Outsourcing welded fabrication reduces capital investment, adds capacity flexibility and gives you access to a specialist team. But choosing the wrong supplier leads to late deliveries, nonconforming parts and missing documentation — which means downtime on the assembly line and customer complaints.
The 10 criteria below are designed to help purchasing and quality teams systematically evaluate a subcontract welding supplier, from the first meeting through to the audit.
1. Welding Quality Certifications
The first documents to look at are EN ISO 3834-2 (comprehensive quality requirements for welding) and, for structural steel, the EN 1090-2 certificate. Check that the execution class (EXC) on the certificate meets your project's class. Details: What is EN 1090 EXC3?
2. Management System Certificates
ISO 9001 quality, ISO 14001 environmental and ISO 45001 occupational health and safety certificates show that the supplier manages its processes in a documented and auditable way. They are usually a prerequisite in the supplier approval processes of major OEMs.
3. Approved WPS / WPQR Portfolio
Does the supplier already have an approved procedure for your material group and thickness range? If not, a new WPQR process must be started, which can delay the first delivery by weeks. See What is a WPS?
4. Qualified Welders
The process, position and material scope of the welder certificates must match your work. For a detailed checklist, see our welder certification guide.
5. Welding Coordination
There should be a responsible welding coordinator (IWE/IWT) in accordance with EN ISO 14731. This person owns technical decisions from WPS selection to the NDT plan. See the role of the welding engineer.
6. NDT and Inspection Capability
Apart from visual testing (VT), are methods such as MT, PT and UT performed in-house or sent to an external laboratory? What EN ISO 9712 level do the inspection personnel hold? Method comparison: NDT methods.
7. Integrated Production Chain
Carrying out cutting, bending, welding, machining and surface treatment under one roof, or in a coordinated way, reduces intermediate transport, waiting time and confusion over responsibility. Working with a single point of contact also means the tolerance chain is managed by one party.
8. Full Traceability and Documentation Package
Material certificates (EN 10204 3.1), consumable batch, welder ID, preheat records, NDT reports and the dimensional inspection report should be supplied with the delivery. Digital access to documents is a plus.
9. Capacity and Delivery Performance
Ask about the supplier's current utilisation rate, shift pattern and on-time delivery rate over the last 12 months. Find out whether there is headroom for sudden increases in volume.
10. Technical Communication and Engineering Support
A good supplier doesn't just build to the drawing; it offers design for manufacturability (DFM) suggestions on weld preparation, welding sequence and distortion risk. These suggestions are often the most effective source of cost optimisation.
Quick Evaluation Table
| Criterion | Evidence to Request |
|---|---|
| Certifications | EN ISO 3834-2, EN 1090-2 (EXC), ISO 9001/14001/45001 |
| Procedures | WPS/WPQR list, material and thickness ranges |
| Personnel | Welder certificates, welding coordinator, NDT personnel levels |
| Quality | Sample documentation package, inspection report, nonconformance management |
| Operations | Capacity, delivery performance, response time |
Recommendation: Place the first order as a small pilot batch and assess the documentation package, inspection report and lead time in concrete terms.
Frequently Asked Questions
Which certifications should a welding subcontractor have?
First and foremost, an EN ISO 3834-2 welding quality certificate and, for structural steelwork, an EN 1090-2 certificate (in the appropriate EXC class). ISO 9001, ISO 14001 and ISO 45001 are also common supplier prerequisites.
What happens if the supplier has no approved WPS?
A new WPQR process (test weld and destructive testing) must be carried out. This extends the first delivery schedule and adds cost.
Why is a pilot order important?
A pilot batch lets you see the supplier's quality, documentation discipline and delivery performance on a real job, reducing risk before series production.
Ready for Your Supplier Audit
Review our certificates, WPS list and sample documentation package — let's start with a pilot order.
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