How to Weld Alloy 20 to 316 Stainless Steel
Welding dissimilar metals can be a daunting task, especially when dealing with materials like Alloy 20 and 316 stainless steel,…
Welding Alloy 20 steel is a meticulous task that demands precision and expertise, particularly because of its unique properties and widespread use in industries where corrosion resistance is crucial. From chemical processing plants to pharmaceutical facilities, Alloy 20 is prized for its ability to withstand harsh environments. However, achieving a flawless weld on this material isn’t straightforward. It involves understanding the intricacies of its composition, selecting the appropriate welding techniques, and employing the right filler metals and shielding gases. This article delves into the best practices for welding Alloy 20, covering everything from TIG and MIG welding methods to troubleshooting common issues like hot cracking and maintaining interpass temperatures. Whether you’re dealing with dissimilar welding or looking to perfect your technique, this comprehensive guide will equip you with the knowledge to ensure durable, high-quality welds on Alloy 20 steel. Dive in to discover the secrets of mastering this challenging yet rewarding welding process.
Alloy 20, also called Carpenter 20 or INCOLOY 20, is a versatile nickel-iron-chromium alloy. It is renowned for its exceptional resistance to acid attack, especially sulfuric acid. This makes it widely used in environments where severe corrosion is a concern. Industries like chemical processing, petrochemical, pharmaceutical, and food processing rely on Alloy 20 for its durability in harsh environments.
The unique properties of Alloy 20 make it suitable for a range of demanding applications.
Reactors, mixing tanks, and heat exchangers benefit from its resistance to sulfuric acid and corrosive chemicals.
Equipment used in the manufacture of pharmaceuticals often encounters corrosive substances, making Alloy 20 a preferred material.
The alloy’s resistance to organic acids and chlorides makes it ideal for use in food processing environments.
Components such as piping systems and storage tanks in petrochemical plants are often made from Alloy 20 to withstand harsh chemicals and high temperatures.
The superior corrosion resistance and mechanical properties of Alloy 20 are largely due to its specific chemical composition, which includes significant amounts of nickel, chromium, and molybdenum. Precise welding techniques and careful control are crucial to maintain these properties.
Improper welding can cause sensitization. This is where chromium carbides form at grain boundaries, reducing corrosion resistance and potentially leading to failure.
Attention to detail is required when welding Alloy 20 to prevent defects like hot cracking and intergranular corrosion. This necessitates the use of appropriate filler materials, controlled heat input, and the maintenance of suitable interpass temperatures.
Following best practices and using the right welding techniques ensures Alloy 20’s properties are maintained, resulting in durable, high-quality welds for demanding applications.
Alloy 20, also known as UNS N08020, is a super-austenitic stainless steel recognized for its high resistance to corrosion and excellent mechanical properties. Its carefully balanced composition enhances performance in harsh environments.
Alloy 20 is specifically designed to resist corrosion in a variety of aggressive environments, especially in environments with sulfuric acid. Its unique chemical composition makes it highly resistant to pitting, crevice corrosion, and stress corrosion cracking.
Welding Alloy 20 can be challenging but is essential for maintaining its desirable properties.
Hot cracking, also known as solidification cracking, occurs when the weld metal solidifies and contracts. Alloy 20 is particularly susceptible to this because of its high nickel content. Preventing hot cracking requires careful control of welding parameters and the use of appropriate filler materials.
Maintaining an appropriate interpass temperature is crucial when welding Alloy 20. High interpass temperatures can create unwanted phases that reduce corrosion resistance. Controlling the heat input and allowing the material to cool between passes helps prevent these issues.
Thermal cracks can occur due to the alloy’s low thermal conductivity and high thermal expansion coefficient. Intergranular corrosion is another concern, especially if the material is exposed to high temperatures during welding. Proper heat control and stabilizing elements like niobium are essential to mitigate these risks.
Alloy 20 exhibits excellent mechanical properties, which are maintained through proper welding techniques.
Alloy 20 has excellent tensile strength (≥551 MPa or ≥80,000 PSI) and yield strength (≥241 MPa or ≥35,000 PSI).
Maintaining these mechanical properties requires precise control of welding parameters to avoid overheating and ensure a strong, defect-free weld.
Understanding the material properties and challenges of welding Alloy 20 is essential for achieving high-quality, durable welds. By carefully managing chemical composition, heat input, and welding techniques, it is possible to preserve the alloy’s exceptional corrosion resistance and mechanical strength, ensuring its suitability for demanding applications across various industries.
