Pressure testing is a test that is carried out at any under construction site after the installation of the pipes before we put them into the use. This is done to evaluate the certain limits of pipelines in terms of reliability, maximum capacity, leaks, joint fittings and pressure. Without testing the installed pipelines one cannot ensure if pipes meet the standard installation requirements. While non-technically basic purpose of developing the system for pipelines is to ensure the safety of labor working on the construction site and outline the safety practices that must be carried out while testing pipes.
The main responsibility of pressure testing lies on two personal, plumbing foreman and project engineer. They perform the hydrostatic test to find out leakages or damages in the pipelines. The information received from the test helps construction personnel to maintain the safety standards and keep the pipelines in good working condition. This information is documented and signed by the assigned personal.
The system use two methods: hydrostatic pressure testing and pneumatic pressure. These test methods use the quick couplings and air compressors as the testing equipments.
Hydrostatic: This method uses clean, fresh city water and after testing done on the compressed gas pipes water is removed and dry the pipes with blowing dry, oil free air or nitrogen through pipes.
Pneumatic: This type of testing is done with dry oil free air or nitrogen on the piping system.
Stress Relieving And Strength
Often there is argument presented that higher test pressures exceeding 100% of the SMYS will increase the “strength” of the material and will “stress relieve” the material. Both arguments have no technical basis to the point they are made. We will briefly discuss both these arguments here:
1. Higher test pressure will “increase the strength.” As the material is stressed beyond its yield point, the material is in plastic deformation stage, which is a ductile stage, and hence it is in the constant process of losing its ability to withstand any further stress. So, it is not increasing in strength but progressively losing its strength.
2. The second argument of “stress reliving” is linked with the “increase the strength” argument. The stress relief of material is carried out to reduce the locked-in stresses. The process reorients the grains disturbed often by cold working or welding. The stress relief process effectively reduces the yield strength. Thus, it does not “strengthen” the material. Note: It may be pointed out that a limited relaxation of stresses does occur by hydro testing, but the test pressure should be less than the material’s yield point.
Once you have finished testing the pipelines, a report will be given to the owner of the site that pipes have passed all pressure tests before covering them by walls or ceilings. Repair leaks during the tests and keep testing the failed pipes until you get the perfect result. Keep a graphical set of testing. Also stamp the information of tester on the piles including serial number, manufacturer and manufacturing date, REE (Rejection Elastic Expansion) and maximum expansion specified by the manufacturer for safety.
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