The choice between a complete joint penetration (CJP) weld and a partial joint penetration (PJP) weld is an engineering decision, not a fabrication convenience. But it directly shapes what goes into your WPS, what inspection is required, and whether you need a PQR to back it up. Getting the distinction right — and documenting it correctly — is one of the more frequent pain points in QC audits for structural fab shops.
This article walks through how AWS D1.1:2025 governs CJP and PJP joint selection, the prequalified joint provisions that eliminate the need for a PQR, and the WPS documentation differences between the two.
What CJP and PJP Mean Structurally
A complete joint penetration (CJP) weld fills the entire cross-section of a groove joint between the two base metal pieces. The effective throat equals the full thickness of the thinner base metal. Under AWS D1.1:2025 Clause 2, CJP welds are treated as having 100% joint efficiency for tension across the weld plane, compression, and shear.
A partial joint penetration (PJP) weld penetrates only a specified depth into the joint. The effective throat is less than the full thickness of the thinner piece, and the connection design must account for the unfused root area. AWS D1.1:2025 Clause 2 assigns PJP welds a reduced effective throat in strength calculations, and they carry fatigue performance limits that make them unsuitable for certain load cases.
The structural engineer of record (EOR) specifies which type is required on the drawings. Fabricators don't choose — but they do need to recognize whether the joint detail on the drawing represents a CJP or PJP, because that determines the WPS requirements.
When CJP Is Required
AWS D1.1:2025 and the referenced AISC standards establish conditions that mandate CJP welds:
Tension perpendicular to the weld axis. Any groove weld in a T-joint, corner joint, or butt joint that carries tensile load oriented across the weld must be CJP. A PJP weld in this configuration has an unfused root that acts as a notch, and AWS D1.1 does not allow it in tension-loaded joints without specific engineering justification.
Cyclically loaded or fatigue-classified connections. AWS D1.1:2025 Annex B (fatigue) assigns joint categories based on weld type and geometry. CJP welds in categories B through E achieve better fatigue performance than PJP welds. If the contract specifies AISC 360 fatigue design or the structure is subject to cyclic loading, the joint type is prescribed, not discretionary.
Seismic moment connections. AISC 341 for seismic structural systems (and AISC 358 for prequalified connections) require CJP welds in the beam-to-column moment connection flanges. The documented history of PJP weld failures in the 1994 Northridge earthquake is the reason these requirements exist. A shop working on a seismic lateral force-resisting system needs CJP WPSs for these joints.
For shops dealing with seismic requirements, see AISC 341 seismic provisions: WPS and PQR requirements.
When PJP Is Acceptable
PJP welds are structurally appropriate and code-compliant in a wide range of situations:
- Column splices loaded in compression
- Fillet-weld-equivalent applications where joint efficiency is designed based on effective throat
- Web plate-to-flange connections in built-up members where the load path is primarily shear
- T-joints in compression-only members
PJP welds are common in heavy column splices, base plate connections, and built-up girder webs. They're also specified when the full CJP isn't structurally necessary but a fillet weld would require excessive size to achieve the required strength.
Prequalified Joint Details: Eliminating the PQR
AWS D1.1:2025 allows fabricators to use prequalified joint configurations without a PQR, provided all prequalification conditions are met. This is one of the most significant productivity advantages the code offers.
Prequalified CJP joint details are found in AWS D1.1:2025 Annex A (tables of prequalified joint configurations by welding process, position, and base metal thickness). These cover double-bevel groove welds, single-bevel groove welds, V-groove and U-groove profiles with specified root opening and groove angle tolerances. If your shop's joint geometry matches a prequalified detail and you're using an approved base metal and filler metal combination, no PQR is required.
Prequalified PJP joint details follow similar provisions. The key documentation requirement for PJP is the specified effective throat — the depth of groove preparation required to achieve the design effective throat. AWS D1.1:2025 specifies a deduction from the nominal groove depth to the effective throat based on the included angle of the groove (typically 1/8 in for angles ≥60° and larger deductions for flatter angles).
The WPS for a PJP weld must document:
- The groove type (bevel, V, J, U)
- The specified groove depth (S) and the effective throat (E)
- Root opening and root face dimensions
- Whether backing is used
Omitting the effective throat from a PJP WPS is a documentation deficiency — the inspector cannot verify that the joint meets the design requirement without it.
Rule library based on AWS D1.1:2025; verify against your governing edition (the AHJ or contract may specify 2020 or earlier).
WPS Documentation: CJP vs PJP Differences
The WPS parameters — amperage, voltage, travel speed, preheat — are the same whether you're running a CJP or PJP weld. The documentation differences are in the joint geometry section:
CJP WPS joint geometry:
- Joint type (butt, T, corner)
- Groove type and dimensions per the prequalified or qualified detail
- Backing bar specification (if used) or "back-gouge required"
- No effective throat statement needed — by definition, effective throat = material thickness
PJP WPS joint geometry:
- All of the above
- Specified groove depth (S) — how deep the groove is cut
- Effective throat (E) — the design throat, which equals S minus the deduction for groove angle
- Explicit statement that the joint is PJP
A common error is writing a PJP WPS that only documents the groove depth without the effective throat. The effective throat is the structural value; the groove depth is the fabrication instruction that achieves it.
For more on WPS documentation standards, see WPS essential variables vs. nonessential variables under AWS D1.1 and WPS template vs. Annex M form requirements.
Inspection Requirements: What Changes Between CJP and PJP
CJP welds in tension-loaded connections are subject to mandatory ultrasonic testing (UT) under AWS D1.1:2025 Clause 9.25 for materials 5/16 in and thicker. This is not an owner option — it is a code minimum for statically loaded structures. For dynamically loaded structures, UT is required for all CJP welds regardless of thickness.
PJP welds do not typically require volumetric NDE (UT or RT) under the code minimum, because the unfused root is an accepted design feature, not a discontinuity. Visual inspection per AWS D1.1:2025 Clause 9.23 applies to all welds, including PJP.
This inspection difference has cost implications for bidding. A joint redesigned from CJP to PJP — with EOR approval — eliminates UT requirements and can meaningfully reduce inspection costs on large structural packages. Conversely, a CJP specified where a PJP was designed in can drive unexpected NDE costs on a fixed-price contract.
The Audit-Ready Joint File
For AISC-certified shops, the quality control system must demonstrate traceability between the engineering drawings, the WPS, and the actual joint profile. Best practice for both joint types:
- Drawing reference on the WPS — note which drawing detail (or AWS prequalified joint designation) the WPS covers
- Fit-up inspection records — document that the joint dimensions matched the WPS before welding
- Effective throat verification — for PJP welds, the CWI should confirm the groove depth was achieved before welding resumes after fit-up inspection
A CJP weld with inadequate root penetration is not a PJP weld — it's a defective CJP weld. The NDE requirement doesn't change just because the root area is unfused. Getting joint designation, documentation, and inspection aligned prevents the rework and nonconformance reports that slow down final inspection.
For a complete pre-delivery checklist covering WPS submittals, NDE records, and joint documentation, see WPS submittal package and EOR review checklist. If you're building or updating a WPS library that covers both CJP and PJP joint types, the WPS generator at wpswelding.com structures the joint geometry fields to match AWS D1.1:2025 documentation requirements.