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Edge joint: meaning and how to check it

Fillet Gauge editorial teamSources checked 3 min read

An edge joint is two or more members laid face to face, parallel or nearly parallel, with their edges lined up and welded together along those edges. It's mostly a thin-material joint: flanged sheet, the rims of tanks and covers, and parts that won't carry much load across the weld. The weld joins edges, not faces.

Two edge joints drawn end on: two plates standing face to face with one weld across both top edges, and two sheets with edges bent up to meet and welded along the flange tops
Square edges on the left, flanged edges on the right.
Use this diagram

How to recognise an edge joint

  1. Faces together, edges flush. The members touch (or nearly touch) face to face, and their edges sit side by side. Picture two sheets in a stack with the weld along one end of the stack.
  2. Find the weld on the edges. The bead covers the ends of both members at once. There's no inside corner for a fillet.
  3. Look for flanges. On sheet, the edges are often bent up so two flanges stand face to face. That's still an edge joint, and the weld goes along the top of the flanges.

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Definitions and Terminology

A fatigue crack in a cyclically loaded fillet-welded attachment started along the line where the surface of the weld blends into the flange plate. At which weld feature did the crack start?

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Common mix-ups

  • Edge joint versus edge weld. The edge joint is the joint type. An edge weld is a weld type, with its own symbol, that's typically used on it. Read the edge weld symbol page for the symbol side.
  • Edge versus corner. A corner joint has the members at an angle, meeting at their edges like an L. An edge joint has them parallel.
  • Edge versus lap. In a lap joint the members overlap and the welds sit at the edge of one plate against the face of the other. In an edge joint the edges are flush and the weld covers both edges together.
  • Edge versus butt. In a butt joint the members are side by side in one plane, edge against edge. In an edge joint they're stacked, face against face.

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Edge joints on the CWI exam

Joint types are in Definitions and Terminology, at least 12% of the closed-book Part A. The edge joint is the one candidates name least often, which makes it a common trap when it's drawn next to a corner or a lap.

The edge weld symbol also sits under Symbols, Welding and NDE, at least 10% of Part A, so expect the joint and the symbol to be tested together.

Structural codes such as D1.1 rarely use edge joints for load-carrying welds, so they're a smaller target on Part C. Check your own copy if a Part C reference asks about one.

Practice it

The CWI Part A flashcards cover the symbol, metallurgy and discontinuity terms that sit around the joint names. The welding terms glossary has all five side by side with the weld terms that go with them.

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Facts checked 25 October 2026 against the sources listed above. If something has changed, tell us and we will correct it within 2 business days.

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