Weld Symbols — Engineering Reference

AWS A2.4 welding symbol guide: fillet, V-groove, bevel, plug and slot symbols. Arrow/other-side, all-around, field weld, intermittent dimensions explained.

Overview

Welding symbols are the standard graphical language used on structural drawings to communicate weld type, size, length, location, process, and inspection requirements between the engineer, detailer, and fabricator. The governing standard in North America is AWS A2.4 (Standard Symbols for Welding, Brazing, and Nondestructive Examination). In Australia, AS 1101.3 applies, while European practice follows EN ISO 2553.

A welding symbol consists of a reference line (horizontal), an arrow pointing to the joint, and various elements placed above, below, or at the ends of the reference line. The side of the reference line indicates whether the weld is on the arrow side (below the line) or the other side (above the line). A flag at the junction of the reference line and arrow indicates a field weld (to be performed on site rather than in the shop).

Anatomy of a welding symbol

The components of a complete welding symbol per AWS A2.4 are:

• Reference line — the horizontal line that carries all weld information. Multiple reference lines can be stacked for multi-pass or sequential welds.
• Arrow — points to the joint location on the drawing. The arrow side of the joint corresponds to symbols placed below the reference line.
• Weld symbol — the geometric shape indicating the weld type (triangle for fillet, V for groove, etc.), placed on the appropriate side of the reference line.
• Dimensions — weld size appears to the left of the symbol, weld length to the right. For intermittent welds, length and pitch are shown as length-pitch (e.g., 3-6 means 3 in. long at 6 in. center-to-center).
• Tail — optional; contains supplementary information such as the welding process (e.g., SMAW, GMAW), electrode specification (E70XX), or a reference to a welding procedure specification (WPS).
• Finish symbols — C (chipping), G (grinding), M (machining) indicate the method of surface finishing after welding.

Common weld type symbols

Fillet weld symbol configurations

Groove weld preparation dimensions

Fillet weld size reference

phi x Rn = 0.75 x 0.60 x 70 x (weld size x 0.707). Minimum size per AISC Table J2.4.

Intermittent weld patterns

Percent welded = weld length / pitch x 100. Lower percentages reduce distortion and cost.

Supplementary symbols

• All-around symbol — a circle at the arrow/reference line junction indicates the weld continues completely around the joint (e.g., around the perimeter of an HSS connection).
• Field weld flag — a solid flag (triangle) at the arrow/reference line junction means the weld is to be made in the field, not in the shop.
• Melt-through symbol — a filled semicircle on the opposite side indicates complete joint penetration is required with visible root reinforcement.
• Spacer symbol — a rectangle on the reference line indicates a backing bar or spacer is specified.
• Contour symbols — flush (straight line), convex (arc), or concave (inverted arc) indicate the required weld face profile after finishing.

AWS vs. ISO vs. AS symbol differences

Method A in ISO 2553 matches the AWS convention. Method B (used in some European countries) reverses the arrow/other-side convention, which can cause confusion on international projects. Always confirm which convention the project uses.

Reading weld symbols — practical examples

Example 1: A right triangle below the reference line with "5/16" to its left and "6-12" to its right: 5/16 in. fillet weld, 6 in. long, spaced at 12 in. center-to-center (intermittent), on the arrow side.

Example 2: Same triangle both above and below with matching "3-6": staggered intermittent fillet weld, 3 in. long at 6 in. pitch, on both sides with segments offset.

Example 3: A half-V below the reference line with "45 degrees" inside and "1/4" at the root, tail note "E70": single-bevel groove weld, 45 degree included angle, 1/4 in. root opening, E70XX electrode.

Example 4: Triangle below the line with "3/8" to left, a circle at the junction, and a flag: 3/8 in. fillet weld, all-around, field weld. Common for HSS brace to gusset connections.

Worked example — moment connection weld symbols

A beam-to-column moment connection in an SMF requires:

1. Flange welds: CJP groove welds (single-bevel, arrow side) with backing bar removed. Symbol: half-V below line, melt-through symbol on other side, flag for field weld, tail note "AWS D1.8".
2. Web weld: 5/16 in. fillet weld, both sides, continuous. Symbol: triangles above and below line with "5/16" to left of each.
3. Continuity plates: 1/4 in. fillet weld all-around to column web. Symbol: triangle with circle, "1/4" to left.
4. Shear tab: 5/16 in. fillet weld to column flange, arrow side, continuous length 10 in. Symbol: triangle below line, "5/16 x 10".

Weld symbol specification checklist

When reviewing shop drawings, verify these 10 elements:

1. Weld type — fillet, groove (V, bevel, U, J), plug, or slot
2. Weld size — fillet leg size or groove effective throat
3. Weld length — continuous or specific length with pitch
4. Location — arrow side, other side, or both sides
5. Process — SMAW, GMAW, FCAW in tail note (if required)
6. Electrode — E70XX, E80XX in tail note
7. Joint preparation — groove angle, root opening, root face
8. NDE requirements — UT, MT, PT, VT noted in tail or specification
9. Contour/finish — flush, convex, or as-welded
10. Field/shop designation — field weld flag present or absent

AWS A2.4 Weld Symbol Anatomy

Per AWS A2.4 "Standard Symbols for Welding, Brazing, and Nondestructive Examination," every complete welding symbol consists of standardized components arranged in a specific format. Understanding the anatomy is essential for reading fabrication drawings:

The reference line orientation follows these rules:

• Arrow side: Symbol below the reference line = weld on arrow side of the joint
• Other side: Symbol above the reference line = weld on the other side of the joint
• Both sides: Symbol on both sides of the reference line = weld on both sides of the joint
• No side designation: Symbol centered on the reference line = no arrow side preference (rare)

