AWS D10.18M (welding ferritic/austenitic duplex stainless steel piping and tubing) provides welding practices related to stainless steel reinforcing bars. The AWS standard is a specialized guide developed by the American Welding Society. Duplex stainless steels are widely used in industries requiring high strength and excellent corrosion resistance. This standard provides essential guidance on filler metal selection, welding techniques, joint design, and quality control to ensure the integrity of welded joints. Understanding AWS D10.18M helps professionals to achieve consistent and high-quality welds in demanding applications. In this article, read all about the AWS D10.18 Standard in detail.
Post Highlights:
- What is AWS D10.18 Standard?
- AWS D10.18 Requirements
- AWS D10.18 Welding Processes
- AWS D10.18 Joint Design
- AWS D10.18M/D10.18:2018 (Contents)
- AWS D10.18 Testing Methods
- AWS D10.18 Best Practices
- AWS D10.18 Welder Qualification Procedure
- AWS D10.18 vs AWS D10.12
- AWS D10.18 Industrial Applications
- AWS D10.18 Common Challenges
What is AWS D10.18 Standard?
AWS D10.18 is a welding standard that provides guidelines for welding ferritic/austenitic duplex stainless steel piping and tubing. The AWS code covers recommended practices, filler metal selection, welding procedures, and quality control. This ensures high-performance, corrosion-resistant welds in industrial applications such as petrochemical and marine systems.
Duplex stainless steel combines roughly equal parts of austenite and ferrite. This offers high strength, excellent corrosion resistance, and good weldability. The steel is used in demanding environments like marine, chemical processing, and oil and gas industries. It keeps both mechanical performance and resistance to stress corrosion cracking.
AWS D10.18 Requirements
Some key requirements include-
1. Material Compatibility – Specifies the types of ferritic/austenitic duplex stainless steels covered and their welding characteristics.
2. Welding Process Selection – Recommends suitable welding processes such as GMAW, GTAW, and SMAW for effective welds.
3. Joint Design – Outlines acceptable joint configurations and fit-up practices. This ensures proper weld quality and penetration.
4. Filler Metal Selection – Guides on choosing compatible filler metals to maintain the correct ferrite-austenite phase balance.
5. Pre-Weld Preparation – Covers alignment, cleaning, and surface preparation requirements. This prevents contamination and defects.
6. Welding Parameters – Defines interpass temperature, acceptable heat input, and travel speed. It controls microstructure and minimizes defects.
7. Post-Weld Considerations – Includes inspection, non-destructive testing (NDT), and post-weld cleaning or treatment to ensure weld integrity.
8.Welder/Procedure Qualification – Sets standards for qualifying welders and welding procedures. This ensures competency and repeatable quality.
9. Quality Assurance/Inspection – Details testing methods, visual inspection, and acceptance criteria to verify weld compliance.
10. Safety Practices – Highlights essential safety measures during welding operations to protect personnel and equipment.
AWS D10.18 Welding Processes
Some key welding processes include –
1. Gas Tungsten Arc Welding – TIG is preferred for root passes and thin-walled tubing. It offers precise control and high-quality welds with minimal heat input.
2. Shielded Metal Arc Welding – Stick is commonly used for field welding and repairs. It is suitable for thicker sections with proper control of heat input.
3. Gas Metal Arc Welding – MIG is efficient for production welding with high deposition rates. It requires proper shielding gas and parameter control for duplex steels.
4. Flux-Cored Arc Welding – FCAW offers high productivity and good mechanical properties. It is suitable for thicker materials in shop or field environments.
5. Submerged Arc Welding – SAW is used for heavy wall thickness and long welds. It requires careful control to avoid excessive heat input affecting phase balance.
6. Plasma Arc Welding – PAW is less common but provides precision and deep penetration. It is suitable for automated welding of specialized duplex components.
AWS D10.18 Joint Design
The key joint design considerations include-
1. Butt Joints – Commonly used for pipe and tube welding. Proper beveling and alignment are critical to ensure full penetration and phase balance.
2. Socket Weld Joints – Suitable for smaller diameter piping. It requires precise fit-up and control to avoid excessive heat input and crevice corrosion.
3. Branch Connections – Used in piping systems where pipes intersect. This requires careful joint preparation aa nd welding sequence to prevent incomplete fusion.
4. Groove Design – Specifies appropriate groove angles and root openings. It allows proper filler metal access and ensures adequate penetration.
5. Back Purging Consideration – Recommended for root pass protection, especially in butt joints. This prevents oxidation and maintains the corrosion resistance of duplex stainless steels.
6. Fit-op Tolerance – Tight control of gap, alignment, and joint preparation is essential. This reduces stress concentration and maintains weld quality.
