Welding symbols

Reading a symbol

1. 1Arrow line: touches the joint, usually at 135°.
2. 2Continuous reference line, parallel to the drawing’s bottom edge.
3. 3Dashed identification line (system A): other side.
4. 4Elementary symbol: shape of the weld.
5. 5Section size: a = throat, z = leg, s = penetration.
6. 6Tail: ISO 4063 process, quality level, position, filler.

Arrow side or other side

• ASystem A (two lines)

  Symbol on the continuous line (1): weld on the arrow side. On the dashes (2): other side. Above or below does not matter.

• BSystem B and AWS A2.4 (one line)

  Below the line (1): arrow side. Above (2): other side.

A drawing must state which system it uses; A and B are never mixed. No dashed line: read “below = arrow side”.

Elementary symbols

• Square butt (I)

  Thin plates, no bevel.

• Single-V butt

  Both edges bevelled.

• Single-bevel butt

  One edge bevelled: the arrow points at the part to bevel.

• Single-V with broad root face (Y)

  V bevel above a root face.

• Single-bevel with broad root face

  One edge bevelled, root face kept.

• Single-U butt

  Thick plate: less weld metal than a V.

• Single-J butt

  One edge machined to a J.

• Fillet weld

  The vertical side of the triangle is always on the left.

• Plug (hole or slot)
• Spot (resistance)

  Centred on the reference line.

• Seam (resistance)

Supplementary symbols

• Flush

  Flat surface, ground flush.

• Convex

  Rounded reinforcement.

• Concave
• All round

  Circle at the arrow/line elbow: the weld goes all round the part.

• Field weld

  Flag at the elbow: weld made on site, not in the shop.