輪郭記号と仕上げ記号

The contour symbol on a welding symbol specifies the required shape of the finished weld surface. Per AWS A2.4:2020 Section 6.13, there are three contour shapes: flush (flat, indicated by a straight line), convex (raised, indicated by a convex arc), and concave (recessed, indicated by a concave arc). The contour symbol is placed on top of the weld symbol on the reference line. When a contour symbol appears without a finishing designator letter, the contour may be achieved by any method including welding technique alone. When a finishing designator letter is added (G, M, C, H, P, R, or U), a specific mechanical finishing method is required after welding.

G on a welding symbol is the finishing designator for grinding, per AWS A2.4:2020 Section 6.13.2. When you see G next to a contour symbol (flush, convex, or concave), it means the weld must be mechanically ground to achieve that contour. For example, a flush contour symbol with G means grind the weld flush with the base metal surface. The finishing designator specifies the method but does not specify the quality or roughness of the finish. Grinding is the most commonly specified finishing method in structural steel fabrication, particularly for CJP groove welds at moment connections where flush surfaces are required for fatigue performance.

AWS A2.4:2020 Section 6.13.2 and Section 6.13.3 define 7 finishing designator letters: G for grinding, M for machining, C for chipping, H for hammering, P for planishing, R for rolling, and U for unspecified mechanical finishing method. Each letter is placed next to the contour symbol to specify how the weld surface must be finished. The letters do not specify the quality or surface roughness of the finish. U is used when mechanical finishing is required but the specific method is left to the fabricator. These designators apply only to mechanical finishing methods, not to contour achieved by welding technique alone.

Flush contour means the weld surface must be level with the base metal, creating a smooth transition with no reinforcement above the plate surface. Convex contour means the weld surface is intentionally raised above the base metal in a rounded profile. Both are specified using contour symbols per AWS A2.4 Section 6.13. Flush contour is required for fatigue-critical connections because weld reinforcement creates stress concentrations at the weld toes. D1.1:2025 Clause 7.23 specifies flush finishing requirements for butt joints in cyclically loaded structures. Convex contour is acceptable for most statically loaded connections where fatigue is not a design consideration.