Nozzle external corrosion allowance

[RiyadhBPV]

To account for nozzle external corrosion allowance, PV Elite requires adding both internal & external corrosion allowances and input the sum in the Total Corrosion Allowance field in nozzle input form. I added an inside nozzle projection and i found that the calculation of area available in nozzle projecting inward is strongly affected by the previous sum. If we discuss the affected parameters we can find the followings:
1. Available thickness of the shell becomes the nominal thickness minus the sum.
2. Available inside thickness of the nozzle becomes the nominal thickness minus twice the internal corrosion allowance.
3. The available inside projection becomes the input inside projection minus the internal corrosion allowance.
When i calculate the area available in nozzle projecting inward by hand i found that my area is larger than PV Elite area.
When i considered the previous sum "internal" i got the PV Elite area.
Any body can help understanding this issue.
Many thanks

 

[Trestala]

1. Available thickness of the shell becomes the nominal thickness minus the sum.

In PVElite and its nozzle area of reinforcement calculation, the shell thickness it uses is the shell thickness minus the corrosion allowance input in the Element Data (Shell itself) which has a separate internal and external CA input, not the corrosion allowance (as total) on the input field on the nozzle.

2. Available inside thickness of the nozzle becomes the nominal thickness minus twice the internal corrosion allowance.

On the internal projection part it should be like that. However, you can just remove the external CA and just use the internal CA and just manually verify there is an excess thickness to account for the external CA.

When i calculate the area available in nozzle projecting inward by hand i found that my area is larger than PV Elite area.

The software is limited since it asks for the total CA of the internal and external. So just adjust your input to internal CA only and just manually verify if there is an allowance for the external CA. Or, if the results is acceptable as-is, then just keep it since it is conservative.

 

[RiyadhBPV]

#Trestala​

Thank you for your great reply
I want to understand something that is confusing me
If you specify only a shell's external corrosion allowance and no corrosion is specified for the nozzle then PV Elite applies the external corrosion allowance to the nozzle even if the total corrosion allowance in nozzle input form is zero.
In the other hand, If you specify only a shell's internal corrosion allowance and no corrosion is specified for the nozzle then PV Elite applies NO corrosion allowance to the nozzle.
How can i understand this issue taking into consideration that the vessel and the nozzle are subjected to the same environment.
Note: The case i check is only for a nozzle without a reinforcement pad and no internal nozzle projection is specified.
Thank you for your patient.