Subcommittee on Pressure Relieving Systems

Minutes API 520 TF Fall 2010 Page 1of 6

Meeting Minutes

Subcommittee on Pressure Relieving Systems

NOVEMBER 2010 TASK FORCE ON RP520

Nashville Sheraton Music City Hotel

08:30 A.M. – 06:00 P.M. Sheraton Music City Hotel

Monday, November15, 2010 Belle Meade Room

Phil Henry (Chairman) opened the meeting at 8:35 AM. About 50 people in attendance.

1. Introductions and registration of attendance
2. Sorin Lupascu volunteered to keep the minutes
3. Approval of meeting minutes
4. Spring 2010 API RP520 Task Force -New Orleans Meeting Minutes

Comments:

-request to attach referenced OSHA (Occupational Safety and Health Administration) letter to the minutes

-request to circulate minutes to task force members prior to meeting

-clarified acronym: JIP= Joint Industry Project

1. Review of 520 Part 2 Ballot 1 Comments

Action Items:

1)Steven Palmer will review Appendix B (Installation and Maintenance of Pin-Actuated Non-Reclosing Pressure Relief Devices) for consistency and its coverage of “pin-actuated” vs. “buckling pin-actuated” pressure relief devices.

2)Don Eure to draft Figure 3b showing the disk mounted in a horizontal segment of pipe with a weep hole at a low point in this line. For Figure 3a use existing Figure 3 but show a weather cap on the end of the pipe. Bill Ciolek, Lon McDaniel and Tim Weber have volunteered to review Don’s sketch and to get it back to Phil Henry timely for inclusion in ballot 2.

The task force reviewed open comments in the “Ballot Comments and Resolution” spreadsheet. Minutes captured during the review are listed below, with each comment identified by its clause subclause number as referenced in the spreadsheet handout. Comments still outstanding after the Monday, November 15 meeting were addressed during the same week on Thursday, November 18. Tabulated summary below lists resolution of comments reviewed during both meetings.

Table 1. Ballot Comments and Resolution Summary (Nov. 15 & Nov. 18, 2010)

