Dear Sirs,

I have one question on UG-45 thickness calculations.

In the following example the final required thk is 6.4227 mm & the available nozzle neck thk is 7.6454 mm (after reduction of mill under-tolerance).

UG-45 Minimum Nozzle Neck Thickness Requirement: [Int. Press.]
Wall Thickness per UG45(a), tra = 3.6701 mm.
Wall Thickness per UG16(b), tr16b = 6.0875 mm.
Wall Thickness per UG45(b)(1), trb1 = 7.7167 mm.
Wall Thickness per UG45(b)(2), trb2 = 6.3459 mm.
Wall Thickness per UG45(b)(3), trb3 = Max(trb1, trb2, tr16b) = 7.7167 mm.
Std. Wall Pipe per UG45(b)(4), trb4 = 6.4227 mm.
Wall Thickness per UG45(b), trb = Min(trb3, trb4) = 6.4227 mm.

Final Required Thickness, tr45 = Max(tra, trb) = 6.4227 mm.
Available Nozzle Neck Thickness = .875 * 8.7376 = 7.6454 mm. --> OK

The vessel is underground & hence it has internal corrosion allowance of 3 mm & external corrosion allowance of 1.5 mm. PVElite have not accounted the external corrosion allowance in the calculations for nozzles only. However if we add the external C.A. of 1.5 mm then the final required thk becomes 6.4227 + 1.5 = 7.9227 mm & this thk is greater than the available nozzle neck thk of 7.6454 mm. So the result is nozzle is failing. How to include External C.A. in the nozzle calculations?

Now, the pipes we have ordered are without mill under-tolerance. Therefore the available nozzle neck thk should be 8.7376 which is greater than 7.9227 mm, hence the design is safe.Please explain me how to do this in PVElite?

Hello,

If u have Internal n external CA, the enter cumulatively in input field of PV-elite.

The above is not a correct solution as same leads to wrong diamter of openings in corroded condition and overall reinforcement calculations will not be correct.

The correct solution is that M/s COADE must add separate fields for internal and external corrosion allowance in nozzle design dialoge too.

Thanks.

Mukesh

any formal COADE taker

Hello Mak

PV Elite does not have a provision for external corrosion allowance on nozzles and reinforcement pads. I suggest you add the external corrosion allowance to the internal corrosion allowance for the nozzle, and reduce the thickness of the reinforcement pad by the external corrosion allowance. You may also have to adjust the outside welds for the external corrosion allowance.

This will give you a conservative result.