Application of UG 99 & 100 for old vessels 1

[10815L]

Hi all,
according to ASME VIII DivI, UG 99 is applicable for all pressure vessels for hydrostatic test at 1.3 ( design pressure ) and UG 100 for pnumatic test at 1.1 of maximum operating pressure. Interpretation is very clear in para B ( UG 99), my question is about once the vessel is manufactured in workshop and hydro tested, stamped then why we need again hydro test after maintenance even their is no head or shell opening during the maintenance. Pneumatic test at working pressure not enough instead of hydro test.particularly columns (like glycol cont actors and three phase separators).for old vessels say 20 year old vessels we can apply UG 100 instead of UG 99.
10815L

 

[metengr]

There is no reason to perform an in-service hydrostatic test unless you are mandated to use this test to verify the vessel is acceptable for another "x" years of service (which I do not agree with and some use as a crutch). My main reason for objecting to hydrostatic testing is having to either remove or gag safety relief devices, which can result in damage.

Hydrostatic testing is a one-time proof test to check for leaks in materials and connections once new construction is completed. Beyond this there is no need to be using a hydrostatic test as a means to justify continued operation. I know that some jurisdictions or regulatory bodies require a code hydrostatic test after the vessel has been in service for 30-50 years to prove the vessel is acceptable for continued service. This line of thinking not practical unless the vessel is being subjected to hydrostatic testing to try to condemn it because the information a hydrostatic test will provide is if the vessel will hold water today, and not 10 years from now. The more practical approach would be to use nondestructive testing and comprehensive inspections to ensure future reliability and serviceability of the vessel.

The only reason I see a hydrotest being considered is if the vessel cannot be accessed on the ID surface to perform visual and NDT. Even in this case I would argue an operating pressure squeeze would suffice to check for leaks with NDT being performed on the external surface.

 

[10815L]

Many Thanks metengr for answering in depth and with practical approach, more than one decay in refinery i never seen this approach as i'm facing in oil producing company.
The main thing is standards and training for new technology.
Thanks again.
10815L