456A Blueprint Reading, Weld Symbols & Joint Preparation 2

Question 1

What is the difference between 'effective throat' and 'actual throat' of a fillet weld?

Accepted Answer

Actual throat is the distance from the root to the face including convexity; effective throat is the shortest distance from the root to the weld face (hypotenuse), which is used for strength calculations

Answer

For an equal-leg fillet weld with leg size 'w', the effective (theoretical) throat = w × 0.707. It is the shortest distance from the root to the theoretical face of the weld and is used for stress calculations. The actual throat includes any weld convexity above the theoretical face. Codes use the effective throat for design purposes as convexity is not considered reliably load-bearing.

Question 2

On a structural drawing, a fillet weld symbol shows '8' to the left and '150-300' to the right of the fillet symbol. What does this specify?

Accepted Answer

8 mm leg fillet welds, 150 mm long, spaced 300 mm apart (intermittent welds)

Answer

In standard weld symbol notation: the number to the left of the symbol is the weld size (8 mm leg), and the number(s) to the right indicate weld length and pitch. '150-300' means weld segments 150 mm long at 300 mm pitch (centre-to-centre spacing). This is an intermittent fillet weld specification — commonly used for non-critical connections to reduce heat input and cost.

Question 3

What does a double-sided V-groove symbol (X-groove) indicate on a drawing?

Accepted Answer

Full penetration groove weld to be made from both sides of the joint

Answer

The double-V groove (X-groove) symbol shows V-groove symbols on both sides of the reference line, indicating that the joint is to be prepared (bevelled) and welded from both sides. This is used for thick plate where welding from one side would require an excessively wide groove, resulting in excessive weld metal and distortion. It provides full penetration with less total weld metal than a single V.

Question 4

What is a 'backing symbol' (rectangle) on a groove weld symbol and what does it specify?

Accepted Answer

A backing bar or backing material is to be used at the root of the joint to support the root pass and ensure full penetration

Answer

The backing symbol (a rectangle below the reference line, on the other side from the weld symbol) indicates a backing bar or ring is required. In most structural applications, a CSA/ASTM steel backing bar is permanently fused into the joint. On process piping and pressure vessels, a removable ceramic or copper backing may be used. The presence or absence of backing affects the required root opening and edge preparation.

Question 5

What does the 'contour symbol' on a weld symbol specify?

Accepted Answer

The required finished profile of the weld face — flat, convex, or concave — and whether finishing is required

Answer

Contour symbols are placed above or below the weld symbol to specify the desired weld face profile: a straight line (flush/flat), a convex arc, or a concave arc. A letter below the contour symbol specifies the finishing method: G (grinding), M (machining), C (chipping), R (rolling), or U (unspecified). These specifications are important for fatigue-critical joints where notches at the weld toe must be minimized.

Red Seal Welder 456A Practice Test

Red Seal Welder 456A Practice Test

456A Blueprint Reading, Weld Symbols & Joint Preparation 2