Reading of Weld Symbols and Fit-up Layout
What this domain tests
Decoding a welding symbol into a real joint preparation, and the marking and fit-up that turns that symbol into an aligned, correctly gapped assembly.
Core rules
- Symbol anatomy. Arrow line pointing to the joint, reference line, identification line, tail (process or specification), elementary symbol on the reference line, plus size, length and pitch dimensions.
- Side convention. In the IS 813 / ISO 2553 convention, a symbol above the reference line means the arrow side; below means the other side. AWS A2.4 is the reverse - read the title block to know which convention the drawing uses.
- Supplementary symbols. Circle at the junction = weld all around; flag = site weld; two arrows = weld between; straight line on the symbol = flat contour; concave/convex marks = finishing method.
- Size conventions. Fillet size is leg length z, not throat a; throat a = 0.7 z. Butt weld symbols carry groove angle, root gap and root face.
- Fit-up. A 60° single-V needs about 30° bevel each face, root face (land) 1.5–2 mm, root gap 2–3 mm for SMAW; high-low misalignment kept under about 10% of thickness or 1.5 mm, whichever is smaller.
Worked example
A symbol shows a V on the reference line labelled 60°, root gap 2, root face 1.5, with a circle at the junction and tail '111', drawn above the reference line. Interpretation: single-V butt weld, 60° included angle (30° bevel per plate), 2 mm gap, 1.5 mm land, welded on the arrow side only, all around the component, by manual metal arc (process number 111). The fitter must bevel both plates to 30°, leave a 1.5 mm land machined square, tack at four points with a 2 mm gap wire in place, and check the gap after tacking because shrinkage closes it.
Traps
Reading fillet size as throat instead of leg; ignoring the tail process number; applying the AWS side convention to an ISO drawing; forgetting that the root gap must be re-checked after tacking.