What does the tail on a weld symbol mean?

The tail is the fork at the left end of the weld symbol reference line. Per AWS A2.4, the tail is used to specify supplementary information that does not fit into the standard symbol elements — typically a WPS number, a welding process designation, a reference standard or specification, or an inspection requirement. When no tail is needed, it is omitted from the symbol.

Is the tail mandatory on structural welding drawings?

No. AWS A2.4 makes the tail optional — it is used only when supplementary information must be communicated. Many structural drawings omit tails for routine fillet weld connections and only include them when a specific WPS number, NDE requirement, or special condition must be called out. However, when a tail is present, its content is contractually binding and must be followed.

Can a WPS number be specified in the tail?

Yes. Recording a WPS number in the tail is a common practice on structural projects where multiple WPS documents cover different base metal combinations, joint types, or positions. When a WPS number appears in the tail, the welder must use that specific procedure for the joint — not a different procedure that might otherwise cover the same joint by its essential variable range.

What goes in a tail to call out NDE requirements?

A tail can reference an NDE requirement using the process abbreviation or a project specification section number — for example, 'UT' for ultrasonic testing, 'RT' for radiographic testing, or a project spec paragraph like 'Sec. 3.4.' The weld symbol then communicates both the weld detail and the inspection requirement in one notation. For complex NDE callouts, a general note on the drawing is often cleaner than loading the tail.

Weld Symbol Tail Notes Under AWS A2.4: CWI Reference Guide

What the tail on a weld symbol means, what fabricators can put there, and how CWIs verify that tail-specified WPS numbers and standards are being followed.

Most structural welding drawings keep weld symbols simple: a reference line, a fillet or groove symbol on the appropriate side, a size, and sometimes a length. But occasionally a fork-shaped tail appears at the left end of the reference line — and that tail can carry information that changes how the welder approaches the joint and how the CWI inspects it.

AWS A2.4 (Standard Symbols for Welding, Brazing, and Nondestructive Examination) is the governing standard for weld symbol notation. This article explains the tail, what can legally go there, what fabricators commonly put there, and how CWIs use it during inspection.

The anatomy of a weld symbol tail

In the AWS A2.4 system, the standard weld symbol consists of:

Arrow: Points to the joint location
Reference line: Horizontal line connecting to the arrow
Weld symbol: Placed below (arrow side) or above (other side) the reference line
Dimensions: Size, length, and pitch adjacent to the weld symbol
Supplementary symbols: All-around, field weld, melt-through, backing, etc.
Tail: A fork at the end of the reference line opposite the arrow

The tail is explicitly defined in AWS A2.4 as the location for "specification, process, or other reference." The standard is intentionally permissive: it does not limit what can appear there, but the content must be clearly interpretable by both the welder and the inspector. When nothing needs to be called out, the tail is omitted entirely. Its absence does not mean anything is missing — it simply means the drawing author had no supplementary information to add.

What fabricators and engineers put in the tail

In structural steel practice, four categories of information appear most often in weld symbol tails:

1. Welding process designation

Abbreviations from AWS A2.4 Annex A — SMAW, FCAW-G, GMAW, SAW, GTAW, and others — can appear in the tail to specify which process must be used for a joint. This is common when:

A project specification restricts certain processes in specific locations (for example, prohibiting FCAW-S in fatigue-critical zones or requiring GTAW for the root pass on pipe penetrations).
Different process requirements apply to shop and field welds on the same member, and the engineer wants to make the distinction explicit on the drawing.

When a process is specified in the tail, the WPS covering that joint must also be qualified for that process. A welder substituting SMAW for a FCAW-G tail callout — even if the SMAW WPS covers the same base metal and joint type — is out of compliance.

2. WPS number

On projects with a formal welding procedure library, the structural engineer or fabricator may populate the tail with the specific WPS number that applies to the joint — for example, "WPS-12" or "P-A36-FCAW-2F." This removes any ambiguity about which procedure covers the joint when multiple WPSs in the library could technically qualify it by their essential variable ranges.

From a QC standpoint, tailing a specific WPS number is both a help and a responsibility. It is a help because the inspector can verify the exact WPS at the weld location without cross-referencing base metal, position, and process. It is a responsibility because the WPS number must be kept current: if WPS-12 is revised and renumbered, the drawings must be updated or a revision note issued, or the tailed number becomes stale. See WPS revision control best practices for how to manage this in a library.

