Depth of fusion is always relevant. I don’t have this standard in front of me to be specific on the wording but I read it to mean that the weld side should be 90% in size as related to the thickness of the base materials its being welded to. I also believe there talking about (depth of fusion) the throat dimension, which is .707” in size measured against the leg, assuming we are talking about equal length fillet welds.

BamaDave

simons, I think you might be beating yourself up on technicalities that it does not address within the statement "The joint penetration shall extend to the joint root". I am not familiar with AWS D8.8-97, but it seems the statement is in a section regarding weld sizes. I'm sure there is a section in the code regarding inspction acceptance criteria. The inspection section should discuss the "fusion" requirements. As I have seen in my experience dealing with different codes, you have to look at different sections to find an answer to a question you have. The statement you have deals only with weld size and penetration requirements. They are trying to convey that they want the weld size as stated, and they also want to make sure that it is penetrating into the joint. Fusion is irrelevant in this statement. But, as I said, look in the "inspection section and it may mention something about aceeptance criteria for visual inspection. Here should lie you answer to you fusion question. If it says something about "welds shall have complete fusion", or something close, there is your answer. The whole weld, toes, legs, roots would require complete fusion. Hope this helps. And, like I said, look around in the code. All over the code, as it may not be in the "inspection" section.