What is z-loss in a PJP groove weld?

Z-loss is the 1/8 in. (3 mm) reduction applied to the effective weld size of a PJP groove weld when the included groove angle is less than 60°. AWS D1.1:2025 requires this deduction because narrow-angle grooves don't allow consistent root fusion in production conditions. The effective weld size is the depth of chamfer minus 1/8 in., not the full groove depth.

When does a PJP groove weld NOT get the z-loss deduction?

When the included groove angle is 60° or greater, the effective weld size equals the full depth of chamfer with no deduction. At 60° and above, the groove geometry allows reliable root fusion, so the code does not reduce the claimed penetration depth.

If a design requires 3/4 in. effective throat on a 45° bevel PJP, how deep must the groove be cut?

7/8 in. deep. With a 45° groove angle (below 60°), z-loss applies: effective weld size = groove depth minus 1/8 in. To achieve 3/4 in. effective throat, the groove must be 3/4 + 1/8 = 7/8 in. deep. A 3/4 in. deep 45° bevel only delivers 5/8 in. of effective weld size — a common design and fabrication error.

How does a CWI verify effective throat on a completed PJP groove weld?

A CWI cannot directly measure effective throat on a completed weld without a macro cross-section specimen. The inspector relies on pre-weld measurement of groove depth (weld gauge depth probe) and groove angle (bevel protractor) to confirm the joint preparation matches the WPS. This is why pre-weld inspection is the critical hold point for PJP groove welds.

Jun 13, 20267 min read

PJP groove weld effective throat: AWS D1.1 z-loss rule

Partial joint penetration groove welds below 60° lose effective throat to z-loss. AWS D1.1:2025 rules for effective weld size and what they mean for WPS coverage.

AWS D1.1 WPS PJP Groove Welds CWI Inspection Structural Steel

New to procedures? Start with WPS welding: what a welding procedure specification is, with a filled-in example.

A partial joint penetration (PJP) groove weld is designed to deliver a specific weld strength without fusing through the full joint thickness. The throat dimension that controls that strength — the "effective weld size" in AWS D1.1 terminology — is not simply the depth of the groove. For groove angles below 60°, AWS D1.1:2025 applies a mandatory reduction known in practice as "z-loss." Getting this distinction right matters at three points: structural design, WPS preparation, and CWI inspection.

PJP groove welds and why groove depth isn't the whole story

When a structural engineer sizes a PJP groove weld, they compute a required effective throat — the minimum dimension through the weld throat that carries the design load. The design is based on this effective dimension, not on the physical depth of the groove preparation.

For a CJP groove weld, the effective throat equals the base metal thickness (full fusion). For a PJP groove weld, the effective throat is the depth of reliable fusion, which depends on the groove geometry. The deeper and wider the groove, the easier it is for the welder to fuse to the root. Below a critical groove angle, full root fusion becomes unreliable in production conditions, and the code accounts for that with a formal deduction.

The z-loss rule: how AWS D1.1:2025 treats narrow-groove PJPs

AWS D1.1:2025 establishes two cases for PJP groove weld effective weld size based on the included groove angle:

Groove angle 60° or greater: Effective weld size equals the depth of chamfer. No deduction. At 60° and above, the groove opening is wide enough for the welder to reliably reach and fuse the root of the joint, so the full groove depth counts toward weld strength.

Groove angle less than 60°: Effective weld size equals the depth of chamfer minus 1/8 in. (3 mm). This is the z-loss deduction. The narrower groove restricts electrode access and puddle manipulation at the root. Even a skilled welder cannot guarantee consistent root fusion at the tip of a sharp bevel, so the code deducts 3 mm from the claimed penetration.

The practical arithmetic: a 3/4 in. deep 45° single-bevel groove produces an effective weld size of 5/8 in. (3/4 minus 1/8). A 3/4 in. deep 60° double-bevel V-groove produces an effective weld size of 3/4 in. (no deduction). If the design requires 3/4 in. of effective throat, these two geometries are not interchangeable.

The z-loss deduction is a geometric correction, not a design safety factor. It's the code's acknowledgment that the "full depth" model breaks down for narrow-angle grooves in production. It does not change the allowable stress on the effective throat — it changes how the effective throat is calculated.

What this means for fabrication drawings and WPS preparation

A common coordination error between design and fabrication: the structural engineer specifies effective weld size on the design drawing (as is correct), but the fabrication shop preps the groove to match the effective weld size dimension without adding back the z-loss.

A design note reading "3/4 in. PJP" on a 45° bevel joint is interpreted by the shop as "cut to 3/4 in. depth." The actual effective weld size delivered is 5/8 in. — a 17% shortfall from the design requirement. This error is invisible after welding is complete because you can't see the groove depth in the finished weld.

The WPS for a PJP groove weld must specify both the groove angle and the groove depth — not just the effective weld size. The WPS is the production instruction; it must tell the welder and the CWI what to actually cut. A WPS that says "effective weld size: 3/4 in., groove angle: 45°" should also state "groove depth: 7/8 in." to make the z-loss math explicit and auditable.

When a prequalified PJP joint is used, AWS D1.1:2025 prequalified joint tables list both the groove preparation geometry and the resulting effective weld size, so the z-loss arithmetic is embedded in the table. The shop reads both values directly. Problems arise when a shop designs a custom groove angle that departs from the prequalified details, or when the detailer writes a joint note without checking whether z-loss applies.

For an overview of the prequalified joint detail framework and which groove configurations are available, see prequalified WPS joint design and Clause 5 geometries.

