Dissimilar Metal Welding
Welding Procedure Qualification
Material Compatibility
Welding Dissimilar Metals: How WPS and WPQR Qualification Is Planned for Carbon Steel–Stainless Steel Joints Globally
By First Welding Certification Technical Editorial Team
6 Min Read Time
11 Nov 026
Table of Contents
Key Considerations for Dissimilar Metal Welding Qualification
Base Metal Identification
Filler Metal Selection
Welding Parameter Control
WPS & WPQR Qualification
Introduction
Dissimilar metal welding is the process of joining two different metals that have different chemical compositions, material classifications and metallurgical properties. A common industrial example is joining carbon steel to austenitic stainless steel. Manufacturers may use this combination when they require the strength and cost advantages of carbon steel together with the corrosion resistance of stainless steel.
Other examples include:
- Carbon steel to stainless steel
- Different stainless steel grades
- Low-alloy steel to stainless steel
- Nickel-based alloys to steel
The welding procedure must consider the actual materials, joint design, service conditions and qualification requirements.
Why Carbon Steel and Stainless Steel Are Welded Together
Manufacturers combine different materials to meet specific engineering and production requirements.
Cost optimisation: Carbon steel is commonly used for structural and general fabrication requirements, while stainless steel can be selected for areas requiring improved corrosion resistance.
Corrosion resistance: In chemical processing and storage equipment, stainless steel may be used in areas exposed to corrosive products, while carbon steel is used in other sections.
Design flexibility: Different materials may be combined to meet temperature, pressure, strength and corrosion requirements.
Challenges of Dissimilar Metal Welding
Joining different materials introduces several technical considerations.
3.1 Chemical Differences
Carbon steels and stainless steels have different alloy compositions. Welding consumables and welding methods must account for the properties of both materials. Incorrect consumable selection can affect weld-metal properties.
3.2 Thermal Expansion Differences
Different metals expand and contract at different rates during heating and cooling. This can influence residual stress and distortion in the completed component.
3.3 Dilution
During welding, portions of the parent materials melt and mix with the deposited weld metal. This influences the final weld-metal composition. Manufacturers should consider consumables, welding methods and joint design when developing the procedure.
3.4 Heat Input and Cooling
Heat input and cooling conditions can influence the metallurgical properties of the weld and heat-affected zone (HAZ). The welding procedure must establish appropriate parameter ranges according to the relevant standard.
3.5 Corrosion
The completed joint must be assessed for its intended service conditions. Temperature, pressure, chemical exposure and corrosion requirements can influence material and consumable selection.
How WPS and WPQR Help Dissimilar Metal Welding
WPS and WPQR provide documented control and qualification of the welding procedure.
Welding Procedure Specification (WPS)
A WPS provides production welding instructions, including:
- Parent material identification
- Welding process
- Joint preparation
- Filler material classification
- Welding position
- Preheating requirements
- Interpass temperature
- Welding current and voltage ranges
- Travel speed and other applicable parameters
- Post-weld heat treatment requirements, where applicable
The exact information depends on the standard used to prepare the WPS.
Welding Procedure Qualification Record (WPQR)
A WPQR records the actual welding conditions used during procedure qualification and the results of the required examinations and tests.
It may include:
- Parent material identification and thickness
- Welding process and consumables
- Actual welding parameters
- Test-piece information
- Visual and non-destructive testing results
- Mechanical test results
- Additional tests required by the relevant specification
- Qualification range and limitations
The WPS must be supported by an appropriate qualification route wherever required by the applicable standard or project specification.
Key Considerations Before Welding Qualification
Before conducting a welding qualification test for dissimilar metals, manufacturers should consider the following.
Parent material identification: Confirm the exact grades and specifications for both materials. Review material certificates to establish correct identification.
Material groups: Identify the applicable material groups and combinations under the qualification standard. Do not assume that qualification for one material combination automatically covers all other combinations.
Consumables: Select filler material based on the parent materials, joint requirements and intended service conditions. Consider the required weld-metal properties.
Joint design: Identify the joint configuration, such as a butt joint, fillet joint or branch connection. Qualification routes and testing requirements may differ.
