Cause analysis of the cracking at the gas outlet edge of a gas turbine combustor

Following a 100-hour bench test, multiple cracks were detected at the gas outlet edge of a can-annular combustor. Macro- and microscopic inspections show local distortion and discoloration in the semi-circular overheating zone and cracks propagated along both dendritic boundaries and grain boundaries. Detailed metallographic inspections reveal the microstructural transformation in the overheating zone, where fine disperse phases exhibiting higher hardness precipitated and reduced the plastic deformation capacity of the material. Nonuniform distribution of the combustor flame resulted in elevated cyclic thermal strain which mainly undertook by dendritic boundaries, leading to premature thermal fatigue cracking. Relevant suggestions are proposed to improve service safety.