Welding

What Is Buttering in Welding and How It Enhances Structural Integrity

What Is Buttering in Welding

Buttering in welding refers to the process of adding material by welding on one or both faces of a joint before preparing the joint for final welding.

It serves several purposes, such as providing a suitable transition weld deposit for completing the joint, compensating for poor joint preparation, and minimizing the impact of post-weld heat treatment on sensitive materials.

Buttering can also eliminate carbide precipitation in stainless steel and is commonly used in steam turbine manufacturing to butter casing materials with carbon steel.

The ASME Section IX governs the welding procedure qualification for buttering.

An example of buttering is when welding P91 pipe to a stainless steel pipe using ERNiCr-3 material, and it is also employed in avoiding stubs at nozzle connection sites in steam turbine manufacturing.

Field welding of carbon steel nozzles/pipes to the carbon steel butter is possible without requiring subsequent post-weld heat treatment.

Did You Know?

1. In welding, “buttering” refers to the process of applying a thin layer of weld metal to a surface before the actual welding. This is done to build up the thickness and bond strength in order to prevent distortion during the main welding process.

2. The term “butter” in buttering comes from the appearance of the weld metal when it is applied to the surface. Due to its smooth and shiny texture, it can resemble a layer of butter spread on a piece of bread.

3. Buttering is commonly used in welding processes such as cladding or hard-facing, where a specific type of weld metal is applied to the base metal to enhance its properties, such as resistance to wear, corrosion, or high temperature.

4. Buttering is also used as a technique to repair defects or damage in a base metal. By applying a layer of weld metal, the damaged area can be filled, restored, or reinforced, ensuring the structural integrity of the material.

5. The choice of weld metal used for buttering can vary depending on the application. Different alloys, compositions, or even special coatings can be used to provide the desired properties or match the characteristics of the base metal being welded.

Introduction To Buttering In Welding

Buttering in welding is a technique that involves welding additional material onto one or both faces of a joint before the final welding process. This technique serves several purposes: it helps to create a suitable transition weld deposit, compensates for poor joint preparation, and enhances the overall structural integrity of the welded joint.

The buttering process is widely utilized in various industries, including power generation, manufacturing, and construction, to ensure the quality and strength of welded components**.

In welding, joint preparation plays a crucial role in achieving strong and durable welds. However, there are instances when the joint preparation does not meet the desired standards due to fabrication errors, insufficient material thickness, or design constraints. In such cases, the buttering technique can be employed to add extra material to the joint, ensuring a proper fit-up and allowing for a better weld.

Benefits Of Buttering In Welding

The technique of buttering in welding offers several benefits, contributing to the overall quality and reliability of the welded joint. One of the primary advantages is that it provides a transition weld deposit. This deposit acts as a buffer between the base metal and the final weld, ensuring a smooth and controlled transition of the metallurgical properties. It helps prevent any abrupt changes in material composition, reducing the risk of cracks, distortion, or other defects in the welded joint.

Moreover, buttering compensates for poor joint preparation. In cases where the joint surfaces are not perfectly aligned or have irregularities, buttering allows the welder to fill in the gaps, resulting in a more uniform and robust joint. It ensures that the actual welding process can be carried out effectively, even if the initial joint condition is not ideal.

Additionally, buttering minimizes the effect of post-weld heat treatment (PWHT) on sensitive materials. Some materials, such as certain stainless steels, can experience carbide precipitation when subjected to PWHT. By applying buttering, the original material is shielded from direct exposure to the heat treatment, reducing the risk of carbide precipitation. This is particularly important when welding dissimilar metals, such as P91 pipe to a stainless steel pipe, where buttering can eliminate potential issues caused by PWHT.

Minimizing The Effects Of Post-Weld Heat Treatment

Post-weld heat treatment (PWHT) is a crucial step in welding, done to relieve residual stresses and improve the mechanical properties of the weld. However, PWHT can have adverse effects on certain materials, leading to undesirable changes in their microstructure and properties.

Buttering plays a significant role in minimizing these effects.

For instance, when welding P91 pipe to a stainless steel pipe, the use of buttering can prevent carbide precipitation in the stainless steel caused by PWHT. Carbide precipitation can significantly degrade the corrosion resistance and mechanical properties of stainless steel, making it susceptible to failure. By applying a suitable buttering material like ERNiCr-3, the butter layer serves as a barrier, shielding the stainless steel from the heat treatment, thus preserving its integrity.

