A lap joint flange, also known as a backing flange or a loose ring flange, is a two-part flange assembly commonly used in piping systems. It consists of a stub end, which is welded to the pipe, and a backing flange that slides over the pipe before the stub end is welded in place. This unique design offers several advantages over other flange types, making it a popular choice for various industrial applications.
Compared to other flange types, such as weld neck flanges or slip-on flanges, lap joint flanges offer distinct benefits. One key advantage is the ability to use different materials for the stub end and the backing flange. The stub end, which is in direct contact with the process media, can be made from the same material as the pipe to ensure compatibility and corrosion resistance. The backing flange, on the other hand, can be made from a less expensive material since it does not contact the process media directly. This flexibility in material selection can lead to significant cost savings, especially when dealing with expensive alloys or corrosion-resistant materials.
Another advantage of lap joint flanges is their ease of alignment during installation. Unlike weld neck flanges, which require precise alignment before welding, lap joint flanges allow the backing flange to rotate freely on the pipe. This feature simplifies the alignment of bolt holes during installation, saving time and effort. Additionally, lap joint flanges are ideal for systems that require frequent disassembly for maintenance or inspection purposes. The two-part design allows for easy removal and reinstallation of the backing flange without disturbing the welded stub end.
While lap joint flanges offer several benefits, they also have some limitations compared to other flange types. They are generally not suitable for small piping sizes due to their bulkier design. Additionally, the two-part assembly may not be as strong as a one-piece weld neck flange in high-pressure or high-temperature applications. However, for many common industrial applications, lap joint flanges provide a cost-effective and practical solution.
A lap joint flange is a unique flange design that consists of two separate parts: a stub end and a lap joint ring flange, also known as a backing flange.
1. Stub end: The stub end is a short piece of pipe with a flange-like hub on one end. It has a sealing face on one side and a beveled edge on the other for welding to the pipe. The stub end is typically made from the same material as the pipe to ensure compatibility and corrosion resistance.
2. Lap joint ring flange (backing flange): The lap joint ring flange is a loose ring that fits over the pipe and rests against the back of the stub end hub. It has bolt holes that match the flange size and pressure class. The backing flange does not contact the process media and can be made from a different, less expensive material than the stub end.
1. Stub end welded to pipe: The stub end is welded to the pipe using a butt weld. The beveled edge of the stub end matches the pipe end, allowing for a full penetration weld. This weld can be inspected using non-destructive examination (NDE) methods such as radiography or ultrasonic testing.
2. Flange ring slides over pipe before welding stub end: Before welding the stub end to the pipe, the lap joint ring flange is slid over the pipe and positioned behind the stub end. The flange ring remains loose and is not welded to the pipe or stub end.
The sealing face of the lap joint flange assembly is formed by the stub end. The stub end hub has a raised face or a grooved face, depending on the design and application. The raised face provides a sealing surface for gaskets, while a grooved face allows for the use of ring-type joints (RTJs) for high-pressure applications.
One of the key features of a lap joint flange is that the backing flange remains loose and can rotate freely on the pipe. This allows for easy alignment of the bolt holes during installation, as the flange ring can be rotated to match the bolt holes of the mating flange. This feature simplifies installation and reduces the need for precise pipe fitting and welding.
a lap joint flange is a two-part flange assembly consisting of a stub end welded to the pipe and a loose backing flange that slides over the pipe. The stub end forms the sealing face, while the backing flange provides the bolt holes and can be made from a different material. The ability of the flange ring to rotate freely simplifies bolt hole alignment during installation.
Lap joint flanges are manufactured to meet various industry standards, ensuring compatibility and performance across different applications. The key specifications for lap joint flanges include dimensions, pressure classes, stub end patterns, and facing finishes.
1. ASME B16.5 - up to 24": The ASME B16.5 standard covers lap joint flanges with nominal pipe sizes (NPS) from 1/2" to 24". This standard specifies the dimensions, tolerances, and ratings for flanges in this size range.
2. ASME B16.47 - 26" to 60": For larger lap joint flanges, the ASME B16.47 standard applies. This standard covers flanges with NPS from 26" to 60", providing dimensional requirements and pressure-temperature ratings.
1. ASME 150 to 2500: Lap joint flanges are available in various pressure classes, ranging from ASME 150 to ASME 2500. The pressure class determines the flange's thickness, bolt circle diameter, and the number and size of bolt holes. Higher pressure classes have thicker flanges and more bolts to withstand higher pressures.
