Investigation of weld cracking of a BOG booster pipeline in an LNG receiving station

Abstract The weld cracking failure of a boil of gas (BOG) booster pipeline in a liquefied natural gas (LNG) receiving station was investigated through macroscopic observation, physical and chemical inspection, optical microscope, scanning electron microscopy (SEM) and energy dispersive spectrometry techniques (EDS). The finite simulation analysis (FEA) method was used to examine the effect of compressor vibrations on the welding. The results showed that the crack originated from the outer surface of the butt weld between the main and supporting branch pipes. Due to the poor machining dimensional accuracy of the welding fit, three pass welding with a large amount of metal filling was processed to connect the weld. The microstructure analysis results of the weld indicated that several solidification cracks were generated between the welding passes. Moreover, many inclusions and harmful super-sized second phases were generated in the weld, with several microcracks occurred around these inclusions and second phases. The finite element analysis (FEA) calculation results showed that the vibration of the compressor did not directly lead to weld cracking, however, under the influence of the vibration, the multi-source solidification cracks and microcracks originated from the surface of the butt weld, and propagated through the whole weld, which were lead to the cracking failure. Several suggestions to prevent such a failure were proposed to avoid the occurrence of similar accidents.