3. Reference standard or specification section

A tail can point to a standard or project specification rather than a WPS number. Examples:

"AWS D1.1" — confirms the joint must comply with AWS D1.1 (useful when multiple codes apply to a project).
"Spec. Sect. 05120, Para. 3.2" — references a section of the project specification containing welding or NDE requirements.
"AISC 360 Sect. J2" — calls out a specific code provision governing the joint design.

This form of tail is more common on institutional or owner-driven projects (hospitals, government buildings) where the QC inspector verifies not just the physical weld but also the traceability of the joint back to a specific contract document.

4. NDE requirements

Inspection method callouts in the tail are used when NDE is required for specific weld locations rather than applied project-wide. Common forms:

"UT" — ultrasonic testing required on this joint
"RT" — radiographic testing required
"MT" — magnetic particle testing
"PT" — liquid penetrant testing

The tail notation for NDE supplements (and does not replace) the NDE plan required by AWS D1.1. When spot NDE applies to a percentage of joints, the tail method of calling it out is less common than a general drawing note or a separate inspection plan. But for joints that must be 100% UT regardless of the project's general NDE sampling rate — seismic-critical or tension-loaded CJP groove welds, for example — a tail callout on those specific weld symbols communicates the requirement directly to the erector and inspector at the joint level.

CWI use of tail information during inspection

The weld symbol tail is a primary reference during the CWI's pre-weld and in-process inspection. The practical steps:

Pre-weld: The CWI reviewing a joint should confirm that any process or WPS callout in the tail is matched by the work package. If the tail specifies "FCAW-G, WPS-08" and the welder's package includes WPS-08 but the wire spool installed is a self-shielded FCAW-S electrode, that is a nonconformance before the first arc is struck.

During welding: If a WPS number is tailed, verify that the welder is using parameters (amperage, voltage, travel speed) consistent with that specific WPS — not a different procedure from the library. For production parameter monitoring and logging, the WPS number from the tail should appear in the weld log for traceability.

Post-weld: If the tail specifies NDE, the CWI triggers the NDE requirement for that joint specifically. This is separate from any project-level NDE sampling plan. Missing NDE on a tail-specified joint is a documentation gap that auditors catch.

Common tail-related errors on structural drawings

Several mistakes recur in practice:

Stale WPS numbers. A drawing set tailed with specific WPS numbers becomes a liability when the WPS library is revised. The tail references must be updated when WPS numbers change. Fabricators using a WPS software system that maintains revision history can catch this; shops running paper binders frequently miss it. See how long is a WPS valid and managing edition transitions for retention and revision considerations.

Process callouts without supporting WPS. An engineer tails "GTAW root / SMAW fill" on a connection drawing, but the fabricator's WPS library includes no dual-process GTAW + SMAW procedure for that base metal. The tail specifies a requirement that cannot be met with the available documentation. The fix is either to qualify the dual-process WPS or to negotiate a revision to the drawing before fabrication begins — not to ignore the tail notation.

NDE tails without inspection plan support. A tail that calls "RT" on a specific fillet weld creates a problem if the project's RT procedure covers only groove welds. Fillet welds are generally not radiographed under AWS D1.1; if the engineer intends UT instead, the tail should read "UT" or the specification should clarify. A CWI who sees an RT tail on a fillet weld connection should raise the discrepancy before the weld is completed, not after.

Conflicting tail and note. Drawing general notes sometimes specify a blanket welding requirement that conflicts with an individual weld symbol tail. For example, a general note requiring FCAW-G for all welds in the shop, combined with a tail on a specific detail specifying SMAW, creates an ambiguity. The specific symbol (the tail) typically governs over the general note in standard contract interpretation, but the conflict should be flagged to the engineer of record for resolution before fabrication.

When no tail is present

Absence of a tail means the drawing author did not have supplementary information to communicate via the symbol. It does not mean the welder has a choice of process, that NDE is waived, or that any WPS applies. All other project-level requirements — the contract specification, the welding procedure submittal approval, and the NDE plan — still apply. The tail is a mechanism for drawing-level specificity, not the sole source of welding requirements.

For the CWI working through a mixed drawing set (some symbols with tails, many without), the inspection framework is:

Check the weld symbol for process or WPS tail — if present, verify it.
If no tail, apply the approved WPS library and project specification requirements.
Apply the project NDE plan regardless of tail content.

This sequencing ensures that tail-specified requirements get the attention they signal, while the absence of a tail does not create a documentation gap. For a full CWI pre-weld inspection checklist covering weld symbol interpretation, joint fit-up, and material verification, see the CWI pre-weld inspection checklist under AWS D1.1 article. And for shops building the WPS library that gets referenced in tails, the WPS software comparison for structural fab shops page covers tools that support library management and traceability.