Fracture failure analysis of valve bolt in the gas transmission station

Pipelines are important tools for transporting natural gas. With the increasing demand of natural gas, more and more long-distance pipelines are being constructed. Gas transmission stations are used for gas purification, mixture, pressure regulating, metering, and so on. In a gas transmission station, many valves need to be connected with pipelines, and bolts are frequently used in the connection between pipes or between pipes and valves. The failure of a bolt is dangerous for the safe operation of gas transportation. The failure of a bolt connection is very serious and dangerous for machinery or mechanical structures. In the natural gas pipeline connection, a bolt failure may cause gas leakage and even gas explosion due to its flammability. Fracture failure analysis of a valve bolt on a filter separator in a gas transmission station was carried out in this research. Effects of bolt pretightening force and fatigue load were simulated using finite element modeling. Macro and micro fracture observations indicated that inclusions in the steel caused increased risk of screw fatigue fracture. Furthermore, corrosion from the external environment accelerated the crack extension and eventually led to fracture of bolt.