Re: hydrotest derating

From: <John>
Date: Thu Jan 12 2006 - 21:25:00 EST

A comment from one of my better known colleagues....

   I'm working In PR on a shut down so I have little time right now to lend more of a hand....

aluser2 <alwynk@shaw.ca> wrote:

   folks+ 2, espec the +2,
Havent actually asked a question here but heres food for thought.

Re Hydrotest. - for high temp lines
Assuming you wish to hydro up to the max limit of the flanges ,

doesnt it make sense that the flange hydro limit should be derated by the inverse of the code temp ratio.

if you hydro to the max of the flanges and then operate at a high temp ratio, adjusting by this factor would put you over the flange limit. You should be limited to slightly less than flange limit by the ratio of the stresses fromto operating to test

If operating at high temperature forces you to increase the hydro pressure to adjust for temp surely the allowable flange limit (and the hydro to operate there) is reduced by the same amount.

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so the pressure limit (limited to p') woulld be derived from the hydro limit ie.

1.5p' (hydro) =1.5 x p(flange limit) x Sdesign/Stest

so you would be testing to run at p' (for the max possible line rating) and in service (at temperature)
thereby operating @ p "effective."

Albeit all the other code rules and the inherent assumptions.

IF nothing else, I'm sure Chris will want to establish the first principles truth and others may know the committee thinking.

regards and thanks

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Best Regards,

John C. Luf
Cleveland Ohio U.S.A when I'm not in Austria

Member B31.3, Piping Engineer - Stress Analysis, Pipe Supports, Component Design, and Surge Analysis... and according to my daughters master of unimportant trivia

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[Non-text portions of this message have been removed] Received on Thu Jan 12 21:25:00 2006