P. Saunders to respond to P. Henry
regarding using rated flow versus
required flow for liquid trim valves on
the inlet loss calculations
P. Henry to send section 4.2.2.1 to
pressure relief valve vendors for
comment
B. Weber to provide some cautionary
wording on exposing thermal relief
valves to other overpressure scenarios.
P. Henry to work on text for sizing
outlet piping from thermal relief
valves.
Responsible
Date
Comp.
Y/N
B. Ciolek
P. Henry
11/08
No
P. Saunders
11/08
No
P. Henry
11/08
No
meeting.
B. Weber
P. Henry
B. Weber provided revision 11/24/2008.
TF reviewed and modified in Denver,
4/2009. P. Henry sent revised version to
Weber in 10/2009 for review.
Need to add Kc factor to equation on
page 115 of the 2008 edition of 520
Part 1
Inquiry 520p1-I-09 from Tanker
Pacific Management related to
modifying Figure 1 as a result of the
lowering of the hydrotest pressure
ratio from 1.5 to 1.3
P. Henry
01/09
N
P. Henry
04/09
N
Verify that CDTP temperature
adjustment is based on relieving
temperature as stated in Part 1
In 8th edition of part 1, the definition
for C on top of page 57 says it is the
ratio of specific heats. It should say
that C is a coefficient determined from
the ratio of specific heats.
Modification of Part 2 to require
provision 6.3.1.d to apply to outlet
isolation valve as well. Why not make
6.3.1 and 6.3.2 identical?
Unassigned
04/09
N
P. Henry
02/09
N
Inquiry from Middough related to use
of Ideal gas equations, Inquiry 520p1-
Status
P. Henry completed text on sizing of
outlet piping.
P. Henry to issue errata to API.
Reviewed during Denver 04/09 meeting.
TF agreed that no changes to 520
required. P. Henry to respond back to
API to refer the inquirer to API 521 and
the discussion on corrected hydrotest
pressure.
C. Brooke discovery.
P. Henry to issue errata to API.
C. Kraus
04/09
N
C. Brooke
D. Cobb
R. Thomas
L. McDaniel
P. Henry
A. Shackelford
P. Henry
C. Brooke provided revision to 6.3.2.g.
In Denver (04/2009), C. Kraus
volunteered to review combining the
sections and to look how parts of ASME
Section VIII Appendix M might be
incorporated. She will also expand on
cautions of using butterfly, globe and
check valves in relief piping.
02/09
N
Proposed modification provided
11/4/09, review in Dallas
A. Shackelford to answer inquiry
questions. A. Shackelford to draft a
Item #
Description
Responsible
Date
Comp.
Y/N
I-02/09
Status
response with a D. Cobb, S. Cloutier, G.
Hernandez review.
Aubry completed draft 04/2009. Phil
sent to Cobb, Cloutier and Hernandez
for review on 10/15/2009.
2009-07
Inquiry from Bectel related to sizing
for non-Newtonian fluids
M. Porter
F. Self
01/09
N
Reviewed in Dallas, 11/2009. TF
decided not to issue as formal inquiry.
Text will be utilized as potential source
to modify next revision of Part 1.
API 520 does not handle non-newtonian
fluids.
We will keep this an informal
inquiry. M. Porter and F. Self to
informally contact the sender for any
follow-up items.
Both Porter and Self contacted Dr. Rao
on 5/4/2009 and pointed out the CCPS
book that has a discussion on this topic.
P. Henry to add topic of Non-newtonian
sizing to next revision of 520 Part 1. See
2009-09.
2009-08
2009-09
2009-10
2009-11
2009-12
Review requirement in Part 1 to base
the CDTP temperature correction on
the relieving temperature, see 2.2.3.2
Add sizing procedure or reference
procedure related to sizing of PRDs
for non-newtonian fluids
The issue of high body-bowl built-up
back pressure on PRVs that have low
outlet to inlet area ratios needs further
study.
This may lead to a modification in
API 520 related to the 10% built-up
back pressure limitation on
conventional valves.
Modifications to the iterative
procedure for sizing viscous PRVs in
API 520 Part 1 needs to be considered.
Additional guidance on the viscosity
limit (or Reynolds number limit) for
PRVs may be developed..
Add to 520 part 2, a list of items that
would make up a typical “Engineering
Analysis” for exceeding the 3% rule
Unassigned
04/09
N
Unassigned
04/09
N
R. Danzy
C. Buxton
J. Kolenc
04/09
N
The PRV vendors are asked to look for
any built-up back pressure test data they
can share on 4L6 conventional valves
and above
R. Danzy
04/09
N
R. Danzy to compare present “high”
viscosity sizing technology in the
document using the Kv and compare to
other methods, such as DIERS and
Darby’s work being developed for the
CCPS Effluent book.
F. Self
R. Thomas
04/09
N