In a fertiliser plant, a leak occurred around 1:30 pm on a gaseous ammonia (NH3) pipeline operating at 70°C under 5 bar of pressure. Three subcontractors climbed onto a scaffolding adjacent to the tanks containing hot ammonium nitrate solution (HANS). Exposed to the NH3 cloud formed, one worker lost consciousness and had to be evacuated from the hazardous zone by other team members. The rescue crew placed the victim on oxygen and notified the external emergency services. The 3 employees stayed a few hours at the hospital under observation before returning to work the next day.

During initial investigations, the operator had identified a leak on this 2″ (DN 50) insulated pipeline that supplied the HANS storage tanks with gaseous NH3 from the workshop evaporator. The addition into these tanks of NH3, which was continuously stirred and maintained at 140°C, made it possible to avoid decomposition of the ammonium nitrate solution by holding the pH constant. Without benefitting from an isolation valve, the given pipeline section could not be isolated from the evaporator. A stiff sleeve was installed around the pipeline and an NH3 detection beacon placed nearby.

The operator stipulated that this pipe had not undergone any controls (i.e. periodic inspections) because its diameter was less than 4″. According to the operator, the crack might have developed on this pipeline, which had been designed in “standard steel” subsequent to corrosion under stress, as accentuated by the corrosive atmosphere found in the “nitrate” workshop.

The operator was required to refine the characterisation and analysis of risks related to the hazardous phenomenon described as “a gaseous NH3 leak on an E3107 exchanger output line / miscellaneous process contributions” for pipes outside the confinement zone, in addition to developing an inspection plan for gaseous NH3 transfer pipes (i.e. diameter less than or equal to 4″) and installing isolation mechanisms on the NH3 transfer pipeline so as to isolate the section in the event of a leak.