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    Catastrophic compressor failure...need info



    I am working on assisting a company that suffered a compressor explosion in an ammonia refrigeration system. The reason: liquid ammonia made its way to the compressor. There are a number of compressors used for this system. In order to protect the remaining compressors, I am recommending that they install "traps" or drop legs before each compressor. The company is informing me that these compressors are already protected by the low pressure receiver/accumilator. I need to ask the group if this makes sense. My limited "engineering" understanding of ammonia systems - tells me that every system has to have a low pressure side accumilator - and this vessel(s) are typically located far from the compressors, so how would a low pressure receiver/accumilator be able to protect a compressor from liquid carry over? ANy insights might help me prevent another explosion and save some operators. Thanks in advance.
    Seaturtle.........



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    Re: Catastrophic compressor failure...need info

    Welcome to the forum bsh3239!
    The low pressure receiver/accumulator is between the equipment that could return liquid and the compressor. It should be equipped with a high level float that will turn off the compressors if a dangerous level is reached. A seperate trap is not required.
    There are several ways a compressor can fill with liquid. Among them are no/bad discharge check valves, liquid from a discharge oil trap, and a leaking inter-stage liquid injection solenoid.
    What people call an explosion is usually from a compressor filling with liquid from another source than the liquid line.
    However this is general information. Without knowing the layout of your system it is difficult to offer specific advice.
    If you can give us specifics the members will jump in and give you as much help as we can.
    In your position I would consider calling in a NH3 contractor to evaluate the system and make specific recommendations. Industrial refrigeration systems require specialized knowledge of the components and safety issues. If a NH3 contractor is not available in the area consultants can be found who can come to
    a plant and give you a opinion of what should be done.

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    Re: Catastrophic compressor failure...need info

    Thanks for the quick reply. One more question: It is my understanding that the "safe" way to get liquid off of the wrong side of the compressor - is to use either another compressor to suck it off or use a portable "vacuum" to suck it off and return the liquid to the low side of the system. Is this correct. I understand that there are other ways to do the same thing - but I am focused on the "safe" way. This is why the compressor exploded - they got creative with getting the liquid off of the compressor - and they did not get it all. What is your opinion about adding heat to the system (i.e. blow torches to the pipes - to heat up the ammonia and return it to vapor state? Thanks for your time......

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    Re: Catastrophic compressor failure...need info

    Did the compressor actually blow up as in: parts flying through the air?

    The low pressure receiver should be sized sufficiently to store any reasonable amount of liquid volume while still allowing the liquid to separate from the vapor by gravity.

    I have though seen liquid condense in a suction line and have the liquid run back to the compressors. I have also seen compressors flood-out with liquid for a number of reasons, but have never seen a compressor literally explode into many pieces. not saying it won't happen, but I have not seen it or heard about it yet.

    The safest way to get liquid out of the compressor is to leave the sump heaters on, lock-out the compressor motor and leave the compressor set for a long period of time until the liquid evaporates.

    Quote Originally Posted by bsh3239
    This is why the compressor exploded - they got creative with getting the liquid off of the compressor - and they did not get it all

    If the compressor really did explode the above makes me think they had a part of the compressor package isolated with cold liquid. And it's that which caused the explosion. That's very dangerous.

    Sounds like these guys should not be working on ammonia systems?

    BTW, i just posted this reply and noticed you placed several other posts in different areas. Please don't do that. It makes it more difficult to keep track of and dilutes your responses. And , it sorta looks like spam. Thanks.
    Last edited by US Iceman; 15-11-2009 at 06:00 AM. Reason: added comment
    If all else fails, ask for help.


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    Re: Catastrophic compressor failure...need info

    Hi BSH3239, If you do not understand Ammonia systems go with NH3LVR and call in a specialized NH3 contractor. I have not seen a compressor actually blow up in 24 years working with Ammonia, Have seen the damage from liquid from the surge drum as we call it over here, e.g. discharge valves and piston damage in piston compressors and rotor and main bearing damage in screw compressors. For removing liquid go with USICEMAN one of the best for infomation on Ammonia.
    Arthur.

