by Terri Earley Terri Earley

Bachmann Industries supports Combustion Turbine Power Plants around the globe with engineered solutions to address routine problems associated with damaged Metal Bellows Expansion Joints.


Over time, Metal Bellows Expansion Joints can crack and leak at the turbine exhaust exit, near the diffuser of Combustion Turbine plants as shown here.

The old original metal bellows will fatigue, crack and eventually leak, which is caused by the constant thermal cycling and extreme vibration from the combustion turbine. The original Metal Expansion Joints can last for many years, but when they do fail, the downtime and lost revenue is costly, therefore the corrective actions need to be quick and reliable.  This is where Bachmann Industries demonstrates its strength as an industry leader in technical design and customer service.

A common industry fix is to install a high temperature fabric over metal EJ belt, (FOM) with layers of ceramic insulation. However, this can cause new problems if not attached properly.

Our FEA analysis revealed the problem with the inner ring duct area (nearest to the heat affected zone) “growing” circumferentially, due to the hot gases flowing though the duct.  However, the outer ring flange area, further away from the duct, remained cooler due to ambient air and further from the heat zone, and so it would not grow at the same rate.  This causes thermal stress between the inner ring, attached to the hot duct, and the outer ring, where the Expansion Joint is mounted. This stress can distort the bolt flanges, crack welds and allow hot gasses to leak out, which creates a dangerous situation for personnel and a loss of heating efficiency for the HRSG boiler.


Bachmann’s version of a Fabric-Over Metal (FOM) Expansion Joint for field installation is designed to prevent these common problems. Our improved design uses a Conical Attachment flange to prevent any cracking or fatigue problems.  The conical flange provides an angled “ramp” instead of the old stand-off flanges.