cracking in refractory lined steel stack

huangyhg

cracking in refractory lined steel stack
we recently discovered cracking in a steel stack that is part of a gas turbine/waste heat boiler unit at a refinery.  the stack is only in service when the gas turbine is operating with the waste heat boiler shutdown (i.e. a bypass or auxiliary stack).
the stack in question is 9 ft diameter x 60 ft high.  the stack is fabricated out of 1/4" thick a285-c plate and is refractory lined.  steel temperature during operation is normally below 400’F.  the stack appears to be conservatively designed for its operating conditions.  excessive vibration is not evident.
the majority of the cracks are located near circumferential seams (in or near the haz running parallel to the weld), although some cracks run transverse to welds and others are in the base material remote from welds in various orientations.  plate corrosion has been minimal (confirmed by ut).
one thought that we’re exploring is some sort of external environmental cracking at locations of coating failure, although there is no obvious source for an environmental cracking situation.  does anyone have experience with similar cracking in a stack (or stack-like) structure.  any insight would be appreciated.