Clause / Editorial / Technical / Accepted / Tabled / Withdrawn / Rejected / Comments
6.3.e (now 6.3.2.e) / X / X / Modify language to refer to “isolation valves” and “bleed valves”. Remove the last sentence.
6.3.f (now 6.3.2.f) / X / X / Task force recommended not including in the ballot. It was noted during the discussion that the comment describes an isolation requirement and is outside the scope.
A.2 / X / X / Move sentence to section A.1.
A.3 / X / X
A.9 / X / X / Create New header titled “Service Life”.
A.9 / X / X / Addressed by the previous comment.
B.1&B.2 / X / X / Decided to change title to be consistent with text. Steven Palmer will review Appendix B (Installation and Maintenance of Pin-Actuated Non-Reclosing Pressure Relief Devices) for consistency and assess its coverage of “pin-actuated” vs. “buckling pin” pressure relief devices.
Figure 1 / X / X / Note added referring reader to section 4.2.2. For the basis of pressure loss calculations. Initially submitted as a technical comment.
Figure 1 / X / X / Submitted as alternative to the previous comment.
Figure 1 / X / X / Relocate the support to the centerline of the vent pipe to achieve consistency with the other figures.
Clause / Editorial / Technical / Accepted / Tabled / Withdrawn / Rejected / Comments
Figure 3 / X / X / Don Eure to draft Figure 3b showing the disk mounted in a horizontal segment of pipe with a weep hole at a low point in this line. For Figure 3a use existing Figure 3 but show a weather cap on the end of the pipe. Bill Ciolek, Lon McDaniel and Tim Weber have volunteered to review Don’s sketch and to get it back to Phil Henry timely for inclusion in ballot 2. It was suggested to add a cautionary note of the type “Figure for information online. Design is determined by good engineering” to Figure 3 as well as to other figures in the guideline document.
Figure 3 / X / X / Addressed by the previous comment.
Figure 3 / X / X / Addressed by the previous comment.
Figure 4 / X / X / Comment suggested increasing line size and adding reducer.
Figure 4 / X / X / Revise flow direction and move arrow outside of pipe.
Figure 4 / X / X / Previously accepted and changed (added note directing user to 4.2.1.4).
Figure 6 / X / X / Add discharge piping and modify Figure 6 to be similar to Figure 8.
Figure 6 / X / X / Add note to mention heat tracing for remote sense line to direct user to 9.6.
Figure 7 / X / X / Already addressed by decision to relocate support to the centreline of the vent pipe in Figure 1 to be consistent with other figures.
Clause / Editorial / Technical / Accepted / Tabled / Withdrawn / Rejected / Comments
Figure 7 / X / X
Figure 9 / X / X
Figure 10 / X / X / Relocate bleed valve in figure.
Figure 10 / X / X / Add note to figure with reference to relevant section.
Figure 10 / X / X / Modify language to state “valve not required for atmospheric discharge”.
Figure 10 / X / X / Delete “To closed system or atmospheric piping”.
Figure 11 / X / X / Modify figure to include a three-way valve.
Figure 11,13 / X / X / Add notes to the figures with references to relevant sections on figures.
Figure 12 / X / X / Comment suggested changing Fig. 12 to show the spare PSV on a separate nozzle or add another figure showing this alternate arrangement.
Clause / Editorial / Technical / Accepted / Tabled / Withdrawn / Rejected / Comments
Figure 12,13 / X / X / Comment suggested that an outlet valve would be required for atmospheric discharge if the valves share a common tail pipe or vent pipe.
Figure 17 / X / X
Figure 18 / X / X
Figure 18 / X / X / Consistency issue suggested in Figure 17 and Figure 18 reference to “flare header” and “relief header”. Decided that different phrases are used since there could be different configurations. No change.
Figure 18 / X / X / Already addressed.
Figure 19 / X / X / Comment rejected. This drawing is for vapor service.
Figure 22 / X / X / Add a Safe Location note.
General / X / X / We do not reference the source of equations. Two-phase sizing equation comes from a DIERS publication. Good suggestion for next edition.
Clause / Editorial / Technical / Accepted / Tabled / Withdrawn / Rejected / Comments
27 / 9 / 20 / 4 / 3 / 9

A remark was made on the proposed title change from “Recommended Practice” (RP) to “Standard” recommending the use of Mandatory and Non-Mandatory Appendices as in ASME Section VIII as an alternative to changing the RP label. It was responded that the difference between “RP” and “Standard” is only a nominal one and that since RAGAGEP (Recognized and Generally Accepted Good Engineering Practices) are selected by facility operators,it does not matter whether the document is titled “RP” or “Standard”. It was also commentated that the usage of “shall” and “should” in the document carries more weight than the label in the title of the document.

1. 3% Task Force

a)Status and Update – Clark Shepard

Clark Shepard described the background behind the 3% task force stemming from Ballot 1 and thenintroduced Jim Lay.

Jim Lay (OSHA) noted that OSHA had technical comments on the first draft and he proceeded to share with the task force what he described as being the overarching themes relevant to OSHA’s perspective on this topic. In summary, because RP520 is widely used as RAGAGEP (Recognized and Generally Accepted Good Engineering Practices) OSHA is interested in understanding the documented support for guideline changes that could be perceived as a change in safety factors.

Jim Lay stated that determining specifics on the required level of support for such changes is left up to the task force. Responding to the task force’s request to provide details as to what constitutes adequate support for changes to the 3% inlet pressure loss rule, Jim Lay suggested as potential examples providing experimental results and historic data from industry that rigorously address topics such asPRV chattering, true leakage and reduced capacity. It was noted that an ongoing joint industry study approaches some of these topics. However, the ability to extract guidance from the results may be limited by the scope of the project.

It was noted that the change on the ballot will change the guidance on PRV inlet pressure loss and not the industry practice. It was also noted that the change is ultimately meant to supplement the current Engineering Analysis approach. Additionally, it was commented in the task force that RP520 provides guidance on PRV inlet pressure loss using the “should” statement and not “shall”. A comment emphasized that the origins of the 3% percent rule are not rigorously documented and that the 3% rule can be regarded as a “rule of thumb”.

b)Presentation on Engineering Analysis – Brad Otis

-request to attach presentation to the minutes

Brad Otis provided a historic overview of inlet pressure drop guidance in the API 520 Standard. The Engineering Analysis concept was introduced with no additional guidance in 1994 to allow exceeding 3% PRV inlet pressure loss. The 2010 ballot includes a revision that received feedback from OSHA.

