Re: presure drop during hydrotest

From: <Christopher>
Date: Fri May 12 2006 - 13:29:00 EDT

On May 12, 2006, at 1:10 PM, John Luf wrote:

> Visual examination of all welds/joints is a must in the field of
> piping, the results of the visual examinatrion for leakage is in many
> ways more important than minor pressure drops.
>
> Did you do a close 100% exam of all these connections during your test?
I should have added this to my own post. Thermal expansion is a real long shot. There's also a hooker to trying to calculate the differential expansion between contents and vessel. The vessel is frequently not completely flooded, so the volume change of the contents may produce a negligibla pressure increase. Moreover the wall may be non-uniformly heated. I've seen a lot of instances where pressure drops are ascribed to temperature changes, but it's very difficult to prove and very easy to sharpshoot.

The poster may also want to think carefully about this since a pressure drop is also an indication of local yielding. In qa past life I did a lot of work testing vessels, and we came up with a method of measuring the volume change of a vessel by determining to water influx when we pumped it up. Flooding even simple vessels completely was difficult, and it made a big difference in how definite the measurement actually was. Ambient temperature played much less of a part in pressure drops than did local yielding.
Christopher Wright P.E. |"They couldn't hit an elephant at <a href="/group/PipingDesign/post?postID=o3jSe0wxuK8-GD5fh58s7sjP9xA-WxU0HzEIgFAwV9H8ufpWJepMXxmwsK8-M5ZHRpI30r2icH6o">chrisw@skypoint.com</a> | this distance" (last words of Gen.

____________________| John Sedgwick, Spotsylvania 1864)

<a href="http://www.skypoint.com/~chrisw">http://www.skypoint.com/~chrisw</a> Received on Fri May 12 13:29:00 2006