When and how AWS D1.1:2025 allows combining a partial joint penetration groove weld with a fillet weld to achieve effective throat. WPS documentation requirements and inspection guidance for CWIs and QC managers.
Structural connections do not always need full joint penetration. A Partial Joint Penetration (PJP) groove weld achieves a controlled depth of fusion without penetrating through the full base metal thickness. When the required effective throat exceeds what a plain fillet weld can economically achieve but a full CJP groove is not needed by design, engineers often specify a PJP groove weld combined with a fillet weld on one or both faces of the joint.
This combination appears frequently on:
T-joints in heavy plate where a bevel groove on the web plate is cut to a controlled depth before the fillet weld is deposited.
Corner joints where partial bevel preparation allows a larger effective throat than a plain fillet.
Structural connections with skew angles where the joint geometry favors beveling one member but precludes full-penetration welding without elaborate fit-up controls.
Understanding how AWS D1.1:2025 treats effective throat for combined welds — and how to write a WPS and inspection plan for them — is a practical skill for CWIs and QC managers on structural steel projects.
Defining Effective Throat for Combined Welds
For a pure fillet weld, the effective throat is the perpendicular distance from the root to the theoretical weld face along the 45° throat line — equal to 0.707 times the fillet leg for an equal-leg fillet. For a PJP groove weld deposited into a beveled joint, the effective throat is the depth of groove fusion minus a reduction that depends on the groove angle: for groove angles less than 45°, a 3/16 in [5 mm] reduction from the depth of preparation is typical; for groove angles of 45° or greater, the effective throat equals the depth of preparation.
When a fillet weld is added to the face of a PJP groove weld, the effective throat of the combined weld is the distance from the theoretical weld root to the effective weld face of the combined cross-section. In most structural T-joint and corner joint geometries, the combined effective throat is greater than either the PJP groove or the fillet weld alone because the fillet leg extends the throat dimension beyond the groove face.
AWS D1.1:2025 addresses combined welds in its weld size and effective throat provisions. Designers must specify both the groove depth (or S, the size of the PJP groove) and the fillet leg size on the design drawing to fully define the required weld. The inspection records must verify both.
Rule library based on AWS D1.1:2025; verify against your governing edition.
Minimum Fillet Weld Size: Table 7.7 Still Applies
Even when a fillet weld is part of a PJP plus fillet combination, the fillet leg must still meet the minimum fillet weld size requirements in AWS D1.1:2025 Table 7.7. Table 7.7 sets a minimum fillet leg based on the thickness of the thinner of the two parts being joined, using the base metal thickness at the joint. For low-hydrogen processes (SMAW E7018-class electrodes, SAW, FCAW-G), a slightly different minimum applies than for non-low-hydrogen processes.
For a combined weld on a T-joint where the web is the thinner part, the minimum fillet leg is established by the web thickness — even though the groove preparation provides additional throat. This minimum cannot be waived simply because the groove provides adequate effective throat for the design force. The intent of Table 7.7 minimums is to prevent weld cracking in the HAZ of the thinner base metal during cooling; that concern exists regardless of effective throat adequacy.
Practical implication: when designing a combined PJP + fillet for a thin web connecting to a thick flange, confirm that the fillet leg specified on the drawing meets Table 7.7 for the web thickness.
WPS Documentation for Combined PJP Groove + Fillet
There is no separate WPS type for combined welds — the WPS must describe the welding operation that produces the full weld cross-section. For a combined PJP groove and fillet deposited in a single setup:
Joint design: The WPS should reference or describe the joint design, including the bevel angle of the groove, the root opening, and the intended depth of groove preparation. If the WPS references a prequalified joint designation from AWS D1.1:2025 Clause 5 (for the groove portion), that designation defines the groove geometry. The fillet portion is then added to the groove face.
Process and parameters: The groove portion and the fillet reinforcement portion may use the same welding process and parameters, or the shop may choose to run the groove passes with one set of parameters and the fillet passes with another. Either way, the WPS must document the applicable process, electrode, and parameter range for each portion.
Sequence of passes: The WPS should describe whether the groove is filled first and then the fillet cap deposited, or whether fillet passes and groove fill passes are interleaved. CWIs use this information to verify the correct welding sequence during production inspection.
