The EN 13480-3 scope is specified as ‘the design and calculation of industrial metallic piping systems, including supports. The design criteria, as laid out in clause 4, include the internal and/or external pressure amongst others

A fair amount of the EN 13480-3 deals with the design of piping components, clause 6, 7, 8, 9, 10 annex B, C and E. The piping components include pipe, bend, elbow, miter bend, cap, pipe-pipe branch with or without reinforcement, tee, y-type branch, bolted and welded flat head, most of the commonly used pipe system components.

The piping components are usually sufficiently defined to even execute calculations for custom made components. However, the definition of the Tee could be further refined, in the same fashion as other components. The proposal is to add four images and the related description that further adequately detail the material area, the pressure area and limits of reinforcement.

There have already been comments on this proposal which are addressed at the end of this document in the ‘Discussion’ section. The last section compares the calculation method of the EN 13480-3 and EN 10253-2 Type A/B Tees.



The proposal is to add the below images to EN 13480-3 clause 8 including the fourth on the next page:


Figure 8.3.9-3 - Thick wall

Figure 8.3.9-4 – Thin wall

Figure 8.3.9-5 – limits detail

The reinforcement limits lengths, ls and lb, are depending the equivalent diameter and the analysis thickness for both the run and the branch part. This is consistent with the formulas 8.4.1-2 and 8.4.3-1.

The limit length is measured in a straight line from the reference point. This is consistent with figure 8.6.1-1. The reference point in this case is the outside diameter of the run for the branch limit length lb and the outside diameter of the branch for the run limit length ls. This is consistent with figure 8.4.3-1, figure 8.4.3-2, figure 8.4.3-4 and figure 8.4.3-5.

The equivalent diameter is taken at the point of the limit length. This is consistent with figure 8.4.3-1, figure 8.4.3-2, figure 8.4.3-4 and figure 8.4.3-5.

The analysis thickness is defined at the point of the limit length. This is consistent with figure 8.4.3-1, figure 8.4.3-2, figure 8.4.3-4 and figure 8.4.3-5.

The advantage of this consistent approach is, that if the radius is set to zero, the calculation areas and the calculation will show the same result as the isolated opening of a pipe-pipe branch in clause 8.4.

Further detail figure for a Tee with reinforcement on the inside and the outside to be added is like:

Figure 8.3.9-6 inside and outside reinforcement

The above image would complete the different possibilities with possible reinforcement on the outside of the Tee. The variable names for the outside radius of the crotch and the crotch thickness would be added to the legend to further define the Tee shape.

The limits in above images need to comply with the formulas:

Formula 8.4.1-2 reinforcement limit in run pipe direction

Formula 8.4.3-1 reinforcement limit in the branch pipe direction

The limits, diameter and wall thickness are at the (exact location) as calculated by above formulas.



The current definition of the tee does not present the handling of tapering. The influence on the material and pressure area significant and is a matter of concern.

Below is a real-life example of Tee EN 10253-2 DN200xDN200 Series 6 type B with ends of 16 mm and connecting to a 16 mm pipe. The material is P235GH and the design conditions were:

  • Pressure: 15.4 MPa (154 bar)
  • Temperature: 160 Celsius


Figure 1: Un-tapered Tee with connecting pipes

The above setup of Tee and connecting pipes will not be the actual construction. Tapering will be done on the Tee to have a proper transition to the connecting pipes. The tapering is not only for better process flow but also for the welding and reducing stress concentration in the Tee – pipe transition area.

The pipes and Tee and with standard 1:4 tapering will look like below image:


Figure 2: example tapered Tee with connecting pipes

The tapering reduces the material area and increases the pressure area.

One could argue that the tapering should not engage within the crotch area and should stay on the cylindrical section only. In that case the tapering would become very steep:


Figure 3: example Tee with tapering outside crotch

This last approach is used for the calculation of the thick walled Tees below to keep the shape and material area of the Tee intact.



