A Welding Procedure Specification (WPS) is a formal, written document that provides clear and detailed instructions to welders and welding operators. It defines the welding parameters and techniques required to produce high-quality welds that meet code requirements and client specifications.
In accordance with ASME Section IX, a WPS outlines variables including joint design, base materials, filler metals, preheat/post-weld heat treatment (PWHT), shielding gas, welding position, and more. These parameters fall under three primary categories:
Classification of Welding Variable
- Essential Variables: Changes to these variables directly affect mechanical properties of the weld. Any change requires requalification of the WPS.
- Non-Essential Variables: These variables do not affect mechanical properties. Changes can be made without requalification but must be documented in the WPS.
- Supplementary Essential Variables: Applicable only when notch toughness is a requirement. Any change to these variables must also be requalified as they affect the toughness of the weld metal or the Heat-Affected Zone (HAZ).
WPS, WPQR, and Welder Certification Process
The process of developing and qualifying a WPS involves multiple stages, as outlined below:
1. Preliminary Welding Procedure Specification (pWPS)
A pWPS is prepared based on client requirements and the applicable code or standard (e.g., ASME, AWS, BS EN). It includes all proposed welding parameters and is submitted to the client for approval prior to qualification testing.
2. Welding Procedure Qualification (WPQ)
Before performing the qualification weld, the Welding Inspector ensures that all the following documentation and equipment are valid and calibrated:
- Mill Test Certificates (MTC) for base materials
- Consumable approval certificates
- Calibration records of the welding machine
- Approved pWPS
During the welding process, all parameters are logged on a Welding Run Sheet. After the weld coupon is visually accepted, it undergoes sampling for further testing.
Sampling Details Include:
- WPS Number
- Welder Identification (Name & ID Number)
- Test Date
The Welding Inspector raises a request for Non-Destructive Testing (NDT) and Mechanical Testing of the weld coupon.
3. Non-Destructive and Mechanical Testing
Testing is carried out according to client specifications and applicable codes. Typical tests include:
Non-Destructive Testing:
- Radiographic Testing (RT) – Mandatory in most ASME, AWS, and BSEN standards for record keeping and third-party validation
- Magnetic Particle Testing (MPT)
Mechanical Testing:
- Tensile Test
- Bend Test
- Charpy Impact Test (if toughness is a requirement)
- Macro Examination
- Hardness Test (as applicable to classification rules)
All test results are reviewed by a qualified Welding Engineer to ensure compliance with the relevant standards.
4. Welding Procedure Qualification Record (WPQR)
After successful testing, the Welding Engineer compiles a complete Procedure Qualification Record (PQR) which contains:
- Approved Procedure Qualification Record
- Welding Run Sheet
- Base Material & Filler Metal Details
- Test Results and NDT Reports
- Material and Consumable Certifications
5. Welder Performance Qualification and Certification
Following WPS approval, welders undergo performance testing under the supervision of a certified Welding Inspector or third-party examiner. The welder must replicate the qualified procedure.
- Test Coupons are evaluated both visually and through mechanical/NDT tests.
- Once the weld passes inspection, a Welder Certificate and Welder ID Card are issued.
Welding Documentation Overview
Typical documentation generated through the welding qualification process includes:
- Preliminary Welding Procedure Specification (pWPS)
- Welding Procedure Qualification Record (WPQR / PQR)
- Welding Run Sheet
- Final Welding Procedure Specification (WPS)
- Welder Performance Qualification Record (WPQ)
- Welder Certificate & ID Card
Conclusion
A properly developed and qualified WPS ensures welding work meets safety, quality, and regulatory requirements. Whether for pressure vessels, pipelines, structural components, or marine/offshore projects, EIWAA’s qualified inspection and welding engineering team can support your project with end-to-end documentation, testing, and third-party certification.