If you're referring to fillet welds made with 70 series electrodes, the maximum allowable stress on the weld would obviously depend on the weld size, and can be calculated using a .928 multiplier. For example, to calculate the maximum stress for a 3/16 fillet weld, multiply 3 x .928, which equals 2.784 kips per inch. So, a 3/16 fillet is good for 2,784# per inch. If the weld is 8" long, the weld is good for 22.272 kips, or 22,272#. A 1/4 fillet is good for 3.712 kips per inch (4 x .928), a 5/16 fillet is good for 4.64 kips per inch (5 x .928), and so on. To answer part of your question, I don't think the method of inspection would change that. The weld may be subjected to tension, compression, bending, shear, or torsion forces, which would also factor in determining the allowable stresses on the welds, and would help determine the fillet size, or whether partial or complete penetration welds would be required to support the design criteria.
Thanks. I know the 'allowable' rule of thumb calculation and the variables that relate to loading. The question is does the allowable increase when one verifies the integrity of the weld by x ray inspection? It makes sense to limit the allowable for uninspected welds and to increase it for inspected welds. I'm trying to verify the inclusion (or exclusion) of this common sense in the code.
I guess I'm missing something. Why would it need to? Why would there be a need or concern for the possibility of an allowable increase when a weld is x-rayed as opposed to a visual? Why even consider limiting the allowable stress for uninspected welds as opposed to increasing it for inspected welds, when by code, all welds are supposed to be inspected? The engineer or detailer has supposedly already calculated the weld strength and size, and if the joint is welded properly, it will perform as designed. So, why would there be a concern or need to look into the possibility of making a visually inspected joint stronger by more stringent testing? If the engineer has concerns about the integrity of the weld, he may choose to specify a method of testing.
If, by verifying that the weld is without defect, its allowable stress is greater, then one can design with less weld metal which equals money in the pocket. And surely you do not suggest that all welds are x-ray inspected. Calculations of weld strength use only a fraction of the strength of the metal. Steels is shear yield at 57% of their tensile strength, commonly. The allowable is much less then that by code standards because of the vagaries of welding processes. And one is not 'making the joint stronger' so much as verifying its integrity and permitting a higher stress level to be employed.
Scott; I'm interested in where the .928 multiplier comes from? Are there other multipliers for different fillers, for example stainless materials?
After 30+ years in this industry all I truly realize is how little I actually know! lol!!! What a great field we share!
In my opinion, Mr. Brotzman's question is answered by ASME Code Section VIII, at least as pressure vessels are concerned.
Section VIII states that when the weld has been fully radiographed the Joint Coefficient is 1 (one), i.e., the weld is as strong as the base metal.
When the weld has been spot radiographed the Joint Coefficient is 0.85, i.e., the strength of the weld is 85% of that of the base metal; and when the weld has not been radiographed the Joint Coefficient is 0.7, i.e., the weld strength is 70% of that of the base metal.
I'll take a look at API 5L (Specification of Line Pipe), which I don't have on hand at this moment, and come back with the answer.
Giovanni S. Crisi
Sao Paulo - Brazil