If you’re welds are required to meet D1.1 criteria, a prequalified CJP does not allow for the omission of weld access holes… they either require backing or backgouging (except for B-L1-S).

But... the commentary in D1.1 states that “weld access holes are not required nor even desirable for every application. However it is important to recognize that any transverse joint in the flange of wide flange, H and similar cross sections made without the use of a weld access hole cannot be considered as a prequalified CJP groove welded joint. This is true, because prequalified CJP groove welded joints are limited to the cases of plain plate elements to plain plate elements shown in Figure 3.3. The decision to use prequalified CJP joints or to use non-prequalified joints without access holes depends upon consideration of several factors which include but may not be limited to the following:

(1) The size of the members being joined.

(2) Whether the joint is a shop or field weld, that is, whether the parts may be positioned for welding so that overhead welding may be avoided and reinforcing fillets may be readily deposited at the location of peak stress concentrations.

(3) The variation in the restraint to weld shrinkage and the distribution of applied stress along the length of transverse joint due to geometry of parts being joined. For example, the high restraint due to the column web in the region of the column flange centerline as compared to lower restraint away from the centerline causes welding residual stresses and applied stresses to peak sharply in the difficult-to-weld region at the middle of beam flange.

(4) Whether, in the case of geometry that affords more uniform restraint without a “hard spot” along the length of the joint, the probability of increased number of small internal weld metal discontinuities, but without the large discontinuity of the weld access hole, might provide a higher strength joint. For example, tests of endplate moment connections (Murray 1996) have shown that joints between beam ends and end plates made without weld access holes, but with unrepaired discontinuities in the region of the web to flange junction provide higher strength than similar connections made using access holes but with fewer internal discontinuities. Research, thought and ingenuity are being directed toward improved details for welding of beam-to-column moment connections. Alternative joint design and details to provide the strength and suitability for service should be considered where they are applicable. Engineering judgment is required. When weld access holes are required, the minimum requirements of 5.16 apply. The minimum required size to provide clearances for good workmanship and sound welds may have a significant effect upon net section properties of the connected members.

With a Wide Flange beam (or I beam) there will always be a small area directly over the web where you cannot achieve full penetration without the use of weld access holes. Other structural shapes like angle and channel can be back gouged from the other side and rewelded to achieve full penetration.

That being said, there are situations (seismic) where some engineers prefer to not use a weld access hole and understand that there is an area over the web where full penetration cannot be achieved. ie Wide Flange beams with full penetration end plates at each end.