air test HDPE
air test HDPE
(OP)
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?
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?





RE: air test HDPE
you might suggest that either he install fittings / valves as necessary and test each quarter mile section - thus requiring a minimal amount of water or option b, haul water to fill the entire line and save the money on the necessary fittings and valves.
RE: air test HDPE
I guess every engineer does it differently. I would never rely on a contractor to write a test procedure, and I don't know anyone else who would either. Maybe it is common in your operation, but I know that if there is a failure on a test on pipe that I designed and someone gets hurt, my name shows up on the lawsuit before all the pieces have fallen to the ground. It really doesn't matter who designed the test procedure you are still liable as the system designer.
brnt,
HDPE failures under test are really quite well behaved. The pipe tends to fail in a bird's mouth split that releases the pressure without a lot of drama and shrapnel (but there is a lot of noise).
For DR-17 I get 135 psig MAWP in water less than 73F with a 50 year expected life. 150 psig is only a 111% test. I don't know if that is OK or not for your conditions. If you are rating it at 100 psig then it probably is OK.
The derates for gas operations do not apply to short duration air tests, so just because you are considering testing with air doesn't necessarily mean that you have to rate the pipe at 32 psig MAWP like you would with methane.
I would really be more concerned that you didn't write the test procedure (are you sure that the contractor has even heard of brittle failure?). I would be really nervous testing HDPE below about 50F ambient with any media, but I am kind of a chicken.
David
RE: air test HDPE
RE: air test HDPE
RE: air test HDPE
RE: air test HDPE
The air entering the pipeline will need to be cooled otherwise its raised temperature could compromise the strength of the material.
If the pipeline is is in open country there is little risk to people if testing with air.
On thing to remember with thermoplastics such as PE the slow rise in pressure using air over 2 miles will make the pipe wall creep. it will be very difficult for you to determine the pressure rise.
Here is an extract from AS2566.2 Buried Flexible Pipelines -Installation.
NOTES:
1 When the test pressure is applied to a leak-free test section, there may be a reduction in pressure (pressure decay) in a non-linear manner, due to the creep response and stress relaxation of the material (see Figure 6.1(a)). Where the pressure decay is plotted against a logarithm of time, the result is expected to be a straight line (see Figure 6.1(b), line A-B). An increase in the slope of the line will indicate that there is leakage in the test section. A change to a steeper slope, as shown by line A-C, indicates the possibility of leakage.
2 Using the decay profile, the effect of leakage can be predicted by amending the calculation to take account of the drop in pressure due to the leak itself. The presence of any air trapped in the pipeline will also effect the shape of the line, since air is compressible and it will act to maintain the pressure over time. This will initially give a false reading. Line A-D, with an initial flatter slope, indicates air was present at the start of the test. The pressure decay method of Appendix M, Paragraph M6 gives guidance on the interpretation of different values for the slope of the line.
AS2566 states:
Compressed air testing shall not be permitted for pressure pipe.
"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.
http://waterhammer.hopout.com.au/
RE: air test HDPE
I know there is potential danger involved in testing with air, but common sense tells me the lines are buried with at least 2 meters of cover--the only areas of danger are the location where the air will be injected and the location where the pressure guages are located.The risk can be managed-- it seems to me.
RE: air test HDPE
This is why cross-country lines are hydro'd, and a dead-weight tester is used. Makes tiny leaks readily evident.
RE: air test HDPE
The impact of temperature variations on air tests is much less than the impact of a change in water temp (i.e., water bulk modulus works out to almost 100 psi/degree F). Change in an air test is based on the ideal gas law which would say if you started at 900 psia and 60F and dropped to 59F the new pressure would be 898 psia. Then you realize that the rate of heat transfer into a gas is at least an order of magnitude slower than heat transfer into water, so over the same time period that I would expect a water test to drop 100 psi I would expect a gas test to drop 0.2 psi.
David
RE: air test HDPE
As usual, I've learned something on the Fora. Never thought of Dead-Weight testing using air.
RE: air test HDPE
htt
"Pneumatic (air) testing of pressure piping systems is not recommended." And also the generic passage relating to all pressure testing of their pipe,
"Safety
Safety is of paramount importance. Leak tests can apply high stress to untried joints and parts in the system.
Failure can occur by leaking or by catastrophic rupture that can cause sudden, violent movement. In some cases, leakage may immediately precede catastrophic rupture.
WARNING – Death or serious injury and property damage can result from failure at a joint or connection during pressure leak testing. Keep all persons a safe distance away during testing.
The test section is to be supervised at all times during the test.
Ensure that all piping is restrained against possible movement from catastrophic failure at a joint or connection. When pressurized, faulty joints or connections may separate suddenly
causing violent and dangerous movement of piping or parts. Correctly made joints do not leak.