AWS D10.18M/D10.18:2018 (Contents)
The table of contents includes-
1. Scope – Defines the purpose of the guide and the types of duplex stainless-steel piping and tubing it covers.
2. Referenced Documents – Lists other standards and codes referenced within AWS D10.18, including ASTM, AWS, and ASME documents.
3. Terms/Definitions – Provides clear definitions for technical terms related to duplex stainless-steel welding used throughout the guide.
4. Base Metal Classification – Describes the types and grades of ferritic/austenitic duplex stainless steels applicable to the standard.
5. Welding Process Guidelines – Outlines recommended welding methods such as SMAW, GTAW, GMAW, and their application to duplex materials.
6. Filler Metal Recommendations – Specifies appropriate filler metal types and classifications for maintaining proper phase balance and corrosion resistance.
7. Welding Procedure Considerations – Covers essential welding variables such as interpass temperature, heat input, and preheat/post-weld practices.
8. Joint Design/Preparation – Details acceptable dimensions, joint types, bevel angles, and preparation techniques for quality welds.
9. Welder/Procedure Qualification – Provides requirements for qualifying welders and welding procedures following AWS standards.
10. Inspection/Testing – Describes recommended acceptance criteria, NDT methods, and visual inspection practices.
11. Safety/Precautions – Emphasizes welding safety practices, including protective equipment, ventilation, and handling of duplex materials.
12. Annexes/Informative Appendices – Includes example procedures, supplementary information, and additional technical data to aid understanding and implementation.
AWS D10.18 Testing Methods
The key testing methods include-
1. Visual Inspection (VT) – The first line of quality control, used to check surface defects, weld appearance, alignment, and overall workmanship before and after welding.
2. Radiographic Testing (RT) – Effective for detecting internal weld defects like slag inclusion, lack of fusion, and porosity in pipe and tube welds.
3. Liquid Penetrant Testing (PT) – Used to detect porosity, surface cracks, or pinholes, especially in root and final weld passes on non-magnetic duplex stainless steel.
4. Magnetic Particle Testing (MT) – It applies only to ferritic or partially ferritic weld zones. This helps to detect surface and near-surface flaws, but is limited to duplex stainless steels.
5. Ultrasonic Testing (UT) – Used to detect internal flaws in thicker sections. Suitable for duplex stainless steels where RT may not be practical.
6. Ferrite Content Measurement – Critical for duplex welds to ensure proper phase balance. Deficient ferrite can impact corrosion resistance and toughness.
7. Mechanical Testing (Destructive Tests) – Includes tensile tests, bend tests, and hardness tests. This assesses weld strength, ductility, and overall mechanical performance.
8. Corrosion Testing – This is optional but important in critical applications. Ensures the weld zone maintains corrosion resistance. It is typically tested through ASTM methods like G48.
AWS D10.18 Best Practices
Common best practices include-
1. Maintain Proper Heat Input – It controls heat input to avoid excessive ferrite or austenite formation. This can compromise corrosion resistance and mechanical properties.
2. Use Recommended Filler Metals – Select filler metals specifically suited for duplex stainless steels. It ensures correct phase balance and weld integrity.
3. Root Passes Back Purging – Always use inert gas back purging (e.g., argon). This protects the root pass from oxidation and maintains corrosion resistance.
4. Monitor Interpass Temperature – Keep interpass temperatures within specified limits (usually below 150°C). This prevents the formation of harmful intermetallic phases.
5. Clean Joint Surfaces – Thoroughly remove grease, oil, and oxides before welding. This prevents contamination and weld defects.
6. Avoid Excessive Weaving – Use stringer beads instead of wide weave beads to limit heat input and preserve microstructure.
7. Minimize Arc Strikes – Avoid arc strikes outside the weld zone. This can lead to localized corrosion and structural weaknesses.
8. Conduct Ferrite Number Checks – Regularly measure ferrite content in welds. Ensure it falls within the recommended range for duplex materials.
9. Pre/Post Weld Cleaning – Use appropriate methods (e.g., passivation pickling) to clean the weld area and restore corrosion resistance.
10. Use Qualified Welders/Procedures – Ensure that all welding personnel and procedures are properly qualified to meet the standard’s requirements.
AWS D10.18 Welder Qualification Procedure
Key components of the Welder Qualification Procedure include-
1. Qualification Purpose – Ensures that welders possess the necessary skills to produce high-quality welds on duplex stainless-steel piping and tubing.
2. Applicable Standards – Welder qualification must conform to AWS D10.18 guidelines. This may reference AWS B2.1 or ASME Section IX for procedure and performance testing.
