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[MW:649] Plant Case of Fire due to Loose Flange Bolts at PSV at Chevron

By Materials & Welding

 Chevron Pascagoula Fire: Importance of Flange QA/QC - Loose Flange Bolts at PSV

A crude unit at Chevron's Pascagoula refinery experienced a big & costly fire back in August. Some of you have probably already seen photos of this fire (attached). The official investigation report has not yet been issued, but the likely scenario of events leading up to this fire has been informally reported as follows:

*       A 4 X 6" or 6 X 8" PSV (size depends on who you talk to) was removed for routine servicing at last TA but when it was reinstalled, the flange bolts were not properly tightened (maybe only hand tightened)

*       The PSV was not easy to access; the loose PSV inlet flange probably leaked a small amount for quite some time, but the small leak was not detected due to the PSV's location

*       Some time well after TA, the PSV started "simmering" due to system pressures getting close to the PSV set pressure.

*       The simmering of the PSV was just the "right frequency" such that multiple of the loose stud nuts backed off the studs and some nuts fell off completely

*       With missing and very loose nuts, the flange opened up enough to cause a significant release, and the fire pictured.  

 

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Best regards,

 

Sunil S. Agrawal

Engineering & Design Tecnimont ICB

Static Equipment Dept. (STEQU)

 


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