Leakage at a joint or connection may immediately precede catastrophic failure. Never approach or attempt to repair or stop leaks while the test section is pressurized. Always depressurize the test section before making repairs." And then again,
"Pneumatic Testing
WARNING – Death or serious injury. Failure during a pneumatic (compressed gas) leak test can be explosive and result in death or serious bodily injury.If failure occurs when using compressed gas as the test fluid, the failure releases the energy applied to stress the piping system, and the energy applied to compress the gas. Such failure can be explosive and dangerous.
Compared to hydrostatic testing, pneumatic testing can be more dangerous because failure during pneumatic testing releases more energy. For safety reasons, pneumatic testing is not recommended."
I'm not exactly sure how one accomplishes all this with all manner of projects e.g. with the heart of the generic pressure testing statement, "Ensure that all piping is restrained against possible movement from catastrophic failure at a joint or connection." but it appears this manufacturer clearly believes (or more likely knows) there are "risks", and they want to be clear of them! I'm not exactly sure also how many "cross-country" pipelines are constructed with such type pipes.
RE: air test HDPE
The discussion of air testing comes up in these forums every couple of months. Every time it does come up there is a group of the same guys that say "DANGER DANGER DANGER Will Robinson, everyone is going to die". Then there is a second group with recurring membership that say "Yes there is a lot of stored energy, but the NASA report grossly overstated the ability of the stored energy in a pipeline to participate in an explosion (assuming instantaneous 100% conversion of potential energy over a miles-long pipeline into kinetic energy focused on a couple of square feet is not reasonable). The reason that the ASME pipeline codes allow air testing is that it can be done safely".
I'm usually the cheer leader for the air-test-is-OK group because I live in the Rocky Mountains and have had tests where using water would result in the low sections being at test pressure and the high sections being at atmospheric pressure, or the high sections being at test pressure and the low sections being broken. I've done dozens of pneumatic tests, and find that with proper procedures, properly executed pneumatic tests of steel, spoolable composite, fiberglass, and HDPE can be done safely with excellent integrity.
With regard to the dead-weight tester seeing a 1/8 inch leak, it will see it but generally you'll hear the leak before the dead-weight tester does. Or you'll see the dirt blowing. I had a leak in a flange that was buried 5 ft underground (yes, I bury flanges too, I have all sorts of unsavoury habits) that was about 1/8 inch. You could see the dust and hear the leak about 30 minutes after the test started. Had that been a water test we never would have seen it (it is really hard to get ALL the air out of a 7 mile test of 12" pipe in hilly country) so some amount of pressure decay has to be acceptable in any test.
David
RE: air test HDPE
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
http
I would have thought that an AWWA standard was relevant to this work.
"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.
http://waterhammer.hopout.com.au/
RE: air test HDPE
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
I looked in ASME B31.8 and found in section 842 that non-metallic pipe (including thermosetting and thermoplastic) must be tested, but it doesn't say anything about the test beyond that it must be tested and some discussion about minimum test pressures. The convention in that standard is that when you are talking about testing a specific material, the code will list exclusions specific to that material within the section. There is no limitation within the section on air testing plastic pipe so you refer back to the basic testing section (841.3) and in section 841.3.1(c) it says
I may have violated some kind of guidance from the Plastic Pipe Institute, but following ASME B31.8, I've tested HDPE with air. I think if anyone ever sues me for doing it, I'm on pretty sound footing.
David
RE: air test HDPE
Maybe its wishful thinking, but the statement in ASTM 2164 that air testing of HDPE should be used in piping systems that cannot be filled with liquid is ambiguous. I could make the case that the forcemains we are installing cannot be filled with liquid because until a future road is built the lines will not have enough cover to prevent them from freezing. Once we fill the lines with water there is no way to get all of the water out.
RE: air test HDPE
For example in petroleum work
ASTM 5L - pipeline pipe .. covers pipe fabrication and performance of PIPE ordered to that 5L standard, which I order all the time.
ASTM 5L has NOTHING to do with assembly and construction of those pipes into a pipeline. It has not a word on how the pipeline should be assembled and tested in the field.
ASME B31.4/8 is what we use for that, among others.
YOU HAVE A MATERIAL SPEC. ASTM specs do not cover CONSTRUCTION.
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
a) should only be done when hydrostatic is not possible and
b) reasonable and prudent methods of safety protection should be followed if it is done.
my opinion is that for the OP, air testing is being considered mostly as a more convenient, expedient and cost effective method. In addition, I would generally not conduct a final test for a line where final backfill / fill was not placed over the top.
RE: air test HDPE
My point is that he needs to get the right code, covering the design, constuction and testing of his water line and then he can do an air test if it is allowed and if he can do that safely. I don't think he's got it. A mill fabricationb test is not a constructed pipeline test procedure.
