The vendor qualification audit process is the staged evaluation a buyer uses to decide whether a fabricator, foundry, heat treater, laboratory or material supplier can be trusted with orders, and to keep checking that trust afterwards. It combines a questionnaire, a document review, an on-site audit, a scored decision and ongoing monitoring, and it works alongside third-party inspection and the ISO 3834 welding quality system.
This guide covers the stages, a risk-based audit depth, a checklist by vendor type, an illustrative scorecard and ongoing monitoring. It includes the metallurgical checks, such as material certificates, heat treatment records and carbon equivalent limits (see the carbon equivalent calculator), that decide whether a qualified vendor delivers conforming product.
- Audit depth should follow the risk of the product or process supplied, not the size of the order.
- A certificate shows a system exists; an on-site audit shows whether the system is used.
- Special processes such as welding, heat treatment, NDT and coating need the closest look.
- Qualification ends in a recorded decision and an approved vendor list, not in a passed audit alone.
- Approval is conditional on continued performance and is reviewed on a set interval.
What Is Vendor Qualification?
Vendor qualification is a documented evaluation confirming a supplier can consistently meet quality, technical and delivery requirements before orders are placed.
The evaluation looks at the vendor’s quality system, technical capability, process control, people, equipment and track record. The result is a recorded decision: the vendor is approved, approved with conditions or not approved for a defined scope, such as a product family or process. Approval for one scope does not extend to another, so a vendor approved to fabricate carbon steel structures is not automatically approved for stainless pressure parts.
The terms vendor and supplier are used interchangeably in industry; this guide uses vendor throughout. A vendor audit is a second-party audit, because the buyer audits its supplier. It differs from an internal audit by the vendor on itself and from a third-party certification audit by an independent body.
Why Qualify Vendors at All?
Buyers qualify vendors because the quality of purchased product cannot be inspected into it at receipt. A casting with hidden shrinkage, a plate with the wrong heat treatment or a weld made with an unqualified procedure may pass a quick incoming check and fail in service.
The management system standard supports this directly. ISO 9001 (Quality management systems: Requirements), in its clause on externally provided processes, products and services, requires the organisation to apply controls proportionate to the risk, including criteria for evaluation, selection, monitoring and re-evaluation of external providers. For welded products, ISO 3834 (Quality requirements for fusion welding of metallic materials) includes requirements for subcontracting, and customers working to ASME or other codes expect vendors to hold valid procedure and welder qualifications. Where a customer or regulator requires third-party oversight, the vendor qualification record is also what a third-party inspector will ask to see. Related guides are in the Welding Metallurgy category and the Materials Testing category.
What Are the Stages of Vendor Qualification?
Qualification runs in seven stages, from defining the requirement to monitoring the vendor after approval:
- Define the requirement and classify the vendor by the risk of what it will supply.
- Send a pre-qualification questionnaire and collect certificates, procedures and references.
- Review the documents and decide the scope and depth of the on-site audit.
- Audit the vendor on site, observing the processes that matter and tracing real orders.
- Score the findings, record the decision and set conditions and corrective action dates where needed.
- Add approved vendors to the approved vendor list with their approved scope and review date.
- Monitor delivery, rejections and corrective actions, and re-evaluate on a risk-based interval.
Small buyers often compress the stages, and low-risk suppliers may be qualified from the questionnaire and certificates alone. The sequence still holds: the evaluation is proportionate, and the decision and its basis are recorded.
How Do You Decide How Deep to Audit?
Audit depth follows the consequence of a failure in what the vendor supplies. A pressure-retaining weld, a forging for a rotating part or a heat-treated component deserves an on-site audit; a catalogue fastener bought in bulk rarely does. Classifying vendors into categories before the audit keeps effort where the risk is.
| Category | Typical supply | Minimum qualification |
|---|---|---|
| A: critical | Pressure parts, castings, forgings, welding subcontract, heat treatment, NDT | Questionnaire, document review, on-site audit, first-article check |
| B: important | Machined parts, standard plate and pipe from stockists, coating | Questionnaire, certificates, audit by sample or desk audit |
| C: commodity | Consumables, hardware, general supplies | Questionnaire or certificate review, performance monitoring |
The categories and rules in the table are examples; each buyer defines its own. The class should also reflect project requirements: a customer or code may require audited vendors for a scope that the buyer would otherwise rate lower. Where a project requires third-party inspection, align the audit with the inspection plan, because inspectors verify work at the vendor’s site.
What Should a Pre-Qualification Questionnaire Ask?
