Failure investigation of a 304 stainless steel geothermal tube

The investigation of this paper aimed at finding the failure cause of a heavily cracked geothermal water convection tube, utilizing electron backscattered diffraction, double loop potentiodynamic polarization test, and energy-dispersive X-ray spectroscopy. Results show the failure was attributed to stress corrosion cracking (SCC). Chloride in the service environment has induced the initiation of SCC cracks. The sensitization of matrix increased the susceptibility to intergranular cracking, which may result from improper heat treatment before service. The residual stress arising from the manufacturing process promoted the failure process. The SCC cracks originated from the internal tube. In the early stage, the cracks propagated along austenite grain boundaries. Thereafter, they transformed into a coexisting mode of intergranular cracking and transgranular cracking. The failure was attributed to the synthetical effect of sensitization, chloride, and residual stress.