ASME B31.3 Vs ASME Sec.9 impact thickness limitation

[Metallurgistrbi]

Hello all;

I was reading the below link for thickness limitation w.r.t "t+6mm" maximum limitation as given in A5 of B31.3 table 323.1 (Prior to 2020 edition)

https://www.eng-tips.com/viewthread.cfm?qid=495511

Now this requirement(t+6mm) is removed in 2020edition, it is being interpreted as 2T thickness(ASME Sec.IX) instead of T+6 mm.

Iam some what confused. should it not be interpreted as T+0mm since T + 6mm is removed?

Consider for Eg a "Curve A material" B31.3 with reference MDMT 0C

The PQR thickness is 14.3mm whose MDT is 2.8C(table 323.2.2A B31.3) and hence impact tested @ 0C.

How can this qualify for 28.6mm whose MDT as per the above table is 23.6C? for MDMT 0C?

How can 2T qualification be logical?
Shouldn't T+0(or 14.3mm) is the maximum qualified???

Thanks in advance for your inputs

Edit 1:-

In addition to above does not the thicker material is more prone to brittle fracture?. So if ASME sec. 9 restricts the minimum qualified, is it not relevant that the thicker material tests be more stringent?

 

[david339933]

So QW-403.6 limits the minimum qualified to T or 5/8". There is no limit on the maximum. It has been this way for a long time.