Pressure Test Area Construction 1

[TheRaven]

Hi Folks,

This is my first post so please be gentle. This is also a bit of a yarn so please bear with me.

I am the H&S manager at the company I work for. We want to start pressure testing pipework on site and I have done some research into this. The HSE guidance note (GS4) states that as a minimum the material should be 3mm thick mild steel to prevent projectiles piercing the test enclosure. So this is the advice I have put forward.

I have just has my MD come and see me to say that he has found a company that makes prefabricated enclosures and that the panelling is made up of a layer of 1.5mm thick steel, some fibre glass then another piece of 1.5mm thick.

So my question is this; Does two pieces of 1.5mm thick steel have the same impact strength as one solid piece which is 3mm thick?

Any help would be very much appreciated.

Cheers,

TheRaven.

 

[redpicker]

There are too many unknowns to give an answer other than, "It Depends".

Talk to the company providing the layered product. I would suspect they have test results showing their product is superior than a single layer product. If the cost isn't an issue, keep the test results on file and use that as justification for use of the layered product.

rp

 

[TVP]

I concur with redpicker.

 

[metengr]

I would suggest you try to pressure test piping with water and avoid the need for barriers. Hydrostatic testing is routinely performed on piping systems (provided the water is treated and the piping system dried after testing) and is safer than pneumatic testing (if this is what you are doing).

 

[arunmrao]

I concur with metengr's observation.

 

[TheRaven]

Thanks for the replies everyone.

To mentengr: we have to have a barrier as if a fitting blew off one of the pipes it would be move like a bullet.

More work to be done it would seem!

 

[moltenmetal]

TheRaven: then I submit that you don't understand hydrotesting and shouldn't be selecting this enclosure. A failure, even a catastrophic one, during a properly-executed hydrotest, does not generate projectiles PERIOD.

 

[Ripz]

moltenmetal.

TheRaven is referring to pressure testing in general and NOT hydrotesting alone. Those condescending responses are uncalled for.

 

[TheRaven]

To Ripz,

It looks as if you have understood what I meant. As for moltenmetal's post (or submission), I had to look over my shoulder as I could only presume that he/she actually worked here and knew exactly what we did.

(There was no-one there when I looked BTW).

Anyway, I have found my own answers to the question I originally posted so thanks to everyone for their input.

 

[moltenmetal]

Please read the posts in order:

metengr said (quite rightly):

"I would suggest you try to pressure test piping with water and avoid the need for barriers. Hydrostatic testing is routinely performed on piping systems..."

TheRaven's response was:

"To mentengr: we have to have a barrier as if a fitting blew off one of the pipes it would be move like a bullet."

My response was that this response indicated to me quite clearly that TheRaven didn't understand hydrotesting and hence had no business designing an enclosure for carrying out such tests. Fittings DO NOT "blow off like a bullet" during a properly designed hydrotest- in fact, getting this to happen even under a badly considered and executed air-over-water test is challenging. The response was addressed to metengr, hence clearly referred to hydrotesting NOT to pneumatic testing.

If TheRaven's response had been, "we are also going to use the facility for limited pressure/volume pneumatic testing, hence the desire for a missile enclosure", my response would have been different. We would have gotten into a discussion of pressure, volume, types of joints, materials of construction under test etc.

I think my response was accurate, not condescending. If you're doing safety protective design without the necessary background knowledge, you might be putting other people at risk as a result of your ignorance. I'm not going to feel bad about calling someone on their ignorance in such a case- in fact I feel that I have a responsibility to do so in a manner blunt enough to actually get the point across.

 

[arunmrao]

I did not find any thing wrong with molten metal's comment. He simply stated that under hydrotesting there are no flying missiles ,hence performing the hydrotest under an enclosure is redundant. Perfect!

 

[MacGyver15147]

The layered panel should be much stronger than a single 3mm. This is how bulletproof armor and windows work. The only down side is once a layer is damaged it needs replaced as they must work together. For example a bullet proof windshield can stop a bullet once but I wouldn't want to be around to see if it can do it again. Also fiberglass is very strong until it gets hit hard enough to break the resin holding it together then you are just left with some flimsy fabric.

 

[racookpe1978]

Concur with Macgyver 15147 above; A two-layer (or more) system of thin ductile metal is better against projectiles than a single one-layer plate of the same total thickness.

A properly executed hydrotest of all of the usual ductile "pipe" materials (with water as the pressurizing fluid) should "distort" or or show leaks or weeps or drips. Your systems should not suddenly rupture, nor should any cap or cover plate or valve or threaded fitting suddenly blow off. If, however, your company policy is to shield against that occurring, then you also need to provide for the people looking at the tests to get up close and really check it for those weeps or drips or spurting water sprays through pinholes. If up close enough to see usefully and thoroughly, then they cannot be locked behind barriers separated from the tested materials.

Others? Non-test people need to stay out, perhaps behind the barriers you are looking to buy.

Your test station needs a remote-operated valve to IMMEDIATELY be able to vent the system if there is a problem; and a specific person needs to be stationed at that valve ready to open it by hand under all conditions. Just being able to stop the pump is also correct, and having a calibrated SECOND test gage is important; but stopping the pump does not vent the system safely.