Using a valve as limit for a test system 2

[dor]

ASME B31.3 para 345.3.4 allows using a valve as a limit for tested piping. "A valve may be used provided the valve (including
its closure mechanism) is suitable for the test pressure."

1. How can it be determined that a valve satisfies this demand?

2. Can we do a pneumatic test on a piping system using a closed valve as a system limit?

 

[bcd]

Best to discuss this with the valve manufacturer. Some valves leak and some could be damaged or have their operational life reduced by subjecting them to higher pressures than they would in normal operation.

Direct answer is yes, it can and has been done, but bad things can happen if you are not careful.

 

[MJCronin]

Most valve manufacturerers will give you the maximum "DIFFERENTIAL PRESSURE" that thier products will sustain.

I agree with the above comments. You are risking damage to the valve and seats by defining the limits to the hydrotest by shutting a valve.

What is the reson that you would want to do this in lieu of using the more traditional "flange and blind" limits to the hydrotest?

Is this yet another idle question by an inexperienced project manager ?

 

[dor]

Thank you for your answers.

MJCronin, I'm just an engineer, more used used with the design phase and amazed by what field engineering will do to get things done(first time on a construction site). To make things worse we're building in the middle of nowhere. So, if you don't have enough blind flanges you have to find other solutions or wait 3-4 month to get the blind flanges. The last solution won't make you very popular with the construction manager. I'm trying to find a solution. I'm sure it's a case by case, i'm sure that testing against valves has been done before.

 

[Duwe6]

Typically, you insert a "test blind" into the flange pair w/gasket on the pressure side. Due to the cost of blind flanges, NOBODY in construction tries to blind all the hydro test boundaries. Just end at a flanged item, and slip in the 'pancake' test blind. Have your fitters cut the smaller diameters out of 1/4 to 3/5" plain carbon steel, and to to 1/2" for the larger [over 8NPS] sizes.

Don't worry about calculating the thickness, as the thicknesses you get will be VERY thick. That is due to calc's giving you the "last 100 years w/o deformation" thickness. For a hydro blind, it only has to last once [although more uses are prefferable] and the failure mechanism is benign. The hydro blind 'pancake' will first hydro-form and develop a permanent eliptical shape, but not leak. Bulge makes is a little hard to remove, but not too tough.

If it bulges until it fails, you just get a [high-pressure for 1/2 second] splash of water. Just stay out of the line of the flange pairs while pumping up to full pressure.