A welding procedure specification (WPS) is a controlled document that explains how a weld must be completed to achieve the required quality, strength and compliance. It helps ensure consistent welding across fabrication projects, supports regulatory compliance and provides traceability throughout production. If you need advice on welding procedures or independent inspection support, contact S. T & W Inspections today on 01795 432 634.
A WPS is not simply paperwork. It provides the documented link between qualified welding procedures, consistent workmanship and reliable inspection throughout a project's lifecycle.
What Is a Welding Procedure Specification (WPS)?
A Welding Procedure Specification (WPS) is a documented set of essential welding variables that defines how a weld must be produced. It provides clear instructions that enable qualified welders to create repeatable welds that satisfy design requirements and applicable standards.
Although the exact content varies depending on the welding process and project specification, a typical WPS includes:
- Welding process, such as MMA, MIG/MAG, TIG or submerged arc welding
- Parent material specification and thickness range
- Approved filler material or consumables
- Joint design and preparation
- Welding position
- Preheat and interpass temperature requirements
- Heat input range
- Welding parameters, including current, voltage and travel speed
- Post-weld heat treatment where applicable
The WPS provides a consistent method that everyone involved in fabrication can follow.
Why Is a WPS Required for Many Welding Projects?
Many industries operate under strict quality and safety requirements where welding failures are simply unacceptable. Pressure vessels, structural steelwork, pipelines, bridges, district heating networks and critical infrastructure all rely on welding procedures that have been demonstrated to produce sound welds.
Standards such as BS EN ISO 15614 and ASME Section IX require welding procedures to be qualified before production begins, demonstrating that they consistently produce welds meeting the required mechanical and quality standards.
For organisations working to standards such as BS EN 1090 or ISO 3834, a qualified welding procedure specification (WPS) also forms an important part of demonstrating compliance during audits and project inspections. For organisations needing support with welding coordination, our RWC services provide independent oversight of welding activities, including WPS review and compliance auditing.
What Is a WPQR and How Does It Validate a WPS?
A Welding Procedure Qualification Record (WPQR) provides the evidence that a proposed WPS has been tested successfully.
Before a welding procedure specification (WPS) can be qualified, a representative test weld is produced using the specified procedure. That weld is then subjected to destructive testing and examination to confirm it performs as intended.
Depending on the applicable standard, testing may include:
- Tensile testing
- Bend testing
- Impact testing
- Macro examination
- Hardness testing
If the results meet the acceptance criteria, the WPQR records the successful outcome and demonstrates that the WPS can reliably produce acceptable welds within defined limits.
What Is the Difference Between a Qualified WPS and a Standard WPS?
Not every WPS has been individually qualified through testing.
A qualified welding procedure specification (WPS) is supported by an approved WPQR completed under recognised qualification standards. This provides greater confidence that the procedure has been validated for specific applications.
A standard WPS may instead be based on published guidance or pre-qualified procedures permitted by certain standards. These are generally used only where the governing specification allows them and where all stated limitations are satisfied.
Project documentation should always specify whether a qualified WPS is required. For many safety-critical applications, relying on an unqualified procedure would not satisfy contractual or regulatory requirements.
What Happens If a Welder Deviates from an Approved WPS?
Even experienced welders must work within the approved limits of the WPS.
Changing filler material, welding parameters, preheat temperature or joint preparation without authorisation may invalidate the procedure for that weld. The consequences depend on the nature of the deviation but may include additional inspection, repair, rejection or complete removal and replacement of the weld.
During production, weld inspectors compare completed welds against the approved WPS and associated documentation. They verify that:
- The correct procedure has been used
- Welding variables remain within approved limits
- Weld preparation matches the specification
- Welder qualifications remain valid
Where non-conformance is identified, it is documented so corrective action can be agreed before work progresses further. This helps prevent minor issues developing into more serious quality or compliance issues.
How Does a WPS Connect with Non-Destructive Testing?
A WPS does not replace inspection. Instead, it works alongside inspection and non-destructive testing to verify that production welds meet the required quality requirements.
Many projects specify both a qualified WPS and a programme of Non-Destructive Weld Testing. The inspection method depends on the project specification and the type of weld being assessed.
For example:
- Visual inspection confirms weld profile, dimensions and visible surface quality.
- Ultrasonic testing examines the internal condition of many welds without causing damage.
- Magnetic particle inspection detects surface-breaking defects in suitable ferromagnetic materials.
- Liquid penetrant inspection may be used where magnetic particle inspection is not appropriate.
Together, approved welding procedures and NDT provide confidence that both the welding process and the finished weld satisfy project requirements.
Why Understanding WPS Requirements Supports Better Project Outcomes
A welding procedure specification provides the foundation for consistent, compliant and repeatable welding. For a broader overview of the standards that govern welding inspection, our guide on weld inspection standards provides a helpful starting point. When supported by a WPQR and verified through inspection, it reduces uncertainty throughout fabrication and helps ensure welding is completed using approved methods.
For engineers, procurement teams and project managers, understanding how welding procedure specifications, qualification records and inspection work together makes it easier to specify contractors, review documentation and maintain quality throughout a project. If you require independent weld inspection, WPS compliance checks or support with welding qualifications and procedures, contact S. T & W Inspections to discuss your project.
Frequently Asked Questions
Is a WPS legally required in the UK?
A WPS is not required for every welding job, but many contracts, industry standards and fabrication codes require qualified welding procedures for safety-critical work. The applicable standard and project specification determine when a WPS is mandatory.
Can one WPS cover every welding job?
No. Each WPS is qualified for specific materials, thickness ranges, welding processes and variables. Different projects may require multiple WPS documents.
Who writes a Welding Procedure Specification?
A welding procedure specification is typically prepared by suitably qualified welding personnel with the technical knowledge to develop procedures that comply with the relevant standards and project requirements. Where qualification testing is required, the WPS is supported by a WPQR before being approved for production use.
Does every weld require non-destructive testing?
Not always. The inspection requirements are determined by the project specification, applicable standards and the criticality of the component. Some welds may require only visual inspection, while others require multiple NDT methods.
Can an independent inspector check WPS compliance on site?
Yes. Independent weld inspectors can verify that approved WPS documents are being followed, review welding records, identify non-conformances and confirm inspection requirements are being met throughout production.
