Welding Inspection for Metal Products: Pre-Shipment Guide
Published September 1, 2026 by muzhuo
Welding Inspection for Metal Products: Pre-Shipment Guide
Why This Matters
Welding defects are the most common hidden failure in imported metal products. A weld can look clean on the surface and fail months later in use — or carry visible cracks, porosity, and incomplete fusion that nobody checked before the container left the factory. For importers of steel furniture, gates, brackets, frames, and machinery parts, a pre-shipment welding inspection is the difference between a product that lasts five years and a liability that comes back.
This guide explains what a professional welding inspection actually checks, based on the workflow we use for welded product batches — including a real 92-piece inspection — so you know exactly what to ask for from your quality inspector.
Why Welding Inspection Matters for Importers
You cannot judge weld quality from a product photo. Defects like internal cracks and incomplete fusion are invisible until the product is loaded, painted, or in service. By the time a weld fails, the container has shipped, the customs clearance is done, and the cost of correction is higher than the product value.
A pre-shipment welding inspection gives you three things:
- Evidence — documented photos of every weld condition before shipment
- Leverage — defects found before loading are corrected at the factory's cost
- Compliance — proof that your product meets the welding standard you specified in the PO
� The cheapest time to find a weld defect is at the factory, before paint, before loading. After shipment, every defect is an argument — before shipment, it's just a correction.
What the Inspector Checks: Surface Defects (Visual Testing)
Visual testing (VT) is the first and most important step. The inspector examines every accessible weld for these defects:
| Defect | What It Looks Like | Severity |
|---|---|---|
| Cracks | Fine lines on or near the weld | ❌ Critical — always reject |
| Porosity | Small holes or pits on the weld surface | ⚠️ Major — depends on density |
| Undercut | Groove melted into the base metal at the weld edge | ⚠️ Major — weakens the joint |
| Incomplete fusion | Weld metal not bonded to the base metal | ❌ Critical — structural risk |
| Overlap | Weld metal rolled over the base metal without fusion | ⚠️ Major |
| Spatter | Small metal droplets scattered around the weld | ℹ️ Minor — cosmetic, but sign of poor parameters |
For critical or load-bearing products, the inspector will also check internal soundness — either by sampling destructive tests or by non-destructive testing (NDT) such as dye penetrant (PT), magnetic particle (MT), or ultrasonic testing (UT), depending on what the buyer's specification requires.
Dimensional Checks: Weld Size and Geometry
A weld can be defect-free yet undersized — and undersized welds fail under load. The inspector measures:
- Leg size (fillet welds) or throat thickness — against the drawing or standard
- Weld length — the weld must run the full joint length
- Reinforcement height — too high means stress concentration, too low means weakness
- Uniformity — consistent width and height along the joint
These are measured with a weld gauge and recorded per piece in the report, with photos.
️ A common finding in Chinese factories: the weld looks fine but the leg size is 3 mm where the drawing requires 5 mm. Only a gauge, not the eye, catches this.
Sampling: How Many Pieces to Check
Welding inspection sampling depends on the product and the defect:
- Load-bearing or safety-critical parts: 100% inspection. No sampling.
- Standard production batches: AQL sampling (typically AQL 2.5 for major defects, 4.0 for minor) per ISO 2859 / ANSI Z1.4.
- Batch of 92 pieces (our case study): with AQL 2.5 general level II, a sample of 13 pieces covers the batch — but for welded products with visible welds, we inspect 100% visually where cost allows, because visual inspection is fast and defects are highly variable.
� For welded products, always combine: 100% visual inspection of accessible welds + AQL sampling for dimensional and destructive checks. Pure AQL sampling alone misses scattered defects.
Case Study: 92-Piece Welded Product Batch
In our inspection workflow test, a batch of 92 welded products was checked using a structured welding inspection flowchart — every piece visually inspected, dimensional checks on a sample, and all findings photographed.
| Check | Method | Result |
|---|---|---|
| Weld appearance | 100% visual per piece | 3 pieces flagged for rework (porosity) |
| Weld dimensions | Gauge on 13-piece AQL sample | All within drawing tolerance |
| Joint coverage | Visual | 1 piece with incomplete weld length |
| Rework verification | Re-inspection after rework | All cleared before packing |
The key takeaway from this job: two of the four findings were only caught because inspection was structured — a checklist, not a glance. A random look at 10 pieces would have missed the incomplete weld length entirely.
What the Welding Inspection Report Includes
- Reference documents: PO number, drawing/standard, weld specification
- Piece-by-piece results: defect type, location, and photo for every finding
- Dimensional data: measured leg size / throat / length vs. required
- Sampling plan: AQL level, sample size, acceptance criteria
- Rework records: what was reworked and the re-inspection result
- Clear verdict: Accepted / Conditional / Rejected, per your PO's acceptance criteria
A good welding report lets your QC team in your home country verify the factory's work without visiting — the photos and measurements are the evidence.
FAQ
What welding defects are always rejected?
Cracks and incomplete fusion are always rejected — they are structural failures waiting to happen. Porosity and undercut are rejected when dense or deep; minor cases are reworked and re-inspected.
Is visual inspection enough for welded products?
For most consumer and furniture-grade welded products, yes — 100% visual plus dimensional checks on a sample is the right level. For pressure vessels, gas equipment, or safety-critical structures, ask for NDT (PT, MT, or UT) and the factory's welder certificates.
When should welding inspection happen in the production timeline?
Before painting or plating. Paint hides porosity and undercut — the inspector must see bare weld metal. The best window is after welding and grinding, before surface treatment.
Can I judge weld quality from the product photos the factory sends?
No. Factory photos are marketing; they show the best piece from the best angle. An independent inspector photographs every defect found — including the ones the factory would rather hide.
What should I specify in my PO for welding?
State the welding standard (e.g. AWS D1.1 or ISO 5817 quality level), required leg/throat size, whether NDT is required, and that inspection happens before surface treatment. One line in the PO changes the whole inspection scope.
Get Your Metal Products Welding-Approved
Don't let defective welds reach your customers. Our inspectors run structured welding inspections at the factory — visual, dimensional, and documented piece-by-piece — with a report you can show your buyer.
→ — get a quote within 24 hours Book an inspection
→ — send your drawing and PO, we'll define the checklist Contact our team
Related reading: Steel Plate Dimensional Inspection: Tolerances and AQL Sampling Explained for Importers.