What does the B-U2 / B-L1 / TC-U4a code on a WPS mean?

Each is an AWS D1.1 Annex B joint identifier. The letters indicate the joint type (Butt, T-joint, Corner) and conditions (Single-V, Backing, Backgouging, etc.). The number is a specific configuration. Together they identify a unique prequalified geometry.

Can I use a custom joint detail?

Yes, but a custom joint disqualifies the WPS from Clause 5 prequalified status. You must qualify the procedure by test with a supporting PQR. The PQR test coupon must use the custom geometry.

What's the difference between PJP and CJP joints?

CJP = Complete Joint Penetration. The weld penetrates the full thickness of the joined parts and is stronger than the base metal. PJP = Partial Joint Penetration. The weld penetrates only a portion of the thickness; design strength is reduced accordingly. AWS D1.1 lists prequalified geometries for both.

Joint design: prequalified geometries from AWS D1.1 Annex B

AWS D1.1 Annex B is the catalog of prequalified joint details. Use what's in Annex B and your WPS stays prequalified. Use something else, and you qualify by test.

AWS D1.1 Annex B catalogs prequalified joint geometries — V-grooves, U-grooves, J-grooves, fillets, double-Vs — that the technical committee has determined produce reliable welds when made within Clause 5 parameter limits. Use what's in Annex B and your WPS stays prequalified. Stray from Annex B and you qualify the procedure by test.

The Annex B naming convention

Joint identifiers in Annex B have a consistent format:

First letter: B (Butt joint), T (T-joint), C (Corner joint), TC (T or Corner)
Suffix letters: P (Partial penetration), L (Limited thickness), U (Unlimited thickness)
Number: specific configuration

Common ones:

B-U2 — Butt joint, Unlimited thickness, configuration 2 — single-V groove with backing
B-U3 — Butt joint with double-V groove without backing
B-U4 — Butt joint with double-V groove and backgouging
B-L1 — Butt joint with single-V groove and backgouging (limited thickness)
B-P2 — Butt joint with partial penetration single-V groove
TC-U4a — T-joint or Corner joint, Unlimited thickness, double-bevel groove
TC-P4 — T-joint or Corner joint with partial-penetration double-bevel

Fillet welds use a separate convention (single-fillet, double-fillet, all-around).

CJP vs PJP

Complete Joint Penetration (CJP) geometries — B-U2, B-U4, etc. — produce a weld that crosses the full thickness of the joined parts. Design strength of the joint equals the base metal strength. Most structural moment connections are CJP.

Partial Joint Penetration (PJP) geometries — B-P2, TC-P4, etc. — produce a weld that crosses only part of the thickness. Design strength is reduced; the structural engineer accounts for the actual throat. PJP is faster and cheaper, used where reduced strength is acceptable.

The WPS must clearly state CJP or PJP. Audit findings often include CJP claimed in the structural drawings but a PJP joint detail listed on the WPS.

Parameters that travel with the joint detail

When you cite a joint from Annex B, certain dimensions are fixed:

Groove angle (typically 60° or 45°)
Root opening (typically 1/4 in, 3/16 in, or 1/8 in)
Root face (varies by joint type)
Backing material and thickness (when used)
Backgouging requirement (some geometries require it)

A WPS that cites B-U4 but lists a root opening of 1/2 in is internally inconsistent — B-U4 specifies a smaller root opening.

Backing material

Several Annex B joints (B-U2, BTC-P10, etc.) require steel backing. The backing:

Must be the same Group as the base metal (or specifically permitted alternate)
Must be tack-welded into place before main welding
Cannot be removed after welding (unless specifically permitted by drawing)
Cannot serve as the design strength path — it's a fixture for the welder, not a structural element

Some applications allow ceramic or copper backing. The WPS must specify which.

Backgouging

Several geometries (B-L1, B-U4) require backgouging:

After welding from the first side, the back side is gouged out (typically with air carbon arc gouging)
The exposed root pass is inspected for soundness
The opposite side is then welded over the cleaned-out back

The WPS must specify the backgouging method, the inspection step, and the welder qualification for backgouging (typically a non-destructive examination certification).

When to leave Annex B

Three cases:

You're welding to ASME, not AWS. ASME Section IX has its own joint catalog with different identifiers.
The drawings show a custom geometry that's not in Annex B. You must qualify the procedure by test.
You're using a process not in the prequalified list (e.g., GTAW). The procedure must be qualified regardless of joint detail.

In all three cases, the WPS cites the joint detail with a sketch and explicitly states the prequalified path is not used.

Common joint-detail findings

Joint sketch missing. Auditor wants to see the geometry.
Sketch shows different dimensions than the cited Annex B detail. Inconsistency.
CJP claimed in drawings but PJP geometry on the WPS. Drawing vs WPS mismatch.
Backing material spec missing. "Steel backing" alone is incomplete — list the spec.
Backgouging not addressed for a geometry that requires it.

A rule engine that knows Annex B configurations can cross-check the WPS's claimed joint detail against the listed dimensions automatically.