Interpretation of Drawings and Specifications
Interpretation of Drawings and Specifications
This domain tests reading orthographic and isometric drawings, dimensions, tolerances, welding symbols, and supporting documents such as WPSs and codes. The exam expects you to convert a symbol into a real weld: process, type, size, length, location, and quality requirement.
Core rules
- Canadian practice commonly uses third-angle projection: the top view is above the front view and the right-side view is to the right. Confirm the projection symbol if shown.
- A welding symbol has an arrow, reference line, tail, and optional dashed line. The arrow points to the joint. Symbols above the reference line are on the arrow side; below are on the other side.
- Fillet symbol: size is placed to the left of the triangle; length to the right. Intermittent welds add a pitch value, the centre-to-centre spacing, after the length. A circle at the junction means weld all around; a flag means field weld.
- Groove symbols show the groove shape (V, bevel, U, J), groove angle, root opening, and root face. The tail may carry the process, electrode, or specification.
- Dimensions and tolerances override scaled measurements. Do not scale a drawing unless permitted.
- The WPS tells you preheat, current range, polarity, travel speed, and pass sequence; the drawing does not.
Worked example
A symbol shows a triangle above the reference line, “8” to the left, “150” to the right, a circle at the junction, and a flag. Interpretation: an 8 mm fillet weld on the arrow side, 150 mm long, all around the joint, made in the field. If the triangle were below the line, the weld would be on the other side. If an intermittent length and pitch were shown, the pitch is the spacing between weld segments, not the segment length.
Traps
- Reading size as length or length as pitch.
- Ignoring arrow-side versus other-side placement.
- Missing the all-around circle or field flag.
- Treating a tail note as optional when it specifies process or electrode.
- Scaling dimensions instead of using stated values.
- Applying a WPS for the wrong process or position.