Effect of pre?corrosion on Electrochemical Corrosion and Fatigue Behavior of S135 High?Strength Drill Pipe Steel in Marine Environment

摘要

The pre?corrosion on electrochemical corrosion and fatigue behaviors of S135 drill pipe steel weretested in simulated marine environment. The results shows that no passivation can be observed. With theextension of the immersion time, open circuit potential of the steel moves to the negative direction, thecharge transfer resistance decreases, and both the corrosion current density and the corrosion rateincrease. With the increasing of the pre?corrosion time, more larger and deeper corrosion pits areformed, the corrosion products are mainly constituted of Fe2O3, FeO(OH) and Fe3O4, which are porousand not adhering tightly to the steel substrate. With the increasing of the immersion time, the fatigue lifeof S135 steel is significantly reduced, and the fatigue cracks initiate at or near the corrosion pits andmultiple crack sources could be observed. Cleavage steps and fatigue striations are the main features inthe crack propagation zone, the fatigue striations become more obvious and the spacing of striationsbecome smaller with the decreasing of stress amplitudes.