MAP and UG-99(c)

[Nfroh]

Hi,

Compress and as I know other PV computer programs use for the calculation of test pressure according to UG-99(c) the term MAP, which is in my opinion wrong. The Code tells that “basis for calculated test pressure as defined in 3-2” shall be used and not the MAP. App. 3-2 says that ”basis for calculated test pressure… is the highest permissible internal pressure as determined by the design equations for each element using nominal thickness with corrosion allowance included”.
MAP is not the same as basis for calculated test pressure, since the MAP can be calculated in corroded condition also. Moreover, Note 8 in Fig UCS-66.2 defines MAP in corroded condition. What is your opinion?
Thanks

 

[gr2vessels]

Nfroh,
1. The UG-99(c) is optional arrangement between the Client and fabricator, is not mandatory. Normally, use the UG-99(b) test requirements.
2. Is nothing wrong with UG-99(c), but it is optional, hence the calculation pressure is also optional.
3. Any recognized design software provides the option of selecting UG-99(b) or (c), including the footnote (endnote on latest ASME VIII-1). PV Elite calculates and displays all the options, so you select the agreed Test Pressure.
4. The equipment shall be designed and fabricated to enable site hydro test in corroded condition, should the test be required.
Cheers,
gr2vessels

 

[Nfroh]

Hi gr2vessels,

I know that the calculation of UG-99(c) is optional and there is nothing wrong with this paragraph. In my opinion it is wrong to calculate UG-99(c) with 1,3*MAP. According to Code, the test pressure UG-99(c) shall be calculated using 1,3 * “basis for calculated test pressure as defined in 3-2” and not 1,3*MAP.

Moreover, the code defines MAP “as the highest permissible pressure as determined by the design equations for a component using the nominal thickness less corrosion allowance and the maximum allowable stress value from the Table 1A of Section II, Part D at the MDMT” (Note 8 in Fig UCS-66.2). I understand this as MAP shall be calculated in the corroded condition.

It is only one place in ASME VIII-1 where MAP is defined. There is no Code connection between MAP and UG-99(c).

Compress and PVElite both show the test pressure report for UG-99(c) in connection with MAP, which is IMO wrong and can lead to misunderstandings.