Gas Tungsten Arc Welding (GTAW), also known as TIG welding, is a preferred method for welding Alloy 20 due to its precision and control over the weld pool.
Using high-purity Argon gas as a shielding gas is essential to protect the weld pool from atmospheric contamination. Gas lenses can further enhance shielding gas coverage, providing a stable and focused gas flow, which is crucial for maintaining the integrity of the weld.
A slow welding speed combined with low to moderate heat output helps minimize heat-affected zones and reduce the risk of hot cracking. Managing heat input carefully is vital to prevent thermal stress and ensure a high-quality weld.
ER320LR is the recommended filler metal for TIG welding Alloy 20. This filler metal matches the chemical composition of the base material, ensuring compatible mechanical properties and corrosion resistance.
Maintaining a stable arc is crucial for consistent weld quality. Using a short arc length and keeping the tungsten electrode clean can prevent contamination. Additionally, thoroughly cleaning the workpiece to remove any contaminants is important for achieving a high-quality weld.
Gas Metal Arc Welding (GMAW), also known as MIG welding, is another effective technique for welding Alloy 20, particularly suited for higher production rates.
ER320LR filler metal is also used in MIG welding. The choice of shielding gas is critical, with mixtures of Argon and Helium commonly used to enhance arc stability and weld pool control. Proper gas flow rates must be maintained to ensure adequate shielding.
Adjusting welding parameters, such as voltage, current, and wire feed speed, is essential to accommodate the unique properties of Alloy 20. Fine-tuning these parameters helps achieve a stable arc and consistent weld quality.
To ensure consistent weld quality, maintaining a uniform travel speed and proper torch angle is important. This helps control the weld pool and achieve the desired penetration and bead profile.
Submerged Arc Welding (SAW) is used for thicker sections of Alloy 20, providing deep penetration and high deposition rates.
E320LR is the recommended filler metal for SAW welding. Preheating the workpiece to remove moisture and contaminants is essential to prevent hydrogen-induced cracking and other defects.
Optimizing the welding speed and heat input is crucial for achieving a sound weld. Too much heat can cause excessive grain growth and reduce corrosion resistance, while too little can result in lack of fusion.
To avoid common SAW welding defects such as slag inclusion and porosity, proper cleaning of the weld area and maintaining a stable arc are necessary. Consistent monitoring of the weld parameters helps in producing high-quality welds.
Proper heat control and maintaining a slow, steady welding speed are key to preventing hot cracking. Using appropriate filler metals and ensuring a clean work environment also contribute to defect-free welds.
Controlling the interpass temperature is essential to prevent thermal stress and maintain the alloy’s corrosion resistance. Allowing the material to cool between passes and monitoring the temperature closely can help achieve this.
Thoroughly cleaning the filler rod and workpiece before welding is critical to remove any contaminants that could affect the weld quality. This includes removing oils, greases, and oxides that might be present on the surface.
Ensuring proper shielding gas flow and coverage is vital to protect the weld pool from atmospheric contamination. Regularly checking the gas flow rate and using gas lenses can help maintain optimal shielding conditions.
Using high-purity argon gas is crucial for shielding the weld pool from atmospheric contamination. Gas lenses enhance gas coverage, creating a smoother and more stable flow of shielding gas. This ensures a superior gas envelope around the weld area, which is essential for maintaining weld integrity.
Controlling welding speed and heat input is essential. A slow welding speed helps avoid cold lap issues and ensures proper fusion of materials. Using low to moderate heat input prevents alloying element vaporization and maintains corrosion resistance. Monitor heat input by observing color changes to avoid excessive heat that can compromise material integrity.
ER320LR filler metal is recommended for TIG welding Alloy 20. This filler rod matches the chemical composition of the base material, ensuring compatible mechanical properties and corrosion resistance. Clean the filler rod with isopropyl alcohol before welding to ensure high-quality welds.
Arc stability is crucial for consistent weld quality. A short arc length, especially during autogenous welding, helps prevent contamination. Hold the welding torch perpendicular to the workpiece with a slight travel angle of 0° to 5° to avoid drawing air into the shielding gas. Keep the filler metal tip under the shielding gas to prevent oxidation. Thoroughly clean the workpiece to remove oils, greases, or oxides for a high-quality weld.
Using the right current and voltage settings is essential for welding Alloy 20. Typical settings include:
Proper parameter settings help ensure a stable arc and consistent weld quality.
Keep interpass temperature below 350°F to prevent overheating and maintain weld quality. Allow the material to cool between passes to control heat input and avoid unwanted phases that could reduce corrosion resistance.