1. MSS short pattern: The MSS (Manufacturers Standardization Society) short pattern stub end has a shorter overall length compared to the ASA long pattern. This compact design is suitable for applications with limited space or weight restrictions.
2. ASA long pattern: The ASA (American Standards Association) long pattern stub end has a longer overall length, providing more flexibility for pipe fitting and welding. This pattern is widely used in general piping applications.
1. Smooth: A smooth facing finish, also known as a stock finish, has a surface roughness between 3.2 to 12.5 μm (125 to 500 μin). This finish is suitable for use with flat gaskets or soft materials like rubber or PTFE.
2. Serrated: Serrated facing finishes have concentric or spiral grooves machined onto the sealing face. The serrations can be phonographic (spiral) or concentric. Serrated finishes provide better gasket retention and are commonly used with metallic gaskets, such as spiral wound or ring-type joints.
The table below summarizes the key specifications for lap joint flanges:
Specification | Description |
Dimensions | ASME B16.5 (1/2" to 24"), ASME B16.47 (26" to 60") |
Pressure Classes | ASME 150, 300, 400, 600, 900, 1500, 2500 |
Stub End Patterns | MSS Short Pattern, ASA Long Pattern |
Facing Finishes | Smooth (Stock), Serrated (Phonographic, Concentric) |
Face Types | Raised Face (RF), Flat Face (FF), Ring-Type Joint (RTJ) |
Materials | Carbon Steel, Stainless Steel, Alloy Steel, Nickel Alloys |
By adhering to these specifications, lap joint flanges ensure compatibility, reliability, and optimal performance in various piping systems and applications.
Lap joint flanges offer several key features that make them an attractive choice for various piping applications. These features include cost-effectiveness, suitability for corrosive environments, ease of alignment, and advantages for systems requiring frequent disassembly.
Lap joint flanges can be more cost-effective than other flange types, particularly when dealing with expensive alloys or corrosion-resistant materials. Since only the stub end needs to be made from the same material as the pipe, the backing flange can be made from a less expensive material, reducing overall costs.
The two-part design of lap joint flanges makes them well-suited for corrosive applications. The stub end, which is in direct contact with the process media, can be made from corrosion-resistant materials like stainless steel, nickel alloys, or titanium. The backing flange, which does not contact the process media, can be made from a less expensive material, such as carbon steel or galvanized steel.
Since only the stub end is in contact with the process media, the backing flange is protected from corrosion and erosion. This feature allows for the use of less expensive materials for the backing flange, reducing maintenance and replacement costs over the life of the piping system.
The loose fit of the backing flange on the pipe allows for easy alignment of bolt holes during installation. The flange ring can be rotated to match the bolt holes of the mating flange, simplifying the assembly process and reducing the need for precise pipe fitting and welding.
Lap joint flanges are an excellent choice for piping systems that require frequent disassembly for maintenance, inspection, or cleaning. The two-part design allows for easy removal and reinstallation of the backing flange without disturbing the welded stub end, saving time and effort during maintenance activities.
The stub end of a lap joint flange is attached to the pipe using a single butt weld. This welding configuration allows for various non-destructive examination (NDE) methods to ensure the integrity of the weld. Common NDE methods for lap joint flange welds include:
1. Radiography: X-ray or gamma-ray imaging is used to detect internal weld defects, such as porosity, inclusions, or cracks.
2. Ultrasonic testing: High-frequency sound waves are used to detect weld defects and measure weld thickness.
3. Dye penetrant: A liquid dye is applied to the weld surface, and any surface-breaking defects are revealed by the presence of the dye after cleaning.
4. Magnetic particle: Ferromagnetic particles are applied to the weld surface, and any surface or slightly subsurface defects are indicated by the accumulation of the particles.
The ability to perform NDE on the single butt weld ensures the structural integrity and reliability of the lap joint flange connection, reducing the risk of leaks or failures in critical applications.
lap joint flanges offer a range of key features that make them a cost-effective and reliable choice for various piping applications, particularly those involving corrosive media or requiring frequent disassembly. The single butt weld and the ability to perform NDE inspections further enhance the reliability and safety of lap joint flange connections.
