Hydro test of U or L shaped pipe spools

[Spoonful]

Hi All,

we are about to hydro test some pipe spool, U shaped and L shaped. My concerning is once pipe is blanked off at ends and pressurized, the U shape or/and L shape will tend to straighten itself. Could anyone please share some idea on this? should be this be a concern? if so, any idea on where to start on the calculation on support for hydro test?

Regards

 

[XL83NL]

Long time no see Spoonful, good to have you back. What size (NPS), length and pressure are you testing? The straight and short answer would be no concern, but thats from my humble experience on our typical scope (which usually is small bore piping). Obviously the spools need to be properly supported during the hydro.

 

[pennpiper]

Spoonful

I am now retired but was in Piping Design Engineering for 45 years which included most of my time in the design office, a few years as Engineering Manager in a Pipe Fabrication shop and lots of time in the field (job site). This condition (that you describe) never came up!

Unless your pipe is made out of rubber it will not straiten out under pressure.

And, if it did straiten out under hydro-test condition, how would you keep it in place under normal operational conditions?

This is a "Non-Issue".

Sometimes its possible to do all the right things and still get bad results

 

[Spoonful]

Hi XL83NL,
Gretins. Good feeling someone remembers me.
Pipe size from Dn25 to 80, pressure ranging from 2000-8000kpa operational,so hydro testing at 1.5 of that. On site there will be pipe supports to hold the pressure thrust forces due to bends. Where our in-house hydro there is nothing holding it in place, rather than blanked off at both ends.
The pressure force might be small compared to pipe rigidity, maybe not,is there a quick way to do some calculations just to be sure?

 

[XL83NL]

As pennpiper Mentioned, you don’t have to check them; they’re not present. Regards

 

[GD2]

Spoonful,

Test pressure at 1.5 times the design pressure essentially takes the pipe material to the yield strength.

In many hydrotest, the max test pressure is limited to 90% of SMYS.

In a shop floor, as the spool will be exposed to deformation, my suggestion is that calculate the equivalent test pressure to limit the max hydrotest pressure to lesser of 90% of SMYS and 1.5 times flange rating.

We all know material will come back to original size once the force is released. And we are not talking about cycling stresses here. We are doing one time hydrotest.

To me as long as keep the 90% SMYS check, you should be fine.

GDD
Canada

 

[C2it again]

If the bend is a circular section such as a forged one there should be no 'opening out'.

Pulled bends tend to be oval in section and will open out,albeit a tiny amount. Compare with the similar operation of the highly oval tube in a Bourdon pressure gauge.

 

[XL83NL]

C2it, welcome back. Not able to use your old profile anymore?