Catastrophic compressor failure...need info

[US Iceman]

1.) Read a compressor manufacturer's manual and most of them require or heavily recommend a trap installed in line with the compressor. Almost every refrigeration system that I have dealt with has had to have a low pressure receiver - and yet the compressor manufacturer's still insist on a trap - Is it a good engineering practice to install traps seperate of the low pressure receiver for an additional level of protection for the compressors? What is the group's opinion. I could take the easy way out and tell this employer that they have to follow manufacuter's recommendations and that they need to install traps- however, I realize that there are consequences to systems if I were to make such a bold and "to the point" statement. I want to ensure I understand all sides before I make such a statement.

What they typically refer to as a trap is not a pipe trap, but what is called a suction trap. This is the same thing as a suction accumulator or low-pressure receiver. The lingo in this trade is something like the joke of Great Britain and the US being separated by a common language. Some systems have a lot of different configurations that dictate how that suction trap is also configured or designed.

2.) If the low side (booster) compressors are suffering "slugs" is that a symptom that the low pressure receiver is under-sized?

Could be. Or, it could be caused by something else. It doesn't matter if it's a high-stage or low-stage compressor. Contrary to popular opinion, size is not the only thing that matters. it might be how the system is operated also.

3.) What is a normal frequency for compressor slugging?

Absolutely zero. nada, zilch. Slugging is not normal and should not be accepted.

Without meaning to start a border war, how do PSM audits involve design reviews? The system should have gone through a HAZOP study, so if they missed something I could see how it would impact Hazardous Operations however...

[bsh3239]

To answer the question regarding PSM and design evaluations - you are correct we do not evaluate designs. The one thing that is expected of us is to ensure that the system is designed to good engineering practices (plain english - we read A LOT of standards - very exciting...). Thus if we find something that does not comply with design standards (e.g. ASME boiler/pressure vessels, API - american petroleum industry bulletins, etc) we have to require the employer to bring the system up to standard. A perfect example of this in ammonia refrigeration rooms is: IIAR and RETA all state that it is a good engineering practice to have quick stopping valves on oil drain pipes - we often find regular valves on these drain lines. We then site the industry recommendation and require the employer to install them. That is what I was attempting to get at by my messages - are additional traps really required outside of the LP accumilators - I REALLY appreciated the explaination that a trap is also referred to as the accumilator. When you are not in the business - it is hard to learn the Jargon on the fly. If the forum and the IIARs and RETAs would have told me that YES, it is a good engineering practice - and I determine they were missing from the system, then we would ask the employer to install them. I found this last post very helpful. Thank-you.