Crack Prohibition — The Zero-Tolerance Criterion

What is a Crack?

A crack is a visible discontinuity in the weld metal, base metal, or heat-affected zone that typically opens to the surface and runs through the material depth.

• Cold crack — Forms after welding cools, usually beneath the surface in the HAZ or weld root. Common in high-carbon steel, preheated components, or restrained joints.
• Hot crack — Forms during cooling while metal is still semi-solid. Typical in austenitic stainless, nickel alloys, or undersized welds with high restraint.
• Lamellar tear — Subsurface crack in the HAZ running parallel to the weld surface. Occurs in thick sections with high through-thickness stress.
• Reheat crack — Forms during post-weld heat treatment (PWHT). Rare in structural steel but serious when it occurs.

AWS D1.1 Table 6.1 Acceptance Criterion

Common Crack Causes

• Insufficient preheat — Carbon steel and low-alloy steel susceptible to cold cracking without adequate preheat. Check base metal composition and thickness.
• High restraint — Thick sections, multi-pass welds, or fixtured joints create stress buildup. Slow cooling and stress relief help.
• Undersized weld — Filler metal insufficient to fill joint volume. Creates stress concentration and discontinuity.
• Wrong electrode — Overmatching or mismatched filler (ER70S-2 on 80ksi base) introduces brittleness.
• Fast cooling — Rushing the weld or insufficient PWHT raises hardness and crack susceptibility.
• Contaminated base metal — Mill scale, rust, oil, or high sulfur/phosphorus in base steel promotes cracking.

How to Inspect & Document for the Report

• Visual examination — Look for visible hairlines, gaps, or openings in weld profile and HAZ under bright light. Use magnifying glass (10x) if needed.
• Dye penetrant (PT) — Optional supplementary NDT. Penetrant fills cracks and reveals them under black light. More sensitive than visual alone.
• Document the defect — Record weld ID, crack location (root, face, toe), approximate length, and orientation (linear, transverse, along bead direction).
• Photograph if possible — Close-up photo with reference scale (ruler, coin) shows inspector and client what was observed.
• Mark for rejection — Clearly indicate "CRACK - REJECT" on inspection checklist. No advisory or pass with repair — zero tolerance.

CWI Inspection Tips

• Cracks often appear at stress concentration points — weld termination, toe transitions, or around defects like porosity.
• Subsurface cracks (lamellar tears, cold cracks) may not be visible. Use dye penetrant or UT for high-restraint thick sections.
• After repair, allow slow cooling — use insulated blankets, preheat, or stress relief per WPS to minimize reheat cracking risk.
• If cracking is repeated, investigate the root cause before re-welding. Bad base metal, wrong preheat, or improper cooling is the issue, not the inspection.