Ammonia Refrigeration Foundation Funds Research Project to Develop Pressure Relief Valve Bench Testing Procedure

There has been a longstanding debate among members of the industrial refrigeration industry in the United States regarding the validity of the prescriptive five year replacement requirement for atmospherically vented pressure relief valves.

The May 2008 issue of Condenser, included an article on this topic written by Jack Piho, president of Piho Engineering. This article reviewed the history behind the five year replacement requirement, its introduction by IIAR in 1978 as a recommendation, confirmation that the requirement pre-dates the formation of IIAR and that interpretations of this requirement by OSHA inspectors have on occasion resulted in OSHA citations to IIAR member companies. An explanation of ongoing investigations and recommendations by the IIAR Research Committee was included in the article along with a detailed review of the several revisions made to the Section 6.6.3 Pressure Relief Devices in IIAR Bulletin 110.

The wording of the pressure relief valve prescriptive replacement requirements in the latest revision of IIAR Bulletin 110, Section 6.6.3 provided the basis for further action:
Pressure relief devices shall be replaced or recertified in accordance with one of these three options:

1. Every five (5) years from the date of installation. IIAR originally recommended (in 1978) that pressure relief valves be replaced every five years from the date of installation. This recommendation represents good engineering practice considering the design and performance of pressure relief devices; or
2. An alternative to the prescriptive replacement interval, i.e., five years, can be developed based on documented in-service relief valve life for specific applications using industry accepted good practices of relief valve evaluation; or
3. The manufacturer's recommendations on replacement frequency of pressure relief devices shall be followed.

Exception: Relief devices discharging into another part of the closed-loop refrigeration system are not subject to the relief valve replacement practices.

The pressure relief devices referred to in the part of Section 6.6.3 cited above protect refrigeration system components from exceeding their maximum allowable working pressure (MAWP). Each pressure relief device must be certified by the National Board of Boiler and Pressure Vessels for both set pressure and capacity (i.e., flow rate) and compressed air is utilized for the certification of relief devices used within the industrial refrigeration industry.

Pressure relief devices which reclose after actuation are termed pressure relief valves and functionally incorporate a spring loaded closing mechanism, or disc. The most common type of reclosing pressure relief valve has operational characteristics whereby pressure changes downstream of the valve (back pressure) affect its relieving capacity. A more sophisticated design variant of the common pressure relief valve incorporates a compensating or external reference mechanism which minimizes the effects of back pressure on the operational characteristics. This later variant is often utilized to relieve over pressure into a lower pressure zone of the closed-loop refrigeration system.

Section 6.6.3, sub-section 2), above, provides the framework for establishing a performance based service life for reclosing pressure relief valves. Any such program requires that:

1. The replacement interval be data driven from records obtained by testing replaced relief valves against established criteria to determine suitability for ongoing service.
2. The tests be documented in a standardized format.
3. A database be established from these records.
4. And the resulting information be carefully considered in the process of creating a reliability program for pressure relief valves.

The above-mentioned Condenser article concluded by noting that the IIAR Research Committee was working on establishing a national data base for industrial refrigeration pressure relief valves and gave an example of the type of data that would need to be collected.

However, data collected from multiple sources must use a standardized test procedure in order to be useful. To this end the IIAR Research Committee developed and approved the project scope for a comprehensive pressure relief valve bench testing procedure suitable for in-house testing at individual plant level, or at third party facilities.

The resulting proposal from the Industrial Refrigeration Consortium (IRC) was submitted to the Ammonia Refrigeration Foundation (ARF) for funding consideration and has been approved. The Foundation is a non-profit research and education foundation organized by members of the International Institute of Ammonia Refrigeration (IIAR) to promote educational and scientific projects related to industrial refrigeration and the use of ammonia and other natural refrigerants. This study will help ARF achieve its dual mission of promoting research and educational opportunities.

The objective of the Testing Procedure is to quantitatively determine the opening pressure and qualitatively verify operation (i.e., lift or flow) of a reclosing pressure relief valve after removal from service. Note that flow measurement is not required. At this time; the procedure has been written, the materials have been sourced, and a fabrication contractor is ready to start construction. The schedule calls for completion of the test rig by mid-December 2009. This will allow time to modify the procedure if necessary, with the goal of presenting the project findings to the IIAR membership through a formal Technical Paper to be presented by the project manager, Dr. Todd Jekel of IRC at the March 2010 annual meeting in San Diego, CA.

"The development and publication of a standardized Testing Procedure is a vital step in IIAR's long term objective to create and populate a pressure relief valve service life data base," said Brian Marriott, the ARF Chairman. "This project could not have been funded without the benefit of generous donations made to ARF by the IIAR membership. This is truly the result of your donation money at work".

Research Project Funding Approved By Ammonia Refrigeration Foundation

Joint ASME-ARF Research Project Paves the Way for Safer, Cost-Effective Piping
ARF was founded with the mission of supporting ammonia research and education. ARF will reach an important milestone at the 2009 IIAR Industrial Refrigeration Conference in Dallas when the findings of the first ARF supported research project, the ASME-ARF Low Temperature Pipe Research Project, are reported.

As the title indicates, the research was a joint endeavor with ASME. ARF chose to be a co-sponsor of this research because its results will directly benefit IIAR members by determining whether -20°F is a valid threshold for low temperature piping or whether less expensive piping can be used without impairing safety.

The project was suggested by IIAR member Rich Merrill. In a March 2008 Condenser interview, Merrill said that investigation was needed into the temperature range benchmark of -20°F because no explanation for it was provided in the existing standard. He noted that the present code has many seemingly arbitrary features including "a blanket requirement to impact test any steel if the design temperature is -55°F(-48C) or below, again with no explanation given. In addition, these requirements were written over 15 years ago, and modern steel manufacturing techniques may be creating different material properties than were applicable when the standard was written." ASME Standards Technology LLC is the contracting and project management entity for the impact exemption project. The testing was performed by the Pressure Vessel Research Council, and the results will be presented at the 2009 IIAR Industrial Refrigeration Conference in Dallas, TX.

After the paper is presented in Dallas, it will go through an approval and amendment process before it becomes an integral part of IIAR-2 (Equipment, Design and Installation of Closed-Circuit Ammonia Mechanical Refrigerating Systems) and ASME B31.5 (Refrigeration Piping and Heat Transfer Components).

Future ARF-sponsored projects will focus on safety and mechanical integrity. Two likely areas for ARF-funded research are stress corrosion cracking and sight glass composition.

Stress corrosion cracking in ammonia vessels was chosen as an area for study because most stress corrosion research has focused on ammonia storage tanks for agricultural purposes, a focus that may not be relevant to ammonia refrigeration vessels. This is one of the first stress corrosion research projects to deal specifically with ammonia used in refrigeration systems.

IN CONCLUSION
In the two years since its inception, ARF has become fully operative and self-sustaining. The Foundation is viable because of the generous participation by 79 individual and corporate sponsors in the March 2008 Century Club campaign. The Foundation has assets of $252,000 and another $50,000 has been pledged. This level of endowment permits ARF to be self-sustaining and able to assist in funding projects important to our industry. Your donation can help ARF take its work to the next level and fund more ambitious research projects, scholarships and training programs.

Your ideas for future research and education initiatives are also invaluable contributions to the work of ARF. Please submit your ideas to the Education and Research committees or to the IIAR Board.

The Ammonia Refrigeration Foundation (ARF) is a non-profit research and education foundation promoting educational and scientific projects related to industrial refrigeration and the use of ammonia and other natural refrigerants.