The MISTRAS Engineering Services Group (MISTRAS) was engaged by Wacker Polysilicon North America LLC (Wacker) to perform failure analysis of a 4-inch stainless-steel pipe that leaked in hydrogen service. The process stream consisted of hydrogen with traces of chlorosilanes and operated on an alternating heating/cooling cycle. It was reported that cracks likely formed prior to the leak, with hydrogen being detected by an operator using an air monitoring device. Laboratory examination of the pipe/elbow sample indicated that the inside surface cracked from chloride-induced stress corrosion cracking (chloride-SCC). The cracks initiated at pits on the inside surface, likely caused by localized HCl corrosion. Per the background information provided, presence of moisture was mentioned as a possibility – which would combine with the trace chlorosilanes to form HCl. The fracture morphology was transgranular with branched cracking occurring in cleavage mode. EDS analysis of the fracture surfaces confirmed the presence of chlorides, which are known to promote chloride-SCC. Residual stresses present in the sample, from the forming process and welding, may have also contributed to the damage mechanism. The microstructures of the pipe and elbow materials were typical of formed austenitic stainless steel, consisting of austenite grains along with bands of residual ferrite. Chemical analysis of the pipe and elbow materials indicated that they were close to the compositional requirements for UNS 31603 (316L) austenitic stainless steel.