The PT rating of flanges depends for some material groups on a reference thickness vR. The definition for the vR might be unclear from the EN 1092-1 standard.

The EN 1092-1 explains the background of vR in F.2.4, however only that for different reference thicknesses there are individual PT ratings.

In Annex G.1.2 it states that 'The graduation of vR depends from the product of material from which a flange is manufactured. For the different methods of fabrication see Table 1 of this European Standard'.

In Tabel 1 you will see that a weld neck flange can be forged, machined or for > DN700 bended and electric welded.

Therefore you have to consider the manufacturing method. In case of a forged flange, the hub might be additional forged. This would lead to the assumption that vR would be the flange thickness (at bolt hole) plus the raised face, if applicable.

Red-Bag receives many questions about the PCC EN13480 Tee calculation versus the later issued EN10253 dimensions standard calculation in for example Annex A.

For example: if a Tee is calculated according EN13480 the maximum allowable design pressure at design temperature would be 1.2 N/mm2. If the same Tee is checked with the pressure factor in Annex B (calculated as per Annex A) the maximum allowable design pressure at design temperature would be 1.5 N/mm2.

The conclusion is that the EN10253 maximum allowable design pressure is higher than calculated as per EN13480.

The reasons is that the EN10253 definition of the reinforcement limits is different from the EN13480 or the EN13445.

The below images show the differences:

EN10253 Tee

EN10253 Tee

This image of the EN10253 calculation base shows that the reinforcement limits follow the curve of the crotch

EN13445 Tee

This image of the EN13445 extruded branch (Tee) shows that the reinforcement limits are straight to the outside diameter of the header or the branch

EN13480 pipe-pipe branch

This image of the EN13480 shows the limits of a pipe to pipe branch. The limits are also straight to the outside of the pipes. ()Note: the EN13480 does not have an image as the EN13445 for the Tee)

EN13480 Y branch

This images shows the reinforcement limits for a Y branch. It illustrates that the EN13480 also uses straight lines as per the EN13445.

The difference in allowable design pressure for the EN10253 and the EN13480 is due to the different definition in reinforcement limits (which also has an effect on the pressure area). The EN10253 pressure factor calculation and the corresponding tables are 'INFORMATIVE'. However the PCC application will have in future the possibility to select between the EN13480 calculation or the use of the Annex A, B pressure factors.

The PCC software has for the ASME B31.X two modes of calculation:

  1. Fitting with a specific rating (default)
  2. Fitting without a specific rating

In the first mode (fitting with a specific rating) the PCC software makes only a calculation of the corresponding pipe with the same schedule as per the ASME code.

However for example if you want to make a full detailed calculation of a Tee you have to switch the calculation mode for ASME B31.3 to "ASME B31.3 Use without specific rating". The custom Tee calculation will now be executed in full detail.

Please refer to ASME B31.3 302 Design Criteria, paragraphs 302.2.1 ... 302.2.3. Thus:

Ref. 1, Tee with specific rating -> calculate the Tee as an equivalent straight pipe. This is the default mode for ASME B31.3. The manufacturer of the Tee Schedule 10S is responsible to make the Tee equally strong as the pipe schedule 10S made of the same Tee material.

Ref. 2, Tee without specific rating -> make a detailed Tee calculation according paragraph 304.3. This is the custom mode. Use this when the Tee is of unknown origin or custom made with predefined dimensions. Now you will have to insert or know all detailed dimensions. Usually you can start with the dimension import of a standard fitting.

Below image indicates the setting location in PCC:

PCC fitting setting

 

The values for the flanges (service limits) have been entered by using the standard import in the PCC software. However with the calculations I still get an overrun or error. The P and Pmax should be equal at the different temperatures. I get this mistake for all size. Is this due to rounding or what am I doing wrong? Refer to below image:

 

 

The PCC software gives the correct validation messages. The above happens if you select flanges from one standard and the design conditions from another standard. The flange standards have been changed during the years. Make sure you select consistently the flange standard for the design conditions and the flanges in the pipe classes.

For example selection of the design conditions in the Pipe Class Edit dialog:

 

 

the default materials:

 

 

and the actual selected flanges for the pipe class:

 

 

Now the verification of the flange rating (according ASME B16.5 edition 2009) is consistent with the selected flanges.

This has to do with the 'N' at the end ofr P355N. The standard EN10028-3 says:

6.1 Classification

6.1.1 The steel grades covered by this European Standard are given in four qualities:

 

a) the room temperature quality (P ... N),
b) the elevated temperature quality (P...NH),
c) the low temperature quality (P...NL1) and
d) the special low temperature quality (P...NL2).

Use P355NH in case of design conditions with a warmer temperature than room temperature.