2013 IFFCO AONLA IJF Inspection Atmospheric Ammonia Tank
IFFCO Aonla unit has two Ammonia storage tanks which were commissioned in May-/ June 1988. The two tanks were inspected in the year 2001 and 2002 respectively to ensure their integrity. Storage of anhydrous ammonia at atmospheric pressure in fully refrigerated liquefied form by reducing temperature to its atmospheric boiling point at – 33°C is an efficient, cost effective and safe method of storage. There is likelihood of Stress Corrosion Cracking (SCC) in fully refrigerated Ammonia storage tanks. Therefore, the Inspection of Ammonia storage Tank is required to ascertain the health and mechanical integrity, at specified intervals after the ten years of service. The tanks were de-commissioned one by one and thoroughly inspected employing various Non Destructive Techniques (NDTs) and finally re-commissioned. No stress corrosion cracking, pitting or any other discontinuities in any of the NDTs performed were observed. Also the integrity of foundation and insulation was established. Re-commissioning being a very critical activity, it was accomplished with utmost care as stress corrosion cracking (SCC is promoted by the presence of oxygen in combination with ammonia. This paper describes the methodology adopted for the massive inspection activities along with details of De-commissioning and Re-commissioning. It highlights the safe practices being followed and precautions taken while executing such a challenging job.