Weld reduction factor for transverse weld btw. pipe & flange

[Fran67]

Hello everybody,

I work on a calculation of a piping system composed of a carbon steel flange and a pipe with important wall thickness reduction: the ratio of 87.5% given by the ASME B31.3 between the flange Weld neck (12.5mm) and the pipe thickness (15mm) is not respected (83%).

Individual thickness of the two components are compliant with ASME B31.3 formulas for required min thickness calculation, but do you know if, because of the thickness reduction, i have to consider an additionnal safety factor on the caculation, corresponding to the Weld between the two components?
Maybe the respect or not of ASME B31.8, part required Weld for thickness reduction, has an influence on the calculation?

Thank you for your responses,
F

 

[mk3223]

I am not quite follow the question, for what is the reduction of the the wall thicknesses for pipe and flange. Also, Are they per B31.3 or B31.8?

It's really helpful if a simple sketch can be shared.

 

[KevinNZ]

Why not taper the pipe down to the flange thickness. See B31.3 Fig 328.4.4

 

[Fran67]

Hello,

Sorry I will ask the question with different words:

According to part 7 and figures 1 to 3 of the ASME B16.5, the flange hub thickness can be thicker than the pipe thickness, and in this case provision shall be taken on the bevel.
But, the contrary (pipe th>flange hub th) is not possible because the max ratio flange hub/pipe thickness shall not be higher than 87.5% (chapter 7.5.4)

My question is so: do you know the reasons of the required ratio of 87,5%? of chapter 7.5.4, what would be the risks if the ratio is not respected (80% for example)?
If a ratio of 70% could be accepted by tapering the pipe, why it is not written in the B16.5 ?

Thank you

F