Subcommittee on Pressure Relieving Systems

Meeting Minutes Subcommittee on Pressure Relieving Systems MAY 2011 - TASK FORCE ON RP520 Seattle, Washington

08:00 A.M. – 02:33 P.M. Sheraton Seattle Hotel Wednesday, May 18, 2011 Willow A Room

I. Introductions and registration of attendance Phil Henry (Chairman) opened the meeting. Attendance totaled fifty-six people.

II. Recording of the minutes -- Bill Ciolek volunteered

III. Approval of meeting minutes Fall 2010 API RP520 Task Force – Nashville Meeting

The following changes were registered: • Section III: Change “Joint Industry Study” to Joint Industry Project” • Section V.b, 3rd paragraph: Change parenthetical phrase to read “(safety relief valve)” • Section V.b, 3rd paragraph: In the final sentence, change “ultimate” to “original” • Section V.c: Reference was changed to read “RP520 Part II” • Section VI, bullet 4.2: The parenthetical phrase following “Engineering Analysis” was deleted. • Section VI, bullet 4.2.5: The text will be modified to reflect the understanding that the 2% difference cited between set pressure and reclose pressure was originally 1% based on information reported at the Fall 2010 meeting.

The above changes were approved in principle and a revision will be submitted by Phil Henry to API. A motion to accept this course of action was made and carried by acclamation.

IV. Technical Inquiries

Two technical inquiries were addressed by the task force. • From JGC: For the ideal-gas specific heat ratio k, the inquirer asked about the pressure at which it should be evaluated. Aubry Shackleford reasserted that k is not a function of pressure. He will draft a response, which will be reviewed by Sorin Lupascu and Lon McDaniel. • An inquiry from Middough on section 5.3.3.2.1 of Part I consisted of three questions on the use of back pressure correction when set pressure is lower than the MAWP. Using MAWP instead of set pressure to determine backpressure correction in Part I for balanced bellows valves (item references figures 31(vapor) & 32 (liquid)). Q1: Discussion resulted in consensus that the figures are to be used as shown; substituting MAWP for set pressure is not appropriate. Allowance for higher overpressure resulting from the set pressure being less than MAWP is already represented. It was noted that the answer may have to be qualified to acknowledge that other considerations may limit the allowed back pressure beyond relief capacity. Q2: For conventional relief valves, section 5.3.3.1.3 already addresses the question adequately. Q3: The answer is No. Roger Danzy agreed to draft the response for all three questions; reviewers include Phil Henry, Paulette Saunders, Hari Attal, Denis DeMichael, Nikolai Vassiliev, Mike Porter, Emile Tezzo, Thakor Patel, and Shahar Yoram.

V. Errata to Part 1

Two errata will be published soon on the SCPRS SharePoint site. • Equation B.13 is missing the negative sign. • In equations C.41 & C.43, the symbol P should have a subscript of zero (P0).

VI. 3% Task Force Status and Update of Part 2 Ballot

Clark Shepard reviewed the status of Part II. At the time of the Fall 2010 meeting, the task force was working toward the 2nd ballot, but effort then stalled while attempting to reach a consensus with OSHA. The 5th edition was subsequently reaffirmed in January 2011.

A select group of task force members met with OSHA (Sept 2010), at which time a survey of operating companies’ experience was proposed. Since then API Legal staff has advised against conducting such a survey. A compromise action was to authorize a literature survey for incidents, and such survey is in progress to assist the establishment of support for engineering analysis of a type currently in Part II. The agenda for the Fall 2011 meeting will include a summary of the survey (action Phil Henry). Clark also commented on an April 2011 telecon with OSHA (Jim Lay), during which a few key items were raised about the inlet pressure loss criteria: • There may be a perception that industry is trying to “sweep it under the rug“. • A survey of users may not be satisfactory for addressing OSHA’s concerns, unless there is a “deep dive” into maintenance records and chattering incidents. • OSHA will not take proaction if industry strives to understand and address the issues in a timely way.

Clark’s presentation is attached (see Attachment 1).

VII. Shell Experience with 3% Rule

Brad Otis presented a review of PRV chattering incidents from Shell’s database. Brad’s presentation is attached (see Attachment 2). The objectives included the intent to place the 3% issue into a broader process safety perspective, to promote the development of new guidance for liquid systems, and to take a position on the handling of vapor relief systems where inlet line pressure drop exceeds 3%. The topic will be formally presented at the Mary Kay O’Connor Process Safety Center later this year. The process safety incidents summarized are dominated by liquid cases. Brad feels that a process safety incident involving a liquid relief case is about 100 times more likely than a vapor scenario. His information included a report from 1974 by an unnamed company which found about 15 actual PRV instability-related incidents cases involving relief of liquid. He also described a 1976 API survey of similar systems which was focused on liquid relief; this survey reported 42 incidents which included 9 loss of containment events of which four resulted in fires. He did not conduct any new analysis of the 1976 data. It was noted that liquid trim relief valves did not exist at the time.

