What are common weld defects and how to avoid them?

Weld defects can cause a part to be rejected at the QBQ exam. Here are the most common ones:

1. Porosity — Small holes in the weld

• Cause: Trapped gas (moisture, draft, clogged nozzle)
• Solution: Clean the metal, shield the arc from wind, check the gas flow (the one in the WPS and on the supplier's data sheet)

2. Undercut — Groove in the base metal along the weld toe

• Cause: Current too high, travel speed too fast, incorrect electrode angle
• Solution: reduce the current, slow down and correct the electrode angle — the values are set on a test coupon, per the manufacturer's data sheet

3. Lack of fusion

• Cause: Insufficient temperature, incorrect angle, travel speed too slow
• Solution: Increase current, clean the joint, adjust angle

4. Slag inclusion

• Cause: Slag from the previous pass not completely removed
• Solution: Brushing and grinding between each pass — mandatory!

5. Longitudinal or transverse crack

• Cause: Cooling too fast, hydrogen in the weld, high stresses
• Solution: Low hydrogen electrodes (E7018), preheating, control of cooling rate

Lack of fusion and porosity are among the most frequent grounds for rejection. The acceptance criteria (size and density of indications) are those of CSA W59 and the project specification: they depend on the joint type and the inspection class and are read in the code, not from a single percentage.