Large Dia. Pipe 1

[hickok]

Does anyone have any experience, or suggestions, regarding hydro. testing large dia. (144") pipe?. Are there any shops that can do this? Generally, it is done onsite.

Would also like some input on the necessity of welding interior AND exteior joints of such large pipe, which will eventually be encased in concrete.

Thanks

 

[cvg]

a bit of information might help with the discussion.

Are you the mfg, engineer or the contractor?

What type of pipe are you dealing with?

I assume this is water the pipe is carrying?

What is the operating pressure and temp?

Are you intending to test the pipe or the completed pipeline, installed?

Is it underground pipe?

Any other relevant information...

 

[hickok]

cvg........we are the engineer. pipe is A139. Yes, water is the medium. Design working pressure = 30 psi. We intend to hydro each 40' section. After testing, the pipe will be encased in concrete.

These are AWWA C200 pipe.

 

[dicksewerrat]

What good is it to test each 40 ft. section? Is the line only 40 ft. long? Test larger sections or the whole thing once it is in the trench. You will have to design a hold back for the test plugs. What pressure are you testing at?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[hickok]

Hydrostatically testing the entire piping system in the field presents problems in how to temporarily support the pipe (with the weight of the water) and then there are problems in getting rid of the water after the testing - sewers can't handle it.

 

[cvg]

realistically, you will need to test small sections. But testing just one spool at a time doesn't really do much good in assuring quality of the completed pipeline. Especially if you have not installed the pipe in the trench. Normally we require testing to be done after completion of all laying, joining, backfilling and compacting and after all thrust blocks are cured for at least 7 days. Are you welding all the joints or just the field fitup joints? How are you testing the joints?

I have seen butt strap joints used where the interior was not welded. Will you be lining the interior with mortar?

 

[bimr]

The pipe is probably hydrotested in the manufacturing shop for each 40' section.

Not familiar with this larger diameter pipe, but I know for a fact that smaller pipes are hydrotested in the shop.

 

[cvg]

shop testing provides the quality control for the fabricator who is providing the pipe, but does nothing to assure quality of the completed pipeline. This quality is a function of the contractors installation procedures and cannot be guaranteed by the pipe fabricator. I would fully expect the fabricator to do a shop test. This is required to meet AWWA specs. However, hydrotesting the completed pipeline in the ground is still essential. You can't put a completed pipeline into service without ever checking for leaks!

 

[bimr]

That is exactly the point. Why test again in the field for only 40 feet of piping when it has already been tested in the shop?

 

[rconner]

The ultimate value of a properly run hydrostatic test, and particularly of installed pipe at pressures reasonably above normal operating (I believe for many reasons, some as discussed by cvg on this thread), is undeniable. When hydro-testing equipment (e.g. huge presses with hydraulic cylinders and conveyors etc.) that utilize hydraulic end pressure to make and maintain a water seal is used to test at least full length pipes or pipes without complicated appendages etc., a Shop hydrostatic test is not necessarily cumbersome to large manufacturers at even very high pressures. Domestically (in the USA) however, I understand the available equipment for such routine testing is however limited to 120” diameter. AWWA C200 contains the clause, “Special sections that cannot be tested in a hydrostatic testing machine may be hydrostatically tested by welding on heads, or by use of blind flanges, or as specified by the purchaser.” When alternate Shop hydro-testing methods are considered for pipes or specials, e.g. in effect building a pressure vessel at a factory every time an individual pipe or special is tested, I believe the logistics, schedule, costs, and occupation of fabrication facilities associated with such testing are affected quite significantly. I believe in such cases it would be more common (as suggested by AWWA Manual M11etc.) to utilize other forms of non-destructive testing such as magnetic particle (MT) or Ultrasonic (UT) testing for such special or unusually large Shop work, and perhaps subsequently also special individual, e.g. double-seal testing port arrangements or special joint testers to check the leak-tightness e.g. of field welds etc. As far as supporting pipes full of water in the field, AWWA Manual M11 of course provides guidance on stresses that are developed at various locations for various spans and configurations of saddle or ring girder supports etc. As far as disposing of hydrostatic test water, the issues here are understandable as there are nearly 40,000 gallons (nearly 150m3) per stick of pipe involved; however, one system I believe some Contractors have used to address such issues over the years is as previously mentioned testing long pipelines in sections, that involve in essence moving test bulkheads (either on the ends of shorter test sections, or periodically fastened up inside the pipe), and then use smaller by-pass piping/pumping arrangements that can in essence be used to move (repeatedly re-use a smaller given quantity of test water), instead of testing thousands of feet of pipe that would obviously require flushing a huge quantity of water at some point down a sewer etc.

Regarding the double vs. single welding, and assuming the reference is to lap welds, there are various criteria that are considered in the decision that include: ability to air test the annular space of completed joint, longitudinal stresses, installation constraints and access to the interior or the exterior. More information would likely be needed to offer any more specific response, and perhaps the pipe manufacturer and/or Contractor would likely be helpful in that regard.

 

[GregLamberson]

hickok

rconnor's suggestion on jumping the water from section to section is a good one and commonly used in hydro-testing of long pipelines.

Just a couple of questions - what kind of water is the pipeline transporting? You mentioned the sewers couldn't handle the volumes, but unless there is a strict requirement for water quality, would the pipeline in essence not be filled with product after hydrotesting and go straight to the delivery point? Also, if you test it in place, the weight of the water should not be an issue as it will be designed to hold water anyway, right?

I'll agree with the previous posters, I would not accept a pipeline where each individual joint was tested and not at least in sections - you'll know nothing of the integrity of the pipeline, only of each individual joint.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com