Part 1: Understanding the Fundamentals

Keyword focus: welding procedure specification, WPS, SQWP, ISO 15607, ISO 15609, welding qualification, arc welding procedures

Introduction

A welding procedure specification (WPS) is a critical document that defines how a weld is to be made to achieve the required mechanical and metallurgical performance. Since welding is classified as a special process, its quality cannot be verified solely by inspection of the finished product. For this reason, international quality management systems require welding to be performed according to written and qualified procedure specifications.

The ISO 15600 family provides a comprehensive framework for developing and qualifying WPSs for metallic materials. Two standards in this family form the foundation for every welding procedure specification:

1. BS EN ISO 15607: Specification and qualification of welding procedures (SQWP) for metallic materials – General rules.
2. BS EN ISO 15609: SQWP for metallic materials – Welding procedure specification

ISO TR 25901 supports these standards by defining welding and allied process terminology.

BS EN ISO 15607 outlines the general rules, essential variables, qualification routes, and terminology used in WPS development. BS EN ISO 15609 defines the structure and content of the WPS and provides process specific requirements.

This article introduces the key concepts needed to understand welding procedure qualification in accordance with ISO standards, with a focus on arc welding.

Welding Processes Covered by ISO 15607 and ISO 15609

The ISO framework applies to the major fusion and pressure welding processes used in industry, including:

1. Arc welding
2. Gas welding
3. Beam welding
4. Laser arc hybrid welding
5. Resistance welding
6. Stud welding
7. Friction welding
8. Friction stir welding

The BS EN ISO 15609 series specifies process specific WPS formats:

• ISO 15609-1 Arc welding
• ISO 15609-2 Gas welding
• ISO 15609-3 Electron beam welding
• ISO 15609-4 Laser beam welding
• ISO 15609-5 Resistance welding
• ISO 15609-6 Laser arc hybrid welding

Other relevant process standards include:

• ISO 14555 Stud welding
• ISO 15620 Friction welding
• ISO 25239-4 Friction stir welding
• ISO 18785-4 Friction stir spot welding

These standards ensure that welding operations are planned, documented, and executed in a repeatable and controlled manner, which enhances weld quality and production efficiency.

Material Grouping for WPS Qualification

To simplify WPS development and qualification, ISO standards group metallic materials based on their weldability characteristics. The following standards define the grouping systems used:

• ISO TR 15608 Grouping system for metallic materials
• ISO TR 20172 Grouping for European materials
• ISO TR 20173 Grouping for American materials
• ISO TR 20174 Grouping for Japanese materials

Material grouping is essential for determining qualification ranges, WPS applicability, and WPQR validity.

Competence Requirements and Applicability

The ISO 15607 series applies to manual, partly mechanized, fully mechanized, and automated welding. Qualification of a preliminary WPS using multiple routes is not recommended.

WPSs must be used by competent welding personnel:

• Welders must be qualified in accordance with ISO 9606
• Welding operators must be qualified in accordance with ISO 14732

This ensures consistent execution of the qualified welding procedure.

Note:

ISO 15609-1 defines the mandatory content for WPSs. A WPS is considered preliminary until it is qualified using one of the approved routes.

Development and Qualification of Welding Procedures

Before production welding begins, the manufacturer prepares a preliminary WPS based on welding engineering knowledge and previous experience. The preliminary WPS (pWPS) is then qualified through one of five methods:

1. Qualification based on a welding procedure test
2. Qualification based on tested welding consumables
3. Qualification based on previous welding experience
4. Qualification based on a standard welding procedure
5. Qualification based on a pre production welding test

Standards covering methods 2 to 5 include:

• ISO 15610 Tested welding consumables
• ISO 15611 Previous welding experience
• ISO 15612 Standard welding procedures
• ISO 15613 Pre production welding test

Each method is selected based on the application, material type, joint configuration, and criticality of weld performance.

1. Qualification Based on a Welding Procedure Test

This method involves welding and testing a standard test piece in accordance with the pWPS. It is the most widely used method because it provides direct evidence of weld quality, including weld metal and heat affected zone performance. It is used whenever the properties of the material in the weld metal and the HAZ are critical for the application.

The ISO 15614 series defines the procedure tests.

This method is suitable for applications where weld performance is critical, such as pressure vessels, structural components, and energy systems.

2. Qualification Based on Tested Welding Consumables

This method, defined in ISO 15610, is applicable when the parent metal does not experience significant HAZ degradation. It is used primarily for arc welding and gas welding.

ISO 15610:2023 includes the following limits for the use of this method:

• Parent material thickness t ≤ 40 mm for groups 1.1 and 8.1
• Parent material thickness t ≤ 20 mm for groups 21, 22.1, and 22.2
• Fillet welds with throat thickness a ≥ 1 mm

This qualification route cannot be used when hardness control, impact properties, preheat, controlled heat input, interpass temperature, or post weld heat treatment are required.

