Failure Analysis of the Metal Hose Puncture and Leakage in a Natural Gas Reinjection Station

Abstract The metal hose in the pump room of an oilfield natural gas reinjection station has multiple punctures and leaks. In order to analyze the reasons for the failures, a macro inspection, hydrostatic pressure and blasting test were carried out on a new hose of the same specification. Phase organization analysis, macro inspection, physical and chemical inspection, scanning electron microscopy (SEM), energy spectrum analysis, metallographic analysis and composition analysis of the conveying medium were carried out on the two failed hoses. The results show that the hydrostatic pressure test of the same batch of the new hoses of this specification meets the requirements of the standard, however the burst pressure does not meet the requirements of the standard. The failure is caused by the welding quality problems at the joint connection, welding defects such as weld bead, incomplete penetration and welding slag. The existence of deformation-induced martensite is found in the metallographic structure of the failed hose corrugated tube. There is tensile stress in the service environment, and a high content of corrosive medium Cl- in the conveying medium. Under the action of internal stress, the internal corrosive medium causes corrugation, the tube undergoes stress corrosion, thus initiating corrosion cracks and propagating along the grain boundaries, leading to the cracks and failure accidents.