Water leakage occurred in hot-water pipes made of 304 stainless steel of an antiburning boiler after usage for 8 months. The detection revealed that the 304 austenitic stainless steel in a combustion chamber cracked on the side of the hot water outflow. This study analyzed the cause of cracking of the 304 austenitic stainless-steel hot water pipe by using microstructural, intergranular corrosion, and corrosion product analyses. Results showed that the 304 stainless steel, which met the material requirements, fractured via a mixed cracking that included transgranular and intergranular cracking (mainly transgranular). Moreover, a large amount of single copper accumulated on the crack surface, which indicated that the crack was induced by stress corrosion involving copper ions and mechanical stress. High temperature was another factor that induced cracking because the passive film of 304 stainless steel weakened in hot water. The copper ions came from the inferior brass valves when immersed in hot water with oxygen exposure. Basing on the above results, this type of cracking can be prevented by using 2205 duplex stainless steel (DSS) instead of 304 stainless steel. The stress corrosion behaviors of 304 stainless steel and 2205 DSS in aqueous solution with a certain concentration of copper chloride were analyzed using four-point bending test. Results showed that 2205 DSS did not crack, whereas 304 austenitic stainless failed in the test.