AWS D1.1 · Table 6.1 · Criterion 3

Crater Cross Section — Unfilled Crater Rejection

A crater is a depression at weld termination where the arc is broken. AWS D1.1 requires craters to be filled to the required weld cross-section before moving to the next pass or ending the weld.

What is a Crater Defect?

A crater is a depression or hollow area where the welding arc was terminated. The metal cools with a "dished" or concave profile, creating a stress concentration point and potential crack initiation site.

Longitudinal crater — Runs along the centerline of the weld bead, typical in SMAW when arc is broken without crater fill.
Transverse crater — Perpendicular to weld direction, occurs at pass ends in multi-pass welds.
Crater cracking — Craters are stress concentration sites where cold cracking often initiates, especially in thick sections or high-carbon steel.
Material loss — Crater represents volume of weld metal below the required cross-section, reducing joint strength.

Crater Profile — Top View & Side View

TOP VIEW SIDE VIEW (Crater) ┌──────────────────────────────────────────────────┐ │ Weld bead → ═════════════════════ (arc ends) │ │ ═════════════════════ ▼ │ │ ════════════════════ ╱╱╱ (hollow) │ │ crater ╱╱╱╱╱╱╱╱╱╱╱ │ └──────────────────────────────────────────────────┘ Needs filling before next pass or termination

AWS D1.1 Table 6.1 Acceptance Criterion

Criterion 3: Crater Cross Section

Acceptance Limit: All craters must be filled to the required weld cross-section (per WPS drawing or specification) before pass termination or weld completion.

Unfilled crater visible → REJECTION
Crater below required weld size → REJECTION
Crater filled flush to required profile → ACCEPT

Repair Path: Add crater fill pass. Stop the arc in a transition zone beyond the crater, then move back and finish the final pass centered over the crater area. WPS should specify crater fill technique (e.g., "weave bead, 3 passes through crater zone").

Common Crater Causes

Abrupt arc termination — Electrode pulled away too quickly without filling the crater pool. Crater should be filled as the arc is reduced gradually.
Incorrect run-out tabs — In SMAW, run-out tabs (backup strips beyond the joint) absorb the final crater. If tabs are missing or too short, crater remains in the weld proper.
No crater fill pass planned — Multi-pass welds must account for crater fill (often an extra pass or modified final pass). WPS should specify.
Rapid cooling rate — Heavy sections or preheat loss can cause crater to freeze before being reflowed by the next pass.
Wrong current settings — Too low current in final pass cannot maintain stable arc for crater fill. Increase amperage per WPS range for finish pass.

How to Inspect & Document for the Report

Visual measurement — Compare weld profile at the crater area to the WPS specification. Crater should be filled flush or slightly convex.
Cross-section measurement (destructive test) — For critical joints, cut a sample perpendicular to the weld and measure crater depth below required cross-section area.
Profile gauge — Use a weld profile template (step gauge) to check that crater area meets the required dimension.
Mark on checklist — Record weld ID and pass where crater appears (e.g., "Final pass, weld termination end"). Measure crater depth if visible.
Photograph — Side-view photo shows crater profile against a reference ruler.

CWI Prevention & Repair Strategies

Ensure WPS specifies crater fill technique — extra pass, weave pattern through crater zone, or reduced travel speed at termination.
For SMAW, use run-out tabs on both ends of the joint. Tabs are cut off after cooling; crater is absorbed into the tab material, not the weld proper.
In GMAW/FCAW, implement gradual arc reduction at termination — don't break arc abruptly. Reduce wire feed or current to fill the crater pool as arc is withdrawn.
Train welders to recognize crater formation and practice crater fill technique. Many skills issues stem from inadequate crater fill training.

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