456A Blueprint Reading, Weld Symbols & Joint Preparation 4

Question 1

What is the maximum allowable root face (land) dimension for a standard single-V groove joint when welding with SMAW using a 3.2 mm electrode?

Accepted Answer

1.5–3 mm root face to support the root pass without burn-through while allowing complete penetration

Answer

A root face of 1.5–3 mm (approximately 1/16–1/8 in.) provides adequate support for the molten root pass without excessive risk of burn-through, while still allowing complete penetration with the arc. Too thick a root face prevents full penetration; too thin (or zero) increases burn-through risk. The root face dimension is specified in the WPS and on the joint preparation drawing.

Question 2

What is the purpose of tack welds in joint assembly and what special requirements apply to structural tack welds per CSA W59?

Accepted Answer

Tack welds temporarily hold joint alignment; structural tacks must be made by qualified welders using the approved WPS and must be of adequate size and quality to avoid cracking or inclusion when covered by the final weld

Answer

Tack welds that will be incorporated into the final weld must be made by qualified welders using the applicable WPS (same preheat, low-hydrogen process if required). Tacks must be free of cracks and discontinuities. Cracked tacks must be removed, never welded over. Tack welds at the end of joints that will not be consumed may be removed or feathered (ground) before final welding.

Question 3

What is 'hi-lo' (mismatch) in pipe or plate joint fit-up and what is the maximum allowed per CSA W59 for butt joints in structural steel?

Accepted Answer

Vertical offset between the two base metal surfaces at the joint; maximum 3 mm or 25% of the thinner member thickness, whichever is less

Answer

Hi-lo (offset or mismatch) is the vertical offset between the surfaces of two base metal pieces at a butt joint. Excessive hi-lo causes stress concentration, unequal penetration, and notch effects. CSA W59 limits hi-lo to 3 mm or 25% of the thinner member thickness, whichever is less. On pressure piping (CAN/CSA Z662), limits are typically 1.6 mm for pipe wall thicknesses up to 12.7 mm.

Question 4

What is the purpose of a 'weld run-off tab' at the end of a weld joint?

Accepted Answer

Allows the weld to be started and terminated on temporary extensions, keeping weld defects (craters, start porosity) off the base metal joint

Answer

Run-off tabs (extension bars) are temporary pieces of matching base material tack-welded to the ends of the joint. The weld starts on the run-on tab, proceeds through the joint, and ends on the run-off tab, keeping arc starts and stops (which are prone to porosity, craters, and inclusion) off the structural weld. Tabs are removed and the base metal ends dressed flush after welding.

Question 5

What is the maximum root opening (gap) allowed for a fillet-welded T-joint under CSA W59 before a larger weld size must be specified?

Accepted Answer

5 mm — root openings above 5 mm require increasing the weld leg size by the amount of the gap

Answer

CSA W59 allows root openings in fillet-welded T-joints up to 5 mm (3/16 in.). For root openings up to 5 mm, the weld leg size must be increased by the amount of the gap to maintain the required effective throat. Root openings above 5 mm are generally not permitted without an engineering review or joint preparation change.

Red Seal Welder 456A Practice Test

Red Seal Welder 456A Practice Test

456A Blueprint Reading, Weld Symbols & Joint Preparation 4