What is Hydrostatic testing?
Hydrostatic testing is the most commonly used procedure for checking the performance of pressures vessels. This testing is especially brought into play to verify pressure vessels like cylinders, boilers and tubes either they have leaks or manufacturing flaws that may result in leakage.
Hydrostatic testing is significant for safety of pressure vessels and their strength and stability when operating under pressure. This technique is normally utilised under industry requirements or upon customers’ demand or specifications. Usually, there are more chances of leaks in low pressure devices like pipes and plumbing, which are necessary to be identified. For this purpose, the best technique you can go for is hydrostatic testing, not only to detect leaks in pressure vessels, this technique may also be applied for checking proof pressure and burst pressure as well.
Verification of pressure vessel design is suitable for application or not
Procedure of this hydrostatic testing is simple and easy. Incompressible fluids like oil and water are used for this test. The vessel which is to be examined is filled with anyone of these fluids. This test will confirm if there is any leak, manufacturing flaw and/or enduring change in shape of the vessel. In order to make leaks easier to be detected, add red or fluorescent dye in liquid contained in the vessel. As safety factor, pressure applied for the test should always be higher than operating pressure. The safety margin is normally 150% or 5/3 of operating pressure and depends on regulations applied. For instance, if vessel is rated to 2015psi (139 bar) then it should be tested at about 3360psi (232 bar). Water is the most commonly used liquid in hydrostatic testing because it is more incompressible than any other liquid. The vessel which is to be tested is placed in another sealed vessel filled with water. The adjusted internal pressure for a set time period is applied to the test vessel. This subjected pressure result in expansion of test vessel. The overall and permanent expansion of the vessel is then determined. After this, it is inspected physically and visually that the test vessel has been damaged/permanently distorted or remained safe due to test pressure applied on it. For re-verification, the vessel may be subjected to proof-pressure test which is a modified form of hydrostatic test. Procedure of this test is same that of normal hydrostatic test. The only exception is that the test vessel is checked for distortion or malfunctioning during the course of proof-pressure test.
Generally, water jacket test is employed for testing of small pressure vessels. The vessel to be tested is visually inspected for defects and then put in water filled container and by monitoring water level the change in volume of test vessel is measured. The vessel is then pressurized for about 30 seconds. After de-pressurizing, water level is checked which will be raised if vessel distorts due to pressure change and unable to return to original volume.
Take full and appropriate safety measures during and after hydrostatic test execution. The reason behind is use of high pressure in this test. Make it sure that there remained no pressure trapped in the test vessel or pipeline.
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