Abstract:Fatigue crack growth rates (FCGR) alloy 690 tubes have been obtained in air at room temperature (RT) and 325℃ by using pin-loading tension (PLT) specimen and direct current potential drop (DCPD) method. Testing data has been fitted with Priddle model, thus the threshold stress intensity factor amplitude △Kth and fracture strength Kc were predicted. at higher temperature, fatigue crack growth rates were much faster than that at RT, as a result, the △Kth and Kc decreased in higher temperature. Scanning electron microscopy (SEM) examination of the fatigue fracture surfaces revealed transgranular attack, and the fracture surface were covered with a lot of TiN inclusoins, it’s reasonable to believe that TiN inclusions could enhance fatigue crack initiation and propagation of alloy 690 tubes.