Weld symbols are the primary language between the engineer of record, the detailer, and the fabrication floor. A CWI who misreads a weld symbol in the field — or passes a weld that does not match the symbol's requirements — has a quality escape with a paper trail leading directly to the inspection record. This reference covers the complete AWS standard welding symbol system as applied to structural steel work.
Reference line — a horizontal line; the baseline of all symbol information
Arrow — attached to one end of the reference line, pointing to the joint to be welded
Weld type symbol — a graphic placed on the reference line identifying the weld geometry
Additional elements — dimensions, supplementary symbols, tail, flags — are added as needed.
All information placed below the reference line (same side as the arrowhead direction) refers to the arrow side of the joint. All information placed above the reference line refers to the other side of the joint. When a symbol appears on both sides, both faces of the joint receive the specified weld.
Fillet weld symbols
The fillet weld is the most common symbol in structural work. The graphic is a right triangle with the vertical leg against the reference line.
Reading a fillet symbol:
Size (leg length) appears to the left of the symbol
Length of the weld appears to the right of the symbol (omitted = full length)
Pitch for intermittent welds appears as length@pitch to the right (e.g., 2@6 means 2-in welds at 6-in center-to-center)
A fillet symbol below the reference line = weld on the arrow side. A fillet symbol above = weld on the other side. Both = weld on both sides.
CWI check: measure the actual leg and effective throat. For a 45° fillet, the effective throat = 0.707 × leg. Confirm both dimensions; some engineers specify throat, not leg.
Groove weld symbols
Groove weld type symbols are placed on the reference line. Common types in structural work:
Groove type
Symbol appearance
V-groove
Two angled lines meeting in a V
Bevel groove
One angled line, one vertical
U-groove
Curved U shape
J-groove
One curved, one vertical
Square groove
Two vertical lines
The groove angle (included angle of the groove) and root opening appear within the symbol or in the tail. For prequalified joint details under AWS D1.1:2025 Clause 5, the symbol often references the joint designation (e.g., "B-U2" in the tail) rather than encoding all geometry in the symbol itself. The CWI matches the designation to the prequalified detail table.
CJP vs. PJP: A CJP (complete joint penetration) groove weld is indicated by the full-penetration supplementary symbol or by the note "CJP" in the tail. A PJP (partial joint penetration) groove weld specifies depth of penetration as a number in parentheses to the left of the symbol. Without a CJP indicator and without a PJP depth, interpret the symbol as CJP unless the contract documents specify otherwise — but flag the ambiguity.
Supplementary symbols
Supplementary symbols modify the basic weld type symbol:
Full penetration (CJP): A rectangular box symbol or the letters "CJP" in the tail. Signals that the groove weld must achieve full fusion through the joint thickness. Does not specify joint geometry on its own.
Melt-through: Indicates root reinforcement is required on the other side of a single-side weld — the weld must fully penetrate and show visible reinforcement on the back face. More common in pipe and pressure vessel work, but appears on structural symbols for certain architecturally exposed connections.
Backing: A rectangular backing symbol below or above the groove indicates a backing bar or backing material is required. Steel backing for structural groove welds must meet AWS D1.1:2025 base metal requirements. When backing is shown on one side and a groove on the other, the backing is on the root side.
Contour symbols: Three finish contour symbols appear on the cap:
Concave (arc below cap): grind to a concave profile
Contour symbols are typically accompanied by a finish method letter in the tail: G (grind), M (machining), C (chipping), R (rolling), U (unspecified).
The all-around symbol
A circle at the reference line/arrow junction means the weld symbol applies all around the joint perimeter. Common on column base plates, pipe connections, and closed-section members where welding runs continuously around the full perimeter. CWI implication: inspect 100% of the perimeter, not just the visible faces.
The field weld flag
A filled pennant (flag) at the reference line/arrow junction designates a field weld. Shop drawings typically show both shop welds and field welds; the flag distinguishes them.
For a CWI, field weld flags require:
Confirm the field WPS is qualified and covers the joint — do not use the shop WPS without checking
Check whether IBC Chapter 17 special inspection applies and whether a special inspector is required
Document pre-weld inspection before arc ignition, not after
The tail
The tail is a fork at the end of the reference line opposite the arrow. Information in the tail includes:
Welding process specification (SMAW, FCAW-G, SAW, etc.)
WPS number or joint detail designation
CJP / PJP designation
Reference to applicable standard or special note
If the tail is blank, no special process or reference is required. A tail with a WPS number means the inspector should verify that WPS is current and applies to this joint.
Common field interpretation errors
Ignoring the other-side symbol: A weld symbol above the reference line is easy to miss when attention is on the arrow side. Both sides must be inspected.
Confusing symbol size with throat: The size dimension on a fillet symbol is the leg, not the effective throat. Inspectors using a fillet weld gauge calibrated for throat must convert.
Missing the PJP depth: A groove weld symbol without a CJP indicator and without a depth-of-penetration dimension in parentheses needs clarification. Do not default to CJP in the field; get a written answer from the engineer of record.
Treating "all-around" as cosmetic: The all-around circle is a complete-perimeter requirement, not a suggestion. Partial welds on an all-around joint are a nonconformance.
Field weld without a field WPS: The shop WPS may not be qualified for field positions. The flag means confirm first, weld second.
What is the difference between the arrow side and the other side of a weld symbol?
The reference line bisects a weld symbol. The arrow points to the joint; the side of the reference line the arrow attaches to is the 'arrow side.' Information placed on the same side as the arrow specifies the weld on the arrow-side face of the joint. Information on the opposite side specifies the weld on the other side. A fillet symbol on both sides of the reference line means the joint gets fillet welds on both faces.
What does the full-penetration supplementary symbol mean?
The full-penetration (CJP) supplementary symbol indicates the weld must be a complete joint penetration groove weld. It does not specify joint geometry — that comes from the groove detail, a prequalified joint designation, or a separate detail. Structural engineers often use it on moment connection submittals to flag CJP requirements for the inspector without encoding every bevel parameter in the symbol itself.
How do you read fillet weld size from the symbol?
The fillet weld leg size is a number to the left of the fillet symbol, in the drawing's units (typically inches for structural work). A '5/16' means the required fillet leg is 5/16 in. If arrow-side and other-side sizes differ — '5/16' and '3/8' — each face gets its own dimension. Weld length, when specified, appears to the right of the symbol. No length dimension means the weld runs the full length of the joint.
What does the field weld flag mean for a CWI?
The field weld flag (a filled pennant at the reference line junction) designates welding to be performed in the field, not the shop. For a CWI, this triggers a different protocol: confirm the field WPS is in place, check weather holds per AWS D1.1:2025, and verify whether IBC Chapter 17 special inspection applies. Never assume a field-flagged weld is automatically covered by the shop WPS.