Fracture Failure Research on Feculence Discharge Pipe of LPG Spherical Tanks

The rupturing of feculence discharge pipe happened during the gas-tightness test of LPG (Liquefied petroleum gas) spherical tanks. In order to find out the reasons of fracture failure of feculence discharge pipe, the Scanning electron microscopy (SEM) analysis, mechanical property testing, metallographic examination and energy spectrum analysis of corrosion products were used. The examination results show that both chemical composition and metallographic structure are normal, and the cracking is the brittle cleavage fracture. The energy spectrum analysis of corrosion products reveals that there are many sulfides in the corrosion products. Based on the loading conditions of spherical tanks, crack morphology and corrosion products, the primary reason of pipe cracking is stress corrosion cracking induced by H₂S existed in liquefied petroleum gas. So it is suggested that the examination should be fulfilled for the feculence discharge pipe of such spherical tanks, the cracked pipes should be replaced, and the welding residual stress in the pipes should be relieved before replacing operation.