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
RE: air test HDPE
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
http://www.sandiego.gov/water/cip/guidelines.shtml
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
The standards committee that produce the ASME, AS etc standards designed for metal pipe materials generally do not thoroughly address the design of thermoplastic pipe materials.
There is no mention of creep properties, properties being dependent upon strain rate and temperature in the standards.
If you want to check this out review ASME B31.3 appendices on thermoplastic materials.
AWWA, PPI and thermoplastic resin manufacturers have a much better handle on designing in these materials. they have had to get involved because the legacy standard committees did not weant to completely re write their standards. The Europeans are far in front of the uS standards when it comes to thermoplastics.
As for a pipe manufactuer saying you can pneumatically test their product is ignoring all the requirements of statutories. The last time I checked pipe material manufactuers do not carry professional indemnity insurance and are not design engineers. authorities.
"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.
http://waterhammer.hopout.com.au/
RE: air test HDPE
We simply work in totally different environments. From your posts I get the feeling that most of your work is utilities distribution in reasonably flat areas (elevation changes don't seem to be a major factor in your work). References to ASME B31.3 usually indicate work in a reasonably compact area.
My work is on upstream Oil & Gas in hilly country. It is not unusual for a gas line in this place to change elevation 2,000 ft from end to end--fill that up with water and the low points are 880 psig higher pressure than the high points. Hydrotest simply doesn't meet the actual needs of the piping system very often in this environment. Because of that I've done a lot of work to develop processes and procedures to allow the pneumatic tests that I design to be safe. Not "kind of safe", not "safe enough", but "safe". Yes, I include some analysis (like soak times) that I don't have to considered in hydrostatic tests, but so what? The purpose of a procedure is to accomplish a set of goals within the boundaries of acceptable risk.
I don't think that the industry we support is really germane to what kind of test the OP does. He thinks that the risks that he has control over can be better mitigated with a pneumatic test. I don't care if he's taking about an industrial cooling-water system or a supply lateral off a residential main, he's done the HazOp and the risks of a pneumatic test satisfy his risk tolerance. That should be the end of the story. He shouldn't get a lot of grief about being a cowboy or lazy or whatever the in
If a pneumatic test is safe, then why would someone consider it an inappropriate procedure? The only answer that comes to mind is fear and superstition.
David
RE: air test HDPE
May I ask what is the "normal" and "maximum" test pressures you've done so far for pneumatic tests and if you've done it for steel pipe as well? I work within water sector and haven't done pneumatic tests myself but thinking about the compressor size (power, flow rate) I would need for normal pressures and test section sizes I'm dealing with ... (well, I've put the safety concern aside for the sake of my thinking at this moment!).
RE: air test HDPE
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
Wild-west jokes aside, ASME B31.8 is the code that I am most familiar with, and it doesn't have the page of exclusions that you are talking about. It has a table (841.3.3-1) to lay out maximum hoop stress during an air or flammable-gas test. This table says that if I'm using air or a non-flammable gas then in Location Class 2 I can go to 75% of SMYS, in Class 3 I can go to 50% of SMYS and in Class 4 (i.e., under a high-rise apartment building) I can go to 40% of SMYS. If I want to test with a flammable gas I'm limited to 30% of SMYS. None of these restrictions have ever been much of a problem since most of my clients have a maximum hoop stress at MAWP of 20-30% allowed in their company standards
Pneumatic testing is not reckless. It does require more engineering expertise than is usually applied to hydrostatic testing (not necessarily more than should be applied, but certainly more than is typically applied), but so what? The tone of this thread is really starting to bother me. The implication in many of the posts is that only an irresponsible cowboy would ever do pneumatic testing.
Your comment that all oil pipelines are always tested with water really bothers me. It may be true, but if so our profession has become quite stupid. The 10,000 ft elevation example you talk about has to involve drag sections. I've done that evolution and I'll tell you that a properly designed pneumatic test has a small fraction of the total risks encountered while installing a long drag section of big inch pipe in difficult terrain, to say nothing about the number of untested welds.
Waterpipe,
I calculate an MAWP for my pipeline then determine a test pressure (based on location factors, codes, and company standards). Once I've determined the required test pressure, I evaluate the pipe to determine the hoop stress during the test. Based on this information (along with terrain features, the availability of water, and expected difficulties in dewatering) I design a test. I saw the end of a water test last year where the operator opened the end of the pipe into the bar ditch and drained the water. The test was with river water, but they added a few hundred gallons of biocide--I wonder what the impact of that biocide on the river was in the short term. Dumping hydrotest water on the ground has been illegal for at least 30 years, but the local regulator didn't know it was illegal and didn't care. Yeah, hydrostatic tests are always better and lower risk.
