Re: Gas pipeline explosion in Saudi

Yes, that is what the Aramco engineering standard on pressure testing, SAES-L-056 calls for,

"Unless limited by other in-line components, test pressure at every section of the line shall produce a hoop stress of 90% of the SMYS. The test pressure is calculated based on the nominal thickness less the mill tolerance.
The test pressure shall not be less than the min. test pressure per ASME B31.3."

In the case of hot tap where the fitting is tested with an external pipe pressure. In most of the cases of size, branch and thickness combination, brings the max external pressure possible, calculated per ASME Sec VIII Div 1, as the limiting condition. However there are instances where the allowable external pressure may not be the governing one. In such instances the 90% SMYS hoop stress criteria applies.

From the above it should be inferred that a test pressure any where in between should be acceptable. In the past , on Aramco jobs, I was asked to modify the test pressure to the 90% SMYS value, when it was stated to an in between value.

Incidentally, ASME B31.3 also states the test pressure of 1.5 times design as the minimum. Further, It does not limit the test pressure, so long as it does not exceed the SMYS.

Can you please suggest some reference on the crack propagation failure phenomenon, consequent to tests at pressures, that result in hoop stresses close to the SMYS.

Sajit

              Christopher
              Wright
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                                        Re: [PipingDesign] Gas pipeline
                                        explosion in Saudi
              26/11/2007 07:27
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On Nov 25, 2007, at 11:50 PM, sviswan@technip.com wrote:

> Hot tap is a common thing in Aramco. One of the things that is done
> is the
> 90 % yield pressure test of the fitting assembly.
Hard to believe that a pressure test so severe is actually performed. A pressure cycle to 90% of yield strength pretty much guarantees a sub-critical crack in a defective weld would quickly extend to critical length in service.

.

Save a tree...please don't print this e-mail unless you really need to. Received on Tue Nov 27 00:39:00 2007