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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by aawood1 View Post
    Hi BSH3239, If you do not understand Ammonia systems go with NH3LVR and call in a specialized NH3 contractor. I have not seen a compressor actually blow up in 24 years working with Ammonia, Have seen the damage from liquid from the surge drum as we call it over here, e.g. discharge valves and piston damage in piston compressors and rotor and main bearing damage in screw compressors. For removing liquid go with USICEMAN one of the best for infomation on Ammonia.
    Arthur.
    Arthur.
    I could not of put it better myself.
    BSH3239.
    There is a wealth of experienced guys on this forum from your side of the pond.
    Please use them!
    Your post frightens me somewhat.
    You are honest enough to admit that you don't know enough. Good on you!
    The bit I struggle with is the fact that you indicate that you are an "outside Adviser"
    On a subject you do not know?
    Am I right to be concerned?
    Grizzly

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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by bsh3239 View Post
    Thanks for the quick reply. One more question: It is my understanding that the "safe" way to get liquid off of the wrong side of the compressor - is to use either another compressor to suck it off or use a portable "vacuum" to suck it off and return the liquid to the low side of the system. Is this correct. I understand that there are other ways to do the same thing - but I am focused on the "safe" way. This is why the compressor exploded - they got creative with getting the liquid off of the compressor - and they did not get it all. What is your opinion about adding heat to the system (i.e. blow torches to the pipes - to heat up the ammonia and return it to vapor state? Thanks for your time......
    Torchs are not very good for this sort of thing, A portable propane heater can be used. The safest way is to let it evaporate on its own. Of course if the compressor gets too cold it can fracture the water passages. This is a job for an experienced hand.
    A recovery machine for NH3 (a "vacuum") is hard to come by in the United States.
    A NH3 plant is best in the hands of an experienced operator. Quite often they are selected from a maintenance staff and given no knowledge of how the system works. A good operator has a passion for his craft.
    I remember started up a 12 cylinder Carrier that I has rebuilt. We always monitored a startup for 2 hours just to be on the safe side. The operator came into the engine room and felt the suction and discharge. He then remarked "just like it should be, hot in and cold out" I was speechless.

    A few years ago a accident happen at a cold storage near here. I did not see it but I talked to a serviceman who was there after the fact.
    Apparently they had a Vilter piston compressor with the suction piped into the dischsarge of the engine room. The discharge of this machine went into a heat exchanger that provided underfloor heat.
    As I understand it they had procedures to vent the machine before it was started. I am told this was not followed. Since the suction pressure was so high liquid condensed from the low side. When the machine was started it took the heads off.
    This is my understanding of what happened. Again I was not there.
    I would encourage a certain contributor to this site to contact you. He works as a consultant and can advise you. I believe you need a site visit to inspect the layout.
    Last edited by NH3LVR; 15-11-2009 at 07:42 PM. Reason: Spelling

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    Re: Catastrophic compressor failure...need info

    Bsh,
    are you sure that it is liquid that has done the damage.
    Heard of a similar effect recently when a suction check valve dropped a plate and screwed a screw big time,
    an explosive result , once pulled down not a pretty sight.

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    Re: Catastrophic compressor failure...need info

    1) another source of liquid in nh3 system is the lower than condensing temp of the circulating jacket water temperature . Water circuit should be switched off to the jacket through a solenoid valve .

    2) oil separator during off cycle can also be a source of liquid back to compressor crank-case .

    3) you may have an oil collector tank with a heater which boils off the liquid refrigerant & oil is supplied back to the compressor crank-case through a float .

    4) as the liquid enters the hot cylinder during compression process , extremely high pressure generation occurs which can stall compressors , blast pistons in pieces , valve plates , top of pistons pick holes due to excessively high pressures. At times compressor can explode through head .
    Valve reeds are susceptible to pressures due to incompressible liquid pressures but pressures generated in a cylinder through a large slug of liquid can result in ``explosion `` .

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    Re: Catastrophic compressor failure...need info

    Wow - Thanks for all the replies. I will let the cat out of the bag, as I prompted a number of questions (sorry about that). I am an enforcement officer for a four letter agency that conducts Process Safety Management inspections (do not hate me...LOL). I inspect/investigate incidents in sooo many industries that I can not possible be an expert in all of them. So when I stated that I am advising - that means I am inspecting/investigating. I find these forums so very helpful to provide me with the real life applications and realities that the books can not provide. Some officers are too proud to ask the simple questions for fearing that they will appear stupid. I will never learn if I do not ask the questions - I feel that getting the opinions/insights for as many different sources - I then can provide a better service to the employees that I am asked to protect. With that out in the open - here are some additional facts:
    1.) Yes, the compressor did explode - parts flying across the room - two operators standing in front of it when it "popped" - covered in ammonia - lucky to be here. Yes, it was liquid ammonia that caused it to fail - it was on the wrong side of the compressor and attempts to get the liquid off the compressor failed and upon start up the compressor failed.

