Can anyone describe difference between UG 99(b) & UG 99(c) 1

[pravin143]

Can anyone describe with example difference between UG 99 b & UG 99 C for hydrostatic test

 

[SnTMan]

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

 

[Geoff13]

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.

 

[weldstan]

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.

 

[pravin143]

Dear weldstan, Geoff13 , SnTMan
Thanks for your valuable inputs.