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# How to convert Control thickness to Nominal thickness?

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## How to convert Control thickness to Nominal thickness?

(OP)
Hi guys!
I'm here again.

I'm organizing PWHT requirement using excel.
I have to write only one thickness on a excel table.
My team leader said the table makes people so confused because of two thickness(control thickness, nominal thickness) on one table.
Example of the table is like this.
-Example(from B31.1)-
P No. Thickness PWHT Temperature
=========================================================================
P-15E 13Tn<Pipe<=50Tc 705~775℃
(P-91,92)

cf)Tn means nominal thickness and Tc means control thickness

So I decided convert control thickness to nominal thickness.

The reason of converting is PWHT temperature and PWHT exemption requirement by thickness.

Should I multiple 1.125(considering manufacuring tolerance) by control thickness to convert to nominal thickness?

Replies continue below

### RE: How to convert Control thickness to Nominal thickness?

See thread378-427039: Understanding of PWHT thickness in B31.3
Please review the definition in the standard you are building to.
You will be better served adding a sketch to your table, as there is not a consistent relationship between the two thicknesses.

### RE: How to convert Control thickness to Nominal thickness?

It's not a good idea to PWHT with an Excel table. The best practice is to use the tables for each code. Don't forget Preheat.

Regards

### RE: How to convert Control thickness to Nominal thickness?

Considering that some pipe specs use -12.5% with the '+' side only limited by the next heavier schedule,
while others are minimum wall specs with a -0 and '+' being the next heavier schedule.
You really need to look at each case.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

### RE: How to convert Control thickness to Nominal thickness?

Be careful. See UW-40(f)definition of thickness.

Regards

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