    So here are my trouble spots:
    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.
    2.) If the low side (booster) compressors are suffering "slugs" is that a symptom that the low pressure receiver is under-sized? What would be the first thing to look at if the low side boosters are slugging?
    3.) What is a normal frequency for compressor slugging? I realize it is going to happen - but how many times is getting to the point of too many? The answer may be that it is never acceptible - but give me your opinions.

    I realize that it is not my job to design or inform the employer how their system may or may not be performing well. Technically my job is to audit their managment system of their equipment, so that they can ensure that their employees are safe (i.e. won't be by a compressor that fails). However, if I am able to gain a little more insight by chatting with you all, I may be able to provide better customer service to this employer and enhance my future endeavors in refrigeration plants. My end goal is to see if there is something "big" that this employer is missing (regarding their compressors and the fact that ammonia is making its way to the compressors). I know it can be complicated - with a million explainations as to why - but regardles of the reason - would the installation of a trap, level indicators and cut-outs be the appropriate fail safe measure?
    I thank you all for your time and insights. Good Evening
    Seaturtle.....

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    Re: Catastrophic compressor failure...need info

    A good consultant will he worth his/her weight in gold (the USD is now only paper value
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by bsh3239
    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.

    Quote Originally Posted by bsh3239
    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.

    Quote Originally Posted by bsh3239
    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...
    If all else fails, ask for help.


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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by desA View Post
    A good consultant will he worth his/her weight in gold (the USD is now only paper value
    Being paid in gold is good. Double eagles or Kruggerands is OK too.
    If all else fails, ask for help.


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    Re: Catastrophic compressor failure...need info

    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.

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    Re: Catastrophic compressor failure...need info

    Normally moment liqud traces comes in the compressor noise amperage does give indication.
    Normally experienced technician should be able to assess this and take preventive action.
    Crankcase heater can also help to some extent as long as it is programmed to be on whenever the temperature goes low as is the case when liquid gets in.
    Most important aspect if the balanced system if liquid comes there is a flaw in the system functioning, which again experienced technician will be able gauge.
    In my 33 years experience have heard of releief valve some times blowing up due to pressure build up.
    Even over charging will cause higher suction and higher discharge which may be the cause. But even then the safety relief valve should precede breaking of cylinders piston etc.
    If the compressor has blown it must be due to high pressure as the casing of the compressors are not as high as the receiver.

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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by bsh3239 View Post
    Wow - Thanks for all the replies. I will let the cat out of the bag, as I prompted a number of questions (sorry about that). I am an enforcement officer for a four letter agency that conducts Process Safety Management inspections (do not hate me...LOL). I inspect/investigate incidents in sooo many industries that I can not possible be an expert in all of them. So when I stated that I am advising - that means I am inspecting/investigating. I find these forums so very helpful to provide me with the real life applications and realities that the books can not provide. Some officers are too proud to ask the simple questions for fearing that they will appear stupid. I will never learn if I do not ask the questions - I feel that getting the opinions/insights for as many different sources - I then can provide a better service to the employees that I am asked to protect. With that out in the open - here are some additional facts:
    1.) Yes, the compressor did explode - parts flying across the room - two operators standing in front of it when it "popped" - covered in ammonia - lucky to be here. Yes, it was liquid ammonia that caused it to fail - it was on the wrong side of the compressor and attempts to get the liquid off the compressor failed and upon start up the compressor failed.

    So here are my trouble spots:
    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.
    2.) If the low side (booster) compressors are suffering "slugs" is that a symptom that the low pressure receiver is under-sized? What would be the first thing to look at if the low side boosters are slugging?
    3.) What is a normal frequency for compressor slugging? I realize it is going to happen - but how many times is getting to the point of too many? The answer may be that it is never acceptible - but give me your opinions.

    I realize that it is not my job to design or inform the employer how their system may or may not be performing well. Technically my job is to audit their managment system of their equipment, so that they can ensure that their employees are safe (i.e. won't be by a compressor that fails). However, if I am able to gain a little more insight by chatting with you all, I may be able to provide better customer service to this employer and enhance my future endeavors in refrigeration plants. My end goal is to see if there is something "big" that this employer is missing (regarding their compressors and the fact that ammonia is making its way to the compressors). I know it can be complicated - with a million explainations as to why - but regardles of the reason - would the installation of a trap, level indicators and cut-outs be the appropriate fail safe measure?
    I thank you all for your time and insights. Good Evening
    Seaturtle.....
    Erm!
    Yes, it was liquid ammonia that caused it to fail - it was on the wrong side of the compressor
    So which side of the Compressor was the liquid?
    If it was discharge side?
    Your comment does not make sence related to what you have told us so far!
    Then a trap is irrelevant.
    What we need to establish is what caused the liquid carry over in the first place?
    Then how it was dealt with when it occurred.
    I doubt whether plant design will be the real culprit.
    I still think it would pay to enlist the assistance of one of our American Colleagues.
    I have to ask why did the operatives turn it on?
    How did they determine that there was liquid there and when it had gone?
    Grizzly

