Full penetration means you have weld metal from one side of the joint to the other, i.e. you remove the backing after welding.
Full fusion means the filler metal (or in the case of no filler metal the joining metal) is completely bonded to the parent metal. Ex. soldering is not full fusion.
Hmmm. Not necessarily so. You could have a full pen weld that was not completely fused. Of course then you'd gouge it out and reweld, so in the end you're right.
I believe that you can have a full penetration weld that is not completely fused and it can still be acceptable.ASME B31.3 table 341.3.2 gives limits of allowable imperfections, therefore a full penetration weld that was not fully fused would be acceptable under limitations placed in 341.3.2 symbol C on criterion value notes gives depth and cumulative of lack fusion permissible in relevant service conditions, i am assuming of course that you are working to B31.3
Fusion in B 31.3 is defined as 'the melting together of filler metal and base metal, or of base material only which results in coalescence. If you mean full fusion to be interpretated as complete fusion then complete fusion is defined in section IX as "fusion which has occurred over entire base material surfaces intended for welding, and between ALL layers and passes.
i also take that when you say full penetration you mean full weld joint penetration, joint penetration is defined in ASME section IX as "The distance the weld metal extends from the weld face INTO a joint, exclusive of weld reinforcement"
