What does means that 'calculated pressure" in UG-99 (c)

[mechengineer]

Dear experts,

What does means that 'calculated pressure" mentioned in UG-99 (c)? The Design Pressure or MAWP or MAP? I think that all of the design pressure, MAWP and MAP are "calculated presure".
My understanding is that it is dependent on the agreement between the user and manufacture, it cane be MAWP, MAP, design pessure, or others.

Thanks.

 

[r6155]

You are confused.

calculated test pressure: the requirements for determining
the test pressure based on calculations are outlined in
UG-99(c) for the hydrostatic test and in UG-100(b) for
the pneumatic test. The basis for calculated test pressure
in either of these paragraphs is the highest permissible internal pressure as determined by the design equations,
for each element of the vessel using nominal thicknesses
with corrosion allowances included and using the allowable stress values given in Section II, Part D, Subpart 1
for the temperature of the test.

Regards

 

[david339933]

...as defined in 3-2.

 

[mechengineer]

@david339933, Noted with thanks.

UG-99 (b): 1.3*MAWP*[stress ratio in temp].
UG-99 (c): 1.3*MAP*[stress ratio in temp].

 

[r6155]

Wrong.
See definition of MAP, MAWP and "calculated test pressure"

 

[mechengineer]

@r6155 ,

Correction:

UG-99 (b): 1.3*MAWP*[stress ratio in temp]. The thickness is without CA.
UG-99 (c): 1.3*CTP*[stress ratio in temp]. CTP-"calculated test pressure". The thickness with CA.
MAP for MDMT (to evaluate MDMT). The thickness is without CA.

For UCS-66(b)(1)(-b) and UCS-66(i)(2), a ratio of the maximum design pressure at the MDMT to the maximum allowable pressure (MAP)
at the MDMT shall be used. The MAP is defined 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 working pressure (MAWP) for a vessel is the maximum pressure permissible at the top of the vessel in its normal operating position at the designated coincident temperature specified for that pressure

calculated test pressure (CTP): the requirements for determining the test pressure based on calculations are outlined in UG-99(c) for the hydrostatic test and in UG-100(b) for the pneumatic test. ... with corrosion allowances included ...

But I don't see the difference between MAWP and the MAP in value in one design.

 

[r6155]

1) UG-99 (c): 1.3*CTP*[stress ratio in temp]. CTP-"calculated test pressure". The thickness with CA.
It's OK now

2)You need more reading about design pressure, MAWP and MAP

Regards

 

[Geoff13]

MAP only exists in UCS-66, and is calculated per component in the hot and corroded condition. You cannot speak about MAP for a vessel.

However you can determine the MAP of each component, apply a product head correction to convert it to a pressure at the top of the vessel, and select the smallest of these values. This is the MAWP. The Code permits the design pressure (DP) to be used as the MAWP. If you order the exact design thickness material for even one component then MAWP will equal DP. MAWP will only be higher than DP when all the components are thicker than design. MAWP is used to calculate the UG-99(b) test pressure as you've discussed above.

The hydrotest is meant to be an overstress test to prove the vessel quality. That's what the 1.3 factor is trying to do. However for vessels with large corrosion allowance, the stress in the shell during a UG-99(b) test could be less than the actual stress will be in the future corroded condition! Thus the UG-99(c) test calculates the MAP of each component in the new and cold condition, multiplies by the 1.3 factor, and then corrects for the hydrostatic head to the top of the vessel. The smallest of these values is the calculated test pressure (CTP). There is no temperature correction (LSR) since the calculation is done in the cold condition. The CTP includes the 1.3 factor on each component, so 1.3 is not multiplied afterwards. This higher pressure assures that vessel is overstressed during hydrotest to prove it's quality.

 

[mechengineer]

@Geoff13,
The MDMT (USC-66) in GA for a vessel. The MDMT of vessel corresponding to MAP (governing coponent) is the MAP for the vessel. The concept shall be same as MAWP, applicable for individula components and whole vessel.

Regards

 

[r6155]

1) "The hydrotest is meant to be an overstress test to prove the vessel quality". (as Geoff13 says )
NO. The pressure test is to verify the integrity of the vessel.
2) I disagree with ASME VIII Div.1 respect to calculated test pressure: “...... using nominal thicknesses with corrosion allowances included and using the allowable stress values given in Section II, Part D, Subpart 1 for the temperature of the test”
Must be read:
“...using nominal thicknesses with corrosion allowances included and using the allowable stress values given in Section II, Part D, Subpart 1 multiplied by the lowest stress ratio (LSR)”

Remember: This Division does not specify an upper limit for hydrostatic test pressure.

3) PD-5500 uses the same concept as I say

Regards