Ammonia safety relief valves come in many different shapes and sizes. Similarly, there are also many different manufacturers of them as well. Most of these manufacturers disclose a “shelf life” but none of them disclose a “service life”. This is because it really isn’t within the manufacturers purview to direct on this but rather it is the National Board who specifics service intervals.
This entry is intended to provide some interesting notes or clarifications on safety relief valves specifically how they are used in the ammonia refrigeration industry. If you have any questions pertaining to any of these random tidbits, please reach out and contact Carlson & Stewart Refrigeration and we can try to provide clarity!
1. Did you know you aren’t necessarily required to replace your safety relief valves every 5-years? You are actually only required to have them re-certified every 5-years. Most opt to just replace them outright as it is cleaner and doesn’t require temporary removal of reliefs while the valves are re-certified at some laboratory.
2. Did you know that all ASME rated components must be protected by an ASME rated relief device? Many in the industry have used in-line check valves to act as a relief device where it actually isn’t acceptable practice per ASME Code (thermosyphon oil coolers would be one of them). Evaporative condensers however are an instance where check valves (or small body regulators) can be utilized instead of conventional atmospheric discharge reliefs as long as the AHJ is accepting of this as evaporative condensers are not ASME rated.
3. CSR Engineers recently attended a training and the instructor informed the group that there is a myth in the industry that if a relief valve is piped back into the system, it is not subject to the 5-year inspection/replacement rule. The instructor claims that nowhere in the code language is this exemption granted and if it is an ASME rated relief device, it is subject to the same replacement methodology as all other relief valves in the system.
4. Any relief system modification (additional mass flow or reduction of mass flow) is grounds to conduct a new back pressure study on your relief system. Because the modern backpressure studies tend to be more in depth and stricter than they were in years prior, it could require additional piping changes and engineering time.
There are lots of other “gotcha’s” relating to the design, installation and maintenance of safety relief valves, relief valve outlet piping, relief valve inlet piping. The items in this blog entry are items that are common questions we have received lately and so those of you that subscribe to our blog may be wondering some of these same questions.
Carlson & Stewart Refrigeration is here to help with any of your design, installation or maintenance tasks with your industrial or commercial refrigeration systems!