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    Re: Catastrophic compressor failure...need info

    Do not install a trap or drop leg before the compressor if the system allready has a accumulator/LP separator/LP pot/suction trap/LP reciever ect. .

    The pipe between the LP seporator and the compressor is known as the "dry suction" line. Dry gas only.

    Tell us more about the system if you could. Sorting out refrigeration problems is what fridgys live for.

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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by bsh3239
    If the forum and the IIARs and RETAs would have told me that YES, it is a good engineering practice...
    Sometimes what gets passed around as good engineering practice is dependent upon the individual doing the engineering practice. This can be as far fetched as "that's the way we have always done it and it worked" also.

    The main issue I have with this type of logic is that repeated enough times it becomes construed to be good accepted engineering practice. Sort of like a rumor gaining credibility or repeated enough times where it becomes believable.

    I understand the position you are in. Coming in from the outside and trying to enforce regulations in a field such as this can be a daunting and thankless task.

    Especially when you are faced with the logic of: My refrigerant inventory is 9,990 lbs so I don't have to comply with 1910.111. General Duty clause what's that?

    PS. You are welcome. If the industry did a better job of helping the auditors the systems would improve. An adversarial relationship does no one any good.
    If all else fails, ask for help.


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    Re: Catastrophic compressor failure...need info

    Here is some specifics about the explosion - mainly to share the facts and if it prevents another incident than WOW what a great day.

    O.K. SHORT Version: The system is unbalanced - the operators are struggling to keep the system on-line. They come in one day and all the compressors are frosted over - they drain them via the crank cases - they bring the system back up one by one and again for about 1 month struggle with one cut-out after another triggering and shutting down the system. They get to a situation where they need the defrost system to operate - they focus on the compressor that operated the defrost system. The main operator checks the 3 inch crank case window and does not see any ammonia in the window. He attempts to do a "bump test" meaning quickly pushes the on/off button. When this is done he sees a "puff" of vapor from the head of the compressor. He now knows that there is liquid on the heads of the compressor. They decide to open a by-pass valve on the condenser units and create a suction pattern to draw the ammonia off of the heads of the compressor. They let this situation exists for a fe whours and are watching the temperature increase at the compressor. They achieve a 10 degree temp increase and the pipes at the condenser are "hot" and they determine that hot gas has made its way to the compressor. Decision is made to start the compressor. The operator again checks the window - no ammonia, and he manually rotates the motor shaft and it freely rotates (indicating nothing restricting the compressor = no ammonia on heads). The operator goes back to the start button and again prepares for a "bump test". As soon as the start button is pressed the compressor exploded.

    Current day: The company has been working on the "balance" issue with the system. They have re-routed pipe work on the condensers and have identified some areas that were causing problems. The company has replaced the failed compressor and in the replacement they installed a "drop leg"/"trap" before the compressor as an added layer of protection for the compressor and human error. Thus my journey down the "trap" or "drop-leg" issue started. I needed to ensure that I understood the whole "trap" concept. As soon as you all helped me understand that a "trap" used in the industry should not be seen as a typical trap (pipe trap) and it can be an accumilator - that REALLY helped me make sense of all the things I was reading in the compressor manuals.

    My goal now is to ensure that their standard operating procedures for getting liquid ammonia out of a compressor meets industry standards. They have a procedure that calls for closing three valves on the compressor (without the P &ID In front of me) I assume it is the suction line, the discharge line and a valve on the oil pot/system. Then the procedure calls for applying heat to the system until the frost is gone. then open the valves and follow normal start-up procedure.
    This causes me some concern, as I have seen evidence that "adding heat" means using a torch - (i.e. torch marks on pipes). From the research that I have conducted - the industry standard for getting the liquid out of a compressor is to either use another compressor to suck it off and place into the low side of the system, or to close some valves and let the system sit and the ammonia will find its way back to where it belongs. Any opinions?
    I really appreciate the fact that you all have not "shunned" me because I do not come from the industry and you have continued to provide me with your opinions - It provides me with additional prespectives when I have to attempt to ensure that the companies are complying with the intent of the process safety management system. Thanks

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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by bsh3239 View Post
    Here is some specifics about the explosion - mainly to share the facts and if it prevents another incident than WOW what a great day.

