The 6 welding defects that cause Red Seal exam failure (and how to avoid them)

Introduction

The Red Seal practical exam is the most feared test for welders in training across Canada. According to data from the Bureau de normalisation du Québec (BNQ), the failure rate on the first attempt ranges between 30% and 40%, and the vast majority of failures are caused by a limited number of recurring weld defects. This article reviews the 6 most frequently penalized defects on the Red Seal exam, the tolerances allowed by CSA W47.1, and the techniques to avoid them.

1. Excessive Porosity — Defect #1

Porosity is by far the most common cause of failure on the Red Seal exam. It shows up as small gas pockets in the deposited weld metal, visible to the naked eye or on radiography.

Main causes:

• Insufficient shielding gas (GMAW/FCAW) — a flow rate below 18 ft³/h (8.5 L/min) in the vertical position creates systematic porosity
• Drafts over the welding area — even as low as 8 km/h, they disperse the shielding gas
• Moisture on basic electrodes (E7018) — exposure to open air for more than 4 hours without re-baking at 300-350 °F makes the electrode unusable
• Contaminated surface (oil, grease, rust, paint) in the fusion zone

CSA W47.1 tolerance (clause 12.4): Cumulative porosity must not exceed 5% of the weld surface over a 25 mm section. Beyond that, it's an automatic failure on the exam.

Solution: Systematically check your gas flow with a flowmeter before each pass. Use freshly baked electrodes (E7018 straight from the oven at 120 °C). Clean the welding area with a stainless steel brush over at least 25 mm on each side of the joint.

2. Lack of Fusion — The Sneaky Defect

Lack of fusion occurs when the filler metal doesn't properly fuse with the base metal or between passes. It's the hardest defect to detect visually because it's often below the surface.

Causes:

• Incorrect work angle — an electrode angle that's too tight (< 60° in SMAW) concentrates the arc on one wall only
• Travel speed too fast — the arc doesn't have time to heat both joint walls sufficiently
• Welding current too low — especially in SMAW with E7018, where a current below 90 A for a 1/8 in (3.2 mm) electrode creates a cold puddle
• Insufficient cleaning between passes — trapped slag prevents fusion

Solution: For a 60° V-groove joint with a 1/16 in (1.6 mm) root face, use a 75-80° electrode angle in SMAW, a current of 110-130 A for E7018 1/8 in, and a travel speed of 2 to 3 mm/s. Brush each pass down to bright metal before the next pass — not just the slag, but also the thin oxide layer.

3. Hot Cracking in the Heat-Affected Zone (HAZ)

Cracks in the HAZ are grounds for immediate and irreversible failure, with no possibility of repair during the exam.

Causes:

• Insufficient preheat for high-strength steels (A514, A709 Gr. 50W) — CSA W47.1 clause 7.5 requires a minimum preheat of 150 °C (300 °F) for thicknesses over 25 mm
• Cooling rate too fast — diffusible hydrogen doesn't have time to escape
• High residual stresses in an overly rigid joint

Solution: Follow the preheat temperatures in Table 5.1 of CSA W47.1. For the Red Seal exam on standard carbon steel (A36, 44W), a preheat of 100-150 °C is sufficient for thicknesses from 12 to 25 mm. Use an infrared thermometer to check the temperature 25 mm from the joint before each pass.

4. Undercut — Loss of Section

Undercut is a groove in the base metal adjacent to the weld. It reduces the effective cross-section of the metal and creates a stress concentration point.

Causes:

• Welding current too high — the arc melts the base metal faster than the filler metal can fill it
• Excessive arc length in SMAW — an arc longer than 3 mm (1/8 in) creates systematic undercut
• Poor electrode angle in the vertical-up position

CSA W47.1 tolerance: The maximum undercut depth is 0.8 mm (1/32 in) and the cumulative length must not exceed 25 mm over 300 mm of weld.

Solution: In the vertical-up position with SMAW, reduce the current by 10-15% compared to the flat position. Maintain a short arc (1.5 to 2.5 mm) and use a controlled weave motion with a 0.5-second dwell at the edges to allow the metal to fill the undercut.

5. Slag Inclusions — Leftovers from the Previous Pass

Slag inclusions are non-metallic particles trapped between weld passes. They're detectable on radiography and cause failure if their size or frequency exceeds tolerances.

Causes:

• Inadequate cleaning between passes — slag is a thermal insulator that prevents complete fusion
• Pass profile too convex — the cavities under the hump trap slag
• Inappropriate weaving technique — slag flows ahead of the arc in the flat position if the angle is too low

Solution: Each pass must be cleaned with a chipping hammer followed by a wire brush down to bright metal. For fill passes, cross-brushing (perpendicular to the weld axis) is three times more effective than longitudinal brushing. Plan for 70% of your exam time to be spent cleaning between passes — that's the secret of welders who pass on the first try.

6. Insufficient Root Penetration

For complete joint penetration (CJP) welds, insufficient root penetration is one of the most severely penalized defects.

Causes:

• Root opening too narrow — the arc can't reach the bottom of the joint
• Root face too thick (> 3 mm) — the base metal doesn't melt completely
• Current too low on the root pass
• Electrode angle favoring one side of the joint

Solution: For a V-groove joint with a 1/16 in (1.6 mm) root face and a 3/16 in (4.8 mm) root opening, the root pass in SMAW with E7018 3/32 in (2.4 mm) should be done at 80-95 A. In GMAW, use short-circuit transfer at 17-19 V and a wire feed speed of 150-180 in/min with 0.035 in (0.9 mm) ER70S-6 wire. Root reinforcement should be 1 to 2 mm — no more (risk of snagging), no less (insufficient penetration).

Final Tips for Exam Day

Before you start your Red Seal exam weld, take 5 minutes to:

1. Check the preheat temperature with an infrared thermometer (100 °C minimum for 12 mm 44W steel)
2. Confirm the gas flow rate at 20-25 ft³/h for GMAW/FCAW
3. Verify that your E7018 electrodes have been out of the oven for less than 30 minutes
4. Clean the plate with a grinder over 25 mm on each side of the joint
5. Run a test pass on a scrap piece of steel to confirm your machine settings

Red Seal examiners follow the evaluation grid in CSA W47.1 Annex A. Each defect is weighted: cracks and lack of penetration are automatic failures (critical defects), while porosity and undercut are cumulative. By mastering these 6 defects, you go from a 70% chance of success to over 90%. Happy welding!