Twelve Guardrail Joints, Porosity at Restart, and a Crater Crack
Twelve identical 8 mm lap joints in a guardrail assembly are welded by GMAW at 22 V, 180 A with 1.2 mm ER70S-6 and 75/25 gas. The WPS requires 100% visual inspection and a 10% destructive bend test on production coupons. Visual inspection finds: three joints with clustered porosity at the restart point, one joint with 2 mm undercut along the toe, one with a 3 mm crater crack, and two with heavy spatter and a convex bead profile. Two bend-test coupons from the same batch show a 4 mm long porosity cluster in the root. The welder wants to grind all twelve joints smooth, re-weld them and paint over the result. The customer’s acceptance criteria reference ISO 5817 level C and require repair records and welder identification.
1. Classify each reported condition and decide accept, reject or repair, with reasoning based on the acceptance criteria.
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- Clustered porosity at restarts (3 joints): reject. Clustering exceeds typical porosity limits and points to gas coverage lost at the start - insufficient pre-flow, long stick-out or a dirty restart.
- 2 mm undercut (1 joint): reject. On 8 mm plate this is 25% of thickness and beyond any normal limit (commonly ≤0.5 mm or 10%, whichever is smaller).
- 3 mm crater crack (1 joint): reject without argument. Cracks are not permitted at ISO 5817 level C or any normal level; they must be removed completely, not just capped.
- Root porosity on bend test (2 coupons): reject the batch represented by those coupons. A 4 mm cluster in the root is a real defect; bend testing exposes it because the root is strained.
- Spatter and convex bead (2 joints): spatter is usually cosmetic but must be removed; a convex profile may be acceptable if throat thickness meets the drawing, but it can mask lack of fusion. Inspect, measure and accept only if profile and throat are within the WPS/drawing.
Most of the batch is nonconforming; the two cosmetic joints may be salvageable after cleaning, but the batch cannot be released on the current evidence.
2. The welder proposes to grind all twelve joints smooth and re-weld them. Evaluate this plan, including what must be removed before re-welding and how to verify it.
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Grinding all twelve and re-welding is too broad and not automatically safe. The crater crack must be removed completely - grind or gouge beyond the visible crack, then verify with PT or MT before re-welding; a surface grind is not enough. The clustered porosity at restarts may be removed by grinding to sound metal, but if it extends into the root the joint must be gouged back to the root. The root porosity found on bend coupons means the process, not just the surface, is suspect; the whole batch needs re-evaluation, and repair welding should follow a qualified repair procedure. Repeated repair cycles can reduce toughness and increase distortion, so cap the number of repairs (commonly two) and require engineering approval beyond that. After repair, re-run visual inspection and the required bend/NDT sampling, and do not paint until inspection is accepted. The welder must also correct the restart technique: pre-flow, clean wire, correct stick-out and crater fill.
3. Prepare the documentation and reporting package: what records are required, who signs them, and what traceability is needed?
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Build a traceable package:
- Planning: drawing and revision, WPS number and PQR support, repair procedure if used, customer acceptance criteria (ISO 5817 level C).
- Personnel: welder ID and qualification record, inspector ID and certification, date and shift.
- Materials: base-metal certificates/heat numbers, wire lot, gas lot or supplier, and any backing/consumables.
- Process: machine settings (V, A, WFS, gas flow at nozzle), preheat/interpass if applicable, joint identification.
- Inspection: visual report with defect locations and sizes, bend-test report with coupon IDs and results, NDT reports, and photographs if used.
- Nonconformance: NCR number, description, disposition (repair/reject/concession), root cause, corrective action and customer approval.
- Release: re-inspection results, final acceptance signature, and a statement that all records are complete.
Keep records with the guardrail batch ID so each joint can be traced back to the welder and WPS. Sign and date every entry; an unsigned or incomplete report is not traceability.