Why equal diameter tees are forbidden in the creep range according to EN standards?

[Patafian]

Hi All,

One month ago I put similar question on Boiler and Pressure Vessel forum with no result. Maybe here someone knows.
Some European piping and boiler standards set limit on the ratio of branch to shell inner diameter. This Limit d/D ≤ 0.8 (for extruded outlets 0.7) could be found in EN 13480, EN 12952 and German Boiler Standard TRD 301. ASME standards (B31.1, B31.3, Section I) do not have such limitation.
My questions are:
- what is rationale for that limitation.
- where it originated from (research paper, monograph, book, etc)
- is it pertinent only to pressure-area method of reinforcement calculation

Regards

Patafian

 

[XL83NL]

Good question. No idea honestly. What I would do i contact one of the staff/committee members of EN 13480;

http://www.unm.fr/main/core.php?pag_id=121

 

[BigInch]

Keeping the ODs similar will tend to transfer bending loads from the branch across the joint in the plane of the pipe walls in shear, rather than attempt to distribute the load across the diameter of the mainline pipe.

Technology is stealing American jobs. Stop H1-Bs for robots.

 

[Patafian]

BigInch I agree with you that stress pattern changes with branch to header ratio and when the ratio approaches 1 it is most unfavourable. But this is true for material working in creep range and below as well.
So European standards tell us that equal diameter tee is unacceptable when creep governs material behavior. One could draw conclusion that equal diameter tee in creep is too dangerous, but American standards ASME B31.1, B31.3 or Section I do not recognize that. It is a little bit strange for me.

 

[BigInch]

You can find these kinds of differences even betweeen the ASME codes. You can do all the research you like, but it will not change the code requirements. I would suggest that you simply follow the requirements of the code that you are using, or write and request a clarification.

Technology is stealing American jobs. Stop H1-Bs for robots.