The electric heating pipes used in several water storage water heaters use iron chromium aluminum resistance wire. But if it is a high surface power density electric heating tube (> 25W / cm) or dry burning electric heating tube in fast electric water heater, Ni80 resistance wire is more suitable. Because the aluminum in the iron-chromium-aluminum resistance wire is more easily oxidized at high temperature. And the thermal expansion coefficients of its oxide and base metal are quite different. Therefore, the aluminum exfoliated from the base material during multiple cold and hot cycles began to oxidize again. Repeatedly, the resistance wire becomes thinner and thinner and eventually breaks.