QW-193.1.3

[Fizza453]

We have to qualify tube to tube sheet joint in accordance with ASME Section IX.
Joint is groove plus fillet type. Groove depth is 7 mm and fillet leg size is 3 mm.
QW-193.1.3(a) talks about "Minimum Leak Path Dimension", in the above case is it 7+3=10 mm?
I interpret "minimum leak path dimension" as the distance fluid covers if it were leaking. So it covers 10 mm distance if it were leaking. Please advise.

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[MikeMet]

The short answer is yes. The minimum size of the weld, if a strength weld, is calculated using ASME Sect VIII, part UHX. However, there is no term or definition of "leak path" in Section VIII. So the leak path required by the design is undefined, but most people consider the weld size to be the leak path. Before UHX, Div 2 did have rules for tube to tube sheet mock ups that did talk about a minimum leak path of 2/3T. But no longer no that QW193 governs T/TS welding.
The leak path in a T/TS weld is measured from the bottom of the weld where it meets the annular space between the tube and tube sheet hole to the point on the surface that is closest to the this bottom starting point. In a perfect weld that has full penetration to the bottom of the groove and has the proper size fillet on top, you are correct it becomes 10+3mm. But when you section the mock up you may find the welders did not do a perfect weld and the minimum leak path may be at a 45 degree angle up from the bottom of the weld. I have seen all types of poor welds with minimum leak paths in all directions.