Failure of high pressure ammonia line in a fertilizer plant – A case study

In this investigation the failure of a high-pressure ammonia pipe line made of SA 106 Gr. B carbon–manganese steel has been discussed. The failure in the pipe had occurred in the form of a through thickness pin-hole without any loss of wall thickness or bulging. Fine longitudinal cracks of 4–5 mm in length had also occurred on either side of the pin-hole. The inner surface of the pipe was corrosion free, however, corrosion attack in the form of pitting was observed on the outer surface of the pipe. Laboratory investigations revealed that such pits had formed due to chloride attack at locations where the Fe3O4 mill scale had not been completely removed. As one would expect hydrogen attack concurrently occur, evidences of hydrogen assisted cracking was also found on the fractured surfaces.