WPS coverage and essential variables for PJP joints

The WPS must qualify the joint type (PJP groove vs. fillet vs. CJP), the position, and the process for the specific production application. Essential variable changes that affect PJP groove weld coverage include:

Change in groove angle. Moving from a 60° V-groove (no z-loss) to a 45° bevel (z-loss applies) changes the effective weld size even if the groove depth stays the same. This is a change in joint geometry that must be evaluated against what the WPS and supporting PQR actually qualified. If the PQR was run at 60° and the production detail calls for 45°, the effective weld size delivered is different.

Change in base metal thickness. PJP groove weld qualification by test (when prequalified joints aren't used) has thickness qualification ranges that limit how much thinner or thicker the production base metal can be from the PQR test plate. The AWS D1.1:2025 qualification range for thickness applies to the base metal, not the groove depth.

Change in welding position. A PQR run in the flat position (1G) has limited coverage of other positions. Vertical (3G) and overhead (4G) PJP groove welds require separate qualification if the process is not prequalified for those positions. For the full table of position qualification limits, see welding position qualification limits in AWS D1.1.

CJP vs. PJP: choosing the right joint type

The decision between CJP and PJP affects design strength, WPS requirements, inspection, and cost. PJP welds use less weld metal and generate less heat input than CJP welds of the same joint thickness. They're appropriate for compression-loaded column splices, non-moment beam-to-column shear connections, column baseplate welds, and many fillet-loaded connections where the full joint cross-section strength isn't needed.

CJP welds require full-depth fusion and typically more procedure qualification rigor — the PQR must be run on plate thick enough to support the production thickness range, and many CJP applications require ultrasonic or radiographic testing of completed welds. For CJP groove welds, there's no z-loss — the effective weld size equals the base metal thickness and the full weld must be sound.

The tradeoff: PJP welds are cheaper to deposit but require careful geometric control — a 1/8 in. error in groove depth, on a 45° bevel, means the joint is undersized by 1/8 in. of effective throat. CJP welds are more expensive but offer less sensitivity to groove geometry because the requirement is simply "full penetration."

For a comparison of how these joint types are treated in WPS and procedure qualification, see CJP vs. PJP groove weld selection and WPS.

Inspector verification in production

The CWI's primary hold point for PJP groove welds is pre-weld measurement of groove geometry — before the root pass is deposited. Once welding begins, the groove is no longer accessible. A completed weld over an undersized groove cannot be corrected without removing the weld and re-prepping.

Tools used for pre-weld groove inspection:

Depth gauge probe (weld gauge set): verifies groove depth against the WPS-specified value
Bevel protractor or groove angle gauge: verifies included angle determines whether z-loss applies
Root opening gauge: verifies the gap at the root matches WPS specification

The CWI records these pre-weld measurements in the inspection log for the joint. This documentation is the chain of custody that demonstrates the joint was prepared correctly before welding — it's the only field-verifiable evidence that the specified effective weld size was achievable.

After welding, the CWI performs visual inspection per AWS D1.1:2025 criteria for weld face condition, undercut, overlap, and weld size. But the effective throat cannot be confirmed by post-weld visual inspection alone. The pre-weld measurement record is what makes the completed weld defensible.

If NDE is specified (MT for surface cracks, UT for internal discontinuities), the NDE inspection covers the completed weld volume. For UT on PJP groove welds, the inspection technician needs to know the effective weld size to calibrate the reference for the expected sound path. The WPS and inspection plan should document the effective weld size, not just the groove depth.

The documentation chain for PJP groove welds

A complete set of documentation for a PJP groove weld should trace the connection from design to production:

Design drawing: Effective weld size specified (e.g., "3/4 in. PJP")
Fabrication detail: Groove angle and groove depth specified (e.g., "45° bevel, 7/8 in. depth")
WPS: Groove angle, groove depth, effective weld size, process, position, and preheat all documented
Inspection record: Pre-weld groove measurements confirming depth and angle match WPS

If any link in this chain is absent, the argument that the completed joint meets the design effective weld size is harder to make — and in an AHJ review or engineer of record audit, "harder to make" becomes "not supportable."

Managing this documentation chain across dozens of joint types in a complex structural fabrication project is where manual spreadsheets and paper forms create the most risk. A purpose-built welding procedure tool generates the WPS with the correct effective weld size documented and links it to the joint inspection record automatically. See how it compares to manual WPS preparation.

Rule library based on AWS D1.1:2025; verify against your governing edition — the AHJ or contract may specify 2020 or earlier.

FAQ

Frequently asked.

What is z-loss in a PJP groove weld?: Z-loss is the 1/8 in. (3 mm) reduction applied to the effective weld size of a PJP groove weld when the included groove angle is less than 60°. AWS D1.1:2025 requires this deduction because narrow-angle grooves don't allow consistent root fusion in production conditions. The effective weld size is the depth of chamfer minus 1/8 in., not the full groove depth.
When does a PJP groove weld NOT get the z-loss deduction?: When the included groove angle is 60° or greater, the effective weld size equals the full depth of chamfer with no deduction. At 60° and above, the groove geometry allows reliable root fusion, so the code does not reduce the claimed penetration depth.
If a design requires 3/4 in. effective throat on a 45° bevel PJP, how deep must the groove be cut?: 7/8 in. deep. With a 45° groove angle (below 60°), z-loss applies: effective weld size = groove depth minus 1/8 in. To achieve 3/4 in. effective throat, the groove must be 3/4 + 1/8 = 7/8 in. deep. A 3/4 in. deep 45° bevel only delivers 5/8 in. of effective weld size — a common design and fabrication error.
How does a CWI verify effective throat on a completed PJP groove weld?: A CWI cannot directly measure effective throat on a completed weld without a macro cross-section specimen. The inspector relies on pre-weld measurement of groove depth (weld gauge depth probe) and groove angle (bevel protractor) to confirm the joint preparation matches the WPS. This is why pre-weld inspection is the critical hold point for PJP groove welds.