Analysis on Cracking Reasons of the Ball Valve Used in Natural Gas Pipelines

The ferrule nut of a ball valve used in natural gas pipeline cracked during the service period. Macroscopic observation, fracture surface analysis, corrosion product analysis, chemical composition analysis, microstructure analysis and so on were used to analyze the cracking reasons of the ferrule nut, and the thermal simulation experiment and intergranular corrosion test were carried out. The results show that:the main reasons for cracking of the ferrule nut were that chemical compositions were not qualified and the solution treatment was insufficient; the minor reason for cracking of the ferrule nut was that a large number of non-metallic inclusions caused the electrochemical corrosion.