Reference
AWS D1.1 Table 6.1 Visual Inspection Criteria:
Cracks: None permitted (all loading)
Porosity (static): max dia = lesser of weld_size/4 or 3/16"
Porosity (cyclic): max dia = lesser of weld_size/4 or 3/32"
Underfill (static): max 1/32"
Underfill (cyclic): max 1/64"