It was noted in task force discussion that there is a view based on industry experiencethat a 5% rule is more suitable. It was also noted that 3% inlet pressure loss is not always achievable. Moreover, it was emphasized that inlet pressure loss is just one of the potential factors that may cause valve chattering and that more knowledge is needed in this area.

Brad Otis presented a methodology and associated assumptions employed in an engineering analysis used to identify the potential for instability in existing PRVs for vapour service. The original purpose was to publish this analysis with Roger Danzy in the public domain as an example for the Engineering Analysis process (it was later decided not to publish the analysis).

c)Path Forward

Phil Henry outlined the options for the task force, which has already been awarded an extension for the RP520 Part II document: the present version can be reaffirmed, the guideline can be withdrawn, or comments can be incorporated for continuous improvement through the ballot review process.

There was consensus in the task force that the preferred path forward is to look at technical changes in Ballot 2 that reflect work done at the sub group level to address OSHA concern.

The API standard sponsor, present at the meeting, outlined the API procedure to extend and reaffirm or to withdraw standards. The sponsor noted that although he does not expect a scenario in which API withdraws the standard, the task force must move forward.

Phil Henry proceeded to guide the task force through Ballot 2.

1. Review the Revised Section 4.1 and 4.2
2. 4.2.1 Exceptions to 3% rule

Inlet pressure loss up to 5% may be appropriate (see 4.2.5.) for several instances:

-thermal relief valve applications

-pilot operated relief valves

-applications in which the set pressure is less the 50 psig

-Engineering Analysis

-A task force member asked to identify the origin of using inlet pressure losses exceeding 3% with set pressures below 50 psig. It was noted that in some low pressure applications it may not be possible to meet the 3% rule.

• 4.2.2 Non-recoverable Pressure Loss Calculation

-Effect of valve capacity should be included.

-OSHA recommendation mentioned that consideration should be given to using increased pipe roughness factors in inlet piping systems that are expected to degrade over time, particularly if the 3% limit is exceeded as allowed per 4.2.5.

• 4.2.5. Basis for Exceeding 3% Inlet Losses

Discussions centred around establishment of a suitable margin between calculated inlet losses and blowdown. A 1% margin was initially suggested as it seems to match the intent of the original work where the 3% rule was first developed. The task group eventually decided that a margin between the calculated inlet pressure loss and the valve’s blowdown shall be at least 2% of the set pressure. This provision replaces the previous framework in which the margin was based on the user’s determination. It was noted that for the purposes of this language “inlet pressure drop” refers to “non-recoverable pressure losses”.

• 4.2.5.2. Requirements

List of criteria provided. It was commented that for a bellows valve not all criteria can be met. It was suggested to further brainstorm criteria.

• 4.2.6. Engineering Analysis

There was discussion on the topic of when the Engineering Analysis should be used. The intention is for the Engineering Analysis to appear as a separate point in a list of exceptions to the 3% rule. The task force does not want the Engineering Analysis to apply for new installations. It was noted that the current language of the revised sections does not state specifically that inlet pressure loss should never exceed 5%.

1. Adjourn

Thursday, November 18, 2010: the task force reconvened after the joint session. Ballot comments that remained open after the Monday, November 15, 2010 meeting were addressed. These items are captured by the Table 1 summary in the Monday meeting minutes (see section IV. Review of 520 Part 2 Ballot 1 Comments).

There was discussion on addressing comments offline from now on and raising only selected items in the large group meeting. Phil Henry will get ballot 2 comments out before the Seattle meeting (Spring 2011). Feedback will determine what comments will be worked in the meeting. Specific responsibility for sections will be awarded to individuals at the Seattle meeting (it was later decided not to issue the second ballot prior to the Spring 2011 meeting).

ADJOURNED 12:45 pm