Abstract
The paper presents the results of a failure investigation carried out on a cracked gas inlet chamber. The plant found a crack on a 24 in. pipe, made of 304H stainless steel, near a 3/4 in. steam purge nozzle. The plant carried out repair welding using gas tungsten arc welding. However, after the repair welding and two months service, large size intergranular cracks developed near the steam purge nozzle in addition to fine transgranular cracks near the nozzle of pressure transmitter. The investigation revealed that the alloy originally suffered from thermal fatigue due to steam injection. Then, the repair welding caused chromium carbide precipitations inside the grains, along the grain boundaries, and along slip lines. The presence of steam caused the sensitized material to suffer from intergranular corrosion and intergranular cracking. It was recommended to minimize or eliminate steam purging and to apply solution annealing heat treatment to all repair weldments.
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