Heat input and preheat: Document the preheat and minimum interpass temperature requirements based on the base metal chemistry and thickness, and any maximum interpass temperature limits. For combined welds on thick plate, heat input from the combined groove and fillet passes can be significant.
Joint Preparation and Fit-Up Inspection
The CWI's pre-weld inspection for a combined PJP + fillet joint focuses on:
Groove depth and angle: Measure the depth of groove preparation to verify it matches the WPS joint design. For a specified groove angle (e.g., 45° bevel), verify the angle with a weld bevel gauge. A shallower groove than specified reduces the PJP effective throat and may produce a weld that does not meet the design intent.
Root face: The root face (land) thickness must match the WPS. An excessive root face on a PJP groove — unlike a CJP groove — is not corrected by back-gouging and re-welding from the back; it simply means the fusion depth is shallower than intended.
Root opening: Many PJP groove designs have zero root opening (butted fit), especially on T-joints. Others specify a small root opening for better fusion. Verify that the fit-up matches the WPS.
Fillet leg size: After welding, measure the fillet leg with a fillet weld gauge. The as-deposited fillet leg must meet or exceed the specified size on the drawing and the Table 7.7 minimum.
CJP vs. PJP + Fillet: The Design Decision
A common question from QC managers is when to use a full CJP versus a PJP + fillet combination. The tradeoffs are well established in structural engineering:
CJP groove: Full penetration; full design tensile and shear strength; requires back-gouging or ceramic backing to achieve root fusion; inspection by UT or RT typically required for critical joints.
PJP + fillet: Partial penetration; design strength based on effective throat times weld shear strength; no back-gouge required; simpler fit-up; visual and fillet weld gauge inspection typically adequate; lower cost.
For joints subject to fatigue loading, tensile loads perpendicular to the weld axis, or seismic demand-critical classification under AWS D1.8, CJP is usually required. For joints loaded primarily in shear or compression, PJP + fillet often meets the design requirement at lower fabrication cost.
Inspection Records and Audit Compliance
Audit-ready documentation for combined PJP + fillet welds should capture:
Pre-weld inspection record: groove dimensions checked, fillet leg minimum confirmed from drawing and Table 7.7, preheat verified, WPS revision referenced.
In-process inspection record: interpass temperature measured and within limits, pass sequence matches WPS.
Post-weld inspection record: fillet leg measured (both sides if double fillet), no undercut, no cracks, weld profile meets AWS D1.1:2025 visual acceptance criteria.
How is the effective throat calculated for a PJP groove weld combined with a fillet weld?
For a combined PJP groove and fillet weld, the effective throat is the distance from the weld face to the root of the groove portion, minus any reduction required for groove angle. The fillet weld adds to the total weld throat only in the proportion that its leg extends beyond the groove opening face. AWS D1.1:2025 contains specific provisions for how combined weld sizes are measured and how effective weld throat is determined.
Does a combined PJP groove plus fillet weld require a separate WPS from a plain PJP groove weld?
If the PJP groove and fillet weld are deposited together in a single continuous weld operation, the WPS should describe both. If the fillet is deposited as a separate pass in a separately qualified WPS, each WPS covers its own operation. The key is that the total weld configuration is captured in the design and inspection records.
When does the engineer of record specify a PJP plus fillet combination instead of a pure CJP or pure fillet?
A PJP plus fillet combination is often used when full CJP penetration is not needed for the design force, but a pure fillet weld leg would be too large to achieve the required effective throat economically. T-joints and corner joints in heavy plate connections frequently use this combination when the groove angle allows partial penetration but cannot achieve full penetration without back-gouging.
What AWS D1.1:2025 table gives minimum fillet weld sizes?
AWS D1.1:2025 Table 7.7 sets minimum fillet weld sizes based on the thickness of the thinner part joined. For low-hydrogen processes (SMAW E7018, FCAW-G, SAW), different limits apply than for non-low-hydrogen processes. When a combined PJP groove and fillet is used, the fillet leg must still meet the Table 7.7 minimums based on thinner base metal thickness.