A Conoco incident in 1978 at Commerce City, CO was summarized (ref: D.F. Myers API Paper 5/13/86). A piping failure was “believed to be caused by relief valve chatter”. The PRV in question was located on the overhead accumulator of a C3/C4 Splitter. The initiating event is unknown, but is thought to involve loss of the reflux flow. It was noted that the PRV was sized for vapor relief only, but during a loss of reflux would have certainly discharged liquid eventually. The upset was serious enough to cause both the column overhead PRV to relieve as well.

Relevant Shell incident data including external incidents were presented. About 22 incidents were listed, 18 of which saw liquid relief. Many of the liquid events were deemed to be within acceptable limits for inlet line losses. None of the PRV’s had liquid trim. From all of the information presented, it was concluded that the process safety risk of PRV’s relieving liquid is much greater than those venting vapor.

Brad’s recommendations included: • Develop guidance on valve designs that are more stable for liquid relief • Promoting best practices for liquid relief installations. • Develop guidance on services where both vapor and liquid relief scenarios are expected, including what to do if the situation cannot be avoided. (It was noted that modulating pilots may be an answer, but other approaches should be considered) • Allow users to assess and accept inlet losses greater than 3% for vapor relief scenarios.

In response to a question, Brad noted that two-phase relief could not be ruled out for the incidents categorized as liquid.

Other experience was shared by Roger Danzy. PRV’s have been used as pressure controllers on the discharge of lube oil pumps. If the PRV was a restricted lift valve sized to match the pump capacity, it behaved in a stable manner. Gross oversizing of the valve resulted in unstable control.

It was noted that the ASME B&PV Code non-mandatory Appendix M only mentions compressible flow where 3% is involved. A proposal to ASME may be necessary once the task force decides how to address design issues with liquid relief.

Other comments included the statement that for liquid service, inlet pipe length is more important than pressure loss with respect to PRV stability. The reflected pressure wave which is generated when the disk lifts and travels back to the protected equipment lowers the pressure to the point and causes the liquid to accelerate toward the PRV, which causes liquid hammering because the PRV may be closed again while the liquid is accelerating.

Clark Shepard shared some of Exxon-Mobil’s design guidance on hydraulic surge. The guidance includes using a modulating pilot-operated PRV, limit the length of the inlet line to about 30 ft, and perform acoustic analysis. Like Shell, liquid-filled systems have been at the center of actual PRV incidents for Exxon-Mobil; vapor relief chattering has not. Clark plans to seek approval to release the E-M guidance to help the task force work.

Brad Otis proposed a small group be formed to develop revisions to the standard related to liquid relief.

VIII. Path Forward for Part II

Four options were formulated. 1. Revise Part II for everything except changes to inlet pressure loss criteria. The standard would be updated later after stronger technical support is developed. 2. Use the new text drafted in Fall 2010 re inlet pressure loss, effectively requiring a minimum margin of 2%, and engineering analysis when total > 5%. 3. Option 1 plus delay publishing and work on adding design guidance for liquid filled systems to reduce chattering potential. 4. Option 2 plus delay publishing and work on adding design guidance for liquid filled systems to reduce chattering potential.

An informal show of hands resulted in a consensus to pursue #4 for the 6th edition (although a formal vote was not taken, Denis DeMichael asked to be noted as abstaining). Specific path-forward items include:

• Brad Otis agreed to lead the effort to address the liquid chatter considerations, including whether the design criteria should be restricted to 3% or not. Brad will be assisted by Clark Shepard, Roger Danzy, Paulette Saunders, Abdul Azeez, John Burgess, and Matt Byers. A proposal is expected in time for review at the Fall 2011 meeting. • Phil Henry will create an Annex to Part II which will include the items from the draft text regarding the engineering analysis of inlet line pressure loss, and will feature only one consensus method for this analysis.

Reviewers for these items: Ed Zamejc, Mike Porter, Lon McDaniel, Paulette Saunders, John Burgess, Brad Otis, Emile Tezzo, Clark Shepard, Denis DeMichael.

IX. Review of Action Item List for Parts I and II

The task force reviewed the status of each open item. Refer to Attachment 3 for each item’s detailed description.

Action Item Current Disposition Part II (6th edition) 2204-07 Delay to 7th edition. 2005-05 Hold until outcome from Brad Otis’ liquid chatter sub- group. 2005-07 Phil Henry will prepare wording regarding open yoke 2006-07 Delay to 7th edition. 2008-03 Freeman Self to complete action with Steve Cloutier before Fall 2011 meeting 2008-08 Phil Henry will incorporate the suggested language after checking for Don Eure’s contribution 2009-10 Delay to 7th edition 2011-05 Bill Ciolek will lead. Steve Cloutier, Clark Shepard, Mike (new) Porter, Mohammed Ali, Don Eure, Lon McDaniel to submit input on the issues to Bill. Prepare for Fall 2011 (6th edition). Part I (for 9th edition) 2006-09 Brad Otis will work on text. Review by Roger Danzy and Denis DeMichael 2007-12 The title will be changed to drop reference to refineries. 2008-06 Await results of 2000/28300 parallel effort. 2008-12 Phil Henry to review recent TI before drafting language, and may consult with Roger Danzy. 2008-14 Done 2009-03 & Paulette Saunders, Denis DeMichael and Lon McDaniel 2009 08 will prepare a revision 2009-09 John Burgess will consult with Craig Powers and decide if a method can be proposed for the standard. 2009-11 Roger Danzy to review and pursue an easier sizing process 2010-05 To be addressed with inquiry described above (Roger Danzy) 2011-06 (new) Non-API pilot-operated relief valves with full-bore orifices, what happens when flow chokes in inlet fitting? Cautionary words needed. John Burgess.

