Welding Symbols — AWS A2.4 Reference

A weld symbol is a standardized graphical notation placed on engineering drawings to specify the type, size, location, and extent of a weld. In North America, weld symbols follow AWS A2.4 (Standard Symbols for Welding, Brazing, and Nondestructive Examination). Internationally, ISO 2553 serves the same purpose with some differences in convention — notably, ISO reverses arrow-side and other-side placement relative to the reference line. Every welding symbol consists of a required reference line, an arrow pointing to the joint, a weld symbol graphic (such as the right triangle for fillet welds or the V for groove welds), and optional elements including dimensions, supplementary symbols, and a tail containing process designators or specification references. Mastering weld symbols is a core competency for CWIs, welding engineers, and fabrication detailers because they eliminate ambiguity on the shop floor — the symbol tells the welder exactly what type of weld to make, where to make it, and how large it must be.

A weld symbol refers specifically to the small graphic element that indicates the weld type — for example, a right triangle for a fillet weld, a V-shape for a V-groove weld, or a rectangle for a plug weld. It is one component of the larger notation. A welding symbol refers to the complete assembly of elements that together convey the full welding instruction: the reference line, arrow, weld symbol, dimensions (size and length), supplementary symbols (weld-all-around circle, field weld flag, contour and finishing designators), and the optional tail containing process codes, specification references, or WPS numbers. AWS A2.4 makes this distinction explicit in its terminology section. In practice, many welders and engineers use the terms interchangeably, but on CWI exams and in formal specification writing, the distinction matters — a "weld symbol" is just the type indicator, while a "welding symbol" is the entire graphical instruction on the drawing.

The reference line is the horizontal backbone of every welding symbol, and it divides the symbol into two zones that determine weld placement. The arrow side is indicated by placing the weld symbol below the reference line — this means the weld goes on the same side of the joint that the arrow physically points to. The other side is indicated by placing the weld symbol above the reference line — this means the weld goes on the opposite side of the joint from where the arrow points. When weld symbols appear on both sides of the reference line, the welder must weld both sides of the joint. This convention is defined in AWS A2.4 sections 6.1 and 6.2. Note that ISO 2553 reverses this convention — arrow side is above the line in ISO — which is a common source of confusion on international projects. Always confirm which standard the drawing references before interpreting arrow-side versus other-side placement. Full explanation — A2.4 §6.1 & §6.2 →

A small circle placed at the junction where the reference line meets the arrow is the weld-all-around symbol. It instructs the welder to make the weld continuously around the entire perimeter of the joint without any breaks or gaps. Common applications include tube-to-plate connections where all four sides of a rectangular tube must be welded to a baseplate, circular pipe penetrations through a plate, and gusset plate attachments. Per AWS A2.4, the circle is always placed at the reference line and arrow junction — it does not appear anywhere else on the symbol. The weld-all-around symbol can be combined with any weld type symbol (fillet, groove, etc.) and with the field weld flag. When you see both a weld-all-around circle and a field weld flag at the junction, it means the entire perimeter weld must be completed in the field during erection rather than in the shop.

A filled triangle (flag) at the junction of the reference line and arrow is the field weld symbol. It indicates the weld must be made in the field during erection — not in the fabrication shop. This distinction is critical for structural steel projects because shop welds and field welds are subject to different quality control procedures, different inspection requirements, and often different welding processes. Shop welds are typically made under controlled conditions with SAW or GMAW, while field welds often use SMAW or FCAW due to access constraints and outdoor conditions. Per A2.4 §6.9, the field weld flag may point in either direction. On structural steel erection drawings, field welds are commonly fillet welds at beam-to-column moment connections, splice plates, and bracing connections. CWIs performing field inspection specifically look for the field weld flag to identify which joints require on-site verification and documentation.

The letter G adjacent to a contour symbol on a welding symbol means grind — the completed weld face must be ground to achieve the contour specified by the accompanying contour symbol. The contour symbol can indicate flush (straight line), convex (outward arc), or concave (inward arc) profile. Together, a flush contour symbol plus the letter G means "grind this weld flush with the base metal surface." Other finishing designators defined in AWS A2.4:2020 include M for machining, C for chipping, H for hammering (peening), P for planishing, R for rolling, and U for unspecified finishing method. The finishing designator appears adjacent to the contour symbol, above or below the weld symbol depending on which side of the joint the finish applies to. Grinding is the most commonly specified finishing method in structural steel work, particularly for CJP groove welds at moment connections where a flush surface is required for proper fit-up of connecting elements. See full explanation of the G finishing symbol.

AWS A2.4 and ISO 2553 both define welding symbols for engineering drawings, but they use opposite conventions for indicating which side of the joint is welded. In AWS A2.4, the weld symbol below the reference line indicates the arrow side of the joint, and above indicates the other side. In ISO 2553, this convention is reversed — in the identification system (formerly System A), the symbol on the side of the reference line with the dashed line indicates the other side. This reversal is the single most important difference and the most common source of confusion on international projects. Always confirm which standard a drawing references before interpreting arrow-side versus other-side placement. Other differences include: ISO uses different size shortcodes (a for throat, z for leg, s for depth), ISO has System A and System B variants, and some supplementary symbol conventions differ.