Corrosion Failure Analysis on Heat Exchanger Pipes

The heat exchange pipes in one synthetic ammonia plant were in use for only thirteen months, but obvious leakage occurred in the pipes. Investigations indicated that corrosion of the pipes was quite serious, resulting in corrosion pits penetrating the pipes in some spots. Analysis on the metallurgical structure indicated that no problems existed on the pipe material AISI 1020 low carbon steel; the corrosion inhibitors or scale inhibitors were added in the circulating water. The only problem was deduced to exist in the maintenance of the pipes during the idling period; survey of the maintenance of the pipes during the idling period proved the deduction above. Since no effective measures were taken to protect the pipes in the coolers and the circulating water was not emptied, the corrosion products and scales deposited on the pipes and formed local occluded cells; the occluded cells accelerated the pitting corrosion of the pipes and induced leakage in a short time. © 2017, ASM International.