The questionnaire collects facts and certificates before any visit so the audit can focus on what is unclear. Each answer should name the evidence, and the buyer should check that certificates are valid, in scope and issued by an accredited body where that is expected.
| Topic | Question | Evidence requested |
|---|---|---|
| Quality system | Which management system certifications are held and for what scope? | ISO 9001 certificate with scope and expiry |
| Welding quality | Is welding controlled to a recognised standard? | ISO 3834 certificate or equivalent, welding coordinator details |
| Procedures and personnel | Are welding procedures and welders qualified to the specified code? | Procedure qualification records, welder qualification lists |
| Materials and traceability | How are materials sourced, certified and traced? | Sample material certificates, traceability procedure |
| Equipment and calibration | How are measuring and welding equipment calibrated? | Calibration procedure and register |
| Testing and NDT | Which tests are done in house and which are outsourced? | Laboratory accreditation scope, NDT personnel certificates |
| Capacity and history | What similar work has been completed and what is the current load? | Reference list, capacity summary |
| Subcontracting | Which processes are subcontracted and how are those vendors controlled? | Subcontractor list, control procedure |
What Should an On-Site Vendor Audit Examine?
An on-site audit tests whether the vendor does what its documents say. Walk the process in the order the work flows, ask operators to explain what they do and trace one or two real orders end to end, from the purchase order through material receipt, the special processes, inspection and dispatch. The auditor should be competent in the process being audited and independent of the commercial relationship where possible.
| Vendor type | Key checks on site | Typical evidence and basis |
|---|---|---|
| Fabricator or welding subcontractor | Procedure and welder qualification, consumable control, preheat control, inspection plan followed | WPS and qualification records (ISO 15614-1, ISO 9606-1, ASME IX), ISO 3834 system |
| Foundry or forge | Chemistry control, heat treatment records, traceability from melt to part, NDT of critical areas | Melt and heat treatment records, certificates |
| Heat treater | Furnace calibration and surveys, load thermocouple use, charts matched to the procedure | Furnace charts, calibration records, procedures |
| Testing laboratory | Accreditation scope covers the test, equipment calibration, specimen identification | ISO/IEC 17025 accreditation scope, test reports |
| NDT provider | Personnel certification, written procedures, equipment checks | ISO 9712 certificates, procedures |
| Mill or stockist | Certificate type and content, heat number traceability, storage and marking | EN 10204 certificates, order match |
| Coating or painting contractor | Surface preparation, environmental conditions, film thickness measurement | Inspection records, paint system standard such as ISO 12944 |
For material and process specifics, auditors can use the metallurgical background in the guides to quenching steel, normalising and annealing and stress relieving, and the preheat temperature calculator to check whether the preheat and welding limits a fabricator states are reasonable for the steel. For mechanical testing evidence, see the guides to hardness testing methods and the Charpy impact testing guide.
How Do You Score and Decide?
A scorecard turns findings into a consistent decision. The weights should reflect what matters most for the supply: for a welded fabricator, control of special processes carries more weight than price competitiveness. The table and bar chart show an illustrative weighting that a buyer would adapt.
| Criterion | Weight, % | Examples of what is scored |
|---|---|---|
| Technical capability | 25 | Equipment, skills, experience on similar work |
| Quality system | 20 | Certification, procedures, internal audits |
| Special process control | 20 | Welding, heat treatment, NDT and coating control |
| Traceability and records | 15 | Material and weld traceability, record quality |
| Delivery and capacity | 10 | Lead time, current load, reliability |
| Financial, health and safety | 10 | Stability, safety record |
Decision bands are also set by the buyer. A common structure is approved above an upper threshold, conditionally approved between two thresholds with a time-limited corrective action plan, and not approved below the lower threshold. A major finding in a critical process, such as unqualified welders on a code job, should prevent approval regardless of the total score, since a high average can hide a fatal gap.
How Do You Monitor Vendors After Approval?
Approval is a starting point. Performance data from actual orders shows whether the audit picture holds. Typical measures are on-time delivery, rejection or non-conformance rate at receipt, response time and effectiveness on corrective action requests, and findings from later audits or third-party inspections.
- Review on a schedule. Re-evaluate approved vendors at a set interval, commonly between one and three years depending on risk, and sooner after a serious failure.
- Issue supplier corrective action requests. Require a root cause and a verified fix, the same discipline expected in an internal audit.
- Use first-article and sample checks for new scopes or after a change of process, material or location.
- Keep the approved vendor list current. Record scope, conditions, expiry of certificates and the date of the next review.
Where an inspector from an independent body visits the vendor during the order, their reports are valuable monitoring input and should flow back into the vendor file.
What Are Common Mistakes in Vendor Qualification?