Carefully add filler metal at the weld pool’s leading edge to avoid contact with the tungsten electrode. Keep the filler metal tip under the shielding gas to prevent oxidation and ensure a high-quality weld.
By adhering to these guidelines and best practices, high-quality welds on Alloy 20 materials can be achieved using the TIG/GTAW process. Proper control of welding parameters, shielding gas, and filler metal preparation are key to maintaining the alloy’s desirable properties and ensuring long-term performance in demanding applications.
Choosing the right filler metal and shielding gas is essential for successful MIG welding of Alloy 20. ER320LR is the recommended filler metal because its chemical compatibility with Alloy 20 ensures that the weld maintains the same corrosion resistance and mechanical properties as the base material. Pure argon is typically used for shielding gas, but a mix of argon and helium can be beneficial for thicker sections, allowing for faster travel speeds and deeper penetration.
Cleanliness is crucial to avoid defects like porosity and lack of fusion. Use a stainless steel wire brush and grinding tools to remove contaminants such as sulfur, phosphorus, carbon, moisture, dust, grease, and paint. Clean the filler wire with acetone before welding to ensure no contaminants compromise the weld quality.
Use low to moderate heat input to avoid vaporizing alloying elements, which can compromise corrosion resistance. Do not increase the weld current to compensate for a sluggish puddle, as this can lead to defects like thermal cracks and intergranular corrosion. Employ multi-layer, multi-pass welding with small current and short arc lengths to control heat input and reduce joint stiffness.
Proper joint design minimizes the risk of solidification cracking. Stagger the joints of each weld pass and fill the arc pit at the end to avoid defects.
Preheating is usually unnecessary, but if the base metal temperature is below 15°C, use induction heating to prevent air condensation. Ensure the temperature between weld passes does not exceed 100°C to maintain corrosion resistance.
Adjust welding parameters like voltage, current, and wire feed speed to suit Alloy 20’s properties. Fine-tuning these settings helps control the weld pool and achieve the desired penetration and bead profile.
By following these guidelines, MIG welding of Alloy 20 can be performed effectively, maintaining the alloy’s desirable properties and ensuring high-quality welds.
For Submerged Arc Welding (SAW) of Alloy 20, it is recommended to use E320LR filler metal. This filler metal matches the chemical composition of Alloy 20, ensuring the welded joint retains the alloy’s high corrosion resistance and mechanical properties, which is crucial for maintaining the integrity and performance of the weld.
When welding Alloy 20, specific techniques are needed to prevent defects like heat cracking, intergranular corrosion, and stress corrosion cracking. This includes carefully controlling impurities such as sulfur, phosphorus, and carbon during the welding process.
To avoid heat-related defects, use multi-layer, multi-pass welding with a small current and short arc lengths. This method helps control heat input, reduces joint stiffness, and minimizes shrinkage stress during crystallization.
Preheating is generally not required unless the base metal temperature is below 15°C, in which case induction heating may be needed to avoid condensation. Before welding, thoroughly clean the bevel ends of the Alloy 20 pipes to prevent contamination and ensure a stable welding environment.
Although the SAW process uses flux to shield the arc, ensure the flux is compatible with both the filler and base metals. The flux should protect the weld pool from atmospheric gases, maintaining the alloy’s properties and ensuring a contaminant-free weld.
After welding, Alloy 20 may require post-welding heat treatment to restore its properties. This can involve:
By following these guidelines, welders can achieve strong, corrosion-resistant welds on Alloy 20, suitable for various industrial applications.
Hot cracking often occurs when welding Alloy 20 due to high heat input and rapid cooling. To prevent this, it’s crucial to control the heat and weld slowly and steadily.
Maintaining the correct interpass temperature is crucial to prevent thermal stress and ensure the integrity of the weld. High interpass temperatures can lead to the formation of unwanted phases that reduce corrosion resistance.
Use temperature-indicating crayons or infrared thermometers to keep track of the interpass temperature. Allow the material to cool sufficiently between welding passes to control heat input and prevent excessive temperature buildup.
Proper cleaning of the filler rod and workpiece before welding is essential to avoid contamination and ensure high-quality welds. Contaminants such as oil, grease, and oxides can lead to weld defects like porosity and lack of fusion.
Wipe the filler rod with isopropyl alcohol to remove contaminants, and ensure no alcohol remains before starting. Use stainless steel brushes and grinding tools to clean the workpiece, removing any oxides and contaminants from the surface.
