Keywords: Ammonia safety, Ammonia storage, Stress corrosion cracking, Inspection, Stresses, Welds, Defects.
Anhydrous ammonia is commonly stored in carbon steel tanks and vessels of various sizes and designs.
Stress corrosion cracking (SCC) in ammonia was first identified some 30 years ago in high strength, non-stress relieved steels.
Since then, ICI has been actively involved in developing a policy for safe operation of its ammonia storage facilities based on:
– an understanding of the conditions causing SCC,
– tight operational control of parameters known to contribute to SCC,
– detailed periodic inspection of its storage facilities,
– fitness for purpose assessment for future operation and determination of appropriate inspection interval.
Although, worldwide, SCC has been detected in non-stress relieved storages operating at ambient temperatures and down to -33oC, ICI has succeeded in confining the problem to its storage spheres operating at or near ambient temperature, and even here, rates of cracking have been gradually reduced by improved understanding, operational control, inspection and maintenance allowing controlled increase in operating period between inspections.
S Hewardine, ICI Billingham, UK.
23 pages, 7 figures, 3 tables, 18 refs.