Operating Urea Plants with Small Leaks Poses Potential Safety Risks

摘要

In the synthesis section of a urea plant, the equipment is protected against the corrosive ammonium carbamate solution by a corrosion resistant barrier to the carbon steel. For safe operation, it is of paramount importance to keep all stainless steel surfaces in a passive corrosion state. This is obtained by adding passivation air. Furthermore, situations must be avoided which lead to depletion of passivation air in local areas such as crevices or by having stagnant liquid conditions. Local active corrosion may lead to a leakage of carbamate to the pressure retaining c-steel. Operating a urea plant with a leak is risk full and it is strongly advised to repair the leak immediately, including small leaks. A temporary in-situ repair of a small leak is considered unsafe. Also to dilute the leaking ammonium carbamate escaping from a small leak with steam condensate is not advised. Case histories are presented demonstrating the potential risks involved by not attending to small leaks in a proper way.