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?

 

[cvg]

generally, it is contractors option to determine precise details on the testing. that plan should be prepared and submitted to the engineer for review. it shouldn't be onerous, it should have been included in the bid price. why is it now up to you to find a cheap way for him to do what the contract always required him to do?

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.

 

[zdas04]

CVG,
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

 

[cvg]

zdas - not a personal preference, it is quite common in this neck of the woods for the Engineer to specify the testing requirements, but I have not seen precise means and method specified by the engineer. Granted, I work mostly for public and private utilities, not so much in industrial. So with respect to the OP, contractor would be required to obtain appropriate water supply, pumps, gauges, meters, provide all valves and fittings and other supplies and incidentals to conduct the testing in accordance with the specifications. with respect to air test instead of water, that would be a change order to be evaluated. obtaining a water supply and precise details of the testing are still up to the contractor.

 

[Duwe6]

Also, you may need to ask the Environtal folks of whatever locale you have built in. In the USA, new cross-country sewage/waste water lines require some stingent testing in some states and municipalities. The air test may get vetoed.

 

[cvg]

re-read the OP. construction of a roadway with fill over a pipeline can potentially create new leaks that were not evident prior to the road being built. Some thought should be put into how you will deal with leaks caused by the road builder next year. Not to mention the fact that you might need to drain and then re-fill the line to avoid freezing over the winter.

 

[stanier]

HDPE has been known to fail catastrophically by unzipping along its length. This is PE80C. If this is a modern material it is likely PE 80B or 100 which is MDPE.

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/

 

[brnt]

Thanks for your responses.A complication on this particular job is our firm is subcontracted to a prime contractor who works for the client. We designed the forcemain but the prime contractor wrote the contracts and hired the subcontractor to complete the installation.The prime contractor has a lot on his plate ( building the water treatment plant) and installing the forcemain is considered a relatively minor detail.They did not specify testing procedures in the contract, and thus its debateable who is responsible for extra costs for trucking in water.

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.

 

[Duwe6]

yep, the risk can be easily managed. But start thinking about how large a leak you can have and not see it during a 24-hour test. Thermal effects are HUGE in a pressure-decay [watch-the-gauge] test. And, depending on the density and composition of the soil, and how low the test pressure is, the surrounding soil could partially dam up the leak(s).

This is why cross-country lines are hydro'd, and a dead-weight tester is used. Makes tiny leaks readily evident.

 

[zdas04]

I use deadweight testers on air tests. I use air tests on cross country lines.

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

 

[Duwe6]

Interesting point, zdas04. Water is indeed *(very* sensitive to temperature changes. What is the sensitivity of your dead-weight air testing per mile for small - 1/8" +/- holes?

As usual, I've learned something on the Fora. Never thought of Dead-Weight testing using air.

 

[rconner]

As to risk, you might want to read what a manufacturer of this piping material, that I believe that has been in this pipe business for some time, if under different names i.e. says at

http://www.performancepipe.com/en-us/Documents/PP802-TN Leak Test.PDF

, including the statement,

“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.

 

[zdas04]

I saw a similar warning on a screw driver. Hell, someone posted a picture of a stenciled warning that "plywood causes dangerous dust" in another thread. Those warnings of doom, death, and destruction have gotten so out of hand that they have become background noise.

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

 

[BigInch]

Not involved with water piping, I can't tell you what the correct procedure to follow is, but I sincerely doubt that ASTM F2786-10 is the correct procedure! This specification is certainly NOT appropriate for force main testing. Just reading its SCOPE restricts use of practice ASTM F2786 to PE pressure piping systems that cannot be filled with liquid or cannot tolerate traces of liquids, and excludes use with certain gas piping where specific testing specifications exist in codes or regulations. Given that scope, I can't see now how in any way F2786 could apply to force mains. How did you come to think that it could?

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

 

[stanier]

The Plastic Pipe Institute states in the document at 3.03B below that pneumatic testing of HDPE is prohibited!

http://www.pepipe.org/uploads/pdfs/ms-3_model_spec_pe_pipe_tubing_fittings_water.pdf

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/

 

[BigInch]

Not sure, but I think the exact same Stanier. A probable case of somebody's got the wrong procedure. Didn't know what code applied, found some spec that had the right key search words and then didn't read the scope.

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

 

[zdas04]

I don't know much about the Plastic Pipe Institute (and the link wouldn't open, but today not many links are opening for me), do they trump ASME?

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

Pressure testing with water is recommended whenever possible. However, it is recognized that certain conditions may require testing with gases.

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

 

[brnt]

Biginch--the manufacturer of the pipe states that when testing their pipe one should refer to ASTM 2164. I contacted the manufacturer and they stated they don't recommend testing with air because of the potential danger, but they don't prohibit the use of air testing on their product. Their recommendation is not based on the efficacy of air testing--but on the saftey of the procedure.ASTM 2164 states that the procedure refers to hydrostatic testing, and if testing with air one should refer to ASTM 2786. So I arrived at ASTM 2786 by contacting the manufacturer who referred me to ASTM 2164 which referred me to ASTM 2786.

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.

 

[BigInch]

ASTM specs cover material fabrication and performance.

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."

 

[cvg]

the standard of care is clear, high pressure air testing of waterlines is considered potentially dangerous and not generally recommended to be done.

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.