From cold storage warehouses to food processing plants, all ammonia refrigeration systems — particularly older systems with piping that is aged and outdated — run the risk of dangerous ammonia leaks. While these refrigeration systems are widespread, companies that own older systems or are updating existing systems need to be aware of the safety issues and requirements related to the systems’ relief components.
The International Institute of Ammonia Refrigeration (IIAR) requires the replacement of pressure-relief valves every five years or based on manufacturer recommendations. Documentation should be made each time the valves are replaced, including stamping the replacement dates onto the punch card on each valve to help ensure ongoing compliance.
Do You Need to Update Your Relief System to Comply with Current Codes?
In order to provide the relief system documentation to show compliance with the relevant codes, standards and OSHA regulatory requirements, the following criteria are suggested:
1. A relief vent header system requires no modifications if all the following conditions are met.
a. There is design documentation that the system was installed in compliance with the codes and standards in place at the time of the design and installation. Note, this was not required until 1992, so facilities constructed before 1992 likely will not have this documentation.
b. There is a documented design basis for the vent system that shows compliance with the codes and standards in place at the time the last substantive change to the vent system occurred.
c. There have been no modifications to the relief vent system other than replacement in the types of valves.
2. The entire relief vent header system should be evaluated against current code and updated as required to meet the current code and standards if any of the following conditions exist.
a. There is no existing documentation of the design basis for the vent system.
b. It can be demonstrated that one or more elements of the relief vent do not meet the codes and standards that were in place at the time the relief vent system was initially installed or substantively modified.
c. The relief system has or will undergo substantive modification including 1) addition of new relief valve(s) and/or branch piping to a vent header, 2) addition of header piping, or 3) addition of a diffusion tank or other outlet diffuser.
d. It can be demonstrated that any portion of a modified relief system did not comply with the codes and standards in place at the time of the modification.
Facility management also should be aware of regulations falling under the U.S. Department of Labor’s Occupational Safety and Health Administration (OSHA). Refrigeration systems are regulated through OSHA’s process safety management (PSM) regulations, which include detailed requirements and procedures for employers that use large amounts of hazardous chemicals such as ammonia. These stringent guidelines require employers to continuously and rigorously analyze, update and maintain each element of their processes to ensure worker safety. Failure to meet these regulations can result in severe fines. Each facility should have regular process analyses performed to ensure compliance, to identify any danger or hazards and to ensure that the proper administrative and engineering controls are in place to deal with abnormal occurrences. In addition, process hazard analysis (PHA) should be conducted to ensure the system’s mechanical integrity, including the proper pipe thickness of the venting system. These services can be conducted through a PSM/PHA consultant.
Retrofitting Ammonia Refrigeration Piping
with New Pressure-Relief Valves
On April 25, 2000, the American National Standards Institute approved ANSI/ASHRAE Addendum C as a formal revision to ANSI/ASHRAE Standard 15 — 1994. One of the more significant changes of Addendum C was a new formulation for the line length limit that was based on isothermal compressible flow. The change was to accommodate the backpressure created by multiple valves relieving into a common header. The revised formula required much larger relief piping than the industry had been typically installing.
Often, there are questions regarding a facility’s need to update their relief system to comply with current codes. The guidelines (see sidebar) should help answer those questions.
Physical Warning Signs that Relief Valves Should Be Replaced
Relief valve calculation studies are a common service and offer an in-depth analysis of the overall relief valve system. These studies typically include the following services:
- Evaluation of current relief valve sizing for each piece of equipment.
- Evaluation of existing relief valve piping system.
- Providing documentation for a compliant system if the system is in compliance.
- If required, recommendations to bring the system into compliance.
- Providing diagrammatic drawings outlining recommendations.
- Updated relief valve schedule.
For a compliant system, a study will give you the documentation to show compliance. For a non-compliant system, the study will outline recommendations to bring the system into compliance.
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