R<\/td> Rolling<\/td><\/tr><\/tbody><\/table><\/div><\/figure>\n\n\n\nNote: Symbols follow AWS A2.4. Some projects use ISO 2553 symbols, which look different. Check which symbol standard the drawing set uses.<\/em><\/p>\n\n\n\nFor example, a convex symbol with the letter G tells the welder to grind the weld to a convex contour.<\/p>\n\n\n\nWhy Defining the Profile Properly Matters.<\/h2>\n\n\n\n\nIt avoids disputes.<\/strong> Fabricator, inspector, and client may each read \u201cacceptable shape\u201d differently. A written profile and size remove the argument.<\/li>\n\n\n\nIt protects strength.<\/strong> Throat thickness, not appearance, defines capacity.<\/li>\n\n\n\nIt improves fatigue life.<\/strong> Where loading is cyclic, requiring a flat or slightly concave toe blend can extend service life.<\/li>\n\n\n\nIt reduces rework and cost.<\/strong> It prevents over-welding and undersized welds.<\/li>\n\n\n\nIt supports code compliance<\/strong> with AWS D1.1 [1], API 1104 [2], ASME B31.3 [4], and project specifications.<\/li>\n\n\n\nIt prevents confusion<\/strong> between fillet profile and butt weld terms such as reinforcement and root concavity.<\/li>\n<\/ol>\n\n\n\nPractical Tips for Welders and Inspectors.<\/h2>\n\n\n\n\nConfirm the required leg size and minimum throat before welding.<\/li>\n\n\n\n Measure with a calibrated gauge, never by eye.<\/li>\n\n\n\n Check both toes for undercut and lack of fusion.<\/li>\n\n\n\n Follow the project specification if it is stricter than the code.<\/li>\n\n\n\n Keep inspection records for traceability.<\/li>\n<\/ul>\n\n\n\nConclusion!<\/h2>\n\n\n\n A convex weld adds metal but not strength, and it can reduce fatigue life. A concave weld blends smoothly but can lose throat if overdone. Under AWS D1.1, convexity has clear numerical limits and concavity is judged by the remaining throat. Under API 1104, the focus is on butt weld crown, undercut, and internal concavity, so fillet profile limits usually come from the project specification. Verify with a gauge, use the edition required by your contract, and show the requirement clearly on the drawing with the correct contour symbol.<\/p>\n\n\n\n
References.<\/h2>\n\n\n\n\nAmerican Welding Society. AWS D1.1\/D1.1M:2025, Structural Welding Code \u2013 Steel<\/em>, 23rd Edition. Miami, FL: AWS, 2025.<\/li>\n\n\n\nAmerican Petroleum Institute. API Standard 1104, Welding of Pipelines and Related Facilities<\/em>, 22nd Edition, July 2021, including Errata 1 (September 2023). Washington, DC: API.<\/li>\n\n\n\nAmerican Welding Society. AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination<\/em> (latest edition).<\/li>\n\n\n\nASME. ASME B31.3, Process Piping<\/em> (latest edition).<\/li>\n\n\n\nU.S. Department of Transportation, PHMSA. Letter from API on Welding Procedure and Welder Qualifications using API Standard 1104<\/em>, August 2025.<\/li>\n<\/ol>\n\n\n\nEdition note: Standards are revised periodically. The editions above were the latest found at the time of writing (October 2026). Check the publisher\u2019s website for any newer edition or amendment before relying on this article.<\/em><\/p>\n\n\n\nFAQ’S<\/h2>\n\n\n\n
\n
\n
1. What is the difference between convex and concave welds?<\/h3>\n\n\n
A convex weld has a face that bulges outward, above the straight line between the two weld toes. A concave weld has a face that curves inward, below that line. Both are fillet weld profiles. Convex carries extra metal, while concave blends smoothly into the base plates.<\/p>\n\n<\/div>\n<\/div>\n
\n
2. Which is better, a convex or a concave fillet weld?<\/h3>\n\n\n
