Why we use higher pressure than the normal operating pressure in..
Why we use higher pressure than the normal operating pressure in..
(OP)
Hello
Any body knows why we use a higher pressure than the normal in Hydrotests in water pipelines?
and is it just ok to make the test in the normal operation pressure?
thank you
Any body knows why we use a higher pressure than the normal in Hydrotests in water pipelines?
and is it just ok to make the test in the normal operation pressure?
thank you





RE: Why we use higher pressure than the normal operating pressure in..
TTFN
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RE: Why we use higher pressure than the normal operating pressure in..
In short no you can't just make the pressure test with normal operating pressure.
One needs to make sure that the pipe can cope with an adverse condition should things go wrong as IRstuff stated.
desertfox
RE: Why we use higher pressure than the normal operating pressure in..
thank you all for inlighting me!
desertfox, what do you mean by adverse condition and how it can be happen?
RE: Why we use higher pressure than the normal operating pressure in..
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Why we use higher pressure than the normal operating pressure in..
The reasons I would say for hydrotest are to prove Integrity & close immediate leaks and would include,
Failure Pressure Versus Defect Size
Manufacturing Defects
Pipe manufacturing codes (for example API 5L [9]) give limits of acceptable defects, which set the standard for detection; many mills use internal standards that meet the criteria given in codes but can still miss some defects. Hydrotest ensures that remaining defects are small enough to still allow operation within MAOP. The hydrotest is designed to induce a stress that would cause failure of under-matched or substandard pipe properties (e.g. wall thinning, tensile properties below SMYS, or defects).
Transit by road, rail or boat
May damage the pipe or subject the linepipe to cyclic stresses that can result in fatigue cracks.
Deficient Workmanship
Since pipeline integrity is much more likely to be affected by longitudinally oriented defects than by circumferentially oriented defects, hydrostatic testing is one of the best ways to demonstrate the integrity of a pipeline.
To expose those and any other remaining defects that have survived previous test and inspection processes.
Hydrotest is considered the final test of pipeline integrity.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Why we use higher pressure than the normal operating pressure in..
Adverse condition means an unexpected event like a pressure rise in the system due say to a partial blockage which is not expected.
desertfox
RE: Why we use higher pressure than the normal operating pressure in..
Have a look at these links
http://en.wikipedia.org/wiki/Hydrostatic_test
http://
http://ww
desertfox
RE: Why we use higher pressure than the normal operating pressure in..
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Why we use higher pressure than the normal operating pressure in..
Typically, hydrotests use pressures greater than the normal operating pressure and a service test is where the line is put into service and inspected. Service tests are common for many water systems (for example, the copper water pipe in my house); however, you stated water pipeline. What is the code of construction you are using for your pipeline?
RE: Why we use higher pressure than the normal operating pressure in..
Some believes the major concern is for detecting leaks or construction flaws, others consider the test is performed to create stresses exceeding those at operating conditions. Some feels it is a method to detect errors made in design calculations, others consider it can produce a benefic stress relief effect. I personally consider hydrostatic test as the method to ensure completion, compliance and most of all safety of the equipment. It is the last test to be carried out (as BigInch noticed), and it can be repeated periodically to ensure that new factors, which affect the equipment during its working life, have not jeopardized the system integrity.
RE: Why we use higher pressure than the normal operating pressure in..
Yes ione. Redistribution of localized stresses within the plastic zones can be an added benefit.
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"Pumping accounts for 20% of the world's energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies) http://virtualpipeline.spaces.live.com/
RE: Why we use higher pressure than the normal operating pressure in..
Per B31.3, with the owner's approval and category D fluid, service testing is permitted. A low pressure water pipeline, not exceeding 150 psig, does not necessary need to be tested above the operating pressure. So to answer qaengineerenator question, "is it just ok to make the test in the normal operation pressure?" It depends on the piping code and what you mean by "normal operating pressure". If the owner specified designing to B31.3 then with the owner's approval, and if it the operating pressure is less than 150 psig, and the water temperature does not exceed 366 degF then it would be ok to test at the operating pressure.
There are a lot of good reasons why you should/might test at a higher pressure than operating pressure given in many of the above comments; however, depending on the code, a service test may be sufficient. What are the consequences of a worst case failure? Are the costs associated with a hydrotest significantly greater than a worst case failure? If so, stay away from a service test.