SCPRS Spring 2011 Report

Subcommittee On
Pressure Relief Systems
CRE Meeting
Spring 2011 Meeting
Clark Shepard
Notes or
Expected Publication
8th Edition, December
Work items
beginning in
Spring 2011
9th Edition
Sizing, Selection, and
Installation of Pressurerelieving Devices in Refineries
Part II—Installation
5th Edition,
August 2003
Waiting on 6th
Edition Reballot
6th Edition
Waiting for committee
and API guidance
Std 521
(ISO 23251)
Pressure-relieving and
Depressuring Systems
5th Edition,
January 2007
Issues with DIS
Through ISO
6th Edition
November 2012 (FDIS)
Std 526
Flanged Steel Pressure Relief
6th Edition,
May 2009
7th Edition
Std 527
Seat Tightness of Pressure
Relief Valves
3rd Edition,
July 1991
July 2007
Std 2000
(ISO 28300)
Venting Atmospheric and LowPressure Storage Tanks
Nonrefrigerated and
6th Edition, November
2009 (API adopt back);
ISO release 2008
DIS June 2011
December 2012
Current Edition Date
Std 520 Part 1
Sizing, Selection, and
Installation of Pressurerelieving Devices in Refineries
Part I—Sizing and Selection
RP 520 Part 2
Std 521
(ISO 23251)
Currently greater than 400 comments submitted on 521 Ballot (closing June 15)
Session planned for July 2011 to work on comments
Chemical Safety Board submitted response concerning revisions made to address
2007 CSB recommendations
Five comments provided; response framed during meeting
Task group formed to develop API response (John Burgess - Lead)
Plan to draft response for Fall 2011 meeting
Comment highlights: 1. “unaccepted risk” – point to API 752 and 4. Urging use of
flare - inherently safer alternative – Provide comment when flare is not always
inherently safer.
API Environmental working on industry response to EPA regarding flare
Paul Eichemer attended meeting as liaison for API Environmental;
+ EPA continues to formalize position and is looking at minimum heating value
Providing Table 11 clarification in next edition of API 521
API RP 520 Part 2
Inlet Pressure - Proposals for Path Forward
Revise API 520 Part 2 (6th Edition) Ballot to incorporate all changes except those related to
Inlet pressure drop and other sections addressing PRV chattering reverting back to the 5th
edition wording.
Update guidance addressing PRV chattering in RP 520 Part 2 when there is stronger
technical support for the revisions.
Agree to text reviewed at Fall 2010 meeting allowing 5% with safety margin (2%) and
engineering analysis requirements when exceeding 5%.
Update guidance addressing PRV chattering in RP 520 Part 2 when there is stronger
technical support for the revisions. (note 1)
Ballot after completing 1 and work on adding design guidance for liquid filled systems to
reduce chattering potential.
Ballot after completing 2 and work on adding design guidance for liquid filled systems to
reduce chattering potential.
Note 1 - Consider working with DIERS on engineering model (stability)
Note 2 - Work with API on path forward for Re-Balloting in light of OSHA involvement.
API 526/527 and 2000
2000 – Continue to work document revisions for preparation of ballot
527 – Need to correct publishing mistakes made to the 2007 reaffirmed version
Changes to Pressure Relieving Systems Over Last 5 Years
Improved Pressure Relieving Systems Modeling - Industry has been modeling
pressure relief and flare systems using commercial software to better estimate
pressure relieving rates and flare system hydraulics.
API 521 and 2000 have been adopted as ISO documents increasing global review
and application
API 521 is always undergoing continuous improvement. The last version included
improved guidance on 1) hierarchy of mitigation based on inherent safety, 2)
expansion to address fire types and details of methodology, 3) introduction of low
probability contingencies, 4) expanded flare limits, 5) addition of toxic limits for
atmospheric releases and 6) added cautions around CBDs.
API 2000 content revisions include improved basis for tank vent sizing and added
cautions open vent discharge
PERF 99-05 PRV Stability Project
Project winding down with equations developed to model lift of PRV
Contracted phases complete with final report expected after meeting
Meeting scheduled for Thursday to determine if additional work should
progress, how to use the tool and what is the tools limitations
Results for valves tested at 50 psig and 250 psig appear to indicate model
reasonably predicts chattering based on test data; Needs additional work to
determine unknown variables
Some limitations including:
– Requires variables for each valve; two of which can only be determined
through testing
– Not sure if models can be extrapolated above 250 psig set pressure
– Need to understand effect of larger vessels/system (increased
API 520 (Part 2) – 3% Status and Ballot
API SCPRS approved ballot for 6th Edition with comments
OSHA sent letter with regard to inlet pressure drop revisions in 520 ballot (April 2010)
Met with OSHA to review letter and API’s path forward (Sept 2010)
API SCPRS task group agreed to revisions to inlet pressure drop (5% with safety factor)
– With goal to include a performance basis for exceeding 5%
OSHA’s Jim Lay, attended API Fall 2010 committee meeting.
During API Fall 2010 meeting agreed to develop survey for data collection that would
support inlet pressure drop to 5% is lower risk (Not supported by all members)
– API Law placed hold on 5% inlet pressure drop survey
Reaffirmed current API 520 Part 2 version to meet API/ANSI standards document review
cycle to reset review process for additional 5 years (January 2011)
API task group recommended a ballot (without revisions to inlet pressure drop; using 5th
edition wording)
OSHA continues to inquire on status with regard to API 520 Part 2 - Inlet Pressure Drop
(April 2011)
Subcommittee looking at Lift Criteria/Cycling analysis to allow greater then 5% inlet pressure
PERF Stability project (goal to provide guidance with regard to PRV stability) reviewing
results of funded phases to determine path forward.
API completing literature search on incidents.