Air Testing HDPE forcemain 2

[cdale]

We are putting in an HDPE forcemain. The pipeline will be fusion welded together and I am trying to find out some standard for air testing the pipeline once it is in the ground. The only thing I have been able to find is standards for gravity sewer lines, that doesn't seem to help since I have a higher pressure, air tight line...

My contractor tells me that an air test of 7 psi for 10-20 minutes is sufficient but he has no basis other than experience. The line is for clean water and will be under 20 psi when in operation.

My logic is, on the one hand, the contractors test should be sufficient because if the pipe holds the pressure with no loss then it has no leaks/bad welds. On the other hand, if the pressure we are using in the test is not comparible to the pressure the pipe is going to be operating under then there is a still a chance of failure even if it passes the test...

Any help would be appreciated, thanks...

 

[RWF7437]

Normal procedure for water mains may be used. Those lines are usually tested at 150 psi for one hour, or 1.5 times the normal operating pressure. If your specifications did not spell out the test procedure ( as it should have ) then 1.5 times the normal pressure seems reasonable. The procedure is spelled out completely in most water system specifications and in AWWA standards.

Caution, this is not an air test but a hydrostatic test. Never heard of anyone testing a forcemain using air.

good luck

 

[RWF7437]

http://www.fpua.com/files/DesignConstStand/SEC02620.pdf

 

[Zambo]

Your HDPE pipe supplier should have a test procedure, it will almost certainly require a pressure greater than 7psi and wil be hydrostatic. The difficulty with HDPE is that it expands as you apply the pressure test, thereby appearing as if there is a leak. The normal test procedure will involve pumping until you reach the test pressure and then montitoring the pressure for the next few minutes, a slight increase of pressure should be observed which indicates that the line is sound.

 

[stanier]

DOnt use air above 7psi . Its dangerous and most authorities forbid it.

Modern European and Australian standards dont require test pressures of 1.5 time the design pressure. In fact the hydrotest doesnt tell you very much about the quality of the wleds in the pipeline.

You are much beeter off having quality ontrol of the welding. This includes trained welders with approved (thrid party) weld qualifiaction tests. Qualified weld procedures and routing inspections. It is nothing to have a production weld cut out and sent for testing . The length is then just dragged along 300mmm or so and rewelded.

Make sure that the weld is allowed to cool in the welding machine. Dont let the contractor rush it by cooling it with water or pulling it out of the machine before the time is up.

I have experienced a failed pipeline which had passed a hydrotest!!!!! The welds were dreadful. The contractor had cooled them using a bucket of water, the faces werent trimmed properly and were not clean. temperature control of the platten was all over the place. (DONT let them use crayons for this exercise, the wax contaminates the weld). Temperature elements must have up to date calibration ceertificates.

 

[Zambo]

I last worked with water supply lines in eastern europe, there is no possibility that we would have been allowed to handover without a hydrostatic test report. The logic for this is that HDPE (depending on the grade) is easily damaged, in particular deep scratches to the surface. The pressure test therefore tests the full length of the pipe not just the welds.

 

[DMcGrath]

I concur with the dangers of using high pressure air to test pipe. There is a lot of energy stored in the compressed air, and should a component of the system let go - watch out! Water is easier to see where the leaks are and much safer. The Plastic Pipe Institute (PPI) strongly discourages high pressure air testing, but they do have a procedure for it in their inspection manual.

http://www.plasticpipe.org/pdf/pubs/handbook/inspection.pdf

Lots of other good PE Pipe information on their site as well.

 

[Zambo]

DMcGrath

that was a good link.

you can also order a polyethylene pipe manual at the following

http://www.wrcplc.co.uk/pe/

this can be ordered with a test manual. The test proposed is hydrostatic not an air test.

 

[rconner]

RWF7437,
That is a quite interesting specification at the link you provided. I was just curious if you knew if on pg 9 of 9 of this apparent polyethylene pipeline testing etc. specification you provided, does say the make-up water allowance per "AWWA C600" (I believe incidentally the ductile iron pipeline installation/testing standard) referred to in passage "G." only kick in in the event that the line initially tested per "F." does not pass what I believe is a quite different "Allowable amount of makeup water for expansion during the pressure test shall conform to Chart 6, Allowance for Expansion Under Test Pressure, Technical Report TR 31/9-79 published by the Plastic Pipe Institute (PPI)" in the “F” passage?
I mention/ask this in that I believe the AWWA C600 ductile iron pipeline field testing standard referenced in "G." is (perhaps contrary to some perception promulgated by the hdpe pipe and hdpe welding folks?) considerably more restrictive in this regard than the specifically polyethylene pipe testing publications. Additionally, I believe the “AWWA C600” standard also requires that the test pressure be kept generally within 5 psi of the prescribed test pressure value, and a comparable requirement appears sort of missing in plastic piping testing standards. Getting back to the drastic differences in make-up water allowances I referred to, see the examples as follows, for hypothetical, comparative pipelines only 1,000 feet (305 m) long:

Total “Make-Up” Water Allowed (U.S. gal. /1,000' pipeline in a 2 hr test period@150 psi)*

Nom. Pipe Size hdpe pipe Ductile Iron Pipe**
4 2.5 .8
6 6 1.2
8 10 1.4
10 13 1.8
12 23 2.2
14 28 2.6
16 33 3.0
18 43 3.4
20 55 3.6
24 89 4.4
30 127 5.6
36 180 6.6
42 231 7.8
48 270 8.8
54 314 10
Notes: *The values for hdpe testing are determined with use of the aforementioned chart, that I believe is the same as appears now on pages 23-24 of the document at the Plastic Pipe Institute site at

http://www.plasticpipe.org/pdf/pubs/handbook/inspection.pdf

) , and I think was once also in the Chevron or Performance Pipe “Table 2 Test Phase - Alternate 2 - Make-Up Water Allowance” on page 4 of 5 for hydrostatic testing of polyethylene pipe site

http://www.cpchem.com/performancepipe/literature/technotes/PP802TNLeakTesting.PDF

.

With regard to the original inquiry, a low pressure air test may not hurt anything if safely applied (as others have noted air testing can be more dangerous than water testing with all air removed) and may be a very good test of say general pipe, fitting, or joint leak-tightness at least at that pressure, if e.g. all parts are fully immersed in a tank of water while the pressure is applied, or alternatively the full surface of the part(s) and all joints are effectively “soaped”, while observed for leaking air “bubbles” by a diligent operator. Low pressure air testing may also be helpful in finding gross problems with even underground piping. However, an air gauge needle holding even pretty steady at any test pressure for some time may not mean there is not leakage in an underground system (as air is of course very compressible, and quite a bit more of air must escape over a period of time than water to effect a gauge reading). Many references and other posters have indicated that the proposed “logic” that “…the contractors test should be sufficient because if the pipe holds the pressure with no loss then it has no leaks/bad welds”, may thus not be sound.
If we are talking about an effective test for a buried polyethylene pipeline (with some practical variability of pipe material moduli and field encasement stiffness depending on specific manufacture and application??), in looking at the table above I am also not exactly sure how sound the reasoning is either that if one must pump a 55 gal drum of water back into only a few blocks of buried 20” pipeline to get the pressure back up after just a couple hours test one can be assured that all of the water is “expanding” the pipe and some is not going out small defects or damages in joints or elsewhere? All aspects of quality of fusion welds is perhaps another matter, and I understand really separate technology to address these issues (preferably I would assume before the pipeline is buried!) is still developing in this area as well.