Proper shielding gas flow and coverage are critical to protect the weld pool from atmospheric contamination. Shielding gas prevents oxidation and other defects that can compromise the weld quality.
Use high-purity argon or an argon-helium mix for thicker sections. Adjust the gas flow to ensure proper shielding. Employ gas lenses to create a smoother and more stable flow of shielding gas, ensuring a superior gas envelope around the weld area.
Maintaining a consistent and steady welding technique is essential to ensure uniform weld penetration and prevent defects. Avoid excessive heat input, which can lead to distortion and changes in the mechanical properties of the materials.
Keep the arc length short for a stable arc and to prevent contamination. Use a steady travel speed to control the weld pool and achieve consistent penetration. Hold the welding torch at an appropriate angle to avoid drawing air into the shielding gas and prevent oxidation.
Post-weld treatments like stress relief annealing and pickling remove residual stress and enhance corrosion resistance. These treatments are particularly important when welding Alloy 20 to stainless steel to minimize the risk of corrosion and cracking.
Heat the weld to 1725°F-1850°F (941°C-1010°C) for 30 minutes per inch of thickness, then quench in water. Use pickling solutions to remove any oxide layers formed during welding, restoring the alloy’s corrosion resistance.
By adhering to these best practices and tips, high-quality welds with excellent corrosion resistance and mechanical properties can be achieved when welding Alloy 20.
When welding Alloy 20 to carbon steel, it’s crucial to consider how these metals react to heat. The differences in their properties require careful selection of filler metals and welding techniques to ensure a strong, corrosion-resistant joint.
For welding Alloy 20 to carbon steel, ENiCrMo-3, also known as Inconel 625, is an excellent choice for filler metal. This nickel-based alloy provides a compatible weld with good corrosion resistance and mechanical properties.
Welding Alloy 20 to stainless steel, such as 304 or 316, involves addressing their different thermal expansion rates and ensuring the weld metal can withstand corrosive environments.
For welding Alloy 20 to stainless steel, ERNiCrMo-3 (Inconel 625) is recommended. This filler metal provides a weld that can accommodate the thermal expansion differences and offers excellent corrosion resistance.
Dissimilar welding often involves materials with different thermal expansion rates. To manage these differences:
When welding dissimilar metals like Alloy 20 to carbon steel or stainless steel, it is essential to:
By following these guidelines and techniques, welders can successfully join Alloy 20 to other metals, ensuring the welded joints meet the required performance standards for their intended applications.
Cold lap and lack of fusion are common issues when welding Alloy 20. These defects occur when the molten weld metal does not properly fuse with the base metal, leading to weak joints. Maintain a slow and steady welding speed to ensure adequate fusion by aligning the filler rod properly and ensuring the weld puddle is adequately formed before moving forward.
Excessive heat during welding can cause the loss of alloying elements, reducing the corrosion resistance of Alloy 20, especially in the heat-affected zone. Use low to moderate heat input and continuously monitor for excess heat input, indicated by changes in color. Employ appropriate welding parameters and shielding gases to protect the weld area and minimize the HAZ.
Porosity and inclusions, often caused by contamination or improper shielding gas flow, can compromise the integrity of the weld. Ensure the filler rods and base materials are clean and dry before welding. Proper shielding gas flow and cleanliness are crucial to preventing these defects. Maintain a stable and consistent shielding gas flow to protect the weld pool from atmospheric contamination.
Cracking can occur due to stress concentrations or improper welding parameters. Arrange the welding sequence properly and design the weld shape to minimize stress. Use the correct filler metal composition and control welding parameters carefully to prevent cracking. Ensure the weld area is free of contaminants and properly cleaned before welding.
Alloy 20 pipes have lower thermal conductivity compared to steel, which requires welders to adjust their welding speed accordingly. Slow down the welding speed significantly to avoid cold lap problems. Traveling too quickly can lead to inadequate fusion and other defects. Adjusting the welding speed helps achieve a more controlled and uniform weld.
Increasing the weld current to compensate for a sluggish weld puddle is not advisable, as it can vaporize alloying elements and reduce the corrosion resistance of the metal. Use low to moderate heat output and avoid increasing the weld current excessively. Monitor for changes in color, indicating excess heat. Proper heat management is essential to maintaining the alloy’s desirable properties.
Selecting the appropriate shielding gas and ensuring its proper flow is critical for high-quality welds. For pipes less than 1/8-inch thick, use argon gas with a flow rate of 10 to 20 cubic feet per hour. For thicker pipes, add helium to the argon gas and increase the flow rate to compensate for helium’s buoyancy. This ensures adequate shielding and protection of the weld area.