Lap joint flanges are widely used in various industrial piping applications, offering a versatile and cost-effective solution for many systems. Some of the key applications for lap joint flanges include:
1. Similar pressure-temperature ranges: Lap joint flanges can be used in applications with similar pressure-temperature ranges as weld neck flanges. They are suitable for a wide range of operating conditions, from low-pressure to high-pressure systems, and from cryogenic to elevated temperatures.
Lap joint flanges are commonly used in large diameter piping systems, typically 26" (DN 650) and above. The ASME B16.47 standard covers lap joint flanges in sizes up to 60" (DN 1500), making them suitable for large-scale industrial applications, such as oil and gas pipelines, water treatment plants, and power generation facilities.
The two-part design of lap joint flanges makes them an excellent choice for corrosive environments. The stub end can be made from corrosion-resistant materials, such as stainless steel, nickel alloys, or titanium, while the backing flange can be made from a less expensive material. This combination provides cost-effective corrosion resistance, as only the stub end is exposed to the corrosive media.
Piping systems that require frequent maintenance, inspection, or cleaning can benefit from the use of lap joint flanges. The two-part design allows for easy removal and reinstallation of the backing flange without disturbing the welded stub end. This feature reduces the time and effort required for maintenance activities, minimizing downtime and increasing overall system efficiency.
1. Not for small piping: Lap joint flanges are generally not recommended for small piping sizes, typically below 1" (DN 25). The two-part design and the required clearances for the backing flange make lap joint flanges bulkier than other flange types in small sizes. For smaller piping, weld neck flanges or threaded flanges are often more suitable.
2. Bulkier design: Due to the two-part design, lap joint flanges have a bulkier profile compared to weld neck flanges or slip-on flanges. This increased size and weight may be a consideration in applications with limited space or weight restrictions. However, the benefits of lap joint flanges often outweigh the drawbacks of their bulkier design in many industrial applications.
Despite these limitations, lap joint flanges remain a popular choice for a wide range of piping applications, particularly in large diameter systems, corrosive environments, and situations requiring frequent maintenance or inspection. Their versatility, cost-effectiveness, and ease of use make them an essential component in many industrial piping systems.
lap joint flanges offer a unique combination of features and benefits that make them well-suited for various industrial applications. Their two-part design, cost-effectiveness, and ease of maintenance have made them a popular choice for large diameter piping, corrosive environments, and systems requiring frequent inspection or cleaning. While they may not be suitable for small piping and have a bulkier design compared to other flange types, the advantages of lap joint flanges often outweigh these limitations in many industrial settings.
In summary, lap joint flanges are a versatile and cost-effective solution for many industrial piping applications. Their unique two-part design, consisting of a stub end and a backing flange, offers several key advantages over other flange types.
- Cost-effectiveness: Lap joint flanges can significantly reduce material costs by allowing the use of less expensive materials for the backing flange, which is not in contact with the process media.
- Corrosion resistance: The stub end can be made from corrosion-resistant materials, while the backing flange can be made from a less expensive material, providing cost-effective corrosion resistance.
- Easy alignment: The loose fit of the backing flange allows for easy alignment of bolt holes during installation, simplifying the assembly process.
- Frequent maintenance: The two-part design enables easy removal and reinstallation of the backing flange for maintenance, inspection, or cleaning purposes.
- NDE inspection: The single butt weld between the stub end and the pipe allows for various non-destructive examination methods to ensure weld integrity.
Lap joint flanges are a cost-effective choice for a wide range of industrial applications, particularly in large diameter piping systems, corrosive environments, and situations requiring frequent maintenance. The ability to use less expensive materials for the backing flange while maintaining corrosion resistance in the stub end makes lap joint flanges an economical solution for many piping systems.
When corrosion resistance and easy maintenance are critical factors in a piping system, lap joint flanges are an ideal choice. The use of corrosion-resistant materials for the stub end ensures compatibility with the process media, while the two-part design allows for easy disassembly and reassembly during maintenance activities. This combination of features makes lap joint flanges well-suited for industries such as oil and gas, chemical processing, and water treatment, where corrosive environments and regular maintenance are common.
In conclusion, lap joint flanges offer a unique set of advantages that make them a preferred choice for many industrial piping applications. Their cost-effectiveness, corrosion resistance, ease of alignment, and suitability for frequent maintenance have established lap joint flanges as an essential component in modern piping systems. By understanding the features, specifications, and applications of lap joint flanges, engineers and designers can make informed decisions when selecting the most appropriate flange type for their specific piping requirements.
