Abstract: Three years after the commissioning of a liquid ammonia storage tank in an ice-making enterprise, one crack was found in the straight edge section of the head in the gas-phase space during the first periodic inspection, resulting in ammonia leakage. Through phased array inspection, it was found that there were many transverse cracks in the straight edge of the head on both sides of the head. The defects originated from the heat affected zone of the weld and were basically perpendicular to the surface of the base metal. Through metallographic examination, it was found that there were two kinds of microscopic morphology coveringintergranular and transgranularin the cracks. Through hardness measurement, it was found that the hardness value was higher near the heat affected zone; in addition, no serious thinning was found during thickness measurement. Based on the comprehensive inspection results and the working conditions of the liquid ammonia storage tank, it was determined that the multiple defects of the straight side section of the head of the liquid ammonia storage tank were caused by the ammonia stress corrosion cracking of the inner wall under the combined action of the liquid ammonia corrosion environment and residual stress and the expansion to the outer wall. Aiming at the causes of ammonia stress corrosion cracking, some preventive measures were put forward and some suggestions were put forward for the regular inspection of such equipment.

Key words: liquid ammonia storage tank, straight edge section of the head, ammonia stress corrosion cracking, phased array inspection technology