Recently we had installed four snubbers in two leads (two nos. in each pipeline)of Main steam header (12", 540 deg C) at upstream of turbine. During steam blowing/purging of main steam system (at 420 deg c which is much lesser than design conditions) one out of the snubber piston got bent/deformed. Other three are perfectly intact.As per site data the snubber is subjected to failure due to compression (Thermal mvmt). But Snubbers do allow thermal mvmt.

We are exploring on the possible reasons for failure.. pls give ur suggestions reg this..

Thanks & regards
Anand

Assuming that the snubbers had a capacity to resist shock and allowing gradual thermal movement, the snubber deformed would have got overloaded /locked due to an Impulse loading on it.

If the snubber had resisted a shock load above its rated capacity, then the Purging operation ( formation of slugs/unbalanced loads)may have induced the loads. The reasons for such loading may have to be apparently studied..

It is difficult to visualise without the knowledge of the Piping configuration and the Restraint directions of the snubbers.

To Aid quick visualisation of the snubber arrangement i will describe it briefly..

We have got 2 Main steam lines running parallel in to turbine , Each line have got two Snubbers one on either side (180 Deg Apart) along Pipe axis.. We found that in one of these lines only One Snubber has Failed while the other is perfectly intact After Purging ..

Neelam, Thanks for your reply, I fully agree that it could have happened due to over loading of snubber beyond its capacity , How ever If this is the reason then all 4 snubbers must have suffered Damage, But it was surprising to see that only one was affected.

Don't use snubbers.... they all have miserable in-service records and if they jam up when they need to be free they can cause significant overstresses.

Use gapped restraints instead of these devices they should be used once every blue moon.

I guess that the reason was that the entire load went on a single snubber. Only in theory the load is distributed evenly between the two snubbers. For the same reason, the trunnions or vessel clips are designed for the entire load, not for the half.

Regards,