Hydrostatic Testing Safety

[HSE101]

I am looking for any insight into calculating safe working distances for personnel not associated with a hydrotest whom may be conducting work activities near the location of the test being conducted.

For example, if a 400psig test was being conducted on a 20" Sch40 Carbon pipe, using water as a test medium, what would be a safe distance to work away from the pipe bing tested? 10' for every 100psig? I have looked through countless references, but cannot find any solid answers, only the grey areas. If anyone could give me guidance, it would be greatly appreciated.

 

[vesselfab]

if it is a good hydrotest, with no trapped air, a few feet should suffice as long as they don't look at flange gaskets.

 

[unclesyd]

I concur with the above post, but would like to add a little, don't stand under the line or if has a lot cold spring pulled in it a move back a couple of more feet.

When I first got into the industry it customary to hit the welds in pipe and vessels with a 16 lb hammer except when the temperature was near 40F. It was normally hit twice, once at half pressure and again at full pressure.

 

[HSE101]

That is what I suspected, however, I can't find anything in a reference manual, code, standard or regulation anywhere that gives even a guideline to go by for Hydro, or even a good formula that would show how rapidly the pressure would drop should a side wall rupture occur.

Would either of you know a technical manual or a hydrostatic guideline available that would give me something to go on to present to workers in the field?

 

[chicopee]

water being near incompressible,would quickly depressurize the vessel at the onset of a leak unlike gases. Also there are temperature limits on water used for hydro test,so make sure that you abide by those limits.

 

[chicopee]

One more thing about hydrotests, you bring the pressure to the hydro pressure point (normally 1.5 X MAWP) then depressurize the boiler to the MAWP at which point you perform your inspection.

 

[doct9960]

HSE101,

See page 11 of this NASA Safety Manual...

http://smad-ext.grc.nasa.gov/gso/manual/chapter_07.pdf

The NASA manual mentioned a couple of precautions during hydrotest, but no mention of how much the safe distance should be.

You might also get some insights here...

http://www.bakerrisk.com/Joint-Industry-Programs/Safety-Research

 

[eliebl]

In a hydrostatic test the stored energy is simply how much the vessel or pipe stretches (in all directions) under the applied hydrostatic test combined with the compressibility of the fluid. Since water is virtually incompressible (an argument for another time) there is little stored energy in a hydrotest. There is still the possibility of plugs, caps, flanges and any other detachable components becoming projectiles.

My experince with hydrotesting is largely on cargo transport tanks so the common safe zone was simply the sevice bay in which the tank was located.

EJL

 

[doct9960]

HSE101,

Also try to grab hold of this publication...

http://www.hsebooks.com/Books/produ..._name=HSEBooks&category_name=&product_id=2816

I doubt it mentions any safe distances for hydrotest.

 

[JR97]

Here is a formula I found in a Norwegian Specification. I only have a copy of the page and didn't write down the title of the specification. The only thing on the top of the page is T0240|72-12| and in the footer "Rules, issue 96-02". I only copied it and put it in my file, I never used it. If we hydrotest above 6,000 psi I insist on putting the vessel in a pit cleared of personnel (my arbitrary rule).

Anyway the formula is:

safe distance = (0.15) x (D) x (a)^0.4 x (p)^0.6

where D - internal diameter (m)
a - length / diameter of piece (m)
p - test pressure (bar)

Hope this helps,

JR97

 

[HSE101]

Thanks all, I think I have what I need to do get through this now. Many thanks to you all!