Failure Diagnostics for a Stainless Bellows Liner

[Bambie]

In our plant we have a 72”dia stainless steel bellows assembly in an exhaust equalizing line between two turbine condensers (please see attachment).

Without any significant change in process flows, vibrations levels are increasing.

We suspect the liner may be compromised.

Does anyone know of any means to detect and quantify liner degradation while in service?

So far the proposals have been radiography to detect deformation and ultrasonics to detect weld separation.

Perhaps vibration analysis could detect a characteristic breathing mode frequency shift if the attachment weld is cracking.

 

[metengr]

From my past power plant experience the only way you can detect if you have cracks in an expansion bellows is to have the line out of service for inspection. You can try a sonic gun and monitor noise level but typically the failure mode of bellows like this is from small circumferential-oriented mechanical fatigue cracks located in the convolutions of the bellows, which link-up into larger cracks. Radiography may detect larger cracks, however, I would expect you could hear those using a sonic gun.

 

[Bambie]

Metengr, Do you have any experience with detecting cracks in a LINER attachment weld?

 

[metengr]

The liner attachment weld will typically be a dissimilar metal weld (DMW). Because this is a fillet weld versus butt weld you are forced to perform inspection off-line, probably using a borescope.