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Welder Red Seal · Question

A welder is inspecting a T-joint fillet weld on 3 mm stainless steel, welded without proper backing. They notice a discoloured and rough, sandy appearance on the back side of the weld, commonly referred to as 'sugaring'. What caused this defect?

Sugaring on stainless steel welds is caused by the oxidation of chromium in the material when exposed to atmospheric oxygen at high temperatures during welding.

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Question: A welder is inspecting a T-joint fillet weld on 3 mm stainless steel, welded without proper backing. They notice a discoloured and rough, sandy appearance on the back side of the weld, commonly referred to as 'sugaring'. What caused this defect?

Answer options:

  • Too high a welding current and travel speed. ✅ Lack of proper inert gas shielding on the weld root.
  • Excessive preheat applied to the stainless steel.
  • Contamination from the base metal itself.

Correct answer: Lack of proper inert gas shielding on the weld root.

Explanation: Sugaring on stainless steel welds is caused by the oxidation of chromium in the material when exposed to atmospheric oxygen at high temperatures during welding. This is a direct result of inadequate or absent inert gas shielding (purging/backing) on the root side of the weld. High current can intensify it, but the root cause is lack of shielding.

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