Muhammad Abduh (abduh@reksolindo.co.id)
On 16 April 2001 a fire and explosion occurred at Humber Refinery following the catastrophic failure of an overhead gas pipe. Investigation was carried by The Competent Authority and the plant operator company by legislative mechanism under Control of Major Hazard (COMAH) Regulation 1999. Humber refinery was one of approximately 1000 major hazard site under this regulation. The competent authority consisted of Health and Safety Executive (HSE) UK and Environment Agency (EA).
The cause of the piping system failure was the erosion corrosion
of the 6-inches diameter pipe, known P4363, which carried the overhead line from the De-ethanizer (W413) to the heat exchanger (X452) in saturate gas plant (SGP) unit. The failure occurred down stream of a closely water injection point. Examination to thefailed elbow recovered from the damage site showed wall thickness thinning from 7-8 mm to a minimum 0.3 mm. When the pipe failed it burst open catastrophically causing a full bore type of release the pipe contents.
The water injection point was not the original design of the piping system. Water injection to the vapor stream between the top de-ethanizer column and the heat exchanger was addressed to solve the previous problem of salts or hydrates fouling in heat exchanger X452/3. An injection point was created in P4363 by piping water to an existing 1 inches vent point on the pipe without injection quill or dispersal device and made the water entering the pipe as a free jet.
Erosion-Corrosion
There are studies that noted the synergistic effect ofmechanical impingement and electrochemical corrosion result in greater rate of metal loss than the sum of the two mechanism ( S. Zhuo, N. Stack & R.C Newman)
The highest rate of erosion-corrosion occurred in stagnant region, immediately beneath the jet, where the particles impacted the surface at an angle of 90°, This critical erosion-corrosion region in a piping system are found at the outer side of elbow where the fluid impinges the wall directly at an angle 90°.
NACE 34101: Refinery Injection & Process Mixing
Points
One of the generic guidance to overcome the problem of erosion corrosion in refinery process is NACE 34101 which gas already published as recommended practice for the design consideration of injection system.
RBI Regime was not Effective
This accident also has shown the effect of in-effective implementation of RBI for inspection management. RBI as a comprehensive method shall be supported with complete and adequate data. The ignorance of the operator company for the significant risk contribution of the injection system to the piping were resulted in the failure.
Similar Accidents:
1. Wilmington California United States – October 8,1992
2. North Rhine West Phalia Germany- December 10,1991
3. Yokkaichi Mie Japan – May 2, 1997
4. Mina Al-Ahmadi Kuwait- June 25, 2000
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