Chapter VI of B31.3 – "… each piping shall be tested to ensure
tightness."
The Code further stated "… the test pressure maybe reduced to the
max. pressure that will not exceed the yield strength." This
statement appeared twice in Section 345.
The posting on this threads makes it appears that performing hydro
on newly installed process piping during the pre-commissioning is a
complex and difficult task – it is not. If the hydro test plan has
well thought of then the rigorous detail of analysis previously
stated is not necessary. Basically if one has develop the hydro test
diagram then it is sufficient to evaluate systematically the
limiting components of the piping system (together with the line
designation table) that will dictate the hydro test pressure, the
filling/drain point, pipe support requirements, the blind location
and even the need to install a pressure relieving device.
Following the threads, it looks like that the end0user is expecting
that the hydro will sort of provide a guarantee of safety. Not so.
Piping that pass the hydro can still fail in service – it hardly
qualify as a proof test. Its very purpose is to reveal design
inadequacy and flanges/weld/joint leaks.
- In PipingDesign@yahoogroups.com, "Tushar Rajyaguru"
<trajyagu@l...> wrote:
> Tushar Zope,
>
> First calculate the test pressure as per B31.3, i.e. 1.5 x Design
Pressure x temperature correction, then check that it does not
exceed the yield strength. If this calculated test presure exceeds
the 1.5 times the flange rating you have two alternatives. Here, you
need to use your engineering judgement. 1) reduce the test pressure.
e.g. this may be done when design pressure is actually very low but
due to higher temperature correction factor, test pressure reaches
very high value which is never going to occur. 2) Increase the
flange rating. However let me tell you even if your calculated test
pressure exceeds the 1.5 times flange rating, you can still use the
same flange rating at your own risk as code does not restrict it.
>
> -------------------------------------------------------------------
>
> Friends,
>
> Please assist me with a problem with hydrotest pressures?
>
> For some lines with "calculated" wall thickness (new lines tie-ing
into
>
> existing lines), I have calculated the test pressure as per B31.3,
ie 1.5 x
>
> Des Px temperature correction, then checked that it does not
exceed yield
>
> strength.
>
> But there is also a question of full flange rating, this
calculated test
>
> pressure exceeds 1.5 x full flange rating at ambient.
>
> If we test at the calculated test pressure (as long as it is
within yield),
>
> we would risk distorting the flanges, but the hydrotest would
fulfil its
>
> purpose.
>
> If we test at 1.5 x full flange rating, the flanges would be safe,
but the
>
> test pressure would be too low to fulfil the purpose of the
hydrotest.
>
> Which is the correct method?
>
> Best Regards.
>
> Tushar Zope
>
> Extn: 162
>
>
>
>
>
>
>
>
> [Non-text portions of this message have been removed]
Received on Thu Sep 11 06:41:00 2003