Failure analysis of the outlet pipeline and ball valve of the circulating pump in the desulfurization liquid concentration tower

A leakage occurred in the outlet pipeline of the circulating pump of the desulfurization liquid concentration tower. The pipeline and valves that failed were analyzed. After investigating the general situation of the failure pipeline, macroscopic morphology, composition, molten salt ions concentration, pH value, as well as the metallographic structure were tested. The main failure reason was the synergistic effects of erosion of concentrated salts and the electrochemical corrosion. Especially for the ball of valve, there was a material selection error, and the ball was hollow with thin thickness and weak resistance to erosion and corrosion. The material selection of the branch pipe was also incorrect, and there was a peroxidation phenomenon on the junction area of the weld seam and the branch pipe, which greatly reduced the strength and corrosion resistance. This branch pipe was located near the flange at the outlet of the first valve, and the circumferential direction of the weld seam was facing the fluid direction, which suffered the strongest erosion effect. The combined effects of the above factors had resulted in severe corrosion and thinning of the valve ball, and the leakage of branch pipe near the weld seam during only one week of operation of the pipeline. Further measures have been proposed to prevent pipeline and valve failures.