    O.K. SHORT Version: The system is unbalanced - the operators are struggling to keep the system on-line. They come in one day and all the compressors are frosted over - they drain them via the crank cases - they bring the system back up one by one and again for about 1 month struggle with one cut-out after another triggering and shutting down the system. They get to a situation where they need the defrost system to operate - they focus on the compressor that operated the defrost system. The main operator checks the 3 inch crank case window and does not see any ammonia in the window. He attempts to do a "bump test" meaning quickly pushes the on/off button. When this is done he sees a "puff" of vapor from the head of the compressor. He now knows that there is liquid on the heads of the compressor. They decide to open a by-pass valve on the condenser units and create a suction pattern to draw the ammonia off of the heads of the compressor. They let this situation exists for a fe whours and are watching the temperature increase at the compressor. They achieve a 10 degree temp increase and the pipes at the condenser are "hot" and they determine that hot gas has made its way to the compressor. Decision is made to start the compressor. The operator again checks the window - no ammonia, and he manually rotates the motor shaft and it freely rotates (indicating nothing restricting the compressor = no ammonia on heads). The operator goes back to the start button and again prepares for a "bump test". As soon as the start button is pressed the compressor exploded.

    Current day: The company has been working on the "balance" issue with the system. They have re-routed pipe work on the condensers and have identified some areas that were causing problems. The company has replaced the failed compressor and in the replacement they installed a "drop leg"/"trap" before the compressor as an added layer of protection for the compressor and human error. Thus my journey down the "trap" or "drop-leg" issue started. I needed to ensure that I understood the whole "trap" concept. As soon as you all helped me understand that a "trap" used in the industry should not be seen as a typical trap (pipe trap) and it can be an accumilator - that REALLY helped me make sense of all the things I was reading in the compressor manuals.

    My goal now is to ensure that their standard operating procedures for getting liquid ammonia out of a compressor meets industry standards. They have a procedure that calls for closing three valves on the compressor (without the P &ID In front of me) I assume it is the suction line, the discharge line and a valve on the oil pot/system. Then the procedure calls for applying heat to the system until the frost is gone. then open the valves and follow normal start-up procedure.
    This causes me some concern, as I have seen evidence that "adding heat" means using a torch - (i.e. torch marks on pipes). From the research that I have conducted - the industry standard for getting the liquid out of a compressor is to either use another compressor to suck it off and place into the low side of the system, or to close some valves and let the system sit and the ammonia will find its way back to where it belongs. Any opinions?
    I really appreciate the fact that you all have not "shunned" me because I do not come from the industry and you have continued to provide me with your opinions - It provides me with additional prespectives when I have to attempt to ensure that the companies are complying with the intent of the process safety management system. Thanks
    I think that initial approach is wrong. You shouldn't solve it yourself. It isn't simple issue as quick closing valve on oil pot. Go to IIAR and they will recommend you an experienced engineer to solve this problem. What is the reason of unbalancing? It can be design, installation and/or operation. The reason should be solved not consequences of this reason.

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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by Segei View Post
    I think that initial approach is wrong. You shouldn't solve it yourself. It isn't simple issue as quick closing valve on oil pot. Go to IIAR and they will recommend you an experienced engineer to solve this problem. What is the reason of unbalancing? It can be design, installation and/or operation. The reason should be solved not consequences of this reason.
    Feel confident - I am not even attempting to solve the unbalance issue (I have no business doing such)- we have put that squarely back into the hands of the company - that are using local refrigeration companies to assist them in the reconfiguration of the system. I am just reporting the facts associated with the explosion and to get the opinons from the group regarding the protective measures for compressors and the company's operating procedure for getting liquid ammonia off the compressors.

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    Re: Catastrophic compressor failure...need info

    Frost does not always indicate the presence of liquid refrigerant. It simply means the surface temperature is below the freezing point of water. If you can scrape off the ice and it starts to re-grow rapidly that's probably showing you liquid is present in the pipe/component.

    If you scrape off the frost and it does not re-form odds are no liquid is present in the area scraped free of frost. You have to be careful with this though. Liquid refrigerant may exist in an area where the frost was not removed!

