Decoding AWS Welding Symbols, CJP, and PJP Weld Joints on Shop Drawings for Fabricators

Misinterpreting welding instructions on shop drawings is a primary cause of structural joint failure and costly shop rework. Detailers must strictly adhere to American Welding Society (AWS) standards when conveying joint requirements. Complete Joint Penetration (CJP) vs. Partial Joint Penetration (PJP):

CJP Welds

Require the weld metal to extend completely through the thickness of the joint material, achieving 100% strength transfer. Used for high-stress structural connections.

PJP Welds

Extend into the joint depth without fully penetrating the full material thickness. Applied where joint stresses do not demand full-section strength.

AWS Weld Symbols Interpretation

Shop drawings must clearly convey the weld type (fillet, groove, plug, slot, spot, or seam), weld size, effective throat thickness, bevel angle, root opening, and field weld indicators.

Quality & NDT Specifications

For critical connections, annotations must specify post-weld heat treatment, non-destructive testing (NDT) requirements, and inspection protocols.

 [Weld Size] / [Pitch]
 \ /
 Tail ----<======= Reference Line =======> Arrowhead -> (Points to Joint)
 / \
 [Type Symbol] [Contour/Finish]

Field Welds vs. Shop Welds on Drawings

The field-weld flag — a small triangular pennant at the bend in the weld symbol's reference line — is one of the most consequential marks on a shop drawing and one of the easiest to misplace. A weld shown without the flag is assumed to happen in the controlled environment of the shop; a weld that actually needs to happen on site, after erection, must carry the flag or the fabricator will complete it (or worse, the erector will assume it was already done) before the members are ever in position.

The weld-all-around symbol — a small circle at the bend point — carries similar weight: it tells the welder the joint continues around the full perimeter of the connection rather than stopping at the near side, which matters enormously on tube and HSS connections where the far side of the joint isn't visible from the welder's standing position.

Common Weld Symbol Reading Mistakes

The single most frequent misread is arrow-side versus other-side: a weld symbol placed below the reference line applies to the side of the joint the arrow points to, while a symbol above the line applies to the opposite side — reversing the two puts the weld on the wrong face of the joint entirely. The second most common miss is a fillet weld symbol shown without a size dimension, which under AWS convention should never be released for production; the detailer's own checklist should flag any weld symbol missing its leg-size callout before the drawing goes out.

When to Specify CJP vs. PJP for a Given Joint

The choice between complete joint penetration and partial joint penetration isn't primarily a drafting decision — it's driven by the connection's structural demand, and the detailer's job is translating that engineering requirement into a symbol the welder can execute correctly. CJP is typically specified where the joint has to develop the full strength of the connected members, such as many moment-connection flange welds; PJP is appropriate where the joint only needs to carry a defined, lower load and full penetration would be an unnecessary cost and distortion risk. Detailing a PJP joint as CJP "to be safe" isn't actually safer — it adds welding time, heat input, and distortion risk without a corresponding benefit, which is exactly why the connection design, not drafting convention, should drive the choice.