Other items were suggested for the next edition of Part I.

• The temperature on which to base correction of the Cold differential test pressure (CDTP) is not addressed by the standard. Currently, each manufacturer decides what temperatures to use for the correction by manufacturers based on operating T. Ignoring the T when setting CDTP could cause valve to close late. It was agreed that change is required. Guidance language needed to consider the installation specifics.

• Blowdown tolerance: it was suggested that a dialogue be initiated with ASME to establish a tolerance for blowdown, analogous to set pressure tolerance. Establishing a tolerance would facilitate the use of engineering analysis by providing greater certainty of the actual blowdown. It was pointed out that this would entail submitting a formal request for modifying the language of the B&PV Code. Testing facilities would have to be expanded significantly to implement any such change to the Code. Consensus for action was not reached at this meeting.

X. Other Remarks

During the discussion of the task force plans to resolve the inlet pressure loss issues in Part II, potential violation of antitrust regulations was raised as an issue by Steve Crimaudo. The chair noted that task force members need to be sensitive to and raise any objection to actions that might represent an antitrust violation.

Attachment 1 – C. Shephard Presentation Attachment 2 – B. Otis Presentation Attachment 3 – Action Item List

Work List for API 520 Part 2, 6th Edition Action Item # Description Responsible Modification needed to RP520 Part 2, caution about mechanical loads from initial rupture disk flow should be 2004-07 C. Eskridge considered, steady state flow is based on required flow, mechanical design should consider high transient load What rated capacity should be used for inlet DP calc for an 2005-05 uncertified valve in liquid service? Modification needed to D. DeMichael 520 Part 2? Any built-up back pressure limitations on S1 open yoke 2005-07 PRVs is SVIII service? Clarification needed to Part 2? (6th P. Henry Edition) Research 45 degree cut on vent pipe outlet and provide 2006-07 C. Eskridge recommendations S. Cloutier Inappropriate use of expansion resistance coefficient in 2008-03 F. Self built-up back pressure calculations. (6th Edition) L. McDaniel Propose language for the safe venting of balanced bellows relief valves and language to address the reasons for P. Henry 2008-08 venting the bonnet of balanced bellows relief valve to a D. Eure location free of backpressure(6th Edition) The issue of high body-bowl built-up back pressure on PRVs that have low outlet to inlet area ratios needs further study. 2009-10 Unassigned This may lead to a modification in API 520 related to the 10% built-up back pressure limitation on conventional valves. Rated capacity for inlet losses, in situations where you B. Ciolek 2011-05 have higher required relieving rate than rated (e.g. much S. Cloutier higher overpressures than 10%) (6th Edition) Work List for API 520 Part 1, 9th Edition Action Item # Description Responsible

Need further guidance in Part 1 for cases where valve has B. Otis liquid and vapor release cases, need guidance on sizing 2006-09 R. Danzy (certified vs. uncertified equations) and specification for purchase D. DeMichael Consider a title change for API 520 Part 1 so not only 2007-12 refineries are referenced but to include chemical plants. P. Henry Check with API, remove refineries from title Prepare a change to the text of the 520 Part 1 to clarify the 2008-06 issue of ‘standard’ and ‘normal’ conditions in equations 3.3 P. Henry and 3.4, check with 28300 Modify guidance to PRV datasheets (Line 17) to assist P. Henry 2008-12 user’s with determining the temperature to use for selecting spring materials, check inquiry R. Danzy 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 B. Ciolek 2008-14 set pressure is equal to the maximum allowable working P. Henry 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 Verify that CDTP temperature adjustment is based on P. Saunders 2009-03 relieving temperature as stated in Part 1 – Line 47 L. McDaniel D. DeMichael Review requirement in Part 1 to base the CDTP P. Saunders 2009-08 temperature correction on the relieving temperature, see L. McDaniel 4.2.3.2 D. DeMichael Add sizing procedure or reference procedure related to J. Burgess 2009-09 sizing of PRDs for non-newtonian fluids C. Powers Modifications to the iterative procedure for sizing viscous PRVs in API 520 Part 1 needs to be considered. R. Danzy 2009-11 Additional guidance on the viscosity limit (or Reynolds D. DeMichael number limit) for PRVs may be developed. Explanation on back pressure curves when overpressure is 2010-05 R. Danzy different than the typical 10, 16 or 21% (i.e. 13%, 50%) Non-standard ASME certified pilot-operated valves with full 2011-06 bore orifices, what happens when flow chokes in inlet J. Burgess fitting? Caution is needed