Stud Breaking Problem in Vertical Recip Compressor

1- Where does the studs break ?

2- Mechanical quality of stud material ?

3- How do you induce preload ? torquing ? stretching ? How much torque ? How much stretching?

4- Do you have a washer between nut and piece ? Hardness ?

5- Do you tighten a dry or a lubricated surface ? and thread ?

6- Can you make a sketch of part and stud ?

After answers come we can go on.

By off chance is there the possibility that instead of all vapor there could be slugs of liquid entering the compressor suction? If so, this could produce sudden stresses capable of breaking bolts or rupturing other parts of the compressor.

As well for your comment as for the one made by yesyen it is a remark to be done. In general the weak part of a system can be the bearing either a journal or a ball/roller type has very high chances to be destroyed by such important forces even before the bolts breake. In no case a bearing could live longer than a bolt is the forces are as high as you presume. The bolts break every month but nothing has been said about bearings! This pinpoints a weakness of the bolts and most probably an uncorrect, too little, preloading. This leads to a higher part of the load to be supported by the blot and leads to its failure by fatigue. If only one bolt breaks or only has a higher elasticity due to a progressive crack which reduces the active section the load is no more only a pulling force but a combination of pulling force and bending moment for the rest of the bolts increasing their loading and accelerating their failure. I do not say that you are not right only that if other parts of the compressor do not fail the reaszons you gave are less probable.

I agree with you. That is what I also mentioned that the discussion is relevant if only some parallel failures on valves etc were witnessed. Bearing is nevertheless an immediate one.

The subject studs are normally ground and are fixed in reamed holes. Once the original studs broken for some reason, subsequent replacements are normally from either the general stock or locally manufactured. In either case the chance of having OEM quality is less likely. While the root cause is still prevailing, the inferior quality (strength) only cascade and accelerate the failure.

With lesser data, we mostly recall similar failures that we experienced and tend to suggest irrelevant solutions. In the actual working context, the knowledge and required tools to do right jobs like 'preloading' may even be subjective. M20 stud bolt/nut at such locations, on frequent failures, site people mostly tend to use 'slogging spanners', un-minding the torque values.

What I notice is that the OP is not any more present and not willing to give information to obtain a quality answer. Although this is not as unusual as it can be though it reduces drastically the willingness to help.

Why invest efforts when the directly concerned party does not manifest the slightest interest ?

Ensure the 'piston vs head clearances' (bump clearance) are as per the manual. The thump rule is, the clearance should be 1/3 at the 'crank-end' and 2/3 at the 'head-end'. The intention is to accommodate the thermal expansion of the piston and piston rod. In your compressor it is all the more important, since the top piston could be the extension of the bottom piston. This arrangement calls for extra attention. The space required at the 'head-end' of the top piston should be more than the bottom piston.

This discussion is relevant if only there is some symptom of piston hitting the end cover and the subject studs crack due such knocks. Even otherwise, if there any liquid entrapment, as suspected by Tornado could, would create knocks. The parallel failures could the valves.

What material are the studs made from, and what other service conditions do the studs see in service (temperature, pressure, chemicals, etc....) The issues of stud-breaking might be related to chemical exposure with subsequent hydrogen embrittlement. In that case, maybe having the studs coated with a protective fluoropolymer coating might be in line for offering additional corrosion protection on the studs.

Hello Every Body,

In reciprocating compressor, distance piece bolt gets brocken if the squareness and flatness of the two matting surfaces is not perfect. If surfaces are not properly aligned, it starts failing of one bolt and ends up in brake downs.

Monitor the temperature of the bolted joint, if it is varying to large value then you have take care of the bolting material suitable for the thermal variation.

Further please ensure that pre-load torqueing of the bolts is as per prtocol of manufacturer.

at guru, its not about showing interest dear, the problem iam facing is quite unsual friend, as u c frm the discussion till now, if u hv any query/solution , plz let me knw.

the compressor was installed on 1996, since from commissioning time only, the compressors noticed higj vibrations, LP side cylinder top vibration is 24 and HP side cylinder top vibration is 26 mms.many times in past we are facing stud breaking problem, but in past only one or two (max) bolts found sheared, from year 2005 to 2009, the problem is resolved without doing much in compressor, but from last one year, machine is behaving abnormally unreliable. now a days we face stud braeking problem very frequently, 5 bolts found sheared each time when we open it. after shearing of bolts the machine vibrates tremendously and the same gt tripped at 30 mms limit value.the liners are worn out therefore honning of liners done in august 2010 shutdown. honning limits are within allowable limit factor, provided by OEM. one thing is also unsual, i dnt knw, bt this thing i gt to knw whn iam collecting history o this compressor tht 80% of valve failures is of HP suction valve. I also want to knw reason for the same, Is something is wrong is motion, or foundation.

Also i checked TDC and BDC it is OK, 1/3 and 2/3rd. Also the psiton is not threaded, it gets locked by the help hydraulic bolts and taper locking. Hydraulic p[ressure of about 1700 bar is required for locking, therefore chances of doubting in TDC BDC is not correct acc to me.

Kindly help me out with ur valued suggesstions.

1- you were presented a list of questions you did not answer we are NOT wizards so that we can only make assumptions which are reliable ONLY if we get input. No input no good answers.

2- Why not make a series of pictures to show where you measured the amplitudes, how the bolt broken section looks, how the compressor is designed ?

You want us to give suggestions to problems you present in such a poor way that it is not possible to analyse in a correct way.

3- what happened to the bearings ? to the connecting rods ?

Make an effort according to #2. Other had also complex problems but considered the arguments send information and pictures and got the right answers.

As for interest if you do not give any sign of life for so many days when you need badly an answer how would you call it ?

As a last comment we are not here on an SMS cellular phone site so please use FULL words to explain tour problems.

I'd say it been radically out of balance, since day 1, and is simply shaking itself to pieces.

"TDC and BDC it is OK, 1/3 and 2/3rd." Is it respectively? Then it is wrong. At BDC the clearance should be 1/3 and TDC should be 2/3.

As commented by 34point5, the problem could be prevailing from the day one. I think you do not have another similar machine to compare as to isolate whether this is an unique problem with this particular machine or generic problem with this model. You may compare with few more locations where same model are existing (struggling to exist).

Vertical (or horizontal) inline, multistage compressors are problem prone compared to 'horizontal, balanced, opposed multistage' compressors. In the former design, the vibration amplitudes are cumulated and in the later the vibration produced in one stage is countered/balanced by the other stage. The former is often preferred due to initial cost, penny-wise. Of course you have to pay hefty on maintenance. Sadly asset owners (at times) expect maintainers to handle the problems/shortfalls that are spilled over from manufactures, due to obvious reasons. Some problems that cannot be cured have only one option, endure.