good comments and interesting thoughts.
" hydro test will not cause vessel main shell and
dished ends to get stressed more than 90% of yield stress."
In theory and assuming all the assumptions inherent in Div1 rules are
met and true in practice. Doubtful..... it doesnt always happen. lots of
times there are local
anomalies. Look at the discontinuity stresses going
from head to shell or any other intersection stress or local stress raiser.
The general stress may meet div1 rules of thumb and the built in Safety
factor
2/3rds yield 1/3 UTS protects the unknowns theoretically.
But theres lots of cases
eg re-analysed (before or later), especially as the tools and technology
improves where you find
this margin had vanished.
item 2. I cant see hydrotest stress releiving the welds. How exactly are the
stresses
going to get relaxed?? maybe some local elastic shakedown, but not
realistically from one hydro.
can you elucidate?
al
> I am now getting confused. The hydrotest in general
> cases is done as per code guidelines. ASME B31.3 till
> its last issue had 1.5 times the design pressure, yes
> of course correction for temperature applied for
> elevated temperature services.
> ASME PV Code Sec VIII Div 1 2004 issue asks for the
> vessel to be hydro tested to 1.3 times the design
> pressure, with temp correction in special cases. This
> was necessary as the allowable stresses were enhanced
> in the latest PV Codes by around 15% since year 2001.
> The hydro test will not cause vessel main shell and
> dished ends to get stressed more than 90% of yield
> stress.
> Has any one viewed that the hydrotest is a good means
> of stress relieving of the welds in piping and vessels
> which are not subject to PWHT? One should not avoid it
> as far as practical even in case of SCC conditions, as
> it improves the weld performance in SCC environment.
> Narendra K. Roy
> CCPL Vadodara India
>
>
>
> --- tomcruz55 <tomcruz55@yahoo.com> wrote:
>
> > 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>
> > > >
> > > >
> > > >
> > > >
> > > > =========================================
> > > > PipingOffice - Excel Spreadsheets for Piping
> > Calculations
> > > > <a href="http://www.pipingoffice.us/">http://www.pipingoffice.us/</a>
> > > > =========================================
> > > > Main site: <a href="http://www.pipingdesign.com">http://www.pipingdesign.com</a>
> > > >
> > > > Yahoo! Groups Links
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> >
> >
> >
>
>
>
>
>
> ______________________________________________________
> Click here to donate to the Hurricane Katrina relief effort.
> <a href="http://store.yahoo.com/redcross-donate3/">http://store.yahoo.com/redcross-donate3/</a>
>
>
>
> =========================================
> PipingOffice - Excel Spreadsheets for Piping Calculations
> <a href="http://www.pipingoffice.us/">http://www.pipingoffice.us/</a>
> =========================================
> Main site: <a href="http://www.pipingdesign.com">http://www.pipingdesign.com</a>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>
Received on Wed Sep 07 13:05:00 2005
This archive was generated by hypermail 2.1.8 : Tue Mar 04 2008 - 11:40:44 EST