Using a gas lens can enhance the flow of shielding gas, creating a better gas envelope around the weld area. Choose a gas lens with the largest cup practical for the project. This helps create a smoother and more stable flow of shielding gas, which is essential for maintaining weld integrity and preventing contamination.
Proper preparation of the filler rod is crucial to avoid contamination and achieve high-quality welds. Clean the filler rod thoroughly with isopropyl alcohol before welding, ensuring all alcohol is removed before striking an arc. Use a filler rod made from the higher alloy parent material found in the Alloy 20 pipe. This preparation helps maintain the chemical compatibility and integrity of the weld.
After welding, thorough testing and inspection are necessary to identify any defects or leaks, especially in the heat-affected zone. Conduct tests like hydrotests, air tests, visual examinations, and dye penetrant examinations to ensure weld quality and reliability. These tests help identify any issues that may compromise the weld’s performance.
Below are answers to some frequently asked questions:
To weld Alloy 20 pipes using TIG/GTAW, start by using argon gas as the shielding gas, with a flow rate of 10 to 20 cubic feet per hour for pipes less than 1/8-inch thick. For thicker pipes, consider a mixture of argon and helium to facilitate faster travel speeds. Control the heat input carefully, using low to moderate heat output to avoid vaporizing alloying elements and reducing the product’s lifespan. Maintain a short arc length to reduce heat input and prevent atmospheric contamination.
Weld slowly to avoid cold lap problems, as Alloy 20 has lower thermal conductivity than steel. Use multi-layer multi-pass welding with small current and short arc lengths to control heat input and reduce shrinkage stress. Use filler materials such as AWS A5.4 E320-16/E320LR-16 and AWS A5.9 ER320LR, and ensure the filler rod is cleaned with isopropyl alcohol before use to prevent contamination.
Prevent heat cracking by controlling sulfur, phosphorus, carbon, and other impurities, and maintain an interpass temperature below 200°F. Use a gas lens to ensure a stable flow of shielding gas and start the arc on a carbon steel block or weld fixture for thin materials. Avoid crater cracks by reducing the weld pool size before breaking the arc. Following these guidelines will help achieve high-quality welds with Alloy 20 pipes.
For welding Alloy 20, the recommended filler metals are:
When welding Alloy 20 to dissimilar metals such as carbon steel or stainless steel, AWS ERNiCrMo-3 for TIG and MIG, and ENiCrMo-3 for SAW are recommended. These filler metals handle the differences in base metals and ensure a strong, corrosion-resistant weld.
To avoid hot cracking when welding Alloy 20, follow these best practices:
By adhering to these guidelines, you can minimize the risk of hot cracking and achieve high-quality welds with Alloy 20.
The best shielding gases for welding Alloy 20 are pure argon and argon-helium mixtures. Pure argon is recommended for thinner Alloy 20 pipes (less than 1/8-inch thick) with a flow rate of 10-20 cubic feet per hour (CFH). For thicker Alloy 20 pipes (more than 1/8-inch thick), a mixture of argon and helium is preferred, as helium allows for faster travel speeds and increased heat input. The flow rate for the argon-helium mixture should be increased by 1 ½ to 3 times to compensate for helium’s buoyancy. Using a large gas lens can ensure a smoother and more stable flow of shielding gas, leading to superior weld quality.
To weld Alloy 20 to dissimilar metals like carbon steel or stainless steel, it is essential to consider the compatibility and properties of the materials involved. Use filler metals that are compatible with both base metals, such as ERNiCrMo-3 or 309L, for TIG and MIG welding. For submerged arc welding (SAW), E320LR filler metal is recommended. Preheating may be necessary, especially when welding to carbon steel with higher carbon content. Control the heat input to prevent distortion and ensure weld quality. Proper joint design and cleanliness are crucial to avoid contamination and achieve a strong, corrosion-resistant weld.
Common challenges when welding Alloy 20 include hot cracking, interpass temperature control, and contamination. To overcome these issues, maintain proper heat control by using low to moderate heat input and slow welding speeds. Ensure interpass temperatures are kept within recommended limits to prevent thermal stress. Clean the filler rod and workpiece thoroughly before welding to avoid contamination. Use appropriate shielding gases, such as argon or argon-helium mixtures, to ensure adequate coverage and protection of the weld pool. Additionally, select suitable filler metals like ER320LR to match the alloy’s composition and properties.
