Re: pressure test thoughts

There are cases where we hydro an existing piping system (SCC attack) just slightly above its operating pressure since everytime we do the 1.3X test pressure - cracks just keep opening/appearing. Leak free and lasted till the scheduled turnaround where we jsut demolish/replace in-kind all the affected/suspected pipe works. And yes, we did find the source of the problem.

• In PipingDesign@yahoogroups.com, aluser2 <alwynk@s...> wrote:
  > thats exactly what i have always thought and beleived with one
  exception.
  > 1.XX times mawp is "quite a stressful" strain on a vessel. Hydro
  is a tough
  > way to check if something got badly missed or really screwed up.
  Nothing
  > more. Multiple hydro's on a vessel is not a good thing.
  > Dont forget it has to be adjusted by the temperature ratio, again
  a very
  > blunt instrument.
  > reducing it back to 1.3 was a good thing... we got just the same
  answers,
  > but without putting quite so much
  > unnecessary strain on the vessel/equpt.
  >
  > If nothing is observed you've created a lot of overstrain for very
  little
  > benefit in terms of real knowledge.
  > Bottom line, i think it covers butts,especially the approving
  agency, (on a
  > go/no go basis) etc and the buyer gets a somewhat misplaced sense
  of
  > confidence.
  >
  > ----- Original Message -----
  > From: "Christopher Wright" <chrisw@s...>
  > To: <PipingDesign@yahoogroups.com>
  > Sent: Tuesday, September 06, 2005 9:17 AM
  > Subject: Re: [PipingDesign] Removal of gaskets after pressure test
  of pipi
  > ng system.
  >
  >
  > >
  > > > The hydro test is for checking the soundness of the
  > > > fabrication, not for the efficiency of the joint.
  > > If you'll think about it, a test to 1.3 times the maximum
  allowable
  > > working pressure isn't a very good test, since ASME Code vessels
  has a
  > > margin of failure against bursting of about 3. Only the grossest
  > > construction or design flaws will show up in such a test. It
  happens
  > > from time to time, and the cause usually turns out to be some
  horrible
  > > blunder that should have been caught in the shop or design
  office. In
  > > fact most vessels fail from abuse, fatigue or environmental
  factors,
  > > not design flaws.
  > >
  > > I was told one time a while back by a Code veteran on a
  committee I
  > > worked with, that the vessel hydrotest is actually a leak test
  and the
  > > proof factor (1.5 at the time) was set to make sure that riveted
  joints
  > > wouldn't leak. These days you might be able to pick up pinhole
  leads in
  > > welds or gross distortion leading to a leak, but you don't
  really learn
  > > anything about the vessel construction unless it bursts. That
  said, I
  > > think a hydro-test to 1.3 MAWP is a good idea, but it has about
  the
  > > same diagnostic value as kicking the tires or slamming the doors
  on a
  > > car you're about to buy.
  > >
  > >
  > > Christopher Wright P.E. |"They couldn't hit an elephant at
  > > chrisw@s... | this distance" (last words of Gen.
  > > .......................................| John Sedgwick,
  Spotsylvania
  > > 1864)
  > > <a href="http://www.skypoint.com/~chrisw/">http://www.skypoint.com/~chrisw/</a>
  > >
  > >
  > >
  > >
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