3. Test Joint Preparation – Specifies the required test joint type, base metal, size, and joint configuration. This simulates actual production welding conditions.
4. Welding Process/Parameters – The welder must use the exact process (e.g., SMAW, GTAW). Follow the prescribed heat input, interpass temperature, and technique during testing.
5. Filler Metal/Shielding Gas – Must use approved filler metals and shielding gases compatible with duplex stainless steel. This ensures realistic and valid test results.
6. Position Requirements – Qualification may require welding in specific positions (e.g., 1G, 5G, 6G). This depends on the intended application.
7. Test Specimen Evaluation – This includes both non-destructive (e.g., RT, VT) and destructive tests (e.g., tensile, bend, ferrite content). It verifies weld soundness and skill level.
8. Acceptance Criteria – Test results must meet the acceptance criteria defined in AWS D10.18. This covers weld appearance, defect limits, and mechanical properties.
9. Qualification Record (WQTR) – A Welder Qualification Test Record must be documented. It should detail the welder’s identity, results, test variables, and qualification range.
10. Renewal/Continuity – Welder qualification remains valid if the welder continues to use the process regularly and meets continuity requirements outlined in the standard.
AWS D10.18 vs AWS D10.12
1. AWS D10.18 – This focuses on welding ferritic/austenitic duplex stainless steel piping and tubing. The code provides guidelines for maintaining phase balance, controlling heat input, selecting appropriate filler metals, and ensuring corrosion resistance. This AWS standard is essential for industries like gas, oil, and chemical processing, where duplex steels are widely used.
2. AWS D10.12 – This addresses the welding of mild steel pipe. The AWS standard includes procedures for various welding methods like SMAW and GMAW. It emphasizes joint design, technique, and inspection. This guide is more suitable for general-purpose piping applications in plumbing, construction, and structural work, where mild steel is the primary material.
AWS D10.18 Industrial Applications
Common industrial applications include-
1. Chemical Processing Plants – The standard is ideal for handling aggressive chemicals due to duplex stainless steel’s superior corrosion resistance and strength under pressure.
2. Marine/Shipbuilding – Used in seawater cooling, ballast systems, and exhaust systems due to duplex stainless steel’s durability in saltwater conditions.
3. Desalination Facilities – Applied in piping systems that handle seawater. Duplex steels provide excellent resistance to chloride-induced corrosion.
4. Oil/Gas Industry – The standard is used for offshore and onshore piping systems. It requires high strength and resistance to stress corrosion cracking in harsh environments.
5. Pharmaceutical/Food Processing – Ensures hygienic, corrosion-resistant piping systems with clean, high-quality welds in sensitive environments.
6. Power Generation – Supports high-pressure steam and water systems. Employed mainly in nuclear and thermal power plants, where mechanical performance is critical.
7. Pulp/Paper Industry – Used in corrosive areas like bleach plants and chemical recovery systems. They require durable welds for long-term operation.
AWS D10.18 Common Challenges
Some common challenges include-
1. Arc Strikes/Overheating – Unintentional arc strikes and localized overheating during welding can damage the surface and compromise corrosion resistance.
2. Controlling Heat Input – Too much heat can lead to intermetallic phase formation, while too little can cause a lack of fusion. Both affect weld integrity.
3. Hydrogen Cracking – Duplex stainless steels are susceptible to hydrogen-induced cracking. Must remove moisture, oil, or contaminants before welding.
4. Inadequate Ferrite Measurement – Failure to monitor ferrite content can result in welds that are too brittle (high ferrite) or prone to cracking (low ferrite).
5. Inconsistent Welding Technique – Variations in torch angle, travel speed, or bead placement can lead to weld defects and inconsistent mechanical properties.
6. Maintaining Phase Balance – Achieving the correct ferrite-to-austenite ratio is critical. The improper heat input or filler selection can disrupt this balance.
7. Post-Weld Cleaning Neglect – Skipping or improperly performing post-weld cleaning can leave the weld area vulnerable to corrosion.
8. Weld Oxidation – Lack of proper back purging or shielding gas can cause oxidation in the root pass. It reduces corrosion resistance.
Conclusion
AWS D10.18M serves as a vital resource for ensuring the effective welding of ferritic/austenitic duplex stainless steel piping and tubing. The standard offers detailed recommendations on filler materials, welding processes, and quality control measures. This guide helps maintain the corrosion resistance, strength, and durability of duplex stainless steels. Adherence to this standard both improves the weld reliability and extends the service life of components in critical applications. Overall, AWS D10.18M remains essential for engineers, fabricators, and inspectors committed to meeting stringent welding requirements.
