Hi Sachin,
Coke drum is a critical equipment for any refinery, which undergoes many torturous operating cycle. A proper hydrotest after complete fabrication is mandatory for the equipment integrity. Under UG-100, Sec VIII, DIV-1 allows pneumatic Test in lieu of hydro test, but there are hidden dangers in pneumatic test for a vessel of such mammoth size as stated below:-
· The pneumatic test pressure per UG-100(a) may be lower(1.1 times max) than the hydrostatic test pressure of UG-99(b) but it is not indicative of a less hazardous test condition. The amount of energy stored in the vessel during pneumatic test is far greater than that stored in a hydrostatic test due to the compressibility of air. A vessel that may fail catastrophically during a pneumatic test will be just like a bomb going off; same event for a hydro test will be a little pop and a splash. Safety precautions for a pneumatic test need to be far more stringent than those for a hydro test; personnel should remain at a safe distance far away from the vessel during the pneumatic test. Nearby equipment is at greater risk during the pneumatic test than a hydro test.
The design basis of ASME is on safe and sound manufacturing, not to endanger any pressure vessel and human life. I’ve attached an extract from www.hse.gov.uk . Look at page 13 of this document on pneumatic test. This website has numerous guidelines on health and safety, many related to pressure equipments.
I would strongly feel that Hydro test in vertical condition would be ideal for such large vessels.Wt of water may prove too much for vessel of this size, if the foundation is not strong.
Thanks.
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Kavathekar, Sachin
Sent: Tuesday, September 28, 2010 6:49 AM
To: materials-welding@googlegroups.com
Subject: COKE DRUM PNEUMATIC TEST
Hi all,
My vendor has raised concession request regarding pneumatic test instead of hydrotest of low alloy cladded coke drums to reduce cycle time.
Coke drum size :- 10 M OD X 45 M overall length. As per specification/ contract they have to do hydrotest.
Please share experts your suggestions for acceptance or rejection.
Regards,
Sachin A Kavathekar
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