Antonette's Lessons Learned Story #4: Pipe Pressure Testing  

  Long ago I was the field engineer at the Bell Labs Murray Hill Lab Upgrade and the mechanical contractors were having difficulty providing a passing pipe pressure test. The pipes were gas lines and everyone concerned did not want the issues associated with water testing, such as, demonstrating total removal of the water to avoid future moisture problems. Residue moisture can result in scale, rust and instrumentation fouling. The test medium was air.

It was early winter when I asked the construction manager the status of the testing. He had indicted that they lost pressure during the test and were unable to locate the leak. After asking him what services he was testing, there locations, the test medium and if they used a visual soap test, my next question took him by surprise, "What made him think they failed?" My next step was to review his procedures with him. The system was going outside, inside, through conditioned and unconditioned space. They were measuring the pressure at the source but not the temperature at the various thermal conditions. I will admit I launched right into the technical and lost him. The ideal gas law meant nothing. So I stopped explaining and told them step by step what to acquire, what to record, what to illustrate and how to determine the actual corrected pressure. They provided the test data; I calculated and passed the systems much to their surprise. I swear they thought I was completely full of it but at this juncture they were so behind schedule with additional costs they didn't put much effort into arguing with the person telling them they never had a problem, it was clear to go.

Over the years for whatever reason, gas medium (air/nitrogen) has been an instant sigh of resignation as I have been forced into rejecting each and every test. The furnished documentation records exactly like a water test, which is unacceptable. For most systems, a comment signed and witnessed stating the piping system being tested was in one thermal condition, would at the barest minimum do the trick. What I'm really looking for is the record document to illustrate the system route being tested and commentary of the thermal conditions while being tested. For instance, while in construction there may be additional changes in the thermal conditions. This may be due to interim construction progress and may not represent the final intended design. The pipe could travel from a cool basement to a hot unfinished, under construction, unconditioned upper floor. It could travel in any one or all of the following thermally different spaces; an interstitial, mechanical space, office space, outside, or underground before backfilling. The objective is to know how much pipe (volume) is at what temperature and pressure.

Today, more often I see problems with the commissioning documents that are not done jointly in the design phase so that the contractor has a clear direction for documentation expectations to avoid repeat testing. We like to incorporate contractor training, and field witnessing of the tests. This helps to avoid rejection of the testing documentation. And I really hate rejecting the documentation after receipt and review because it translates into schedule delays, re-mobilizing the contractors with the testing equipment, and cost extra challenges. I have the same human tendency to want to be liked and look good. Being the bearer of bad news (re-test) is really not appreciated by the contractor, construction manager or the client.

The testing procedure for Double containment piping has even more issues because the inner carrier and the exterior containment have to be tested to the same pressure simultaneously to avoid collapse of the inner carrier. Additionally most double containment piping is primarily plastic and subject to larger effects of creep under initial start-up pressurization as well as, larger effects of thermal expansion which impacts the testing. Just look at the increased pipe support and expansion requirements for plastic verses steel. The trick is air testing in the containment side, because if you are planning on monitoring for leak detection, nuisance trips will drive you nuts if you don't remove all the moisture. Here is another tip on why to use air testing, some manufactures have prefabricated double containment pipe with really cool support splines that translates into a structural nirvana (economical support system) but a surface area nightmare for lifting the water film should water testing be used. Manufactures prefer water as the testing medium in the inner carrier pipe. However, if during testing a leak occurs, the resulting water that breaches the containment pipe is another lengthy procedure to remove. Based on contractor comfort an initial low pressure (<10psi) air test can eliminate this concern.

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