    Quote Originally Posted by bsh3239
    The system is unbalanced...
    No, something is really screwed up! They either have liquid management issues in the system, which can be created by improper operation or poor design practices. If liquid refrigerant is getting in the heads on a regular basis and the crankcase is warm and does not have liquid present in it the liquid problem is on the high side of the system. Might be leaking check valves or oil return solenoids. Could be piping also, hard to tell without seeing it.

    I think you probably have an idea now that most of us take this pretty seriously for personal safety. Once we hear a few words about something it can raise a few alarms. As a result, most of us will jump in quickly when someone who is unfamiliar with industrial refrigeration systems starts to make recommendations about something.
    If all else fails, ask for help.


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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by bsh3239 View Post
    Feel confident - I am not even attempting to solve the unbalance issue (I have no business doing such)- we have put that squarely back into the hands of the company - that are using local refrigeration companies to assist them in the reconfiguration of the system. I am just reporting the facts associated with the explosion and to get the opinons from the group regarding the protective measures for compressors and the company's operating procedure for getting liquid ammonia off the compressors.
    1. Protective measures for compressors. Properly designed, installed and operated refrigeration plant.
    2. To remove liquid ammonia off the compressor. Take your time to evaporate this liquid. Air heaters will speed up this process. Crankcase should be warm before you start compressor. Manual compressor rotation should be fast no slow to make should that no liquid left. To start up compressor, discharge valve should be fully open, suction valve should be cracked.

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    Re: Catastrophic compressor failure...need info

    You guys (gals too) have been Great - Thanks so much. You have assited me to not get bogged down in the "trap" issue and I have been able to return to the facility and ask some more very pertinent questions and field verify some additional facts. I wish there were these types of forums available to me when I am dealing with chlorine gas plants, formaldehyde generators, etc. It is just nice to be able to ask questions of people neutral to the situation at hand. I am certain I will return at some point with more situations and questions (we have alot of refrigerated spaces....)
    THANKS AGAIN.

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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by bsh3239 View Post
    They have a procedure that calls for closing three valves on the compressor (without the P &ID In front of me) I assume it is the suction line, the discharge line and a valve on the oil pot/system. Then the procedure calls for applying heat to the system until the frost is gone. then open the valves and follow normal start-up procedure.
    I hope this is not the procedure. Valving off the compressor and applying heat could be dangerous and would not be helpful. When you attempt to move liquid qround in a system in other than the normal manner you have to think very carefully about where it is going. I remember seeing a operator put heat on a compressor for three days before he admitted he could not get the liquid out. What he had done was move it back into the evaporator and every time he started the system he had a flood back again.

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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by bsh3239
    ...chlorine gas plants...
    Yikes!!! Now those are something to deal with from either an inspection or design issue. I've been in one and the pucker factor was pretty high for me. I've also done some design for chlorine condensers and that's a tough one.
    If all else fails, ask for help.


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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by US Iceman View Post
    Yikes!!! Now those are something to deal with from either an inspection or design issue. I've been in one and the pucker factor was pretty high for me. I've also done some design for chlorine condensers and that's a tough one.
    I wanted to provide your group here some feedback: It was really refreshing to find a group of people that take anhydrous ammonia seriously. I am a chemist by formal education - but use my knowledge for practical applications in the chemical industries (i.e. PSM). I RESPECT ammonia - it is an amazing chemical - very versatile and can bite you hard. I have done a number of refrigeration operations - and lately it has seemed that there is way to much complacency regarding the hazards of ammonia - and the state of the mechanical integrity programs reflect this complacency (i.e. not completing all the required maintenance - preventative). Thanks for resetting my faith that there are others like me, that do not underestimate ammonia.
    I love my job - but it can be challenging - my job expects me to be able to be flexible and resourceful enough to find the ansers for every type of industry. Process safety management inspections are done in soooo many places: hydrogen gas plants, acteylene generators, phosgene, semi-conductor plants (uses fuming nitric acid, hydrofluoric acid - all in very large quantities). I learn so much by talking to the front line operators, I listen so intently when they describe what they do and why they do it - sometimes they think Im a little too excited about the siubject matter. Many have stated that I am a crazy woman high on chemicals - LOL...
    THANKS again.

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    Re: Catastrophic compressor failure...need info

    While there are still a few remaining holdouts, most take safety and system integrity seriously. Most people feel forced into complying with mandated regulations, which is unfortunate. My feeling is, if the ammonia refrigeration industry does a better job of policing itself it is actually better for the community.