Neither is better in every case. A convex weld adds metal, but design strength is based on the specified throat, so the extra bulge is not counted. A concave weld reduces stress concentration at the toes but can lose throat if overdone. A flat or slightly concave weld with correct size is generally preferred.<\/p>\n\n<\/div>\n<\/div>\n
\n
3. What is the maximum convexity allowed for a fillet weld?<\/h3>\n\n\n
Under AWS D1.1, allowed convexity depends on weld face width. It is about 1\/16 in (2 mm) for faces up to 5\/16 in, 1\/8 in (3 mm) for faces between 5\/16 in and 1 in, and 3\/16 in (5 mm) for faces of 1 in or more. Verify against your current edition [1].<\/p>\n\n<\/div>\n<\/div>\n
\n
4. How do you check convexity and concavity in a fillet weld?<\/h3>\n\n\n
Inspectors use visual inspection with a fillet weld gauge. The gauge is placed against the weld and reads leg length, throat, and convexity or concavity. For more detail, a macro-etch test shows the weld shape and fusion lines, and MT or PT finds surface cracks at the toes.<\/p>\n\n<\/div>\n<\/div>\n
\n
5. What are the weld symbols for convex and concave contours?<\/h3>\n\n\n
On a drawing, the contour symbol sits on the weld symbol. A flat contour is a short straight line, a convex contour is an arc bulging outward, and a concave contour is an arc curving inward. A finish letter such as G (grinding) can be added. These follow AWS A2.4 [3].<\/p>\n\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n\n\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
Introduction! Concave and convex fillet welds can have the same leg length and still behave very differently in service. A convex weld bulges…<\/p>\n","protected":false},"author":1,"featured_media":2118,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_lmt_disableupdate":"","_lmt_disable":"","footnotes":""},"categories":[23,190],"tags":[],"class_list":["post-2104","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog","category-inspections"],"_links":{"self":[{"href":"https:\/\/isotexinspectionservices.com\/blog\/wp-json\/wp\/v2\/posts\/2104","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/isotexinspectionservices.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/isotexinspectionservices.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/isotexinspectionservices.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/isotexinspectionservices.com\/blog\/wp-json\/wp\/v2\/comments?post=2104"}],"version-history":[{"count":24,"href":"https:\/\/isotexinspectionservices.com\/blog\/wp-json\/wp\/v2\/posts\/2104\/revisions"}],"predecessor-version":[{"id":2140,"href":"https:\/\/isotexinspectionservices.com\/blog\/wp-json\/wp\/v2\/posts\/2104\/revisions\/2140"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/isotexinspectionservices.com\/blog\/wp-json\/wp\/v2\/media\/2118"}],"wp:attachment":[{"href":"https:\/\/isotexinspectionservices.com\/blog\/wp-json\/wp\/v2\/media?parent=2104"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/isotexinspectionservices.com\/blog\/wp-json\/wp\/v2\/categories?post=2104"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/isotexinspectionservices.com\/blog\/wp-json\/wp\/v2\/tags?post=2104"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
![\"\"](\"https:\/\/isotexinspectionservices.com\/blog\/wp-content\/uploads\/2026\/10\/Concave-and-Convex-Fillet-Welds-1-1024x576.png\")
<\/figure>\n<\/div>\n\n\n![\"Concave](\"https:\/\/isotexinspectionservices.com\/blog\/wp-content\/uploads\/2026\/10\/Concave-and-Convex-Fillet-Welds-2-1024x576.png\")
<\/figure>\n<\/div>\n\n\n![\"\"](\"https:\/\/isotexinspectionservices.com\/blog\/wp-content\/uploads\/2026\/10\/Weld-Contour-Macro-etch-specimen-1024x683.png\")
<\/figure>\n<\/div>\n\n\n![\"\"](\"https:\/\/isotexinspectionservices.com\/blog\/wp-content\/uploads\/2026\/10\/AWS-A2.4-fillet-weld-symbol-1024x683.png\")
<\/figure>\n\n\n\n