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.