    Although a lot of PSM requirements are driven by what is used in process plants a lot of what they do (or should be doing) is also applicable to refrigeration (ammonia, propane, or the generic commercial refrigerants). They are all dangerous.
    If all else fails, ask for help.


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    Re: Catastrophic compressor failure...need info

    You mentioned HYDROFLUORIC ACID!
    Makes NH3 look like a glass of water.
    Too nasty for me!

    True story.
    I was working around, not with HF, one time. I was on the Emergency Response team and was chatting with a Lady. She said something about "What happens if I spill this on myself?"
    I explained that four men would appear from the Facilities Dept in protective suits, drag her into the chase, remove her garments, and after a short cold water shower, rub her down with Calcium Glutamate gel.
    A brief wistful look came to her face, and then a Uh-Oh look.
    She never did spill any on herself.

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    Re: Catastrophic compressor failure...need info

    Makes you wonder if they are using a level probe without hard wired high level switch to stop compressers .

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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by RANGER1 View Post
    Makes you wonder if they are using a level probe without hard wired high level switch to stop compressers .
    Because of the forum/group I was provided with some pertinent info. I went back and I did verify that the low pressure receiver was equipped with a high and low level float. These float switches are connected to magnetic level indicators - that in turn will trigger a cut out and shut down the compressors - which in turn will shut down the entire system.

    Hey I just thought of another question that your group probabily has an opinion about:

    How much ice build-up is too much build-up? I have been using the rather arbitrary number of an inch of ice or more is getting excessive. Please feel comfortable to disagree with this number...Thanks again

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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by bsh3239
    How much ice build-up is too much build-up?
    Where?

    On piping with insulation you should never have ice. Ice on insulated pipe shows a failure of the insulation & vapor retarder. Ice on some control or service valves is not a big deal, since these are not usually insulated to allow for easier service.

    If a low temperature pipe stays at that low temperature constantly the ice only increases the dead-weight on the pipe and increases the heat load due to parasitic heat gain. If the pipe is cycling through temperatures like a hot gas defrost line will the repeated freeze-thaw cycle can promote increased corrosion rates, if the vapor retarder has failed (and most will or have). Corrosion is the main issue the way I see it.
    If all else fails, ask for help.


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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by bsh3239 View Post
    Because of the forum/group I was provided with some pertinent info. I went back and I did verify that the low pressure receiver was equipped with a high and low level float. These float switches are connected to magnetic level indicators - that in turn will trigger a cut out and shut down the compressors - which in turn will shut down the entire system.

    Hey I just thought of another question that your group probabily has an opinion about:

    How much ice build-up is too much build-up? I have been using the rather arbitrary number of an inch of ice or more is getting excessive. Please feel comfortable to disagree with this number...Thanks again
    I don't think that low level should shut off the plant. Low level should shut off the pumps.

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    Re: Catastrophic compressor failure...need info

    Felt like having a rant as computer has been down for a week .
    Obviously this client have some serious problems .
    If you have high level switch it should shut down plant well before compressors get any liquid .Normally have 5-10 sec delay for nuisance trips .
    Hopefully high level switch works and is at right height on vessel .
    Sometimes depending on piprwork plant could shutdown and level can increase in accumulator because wet return pipework has "X" amount of liquid in it .
    In this case you could continue to run liquid pumps to prevent it ie keep circulating it .
    Dry suction header to compressors preferably should also have slight fall back to accumulator so it can help drain it if something bad happens .
    Elbow facing up in vessel on dry suction usually have a 1/2" hole in bottom for liquid to drain back out of header .
    In general most high level in a plants that has worked OK are usually oil related or make up solonoid leaking .

    If oil gets into control column area it slows reading down as liquid ammonia can't get past it to register on float switches etc .
    Have heard on one occation that a vessel was piped up in reverse ie wet return /dry suction mixed up .
    All above is really only related to liquid entering compessor suction or interstage suction .
    Rant over .

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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by US Iceman View Post
    Where?

    On piping with insulation you should never have ice. Ice on insulated pipe shows a failure of the insulation & vapor retarder. Ice on some control or service valves is not a big deal, since these are not usually insulated to allow for easier service.

