Construction and design
The Construction and design domain tests drawing literacy and joint design: reading ISO 2553 weld symbols, selecting a joint preparation, and controlling distortion and residual stress before the first arc is struck.
Weld symbols (ISO 2553)
The arrow points to the joint; the reference line carries the symbol. A solid line means arrow side, a dashed line the other side. Dimensions: a = throat thickness for fillets, z = leg length, s = full penetration. The tail carries the process (for example 135) and supplementary symbols cover all-around, field weld and backing.
Joint design
V, U, J and K preparations trade access against weld volume. A typical 60° included V gives root access; a root face of 1–2 mm prevents burn-through; root gap controls penetration. Backing supports the root but must not fuse into the weld unless its composition matches.
Distortion and residual stress
Shrinkage is longitudinal, transverse and angular. Controls: pre-setting, balanced welding about the neutral axis, backstep and skip sequences, minimum weld volume, rigid fixtures (which raise residual stress), and PWHT for stress relief at about 580–620 °C for C-Mn steels.
Worked example
A drawing specifies a 6 mm throat on a 90° fillet. Leg z = a/0.707 = 8.5 mm. A welder laying an 8 mm leg gives a = 5.7 mm - undersize and rejectable. The throat is the load-bearing section, so leg length must always be converted, never assumed equal to throat.
Traps
Confusing a and z; placing the symbol on the wrong side of the reference line; assuming a larger leg is always acceptable (it adds distortion and cost); treating PWHT as a cure for poor fit-up; forgetting that fixtures increase restraint and cracking risk.