Service conditions: Consider operating temperature, pressure, corrosion exposure and other relevant requirements.
Welding Procedure Qualification
The welding procedure must be qualified according to the relevant standard and project requirements. EN ISO 15614-1 is a relevant standard for qualification of arc and gas welding procedures for steels. Its applicability must be checked against the materials and construction code.
A typical qualification process involves the following steps.
Step 1: Review the requirements
Identify the relevant construction standard, material specifications, joint requirements and qualification route.
Step 2: Develop a preliminary WPS
Prepare a draft welding procedure based on the welding process, material combination, joint design and consumables.
Step 3: Prepare the test piece
Prepare the test materials and joint according to the applicable qualification requirements. Ensure that the materials are correctly identified.
Step 4: Perform trial welding
Carry out the test weld under controlled conditions. Record actual welding parameters, consumables, preheating conditions and other required information.
Step 5: Conduct inspection and testing
Depending on the applicable standard and project requirements, testing may include:
- Visual examination
- Radiographic or ultrasonic examination, where applicable
- Tensile testing
- Bend testing
- Impact testing, where required
- Hardness testing, where required
- Additional metallurgical or corrosion testing, where specified
Not all tests are required for every qualification. The test programme must be established using the governing standard.
Step 6: Review the results
Evaluate the inspection and test results against the applicable acceptance criteria. Any non-conformity must be addressed before the qualification is accepted.
Step 7: Prepare the WPQR
Document the actual welding conditions, inspection results, mechanical test results and applicable qualification range.
Step 8: Prepare the production WPS
Prepare the production WPS using the qualified procedure. Ensure that production parameters remain within the permitted qualification ranges.
Example: Carbon Steel to Stainless Steel
Consider a manufacturer producing an industrial pressure vessel with a carbon steel shell and a stainless steel connection. These materials have been selected to provide the required functionality for the equipment.
Before production welding, the manufacturer must identify:
- Correct material grades and specifications
- Relevant construction code and welding qualification standard
- Suitable filler material
- Joint preparation and welding process
- Required welding procedure qualification tests
- Required inspection and documentation
The manufacturer develops a preliminary WPS and carries out the qualification test under controlled conditions. Once the weld passes the required inspection and testing, the WPQR documents the qualified procedure within its permitted range.
The production WPS is then prepared and authorised. During production, welders must follow the authorised procedure, while inspection personnel verify welding records, material traceability and project requirements.
This demonstrates why welding procedure qualification should be planned before critical production work begins.
Frequently Asked Questions
an I use the same WPS to weld carbon steel and stainless steel?
A WPS can only be used for a particular dissimilar material combination when the qualification standard permits it and the supporting WPQR covers that combination and its applicable qualification range.
What standard is used for WPS and WPQR qualification?
EN ISO 15614-1 is a relevant standard for qualifying arc and gas welding procedures for steels. The correct part and edition must be selected according to the materials, welding process and construction requirements.
Is filler material important in dissimilar metal welding?
Yes. Filler material selection influences weld-metal composition and mechanical and service properties. It should be evaluated against both parent materials and the intended application.
What testing is required for dissimilar metal welding qualification?
Testing depends on the qualification standard, material combination, joint configuration and project requirements. It may include visual examination, NDT, tensile, bend, impact or other specified tests.
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Conclusion
Welding dissimilar metals requires more than selecting two compatible materials and joining them using a suitable welding process. Manufacturers must consider material combinations, consumable selection, welding parameters, metallurgical behaviour and intended service conditions.
A properly developed WPS and supporting WPQR provide documented evidence that the welding procedure has been qualified within a defined scope.
Manufacturers working with pressure equipment, piping, chemical processing systems and other fabricated products can reduce production risks by planning welding procedure qualification in advance.
PZVAR supports manufacturers with welding-related conformity assessment and certification activities according to applicable standards and approved scopes.
Planning a welding procedure qualification for your manufacturing project? Contact PZVAR to discuss your WPS, WPQR and welding certification requirements.
First Welding Certification Pvt Ltd (PRVÁ ZVÁRAČSKÁ, a.s.)can help you explore the relevant welding quality and certification requirements for your application.