    If a low temperature pipe stays at that low temperature constantly the ice only increases the dead-weight on the pipe and increases the heat load due to parasitic heat gain. If the pipe is cycling through temperatures like a hot gas defrost line will the repeated freeze-thaw cycle can promote increased corrosion rates, if the vapor retarder has failed (and most will or have). Corrosion is the main issue the way I see it.
    Insulation - that is a given - I always look for water migration into the insulation (vapor barrier leaks). The lesser known stuff is: Pumps - when the pump is completely covered in a thick layer of ice, when an uninsulated line is covered in a layer of ice....In general with these cases - I have been starting to address the ice issue - when there is about an inch depth of ice build - up - mainly due to the added weight of the ice over the system. I will address the valve issue when the ice has completely encased the valve stem - I have even found valves completely encased (stem and handle) in ice. These are no- brainers. The harder cases to evaluate are the pumps and uninsulated lines. I have tried many times to locate literature that would provide guidance on an acceptable level of ice build-up on such items - but I have not been successful.

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    Re: Catastrophic compressor failure...need info

    Ice is a fact of life in low temperature systems. Exposed valves will accumulate it, but your suggestion of the ice covering the valve stem is an issue. If you need to close the valve and can''t, that's an issue.

    ice on pumps I would not worry about though.
    If all else fails, ask for help.


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    Re: Catastrophic compressor failure...need info

    Hi Bsh3239, At this time I'm pumping out and shutting down a 30 + year old Ammonia system and as for ice build up a lot of the liquid line valves have to have the ice chipped away to find the valve spindles. As USIceman has put it Ice is a fact of life in -42oC systems. We have removed lagging from some of the pipework after it's had the liquid and gas removed from that section and it's then taken 3 to 4 days for the ice build up to fall off. And yes we did heat up the oil to boil off the liquid ammonia in it before draining off the oil from the pipework. I have seen liquid pumps with so much ice build up on them that you can not make out what type of pump it is or what make. Only two more moves to make with the ammonia and it's around 20 tons in to the recovery tankers and the system is empty and dead. ( sad day one more old ammonia system gone)
    Arthur.

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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by aawood1 View Post
    Hi Bsh3239, At this time I'm pumping out and shutting down a 30 + year old Ammonia system and as for ice build up a lot of the liquid line valves have to have the ice chipped away to find the valve spindles. As USIceman has put it Ice is a fact of life in -42oC systems. We have removed lagging from some of the pipework after it's had the liquid and gas removed from that section and it's then taken 3 to 4 days for the ice build up to fall off. And yes we did heat up the oil to boil off the liquid ammonia in it before draining off the oil from the pipework. I have seen liquid pumps with so much ice build up on them that you can not make out what type of pump it is or what make. Only two more moves to make with the ammonia and it's around 20 tons in to the recovery tankers and the system is empty and dead. ( sad day one more old ammonia system gone)
    Arthur.
    Indeed a sad day.
    Surprisingly there are new systems being installed.
    It's slow I know.
    But if only more people would learn how Good and energy efficient Ammonia is!
    I suspect there would be more.
    (Good point about the ice build up on liquid pumps-been there myself, many times).
    20 tons Imperial! Thats a fair sized system.
    Cheers Grizzly

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    Re: Catastrophic compressor failure...need info

    Quote Originally Posted by Grizzly View Post
    Indeed a sad day.
    Surprisingly there are new systems being installed.
    It's slow I know.
    But if only more people would learn how Good and energy efficient Ammonia is!
    I suspect there would be more.
    (Good point about the ice build up on liquid pumps-been there myself, many times).
    20 tons Imperial! Thats a fair sized system.
    Cheers Grizzly
    Hi Grizzly, As you say a sad day for this one but's it's being replaced with a new plant rated at 1.2 mega wats system with a smaller Ammonia charge some where around 4.5 tons. On the connections in to the old freezer headers we had around 400 to 600mm of ice build up along the empty new pipe work and upto 20 mm thick in only 14 days on the wet return's.
    Arthur
    Arthur

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    Re: Catastrophic compressor failure...need info

    hello
    I have read this thread with interest and had experience before 1970 of a Also agree safeties high accumulator level stops compressor and low stops pumps.

    Joined a freezer ship in 1970 and u could not get in brine room for ice, took some time with water hoses to see what was in there.

    My other comment is down to service and maintenance and whether oil was responsible not being drained regularly. Had a plant where all dran valves were badly coroded and finally got them changed. Took a lot of oil out of evaps.

    Would of liked some better info on the plant in question.

    Any ammonia leak can then lead to explosions depending on volume in air.

    regards
    alan

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    Re: Catastrophic compressor failure...need info

    second quote
    I had a compressor faulure piston went thru head of an old Sternes NH3 compressor which made it a write off.
    Bottom end failed. This was at an Ice rink and compressor driven by a water wheel. They could not get in to stop it initially.
    alan

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