pravin143, UG-99(b) test pressure is based on the vessel MAWP, if calculated, or design pressure if not. The UG-99(c) test pressure is based on other than the MAWP, and is often used for so-called "shop" hydo based on New and Cold MAWP (often referred to as MAP). See the definition in 3-2, note use of the words "with corrosion allowances included".
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
The purpose of the hydrotest is to over-stress the vessel to help prove it's good. In the case of Division 1 it's a 1.3 over-stress. If there's a flaw in the construction let's find out when it's only full of water.
However for some vessels, particularly ones with a large corrosion allowance, the stress in the new shell thickness may be less than the operating stress in the future corroded vessel. Thus the UG-99(b) test can actually be an "under-stress" check! The highest stresses will only happen at some distant future when it's operating.
UG-99(c) addresses this by back-solving the permitted design pressure for each component's as-built thickness, and then applying the 1.3 factor to the lowest of these values. This should result in a higher test pressure, but should also do a better job of doing an over-stress check of the new vessel.
While testing at a greater pressure would normally be considered a greater risk, the UG-99(c) pressure will still have the typical hydrotest stresses (1.3 St) in the vessel so this shouldn't be a concern.
Under ASME VIII, Div.1, the vast majority of hydrostatic tests of vessels are merely leak tests. The vessel is not subject to high stress in most cases.
