Many times we find bellow for vibration isolation attached with piping connections of rotating m/c like pump, compressor in P&ID itself - is it possible to have good design fatigue life with metallic bellow ?

If the bellow is purely for vibration isolation &/or for absorbing construction mismatch, not for any themal cyclic loading, is there any use of carrying out thermal analysis in Caesar-II for such lines ?

regards,

sam

Sam,

Metallic bellows are “stress analyzed” by the vendors per EJMA similar in fashion to piping systems. As such vibration imposed displacements would create a significant design burden to the metallic joint. I believe if most manufacturers were polled they would state that metallic Ejs are not intended for such usage. However I will pass this interesting question along to a friend of mine he is the chief engineer for well respected manufacturer of these devices.

From my colleauge...

John,

Your statement is valid. Metal bellows are not recommended for vibration isolation purposes. Numerous failures over the years have left us all a bit gun-shy.

Sir,

Thank you very much for this reply. But, the reply from your friend suggests that even when he does not recommend, numerous failures have occured in metallic bellows due to vibration - so many A/E engineer don't follow vendor's recommendation, EJMA & their own organisation's work instructions!

If anyone uses the metallic bellow for vibration isolation, the vendor should know it & design the bellow accordingly with multiply, lowered fatigue life or change the material to rubber or fabric if temperature of operation permits.

regards,

sam

Flexible hose is usually used at suction/discharge to reduce vibration from reciprocating pump.For compressor, I have never seen this kind of design.

Sir,

You have misunderstood me; I just wrote that if we isolate any compressor by metallic bellow, the bellow vendor should know the same & accordingly design the fatigue life of the bellow so that in proactive maintenance, people may change the same after say each couple of years of operation.

regards,
sam

You want to use bellow to isloate vibration from compressor,right?I don't think that it is a "good" way to isolate compressor vibration.API618 give us some guide to control vibration for reciprocating compressor,puslation suppression devices are usually used. Personally,I have never seen using bellow to isolate compressor vibration.

Sir,

Still, inbetween compressor & suction/discharge side pulsation dampner, there may be need for bellows for vibration isolation. If the reason of vibration is acoustic pulsation like that in positive displacement compressors, pulsation dampners are the best answers. But, there may be other reasons for vibration too, for piping.

regards,

sam