Inspectioneering: Determining Inspection Strategies for Anhydrous Ammonia Storage Tanks– A Joint RBI and FFS Approach

When developing and implementing an inspection strategy for any equipment, it is crucial to identify and evaluate all credible damage mechanisms thoroughly. When using RBI for ammonia storage, the inspection strategy strikes a balance between assessing the tank’s condition and managing the associated risks, including those related to decommissioning and recommissioning the equipment. Ammonia stress corrosion cracking (SCC) can develop in carbon steel material when exposed to anhydrous ammonia in the presence of tensile stress and oxygen. Ammonia SCC has led to failures of pressurized, slightly refrigerated, and ambient ammonia storage vessels, particularly in areas with significant residual stress, such as cold-formed heads and welds. Several factors affect susceptibility to ammonia SCC, with oxygen contamination playing a key role in both initiating and accelerating damage.