3. Qualification Based on Previous Welding Experience

Defined in ISO 15611, this method allows a manufacturer to qualify a WPS if there is documented evidence of previous successful welding of similar joints and materials. It is limited to procedures with proven and reliable performance.

4. Qualification Based on a Standard Welding Procedure

ISO 15612 permits the adoption of published standard WPSs. These SWPS documents define allowable parameter ranges in accordance with ISO 15609.

ISO 15612 limits parent materials to selected ISO TR 15608 groups and material thickness to 50 mm. The manufacturer remains responsible for correct implementation.

5. Qualification Based on a Pre Production Welding Test

This method, defined in ISO 15613, is used when weld performance is highly sensitive to production conditions that cannot be reproduced in standard test pieces. Typical cases include:

• Thick to thin attachment welds
• Highly restrained joints
• Components with significant heat sinks
• Complex geometries

Special test pieces are welded under production conditions, and testing may be supplemented to reflect the critical nature of the joint.

Different phases in WP qualification

Activity	Result	Party involved
Development of the procedure	pWPS	Manufacturera
Qualification by any method	WPQR including the range of validity based on the relevant standard of qualification	Manufacturera and, if applicable, examiner/examining bodyb
Finalization of the procedure	WPS based on this WPQR	Manufacturera
Release for production	Approved WPS or work instruction	Manufacturera
a An organization other than the manufacturer can be involved in the case of the qualification of a SWPS. b In certain cases, an external independent examiner/examining body can be required. Manufacturer – person or organization responsible for the welding production

Informative flow diagram for the development and qualification of a WPS.

Conclusion

This first part of the series introduces the fundamental concepts of welding procedure specification and qualification according to ISO standards. It explains the purpose of ISO 15607 and ISO 15609, outlines the major qualification routes, and defines how WPSs are developed and validated.

The next part of the series will explore the these WPS standard is some detail.

Frequently Asked Questions (FAQ) Part 1: Understanding ISO 15607 and ISO 15609

1. What is the purpose of a WPS?

A WPS defines how a weld must be made to meet required mechanical and metallurgical properties. Because welding is a special process where quality cannot be verified solely through final inspection, a WPS provides a controlled and repeatable method for producing compliant welds.

2. What is ISO 15607 and why is it important?

ISO 15607 establishes the general rules for developing and qualifying welding procedures for metallic materials. It defines essential variables, terminology, qualification principles, and the permitted qualification routes. It is the core reference standard in the ISO 15600 series.

3. What does ISO 15609 specify?

ISO 15609 defines the structure and required content of a welding procedure specification. It ensures that each WPS contains all necessary technical information such as joint design, welding parameters, consumable data, preheat, interpass temperature, and post weld heat treatment.

4. Which welding processes are covered by ISO 15607 and ISO 15609?

The standards cover arc welding, gas welding, electron beam welding, laser beam welding, laser arc hybrid welding, resistance welding, stud welding, friction welding, and friction stir welding. ISO 15609 provides process specific WPS formats for these methods.

5. Why are material grouping standards such as ISO TR 15608 important?

Material grouping simplifies welding qualification by categorizing metallic materials according to their weldability. It helps determine WPS qualification ranges, reduces the number of welding tests needed, and supports selection of compatible filler materials and welding parameters.

6. Who is allowed to use a WPS in production welding?

Only competent welders and welding operators may use a WPS in production. Welders must be qualified according to ISO 9606, while operators must be qualified to ISO 14732. These qualifications ensure consistent application of the approved WPS.

7. What is a preliminary WPS?

A preliminary WPS is a draft version of the welding procedure specification that has not yet been qualified. It is used as the basis for welding procedure testing and is validated through one of the ISO approved qualification routes before being released for production use.

8. What are the main qualification routes defined in ISO 15607?

ISO 15607 defines five qualification routes:

1. Welding procedure test (ISO 15614)
2. Tested welding consumables (ISO 15610)
3. Previous welding experience (ISO 15611)
4. Standard welding procedure (ISO 15612)
5. Pre production welding test (ISO 15613)

Each method is selected based on material type, joint configuration, and the criticality of weld performance.

9. How long does a welding procedure qualification remain valid?

A welding procedure qualification remains valid indefinitely unless an essential variable is changed outside the qualified range or an application standard specifies additional requirements. The validity applies to the ranges recorded in the welding procedure qualification record.

10. What is the relationship between the WPS and WPQR?

The WPQR records the results of the welding procedure qualification and defines the allowable ranges for essential variables. The production WPS is developed from the WPQR and provides the welder with the detailed instructions needed to repeat the qualified weld.