- This topic has 0 replies, 1 voice, and was last updated 9 years, 11 months ago by
.
- Posts
The Incident:
In Urea-21 unit on 17th January 2008 at 04.40 hours the weld joint on the common suction line of HP Ammonia feed pumps P-101 A/B had failed and caused heavy Ammonia leak.
The Cause:
– This failure might be due to corrosion, material defect and internal stresses owing to welding joint
– The stresses might have developed on welding due to injection of sealing compound and clampingThe Consequences:
Immediately the plant emergency shutdown was initiated and the affected system was isolated and depressurized. Control valve 21-HV-1021, located at the outlet of Ammonia receiver V-105, on the common pipeline going to the suction of P-105-A/B pumps was closed from the central control room to isolate large Ammonia hold up equipment like Ammonia receiver V-105, MP Absorber C-101, and Ammonia condenser E-109 from the snapped off pipeline. This had helped in significantly reducing the Ammonia quantity leaked into the Atmosphere. A Level-1 emergency was declared and all the affected area was cordoned off and cleared of any workforce present in that vicinity. As all the working staff moved to a safe location nobody had received any Ammonia exposure.The Lessons learned:
– Corrosion-fatigue is the result of the combined action of an alternating or cycling stresses and a corrosive environment.
– On line sealing of leakages either from pipes or weld joints should be avoided which otherwise might cause inadvertent additional stresses, to the component which has been already under the influence of some parental residual stresses.
– Contrary to a pure mechanical fatigue, there is no fatigue limit load in corrosion-assisted fatigue.
– Much lower failure stresses and much shorter failure times can occur in a corrosive environment compared to the situation where the alternating stress is in a non-corrosive environment.
– OMIFCO has decided not to do online sealing for any developed leakages of Ammonia pipe lines.
More information:
- You must be logged in to reply to this topic.