Buttering For Welding P91 Pipe To Stainless Steel Pipe

The combination of P91 pipe and stainless steel is commonly encountered in various industrial applications. However, welding these dissimilar materials can pose challenges, especially when it comes to post-weld heat treatment. The solution lies in the technique of buttering.

When welding P91 pipe to a stainless steel pipe, buttering with an appropriate filler material is essential to avoid carbide precipitation in the stainless steel. ERNiCr-3 is a commonly used filler material for this purpose. It is a nickel-based alloy with excellent resistance to high-temperature oxidation, corrosion, and stress corrosion cracking. By buttering the joint with ERNiCr-3, the stainless steel remains protected from the PWHT, ensuring the durability and reliability of the welded assembly.

To summarize:

  • The combination of P91 pipe and stainless steel is commonly used in industrial applications.
  • Welding these dissimilar materials can be challenging, especially during post-weld heat treatment.
  • Buttering with ERNiCr-3 filler material protects the stainless steel from carbide precipitation.
  • ERNiCr-3 is a nickel-based alloy known for its excellent resistance to high temperatures and corrosion.
  • This technique ensures the durability and reliability of the welded assembly.

Buttering In Steam Turbine Manufacturing Application

In steam turbine manufacturing, buttering finds extensive application in casing materials. Steam turbines operate under demanding conditions with high temperatures and pressures, making the selection of suitable materials crucial. Carbon steel is commonly used for turbine casings due to its strength and thermal stability. However, to achieve enhanced structural integrity, buttering with carbon steel is performed.

Buttering the casing materials with carbon steel provides an additional layer of reinforcement and improves the overall resistance to wear, corrosion, and thermal stress. This technique ensures the reliable performance of the turbine under demanding operating conditions, extending its service life and reducing the risk of failures.

ASME Section IX governs the welding procedure qualification for buttering, providing guidelines and standards for the application of this technique in various industries. It outlines the specific requirements and testing procedures to ensure the proper execution and quality of buttering in welding processes.

In conclusion, buttering in welding is a valuable technique that enhances the structural integrity of welded joints. It offers benefits such as providing a transition weld deposit, compensating for poor joint preparation, and minimizing the effects of post-weld heat treatment. Additionally, buttering is crucial in specific applications such as welding P91 pipe to stainless steel pipe and in steam turbine manufacturing.

  • Buttering with carbon steel provides reinforcement and improves resistance to wear, corrosion, and thermal stress.
  • ASME Section IX provides guidelines for buttering and ensures proper execution and quality in welding processes.

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Frequently Asked Questions

What is buttering in welding process?

In the welding process, buttering refers to the application of additional material on one or both sides of the materials to be joined. This technique is employed to ensure that the gap between the two materials meets the welding standard requirements, as stated in the ASME Sec IX, 2010. By buttering, the distance between the materials is adjusted, ultimately enhancing the quality and integrity of the weld. This technique plays a crucial role in ensuring that the welding process meets the necessary standards and specifications.

What is buttering layer?

A buttering layer refers to a transitional coating applied between two incompatible materials to facilitate their joining despite their different chemical compositions. This layer acts as a mediator, creating a bridge between the two materials that allows for effective bonding. By using a buttering layer, compatibility issues caused by contrasting chemical compositions can be mitigated, enabling the seamless combination of substances that would otherwise be incompatible. This innovative approach ensures improved connections between materials in various industrial applications, addressing the challenges posed by chemical compatibility.

What is the difference between buttering and build up?

In mechanical calculations and repairs, the term “build up” is used to indicate the process of adding thickness to a material. It is typically employed to reinforce or increase the strength of the material. On the other hand, “buttering” refers to the application of a buffer layer when two different materials need to be joined together. The purpose of buttering is to ensure proper adhesion and compatibility between the two materials during transfixion processes.

What thickness is a buttering weld?

When it comes to buttering welds, the thickness of the buttering zone should not surpass 75% of the plate thickness or 8 mm / 5/16”, whichever is smaller. This practice helps rectify any excessive root gap and is carried out in accordance with a qualified main weld procedure.

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