- Accepting certificates as proof of practice. A valid certificate shows a system exists, not that it is followed on the order in hand.
- Using one qualification for every scope. Approval applies to a defined product and process range.
- Auditing the office, not the floor. Special processes are won or lost at the bench, in the furnace and in the NDT booth.
- Letting price override a weak audit. A conditional approval needs a real action plan, with dates.
- Ignoring sub-vendors. Special processes are often subcontracted; the buyer should know who does them and how they are controlled.
- Never re-evaluating. Key staff leave, equipment ages and processes change after approval.
- Averaging away a critical gap. A total score can look acceptable while a critical process fails.
Key Terms
- Vendor qualification
- A documented evaluation confirming that a supplier can meet the buyer’s requirements before orders are placed.
- Approved vendor list (AVL)
- The controlled list of vendors approved for a defined scope of supply.
- Second-party audit
- An audit of a supplier carried out by the buyer.
- Special process
- A process whose result cannot be fully verified by later inspection, such as welding, heat treatment or coating.
- Conditional approval
- Approval given with required corrective actions and dates before full approval.
- Supplier corrective action request (SCAR)
- A formal request that a vendor find the root cause of a problem and verify the fix.
- First-article inspection
- A detailed check of the first item produced to confirm that the vendor can meet all requirements.
Frequently Asked Questions
What is the difference between vendor qualification and vendor audit?
Vendor qualification is the whole process of deciding whether a supplier is approved, including questionnaire, document review, audit, scoring and the approval record. A vendor audit is one step in it: the on-site examination of the supplier’s processes and records.
When is an on-site vendor audit required?
An on-site audit is generally justified for vendors supplying critical items or special processes such as welding, heat treatment, NDT, castings and forgings, or when a customer or code requires it. Lower-risk suppliers can often be qualified from a questionnaire and certificates.
Does an ISO 9001 certificate replace a vendor audit?
No. A certificate shows that a management system was assessed against a standard for a stated scope. It does not show that product requirements for your order are met. Use it as evidence in the questionnaire and audit the processes that matter.
How often should approved vendors be re-evaluated?
Intervals are risk-based and set by the buyer. One to three years is common for audited vendors, with sooner review after a serious failure, a major process change or poor performance data. Performance monitoring continues between audits.
What happens if a vendor fails the audit?
The vendor is either not approved or conditionally approved with a corrective action plan and dates. A re-audit or document check confirms that the actions worked before full approval is given. Major findings in critical processes should block approval.
What should be in an approved vendor list?
The vendor name, approved scope of supply or process, conditions, certificate expiry dates, the date of last audit and the next review date. The scope matters because approval for one product or process does not cover others.
How does third-party inspection relate to vendor qualification?
Qualification decides whether a vendor may receive orders. Third-party inspection verifies the work on a specific order, at hold points defined by the buyer or code. Inspection findings are useful input for vendor performance review.
Conclusion
Vendor qualification protects the buyer by testing a supplier before orders depend on it and by checking continuously afterwards. Classify the supply by risk, collect evidence by questionnaire, audit special processes on site, score the result with a rule that stops a critical failure from being averaged away, and record the decision on an approved vendor list. Then watch performance and re-audit on a schedule set by risk. The details of each check depend on the product, code and standard edition that apply. As the next step, read how independent inspectors verify a vendor’s work in the guide to third-party inspection (TPI) in welding.
About This Guide
This guide was prepared by the MetallurgyZone technical team from the sources listed under Standards and References. Verify requirements against the standard edition, material specification and contract applicable to your application.
Standards and References
- ISO 9001, Quality management systems: Requirements, International Organization for Standardization (iso.org).
- ISO 19011, Guidelines for auditing management systems, ISO.
- ISO 3834 (Parts 1 to 5), Quality requirements for fusion welding of metallic materials, ISO.
- ISO/IEC 17020, Conformity assessment: Requirements for the operation of various types of bodies performing inspection, ISO and IEC.
- ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories, ISO and IEC.
- ISO 9606-1, Qualification testing of welders: Fusion welding, Part 1: Steels, ISO.
- ISO 15614-1, Specification and qualification of welding procedures for metallic materials: Welding procedure test, Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys, ISO.
- ISO 9712, Non-destructive testing: Qualification and certification of NDT personnel, ISO.
- ISO 12944, Paints and varnishes: Corrosion protection of steel structures by protective paint systems, ISO.
- EN 10204, Metallic products: Types of inspection documents, CEN.
- ASME Boiler and Pressure Vessel Code, Section IX, Welding, Brazing, and Fusing Qualifications, ASME (asme.org).