Most of the time the joint in question will be a single bevel groove weld with backing. Instead of welding through the weld access hole, which would then require the welders to be qualified per the supplement, you put the backing bar under the joint from the access hole side of the joint (requires the web to be ground down really smooth thru the center so the backing bar fits good and snug and flat). Then, you weld one side from the downhand/flat position, roll the member, and weld the other side from the downhand/flat position. Neither is welded throught the access hole so even if it is a Demand Critical weld and one is the bottom flange it does not fall into the all three category. Also makes it easier to UT after welding as both can be done from the outside of the flange with the backing bar on the inside.
Single bevel groove welds without backing are prohibited, unless welded from both sides which brings us back to the weld access hole and the supplemental qualification.
2.17 Prohibited Joints and Welds
2.17.1 One-Sided Groove Welds. Groove welds, made
from one side only without backing or made with backing,
other than steel, that has not been qualified in conformance
with Section 4 shall be prohibited except that
these prohibitions for groove welds made from one side
shall not apply to the following:
(1) Secondary or nonstress carrying members.
(2) Comer joints parallel to the direction of calculated
stress between components of built-up members
Have a Great Day, Brent