UG-41(b) says I can use the minimum of W, W11, W22, and W33 in evaluating nozzle weld strengths. In the case of Fig. UG-41.1(b), if if A1>A then W<0. Does this mean ANY nozzle attachment weld strength is acceptable, as long as the weld meets UW-16 requirements?
Yes, indeed.
That code rule is intended at verifying that all the material added for reinforcement outside vessel wall is effectively connected to vessel wall, so that it will perform its function.
But, when A[sub]1[/sub]>A, there is no need of any more reinforcement outside vessel wall, so no need to check that such non existent reinforcement is correctly attached.