ASME VIII Division 2 Design by analysis of welded joints
ASME VIII Division 2 Design by analysis of welded joints
(OP)
Dear forum members,
I am trying to qualify a pressure containing clamp (see first attached image) using Design by Analysis in accordance with ASME VIII Division 2, and I am particularly interested in how the welded regions are treated by the code with regards to joint efficiency.
According to Part 5.1.1.2(b) of ASME VIII Division 2, welds must have a geometry that is listed in Part 4 (which this geometry is not, see second attached image), or they should be assessed in accordance with Part 5, however no specific considerations are specified in the code for how to qualify the weld. My suggested method for analysing the weld would be as follows (note that only visual inspection of the welds will take place):
Using Table UW-12 of ASME VIII Division 1 I would classify the upper weld as a single-welded butt joint without the use of a backing strip, resulting in a joint efficiency factor of 0.6. The lower weld I would classify as equivalent to a double full fillet lap joint, resulting in a joint efficiency of 0.55.
I would then run the FEA, using a factored down allowable stress of 0.6S and 0.55S respectively in the weld regions, for the plastic collapse, local failure and ratcheting check criteria (I am making separate justifications for not running a buckling and fatigue check).
My proposed method would be to use an elastic model to sasisfy the local failure and the ratcheting check, and a limit load analysis to perform the check for plastic collapse. However, since this one is a highly optimised design with low margins I consider I will probably need to switch to elastic plastic methods for the local stress check to get this one to pass.
Any thoughts on this proposed methodology would be very welcome. Best regards, Jonathan
I am trying to qualify a pressure containing clamp (see first attached image) using Design by Analysis in accordance with ASME VIII Division 2, and I am particularly interested in how the welded regions are treated by the code with regards to joint efficiency.
According to Part 5.1.1.2(b) of ASME VIII Division 2, welds must have a geometry that is listed in Part 4 (which this geometry is not, see second attached image), or they should be assessed in accordance with Part 5, however no specific considerations are specified in the code for how to qualify the weld. My suggested method for analysing the weld would be as follows (note that only visual inspection of the welds will take place):
Using Table UW-12 of ASME VIII Division 1 I would classify the upper weld as a single-welded butt joint without the use of a backing strip, resulting in a joint efficiency factor of 0.6. The lower weld I would classify as equivalent to a double full fillet lap joint, resulting in a joint efficiency of 0.55.
I would then run the FEA, using a factored down allowable stress of 0.6S and 0.55S respectively in the weld regions, for the plastic collapse, local failure and ratcheting check criteria (I am making separate justifications for not running a buckling and fatigue check).
My proposed method would be to use an elastic model to sasisfy the local failure and the ratcheting check, and a limit load analysis to perform the check for plastic collapse. However, since this one is a highly optimised design with low margins I consider I will probably need to switch to elastic plastic methods for the local stress check to get this one to pass.
Any thoughts on this proposed methodology would be very welcome. Best regards, Jonathan





RE: ASME VIII Division 2 Design by analysis of welded joints
RE: ASME VIII Division 2 Design by analysis of welded joints
It is not permitted to modify the allowable stress basis to account for non-unity weld joint efficiency. There is no provision for this (and there will not be in the future).
Essentially, if you can't/won't do 100% examination (as described in Table 7.2) to ensure a weld joint efficiency of 1.0, then you can't do DBA.
RE: ASME VIII Division 2 Design by analysis of welded joints
Many thanks for the response. Apologies, I think I got my wires crossed a bit before, I am trying to qualify some regions of a component that fall outside the scope of Division 1, using Article U-2(g) of ASME VIII Division 1. I think I got a bit carried away in trying to qualify the whole component (including the welds) using design by analysis as well. Considering your response my suggestion for a more suitable approach would be as follows:
Use hand calculations to determine acceptability of the welded regions, while incorporating relevant welded joint efficiencies from Division 1.
Use design by analysis from Division 2 to determine acceptability in the non-welded regions of the clamp (using allowable stresses from Division 1). For the plastic collapse failure criteria I would be using limit load analysis, and I wouldn't expect failure at the welded regions. For the local failure criteria and ratcheting check I would only consider regions at a suitable distance away from the welds. As I mentioned I will not be assessing for buckling or fatigue.
I had hoped to be able to validate the whole component using design by analysis, but I see your point that due to the weld geometry and lack of volumetric inspection this would not be a reasonable approach.
Again, thank you for your answer.
Best regards, Jonathan
RE: ASME VIII Division 2 Design by analysis of welded joints
Since you're going to need to perform an elastic-plastic analysis for Local Failure, then you might as well use elastic-plastic for the Plastic Collapse, as well. I would recommend most engineers away from the Limit Load method.
And include the welds in your ratcheting check, too. The only place where the weld joint efficiency comes into the equation is in plastic collapse, anyways (reference the handling of weld joint efficiencies in API 579-1/ASME FFS-1 (2016)).
Since you're designing to VIII-1, using VIII-1 allowable stresses, make sure to use the 2017 Edition of VIII-2. Table 5.5 is now expressed in terms of beta (which is the margin against the ultimate strength).
RE: ASME VIII Division 2 Design by analysis of welded joints