air test HDPE 1

[brnt]

We are presently installing twin 16inch HDPE Dr17 forcemains --total length is 2 miles. They run from a lift station to a water treatment plant. The water treatment plant wont be up and running for at least another year.There is not a water supply near the site and if we were to pressure test with water the contractor would have to truck the water in.This would be onerous on the contractor and he wants to test the lines using air. Another problem associated with testing with water is until a road is built later this year the pipe won't have enough cover to protect it from freezing ( I am in Canada)

The procedure for testing with air is described in ASTM F2786-10.The formula it provides for determining the test pressure to use results in 150psi. Everything else I read tells me this is ver dangerous--yet ASTM gives us the industry standards--and I want to protect myself by following the industry standards.

Any thoughts on this dilemma?

 

[rconner]

Brnt, irrespective of safety issues (and I’m certainly not going to be the one that says they should be ignored!) lets say you were to air test these hdpe lines you say are buried two meters deep in the ground. My rough calculation indicates that each 16” O.D. DR17 pipeline with 14” I.D. starts out containing about 11,300 ft3 of air, of course at near atmospheric pressure. Again not saying it is this simplistic, but if that pipeline volume is then to be pumped up with more air to 150 psi at exactly the same temperature(admittedly ignoring Charles and Gay-Lussac et al), I calculate per Boyle’s law that more than 11 times that volume or more than 125,000 ft3 of air from the atmosphere would then be contained in each of those two bombs.

I will simply ask with that much air involved how would you ever know, whether you are looking at a pressure gauge or deadweight tester, or whatever, that there are not some molecules (heck lets throw ol’ Avogadro into the mix, with more than 6 times 1023 molecules per mole!) seeping out of a damage or joint (even slight leakage in the latter is one indication of a dangerous, improperly welded/fused hdpe joint, per the manufacturer’s words above)???

I do not profess to be an expert in high pressure air(or gas)-testing of vessels or pipes, and frankly with what little I know and particularly e.g. of Murphy’s Law would be “afeared” to be!); however, over the last near 40 years I have watched a good many specified hydrostatic tests of significant lengths of even larger pipelines that are exposed to view, and I have been amazed that even a quite small water seep, e.g. from an improperly bolted or poor gasket selection exposed flanged pipe joint, will result in a noticeable movement of a pressure gauge (at least when design and construction is such that air is effectively evacuated). It almost visibly makes one believe the (again over-simplistic) axiom, “water is incompressible”, and additionally gives one some reasonable confidence in an eventually properly run testing procedure.

As to the comment that bringing up a 20 year old case is not “fair”, I will also admit that I know very little of the details of applicable law (or for that matter how codes relate), and in my work have been fortunate to have had virtually no brushes with same. However, I did have one law class at my university. While that was roughly a thousand years ago and not with regard to Canadian law, one thing I think I do remember however was that Professor saying basically something to the effect that “law” is not necessarily fair, or for that matter even logical. It is what the words in the law say (or I guess how they are nowadays/contemporaneously interpreted?) While I have admittedly been some intrigued by the law since (and have more than once been told I maybe should have taken same up), engineering types, of which I am one, typically have problems with this(and I did not take this up). While I also don’t know anything about Canadian barristers and/or judges, I wouldn’t be surprised that at least their USA counterparts might reach even much further back into case law for precedence, when it suits their purposes! In any case it would appear it wasn’t fair to Buddy Hefner for him to be put in the position he was in!

 

[BigInch]

This accident happened with air, AFTER the HYDROtest!

http://www.osha.gov/dts/shib/shib062104.html

From "BigInch's Extremely simple theory of everything."

 

[zdas04]

That is a really good example of how badly we often do temporary piping. Did you post it to say that we shouldn't even use air to dry a pipeline?

David

 

[BigInch]

No I didn't exactly post it to mean that we shouldn't use air to dry a pipeline. I posted it as more of a warning to emphisize the fact that disasters can still hit us from the blind side. I think it is especially true the more certain we are that whatever we are doing is being managed properly. Especially when we are positively sure that we have all danger points covered. When there are more than three things that have to happen correctly and in sequence for something to work, be prepared for a bite on the hiney from some previously unidentified entity. It is a good reason IMO to do things in the simplest manner, and certainly in the safest manner possible.

From "BigInch's Extremely simple theory of everything."