The bolts of wind farm are prone to fatigue failure during service. Generally, the fatigue stress does not require too much external force. Sometimes the stress generated by bolts is much lower than the yield strength of bolts. In view of the failure problem of connecting bolts used in wind farms, the failure causes of the double-head bolt were studied by macroscopic inspection, chemical composition analysis, metallographic analysis, and scanning electron microscopy. The results showed that the fracture was a fatigue fracture, and the fatigue source area was located at the bottom of the thread tooth. Under the action of long-term alternating stress, the single source crack evolved into multi-source fatigue cracks, where the fracture was related to the larger stress in the process of installation and service. This paper analyzed the causes of bolt failure and put forward effective suggestions for the service environment of wind turbine bolts.

Duplex stainless steel has been widely applied to industry. In this paper, nondestructive testing, chemical composition analysis, metallographic analysis, hardness test, and scanning electron microscope were used to study the causes of the crack in the butt joint girth weld of pipe and flange. Both steel pipe and flange are duplex stainless steel S31803. Through analysis, it was judged that the crack was a crystalline crack, generated in the welding process, which was related to the welding process and the control of the welding installation gap between the steel pipe and the flange with unequal wall thickness.