Interpretation of ASME B16.5 (Welded end valves)

[kevintwk]

Hello all, need some help with interpretation of the code.

Is it correct to weld A350 LF2(Ys, 250Mpa) to A694 F65 (Ys, 450Mpa) directly or should there be a transition piece in between(F52)?

ASME B16.5 , figure 10 states the following in general notes:
"(b) Neither t,, tZ, nor their sum t, + t2 shall exceed 0.5t.
(c) When the minimum specified yield strengths of the sections to
be joined are unequal, the value of tI, shall at least equal the
mating wall thickness times the ratio of minimum specified yield
strength of the pipe to minimum specified yield strength of
the flange."

My interpretation of this is that Clause c states that the value of td shall at least equal the ratio of the yield strengths. This is interconnected with clause b which then states that neither t1,t2 nor their sum shall exceed 0.5t. This is then interpreted as a limit of 1.5 for the yield strength ratio between the welded materials.

 

[LittleInch]

I think your interpretation is correct, but is based on having each YS being used to reduce wall thickness to the maximum extent. It does provide limits on how different wall thicknesses can be joined by welding and tapers

Given the large difference in YS the normal way is to use a transition piece of the higher rated steel, but one end has the lower rated steel wall thickness and then internally tapers at 1: 4 or greater to meet the standard higher yield strength pipe wall thickness.

Also you appear to be using an old verison of 16.5, my 2009 edition has these figures as 12 and 13. Normally a valve WE could be made as figure 12 to allow use of weld metal to fill some of the gap in the wall thickness (i.e. 0.5 t) based on the same ID.

Some figures would help (size, wt ) etc

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way