What does 'TC' mean in an AWS D1.1 prequalified joint designation?

TC stands for T-, Y-, and K-connections (tubular or intersecting member connections). Similarly, B is for butt joints, C is for corner joints, and T is for T-joints in non-tubular applications.

What does the 'S' suffix mean in a joint designation like TC-L1.1-S?

The 'S' suffix means the joint uses steel backing. A 'GF' suffix means the joint has been back-gouged and back-welded flush, removing the original backing. No suffix indicates a standard configuration.

What does the number in a designation like B-U2a refer to?

The number indicates the joint configuration detail number within that category. Lower numbers are generally more basic joint geometries; letters like 'a' denote subvariants. The number ties to a specific figure in AWS D1.1 Annex B.

Can I use a prequalified joint with different dimensions than shown in Annex B?

No. Prequalified status requires using the groove geometry and dimensional ranges shown in Annex B. Changing the groove angle, root opening, or root face beyond the table limits removes prequalified status and requires a PQR.

Reading AWS D1.1 Prequalified Joint Designations: TC-L1.1-S Explained

AWS D1.1 prequalified joint designations look like alphabet soup — TC-L1.1-S, B-U2a-GF — but each character carries specific meaning. Here's the decoder ring every CWI needs.

If you have ever scanned through AWS D1.1 Annex B looking for the right prequalified joint for a connection, you have encountered designations like B-U2a-S, TC-L1.1-GF, and C-U4a. To someone who knows the system, these strings communicate the complete geometry of a qualified joint configuration. To someone who does not, they look like random characters.

This matters practically. When a CWI reviewing shop drawings sees a WPS that calls out TC-L1.1-S, they should be able to confirm immediately whether the joint detail on the drawing matches the prequalified geometry — without flipping through a dozen pages. Understanding the designation system is a basic competency for anyone writing or approving WPSs under AWS D1.1:2025.

The Four-Part Structure

Every AWS D1.1 prequalified joint designation follows this pattern:

[Joint Type]-[Weld Type][Configuration Number][Subvariant]-[Suffix]

Breaking each part down:

Part 1: Joint Type

The first letter group identifies the structural joint geometry:

B — Butt joint (plates edge to edge, or plate-to-plate in the same plane)
C — Corner joint (two plates meeting at approximately 90°, forming an outside corner)
T — T-joint (one plate (web) meeting another plate (flange) at approximately 90°, joining the edge to the surface)
TC — T-, Y-, and K-connections in tubular and HSS members (the intersecting member designation for circular and rectangular hollow sections and similar geometries)

A fabricator making a standard wide-flange beam-to-column moment connection with a CJP groove on the beam flange is working with a T or B joint. A fab shop welding diagonal HSS bracing members to a chord member at 45° is working with a TC joint.

Part 2: Weld Type

The next letter indicates whether the weld is complete or partial penetration, and whether it is a groove or fillet weld:

U — Complete joint penetration (CJP) groove weld (U as in "unlimited" or "complete")
L — Partial joint penetration (PJP) groove weld (L as in "limited" penetration)
F — Fillet weld (for configurations where the prequalified joint uses a fillet rather than a groove)

So B-U means a butt joint with a CJP groove weld. TC-L means a T-, Y-, or K-connection with a PJP groove weld. This single letter tells the reviewer whether full penetration is expected, which drives inspection method selection (CJP often requires UT or RT; PJP may require only VT and MT/PT per the contract documents).

Part 3: Configuration Number and Subvariant

The number identifies the specific groove geometry within that weld-type category. AWS D1.1 Annex B lists these in order within each category, and the number is tied to a specific figure showing the groove angle, root opening, root face, and joint geometry.

B-U2 — butt joint, CJP groove weld, detail configuration 2 (a specific groove geometry from Annex B)
B-U2a — same joint, subvariant "a" (a minor geometric variation, often a different bevel angle or a flipped configuration)
TC-L1.1 — T/Y/K-connection, PJP groove weld, configuration 1, first variant

Subvariants (lowercase letters after the number) typically represent variations in which side the bevel is on, the groove angle range, or whether the configuration is for one-sided or two-sided welding. If the dimensions on the drawing do not fall within the range shown in the specific Annex B figure for that subvariant, the joint is not prequalified.

Part 4: Suffix

The suffix provides additional information about weld backing or completion method:

No suffix — standard configuration, typically open root or with ceramic backing that is removed
-S — steel backing remains in place permanently (common in column splice and beam-column connections where removal is impractical)
-GF — back-gouged to sound metal and back-welded flush; the original steel backing (or root pass) is removed by air-carbon arc gouging, then filled and ground flush

The -S suffix is among the most important to recognize. A CJP groove weld with permanent steel backing (-S) has different ultrasonic testing requirements than one that has been back-gouged and back-welded (-GF). The interface between the backing bar and the base metal creates a reflector that UT scanning must account for. Some project specifications prohibit permanent steel backing in demand-critical welds (seismic applications) for this reason.

Worked Examples

B-U2a-S — Butt joint, CJP groove weld, configuration 2 subvariant a, permanent steel backing. This is a very common designation for beam splice and column splice flange CJP welds. The joint is welded from one side, and the steel backing bar remains.

TC-L1.1-GF — T-, Y-, K-connection, PJP groove weld, configuration 1.1, back-gouged and back-welded flush. Used for HSS brace-to-gusset connections when the root condition must be verified and finished.

T-U4a — T-joint, CJP groove weld, configuration 4 subvariant a. Common for web-to-flange CJP groove welds on fabricated plate girders or built-up columns. No suffix means no steel backing in the standard configuration.

C-U4a-GF — Corner joint, CJP groove weld, configuration 4 subvariant a, back-gouged and back-welded flush. Typical for exterior column cover plate or box column corner joints.

What Prequalified Status Actually Means

A prequalified joint designation means that AWS has determined the joint geometry, when executed according to the WPS requirements in AWS D1.1 Clause 4, does not require a PQR test to demonstrate soundness — provided:

The groove dimensions fall within the ranges shown in Annex B for that designation
The base metals are from the prequalified base metal list (AWS D1.1:2025 Table 4.5 or a qualified combination)
The filler metals meet the prequalified requirements for the process
The WPS addresses all required parameters, including preheat per the applicable table

Changing any of these elements — say, increasing the root opening beyond the Annex B range, or using a base metal not on the prequalified list — removes prequalified status. The shop must then qualify the joint by test (PQR), use a tested WPS covering the modified geometry, or restore the design to a qualifying geometry.

Reading Drawings Against the WPS

A CWI reviewing shop drawings should check that the joint detail shown on the drawing matches the designation on the WPS. Mismatches are common and represent a real non-conformance:

A drawing showing a TC-L1.1-S but dimensions that match a TC-L2.1 configuration
A WPS calling for B-U2a (no suffix) where the drawing shows permanent backing bar (which would require -S)
A joint labeled as CJP (U) that has a design throat less than full penetration (which should be L — PJP)

When in doubt, go back to Annex B. The figures there are the authoritative source. If the detail on the drawing cannot be matched to an Annex B figure within the dimensional tolerances shown, the joint is not prequalified — and someone has homework to do before production starts.

Fluency with the AWS D1.1 prequalified joint designation system is the difference between a WPS package that holds up under audit and one that fails on first review. CWIs who know the system can spot non-compliances in seconds. Those who do not will spend hours hunting for problems they cannot name.

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

For related content, see Prequalified CJP vs PJP Groove Weld Selection and J-Groove and U-Groove Prequalified Joint Design. Generate a compliant prequalified WPS in minutes at wpswelding.com/pricing.