With reference to CEN/TC 267/WG 3 document N334:

It is stated that the diameter and wall thickness for the Tee calculation can be determined at various locations. The location of the diameter and wall thickness in the proposed figures is well defined as is stated in above section. The location is consistent with all other figures and similar to calculations in EN 13480-3 Clause 8 like the pipe-pipe branch connection.

The reinforcing length is calculated by formula 8.4.1-2 for the header direction and the formula 8.4.3-1. The definition of the reinforcement length is well defined. The calculation of the reinforcement length with both formulas give valid results for all Tees with dimensions of EN 10253-2/4.

The reinforcement lengths used in the calculations of the EN 10253-2/4 do not comply with formula 8.4.1-2 and the formula 8.4.3-1.

The Tee and its tapering has a complex form. The purpose of the EN 13480-3 is to provide the best possible solution to determine the strength of a piping component. There is no reason to step away from a more accurate definition or calculation method because it is difficult for a spreadsheet application. There are many more mechanical calculations for piping and static equipment in the EN standards that cannot easily be done with a spreadsheet.

The implementation of the laws of physics is simplified in many calculations. The use of curves or factors overcome the complexity of the full implementation of the physical behavior of the material in combination with the component shape. The calculations codes however should use a consistent approach and keep the calculations as accurate as possible.

The RToD (Dutch Stoomwezen) has this calculation method already for many years, from the 1980’s. The Red-Bag PCC application uses this method since its first release in 2003. All without any problem.

The ASME B16.9 does not state a calculation method. The standard refers for design to testing, FEA or has a circular reference to ASME B31.3 which does not have a dedicated Tee calculation.



A range of Tees from the EN 10253-2 Type A and B have been calculated with the EN 10253 methods and the EN 13480-3 (according the proposed figures) method.

The maximum allowable working pressure (MAWP) has been calculated for both calculation methods. The results in the next tables show the ratio of the MAWP’s as follows:

ratio = MAWP_EN134803 / MAWP_EN10253

The X-axis shows the wall thickness series as per the EN 10253-2 and the Y-axis shows the Tee size. The selected sizes have been used for this investigation from the smallest to the largest: DN15xD15, medium sizes DN200xDN200 and DN200xDN80 and the largest sizes DN1200xDN1200 and DN1200xDN600.

The example summary calculations and the overall MAWP ratio results are part of the attachments.


The above table are the Type A Tees. The non-green colors in above table indicate that the EN 13480-3 method results in a lower MAWP than the EN 10253-2 method, ratio < 1.0.


The above table shows (in green) that, with the increasing wall thickness of the Tee, the EN 13480-3 method results in a higher MAWP than the EN 10253-2 method, ratio > 1.0.

The darker green values are related to the extreme tapering requirements or the X factor not close to 100%



The EN 13480-3 is a calculation code and the EN 10253-1/2/3/4 are dimension and/or material standards.

The proposed four figures for the EN 13480-3 comply with all images, texts and formulas in the current calculation code, and provide a clear definition of the Tee areas.

The proposed figures do not lead to changes in the calculation code.

The proposed figures also define the areas for the calculation of custom Tees: with are larger crotch thickness, actual measured Tee thickness (for unknown schedules/series) and Tees from the ASME standards.



Some of the dimensions need to be reviewed in the EN 10253-2 Type B Tees.

The EN 10253-2 Type B Tee DN15xDN15 Serie 8 with tapering outside the crotch looks like this:


The EN 10253-2 Type B Tee DN20xDN20 Serie 8 with tapering outside the crotch looks like this:


Attachments (not part of this Internet page)

  1. DN200xDN200 Type A Serie 6 EN 10253-2A summary calculation
  2. DN200xDN200 Type A Serie 6 EN 13480-3 summary calculation
  3. DN200xDN200 Type B Serie 6 EN 10253-2B summary calculation
  4. DN200xDN200 Type B Serie 6 EN 13480-3 summary calculation
  5. EN 10253-2 Type A selection of sizes and series
  6. EN 10253-2 Type B selection of sizes and series