Basic Weld Symbols Chart

Per AWS A2.4, the following are the fundamental weld symbols used on structural steel drawings:

For fillet welds on structural steel connections per AISC 360-22:

• Minimum fillet weld size per AISC Table J2.4: 1/8 in. for material <= 1/4 in., 3/16 in. for 1/4 to 1/2 in., 1/4 in. for 1/2 to 3/4 in., 5/16 in. for over 3/4 in.
• Maximum effective fillet weld size: 5/8 in. (for material >= 5/8 in. thick) per AISC J2.2a

Supplementary Weld Symbols

Supplementary symbols modify the basic weld symbols to convey additional requirements:

Practical Weld Symbol Reading Exercises

The following examples demonstrate how to read common weld symbols found on structural steel fabrication drawings:

Example 1: Simple fillet weld

Symbol: Arrow pointing to joint, below reference line = fillet symbol (triangle),
        left of symbol = 5/16, right of symbol = 6
Reading: 5/16 in. fillet weld, 6 in. long, on the arrow side

Example 2: Double fillet weld (both sides)

Symbol: Fillet triangle BELOW reference line = 1/4
        Fillet triangle ABOVE reference line = 1/4
        No length specified on either side
Reading: 1/4 in. fillet weld on both sides, continuous (length implied by joint length)

Example 3: Intermittent fillet weld

Symbol: Below reference line = fillet symbol, left = 3/16, right = 4-8
Reading: 3/16 in. fillet weld, 4 in. long, spaced at 8 in. pitch (center-to-center),
         on the arrow side

Example 4: CJP groove weld with backing

Symbol: V-groove below reference line, backing symbol above reference line,
        all-around circle at junction, tail says "GMAW" and "UT 100%"
Reading: Complete joint penetration V-groove weld, arrow side, with backing bar,
         all-around, GMAW process, 100% ultrasonic testing required

Example 5: Field weld plug weld

Symbol: Field weld flag at junction, plug weld symbol below reference line,
        left of symbol = 1/2, tail says "FCAW"
Reading: 1/2 in. diameter plug weld on arrow side, field-welded using FCAW process

Example 6: Staggered intermittent fillet

Symbol: Fillet below = 3/16 x 3-12, fillet above = 3/16 x 3-12,
        stagger marks (---) on both sides
Reading: 3/16 in. fillet, 3 in. long segments at 12 in. pitch, staggered on both
         sides (offset so arrow-side segments fall between other-side segments)

Example 7: Beam-to-column moment connection (typical)

Symbol: CJP groove weld symbol for beam flanges to column flange,
        fillet weld symbol for beam web to shear tab,
        tail: "E7018-H4R, AWS D1.8 demand-critical"
Reading: CJP groove welds at flanges (demand-critical for seismic), fillet welds at
         web connection, filler metal must meet AWS D1.8 toughness requirements

When reading weld symbols on structural drawings, always check:

1. Which side of the reference line the symbol is on (arrow vs. other side)
2. The weld size (left of symbol) and length/pitch (right of symbol)
3. Whether the all-around or field-weld symbols are present
4. The tail notes for process, electrode, and inspection requirements
5. Any supplementary contour or backing requirements

Common mistakes to avoid

1. Confusing arrow side and other side — placing the weld symbol on the wrong side of the reference line causes the weld to be placed on the wrong side of the joint in fabrication. On international projects using ISO 2553 Method B, the convention is reversed from AWS.
2. Omitting the all-around symbol — when a weld must wrap continuously around a member (e.g., an HSS brace to gusset), forgetting the all-around circle results in only three sides being welded, leaving a critical unwelded face.
3. Missing the field weld flag — if a weld must be done on site (e.g., beam-to-column moment connections), the field weld flag must be shown. Without it, the fabricator may attempt to shop-weld a joint that must be field-connected.
4. Incomplete groove weld designation — groove welds require the included angle, root opening, and root face to be specified. Omitting any of these forces the fabricator to guess, potentially producing an inadequate or over-welded joint.
5. Not specifying backing bar removal — for CJP welds in seismic applications, the backing bar must be removed and the root back-gouged and welded. This must be noted on the symbol or in the specifications.

Frequently asked questions

What is the difference between arrow side and other side? In AWS A2.4, symbols below the reference line apply to the arrow side (the side the arrow points to). Symbols above the line apply to the other side. Getting this wrong means the weld goes on the wrong face.

When do I use the all-around symbol? When the weld must run continuously around the entire joint perimeter. Common for HSS connections, pipe saddles, and any connection where the weld path forms a closed loop.

What does a field weld flag mean? The flag (filled triangle) at the arrow/line junction means the weld must be made on site, not in the fabrication shop. This affects sequencing, access, and inspection requirements.

How do I read intermittent weld dimensions? The notation "length-pitch" appears to the right of the weld symbol. For "3-9": 3 in. weld length, 9 in. center-to-center spacing (pitch). The gap between welds is 9 - 3 = 6 in.

What groove angle should I specify? For V-groove and bevel groove welds, 60 degrees is standard for SMAW. For GMAW/FCAW, 45-60 degrees is typical. Steeper angles require more weld metal. Check AWS D1.1 Figure 3.3 for prequalified joint details.

What is the tail of a weld symbol for? The tail is optional. It carries supplementary information: welding process (SMAW, GMAW), electrode specification (E7018), WPS reference number, or special requirements like NDE method.

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Related references

• Minimum Weld Size
• Weld Electrodes
• Weld Joint Types
• Weld Group Properties
• Weld Inspection
• Welding Procedure
• Steel Fasteners
• Connection Types
• How to Verify Calculations

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