2021 Nand Operation Inspection and Maintenance of Ammonia Storage Tanks in Fertilizer Industry
Ammonia storage tank is an integral part of any ammonia producing and consuming facilities. The tank design has undergone significant improvement from pressurized bullets and Horton spheres for storing ammonia at ambient temperature in small quantities to atmospheric storage tanks for storing ammonia in liquid form at -33 oC in large quantities. The installed capacity of Horton spheres in the country varies from 1000 to 3000 metric tonnes (MT) and atmospheric ammonia storage tanks from 3000 to 20000 MT. Ammonia is a hazardous chemical. Therefore, safety and integrity of these tanks are extremely important for the operating plants and the surrounding community. Horton spheres are covered under SMPV Rules and follow periodic inspections every five years as per the statutory requirement. There is no statutory inspection requirement for atmospheric storage tanks. The atmospheric storage tanks are susceptible to stress corrosion cracking. Periodic inspection through various NDT techniques has been employed to ensure integrity of these tanks during operation. A detailed inspection requires decommissioning and re-commissioning of the tank and hence longer service outage. In order to update the practices followed by various plants in inspection and maintenance of ammonia storage tanks, FAI collected the information from various fertilizer plants. The study covers 68 ammonia storage tanks belonging to 30 fertilizer plants. The paper includes inspection, commissioning and decommissioning practices followed by these plants. Observations during inspection and remedial measures are also covered.
Key Words : Ammonia storage tank, vessel, Horton sphere, atmospheric tank, commissioning, decommissioning, risk based inspection