Piston failure of a recip comperessor

[sgoel]

We are facing a repetitive failure of a piston in a recip compressor handelling propane-butane rich gas. One of the deviation from design is suction pressure, which is running at 2.1 bar G against design value of 1.4 bar G. On the other hand, discharge pressure is lower at 7 bar g , against design value of 8.0 bar g.

I would like to know whether these changes can cause failure of piston. What are the other causes for failure of pistons in recip compressors?

Thanking you in anticipation please.

S Goel

 

[Montemayor]

sgoel:

Before answering any questions on your query, you should be specific, detailed, and clear on what you mean by "piston failure". You, I, and all the engineers on this Forum know that there are multiple types of so-called "piston failures" and we can't be expected to guess correctly as to which failure you are experiencing. All that your description will generate is the proverbial opening of a can of worms.

From the simplicity of your first question, I can only surmise that you shouldn't experience any problems with the compressor and much less with the piston. You are doing less work with less differential pressure across the cylinder - or is it cylinders? You haven't given us a full, mechanical description of your machine, it's service duration, it's make, age, driver, HP rating, rpm, etc., etc.

One common (& dangerous) cause of a piston failure in a reciprocating compressor is the inclusion of liquids with the inlet suction gas to a cylinder. This is a common case when neophytes or inexperienced persons attempt to install and operate such a machine. If your C3-C4 mixture is a saturated one, I would be very suspicious of liquid inclusion with subsequent piston ring failure, bent crank shaft, busted wrist pin, bent piston rod(s), etc. etc.

Do the correct engineering thing: sit down, think, and detail out your problem as if you were in our position and knew exactly nothing about what you have installed and are operating. Give us the application, the process conditions, the compressor's mechanical details and a full description. Then, and only then can you expect any reasonable, intelligent engineering response and answers. I'll await your response.



Art Montemayor
Spring, TX

 

[pmover]

to supplement Art's response . . .

knowing more data about the piston/cylinder would be helpful. "piston failure" may be a result of not being aligned, short length (piston bends at rod connection by not having a skirt), having an uneven pressure distribution along piston face (difficult to determine) causing piston to bend at rod connection, lubrication, etc.

something to ponder . . . but more data would be helpful.

good luck!
-pmover

 

[sgoel]

Art

Sorry for creating a confusion. Compressor is a two stage double acting reciprocating compressor.First stage suction and discharge pressures are 2.1 barg and 7.0 bar g respectively, whereas second stage suction and disharge pressures are 6.8 and 25.0 barg respectively.

The piston in question is a two piece piston. Failure is observed at the location of joint between the two. MOC of piston is Cast Aluminium.

Process gas contains 0.2-0.6 ppmv chloride. Can that lead to some sort of failure mechanism.

Again very sorry for confusion.

 

[dcasto]

Do you have a large enough weep hole in the piston? You can build up pressure in the piston and it can break unless relieved.

 

[sgoel]

No , Piston does not have a weep hole.

 

[Fzob]

One possibility is that there is wear that is causing the piston to ride off center causing stress at the piston to shaft connection at the first piston section.

Check for wear on the piston. These types of pistons often wear on on side causing the shaft to drop off of center. Check the roundness of the piston and the eccentricity the sleeve. If you find you are out of tolerance on the sleeve it may cause the piston to drop below it center.

 

[payam25n]

dear my friend
hi
please check if you have any rod drop alarm or not? if you have it may be because of the pistons failure.
then check the loading valves in sound and temprature.they must be worm and withpout noise.
now check the spill back valve. It may pass the gas or might not be close full.

 

[Hookem]

Is the cylinder double acting? or SACE? or SAHE?

Have you (or had someone else) check for rod load? and for rod load reversal?

Have you verified that lubricating oil in the manufacturer's quantity and quality have been supplied?