Failure Analysis of a Carbon Steel Pipe-Flange Component

A failure analysis was conducted on two flange components that experienced a crack. Crack was found in the vicinity of the weld toe of the component. The flange components are fabricated from ASTM A672-65 CL22 material, and their metallurgical background corresponds to class 22. The flange component was part of the cooling water return system, which also comprises of a carbon steel flange and pipe. The analysis was presented from macro and micro fractography observations, microstructure observation in the vicinity of the crack, chemical composition, and hardness test. The microstructures of the welded region composed of Grain Boundary Allotriomorphic and ferrite, which are expected to favor the formation of cracks and decrease fatigue life. Crack was determined to be transgranular cracking and indicated brittle-to-ductile type of fracture. The HAZ region has a slightly higher hardness than the base pipe and weldment regions. However, hardness value and brittle-to-ductile fracture mode have no significance to the hydrogen embrittlement phenomena. Based on the analysis, it is concluded that the crack is the result of fatigue failure owing to possible stress concentration at the weld toe. By identifying the origin of a crack, similar failures can be prevented, and the service life of engineering components can be extended.