Most of the work I do calls for ANSI 300 kinds of pressure (call it nominal 600 psig MAWP), and most company standards call for 1.5 times (even when Table 841.3.2-1 calls for at least 125%), so it is common to test to 900 psig.
Of course this is not for HDPE. For HDPE I calculate an MAWP, but ASME B31.8 caps HDPE MAWP at 100 psig, so I've never done an HDPE test above 150 psig.
In Oil & Gas we regularly do evolutions on wells that require high pressure air injection so high pressure rental air compressors are readily available. You can test to around 60 psig with a single stage compressor. A two stage gets you to 225 psig. Typically, we use a 2-stage compressor discharging into a single-stage "booster" compressor (I know, calling an after-compressor a "booster" is backwards as it can be, but if you don't use the [irrational] terminology of your industry you get inconsistent results) which can get you to nearly 1,000 psig. If I have to go higher than that, I find it is less expensive to go to nearly 1,000 psig with air and top off with nitrogen than either doing the whole job with nitrogen or getting a fourth stage of compression.
Using nitrogen REALLY scares me. Nitrogen in this quantity is only available as a liquid. This liquid is kind of cold. If the operator is not paying really close attention you can find yourself applying gas at high pressures and sub-zero (Fahrenheit) temperatures which is a really good way to observe brittle failure.
Bottom line on static testing is that any sort of test demands competent engineering design. The risks, costs, and regulations must be considered and the test designed to optimize the risk mitigation and follow the intent (in addition to the letter) of the law.
David
RE: air test HDPE
"Most of the work I do calls for ANSI 300 kinds of pressure (call it nominal 600 psig MAWP), and most company standards call for 1.5 times (even when Table 841.3.2-1 calls for at least 125%), so it is common to test to 900 psig. "
When you can do air tests, test press limit is 1.10 operating pressure in class 1 Div 2 areas, and 1.25 in class 2. Not 1.5
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
http:
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
Regarding the field pressure test, I personally try to stick with the standard/specification that rules the projects. Different codes allow different percentage of SMYS for the MAWP and pressure test and they have their own sets of permissions/constrains regarding using miters, bends, fittings, etc. (read it stress concentration points). You apply the 100% SMYS during the field pressure test to a pipeline that allows 45 degree miter and you don't wana be around the bends during the hydro test.
Zdas04, you are so competent that could see all these sort of issues and manage the risks but this is not the case in many other projects (at least in water sector). I stick to the code/specification that I have in hand when the pipeline is designed by others and I stick to the code/specification when I design the pipeline myself to have a clear cut of liabilities. Well, at least this is how I do it until I'm working as the consultant or owner's Engineer. From the Contractor's point, longer sections (higher test pressures), more cost-effective alternative (perhaps air instead of water) or whatever other options are favorable. I don't have any problem with this provided that the Contractor could make a "justifiable" technical proposal, is "allowed" under the project agreement for such a deviation from the code and has the full "liability" over the pressure test.
RE: air test HDPE
What operator is going to take on the liability for proposing not to follow code.
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
RE: air test HDPE
In this case, the procedure was not part of the brief, but there were some indications. The hydrotest procedure called for backfilling for a very specific reason (and in this case a water test not backfilled would have whipped the 24-inch pipe like a water hose, just like the air did). The reason still existed during the air test and it was irresponsible to skip that step either in the procedure or its execution or both.
The injuries and fatality are very sad, but don't blame them on the air, blame it on the process. There is an excellent chance that a water test not backfilled would have resulted in Mr. William Bielawski III drowning after he was injured instead of "just" being injured. No way to know.
David
RE: air test HDPE
As an example, how can you say this whole air testing thing, practice and procedure, is safe, if you yourself can't even get the procedure right all the time and, just once, maybe, just once, happen to think you can air test to 1.5? That is exactly the kind of things going wrong that cause these and almost every accident. When too many things ALL must go right to make something safe and just one going wrong can kill, the risk is high. When there are a large number of steps in a procedure, even risk management theories fail, A x B ≠ B x A. When you have a safe alternative, you need to consider using that alternative, even if it is a RPIA. Just because you can write a safe procedure to do something, doesn't necessarily mean that performing that procedure will be safe.
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
There are no satey codes on pressure testing pipe.
I am not being flippant but bringing up one incident from 20 years ago is dramatic but not fair.
This pipe is buried at least 2 meters. The pipe can't move. The pipe is exposed once where the air is injected and once where the guages are installed.Can the contractor manage the danger? Just like lowering a section of concrete box culvert into a trench there are procedures to limit the danger.
RE: air test HDPE
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
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!
RE: air test HDPE
http://www.osha.gov/dts/shib/shib062104.html
From "BigInch's Extremely simple theory of everything."
RE: air test HDPE
David
RE: air test HDPE
From "BigInch's Extremely simple theory of everything."