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.

An important statement is in para. 5.1.2: "... flange dimensions C1 to C4 or F shall not be less than 80 % of „vR” for forgings ...". These dimensions are related to the flange ring thickness. This would lead to the assumption that vR would be the flange thickness (at bolt hole) plus the raised face (optionally divided by 0.8), 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 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.

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


This has to do with the 'N' at the end of 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.

The registration is available for Red-Bag customers only.

There are many questions related the calculation of the EN10253 A/B fittings. This article handles a few of these questions

Q1- One of the questions is listed Afnor site:

"Currently the EN13480 part 3 does not provide a calculation method for tee's. Where the EN13480-3 provides a calculation method for (welded or extruded) branch connections and Y pieces, there does not seem to be a formula available to calculate Tee pieces with a radius between the branch and the cylinder.

Although one could assume the calculation method is the same and an assessment has to be made of the reinforcement and the pressure area, this is assumption is not confirmed by the text. Would it be possible to provide us with guidance on how to approach assessment of Tee's according to this EN13480-3 and possibly add a paragraph to the coming edition of the EN13480 on these and possibly other standard fittings?"

A1- The answer is as follows:

"In principle the method described in EN 13480-3, clause 8 can also be used For fittings with a radius between cylinder and branch. The user has to determine the areas Ap and Af by means of plane geometry. For fittings there are special dimensioning rules in EN10253. Thus there is no necessity
to extend EN13480-3 concerning this issue."

The PCC software of Red-Bag does the calculations as per above answer. The radius is currently as a maximum defined in the EN 10253 and therefor the sample calculation in the Annex is not reproducible. The PCC software uses a radius factor and a crotch factor to determine the missing dimensional values. This approach is generally accepted in the industry.

Q2- The pipes are organized in wall thicknesses and the fittings in series. In some cases the wall of the pipe is slightly thicker than the tapered section of the EN10253-B. How do I prevent this mismatch?

A2- The pipe wall thicknesses in the EN10220 are missing a series (or schedule) organization as is available in the ASME standards. We suggest our customers to select the pipe wall thickness corresponding the series in the EN10253 fitting standard. In this case you will have the EN10253-B fitting matching the pipe wall thicknesses. In our opinion the missing series (or schedules) in the EN10220 is omission in the standard.

Q3- I have calculated the pipe wall thicknesses and would like to use the full service fittings of the EN10253-B standard. These fittings are not available or sometimes 5 times more expensive than the limited service fittings of the EN10253-A standard. What should I do.

A3- A cost efficient approach would be to calculate the fittings from the EN10253-A standard with our PCC software and taper the fitting to fit the pipe wall thickness. In most cases you will have to select a stronger series fitting than would be from the EN10253-B standard.