A flange is one of industrial piping systems’ most commonly used components. It connects pipes, valves, pumps, and related equipment, making it indispensable in piping systems. This article will summarize essential information about flanges, including types, materials, standards, installation, and maintenance. By the end of this article, you’ll have a comprehensive understanding of flanges.
Definition of a Flange
Flanges are typically disc-shaped components that connect two pipes or serve as entry and exit points for pipes or equipment. They are joined together using bolts and gaskets between their faces to ensure a secure connection.
Want to know Basic Structure of a Flange.
Brief History of Flanges
The earliest forms of flanges appeared around the late 18th century. Over several centuries of evolution and technological advancements, their design and manufacturing gradually standardized to meet the diverse needs of various industries. Standardization organizations and associations in each sector developed corresponding standards. Flanges have become indispensable to modern industrial processes, providing crucial assurance for safe and reliable piping systems.
Importance and Uses of Flanges in Different Industries
Flanges are essential components for connecting pipes and equipment in the industry. You will find that flanges cover almost all engineering and manufacturing processes that require liquid or gas transmission, processing, and control. Including:
- Chemical Industry
- Petroleum and Natural Gas Industry
- Water Treatment Sector
- Manufacturing Sector
- Aerospace and Marine Engineering
- Construction and Infrastructure
- Food and Pharmaceutical Industry
Types of Flanges:
Flanges can be classified in various ways based on structure, connection method, material, and purpose. The following introduces you to several standard classifications:
Based on Shape and Structure：
A weld neck flange features a long tapered neck that gradually narrows to match the pipe thickness. It connects to pipes or equipment through butt welding. This design ensures even stress distribution at the weld, reducing pressure concentration at the connection point, which enhances the reliability and durability of the weld. Weld neck flanges are commonly used in high-temperature, high-pressure industries such as oil, gas, and chemicals.
A slip-on flange looks like a disc with an annular flange. It is installed by sliding it onto the pipe end and then connecting it to the pipe or fitting it with two fillet welds, one on the inside and one on the outside. The inner diameter of the slip-on flange is slightly larger than the outer diameter of the pipe, so precise alignment is not required. However, it is typically used in low—to medium-pressure systems such as water treatment, HVAC, and chemical piping systems.
A socket weld flange has a recessed area or socket in the center of its connecting end. The socket’s inner diameter typically matches the pipe’s outer diameter to be connected. The pipe is inserted into this recess and then welded along the flange’s inner edge to join the pipe and flange. This flange is usually used in small-diameter piping systems. However, because this welding method effectively isolates the weld from the fluid inside the pipe, socket weld flanges are commonly used in high-pressure and high-temperature environments, such as in chemical, oil and gas, and pharmaceutical industries.
A lap joint flange consists of a loose ring and a short pipe end (a stub end). The loose ring resembles a disc with a large hole in the middle, with an inner diameter more significant than the outer diameter of the pipe. The short pipe end is welded to the pipe and has a shape similar to the face of a regular flange, allowing it to rotate freely. This design means the lap joint flange does not require precise alignment during installation, making it easy to connect with other flanges. It is primarily used in low-pressure and non-critical piping systems that require frequent disassembly and maintenance.
A threaded flange is typically round, and its most notable feature is the threaded inner hole, which matches the external threads of the pipe, allowing it to be screwed onto the pipe. It is used when welding is impossible and is commonly found in low-pressure, low-temperature piping systems such as water supply and drainage.
6. Blind Flange
A blind flange, with no holes in the center, is typically used to seal the end of a pipe or an opening in a pipeline. It is commonly used for maintenance, repair, testing, and similar purposes.
Based on Face Type：
Flanges are typically classified by their sealing surfaces, determining the connection method. The main types include:
The flat face flange features a flat sealing surface, providing a large contact area with the pipe or fitting. Gaskets are usually made of rubber or non-metallic materials. It is typically used for connecting low-pressure or non-critical sealing pipe systems.
2. Raised Face (RF) Flange
The raised face flange features a slightly raised sealing surface, which helps increase the contact pressure between the flange and the pipe or fitting. Common gasket materials include non-metallic materials (such as rubber and asbestos) and metallic materials (such as stainless steel and copper). Raised face flanges are typically used in medium to high-pressure systems to ensure a reliable seal.
3. Male-female (MFM) Flange
The characteristic feature of a Male-Female (MFM) flange is its sealing surface, which is designed with complementary raised and recessed structures: one flange has a protruding sealing surface (male face). In contrast, the other has a corresponding concave sealing surface (female face). This design ensures precise alignment during flange assembly and provides enhanced sealing performance. Common gasket materials include metallic materials like stainless steel and non-metallic materials like rubber or flexible asbestos. It’s important to note that the gasket must match the raised and recessed structure of the flange.
Male-female flanges are commonly used in the chemical and petroleum industries for pipeline systems requiring high-pressure and high-temperature environments.
4. Tongue and Groove （TG) Flange
The tongue and groove face flange features a sealing surface designed with interlocking tongue and groove structures: one has a circular protrusion (tongue face), while the other has a corresponding circular groove (groove face). This sealing surface enhances performance, typically using metallic materials such as stainless steel and soft iron for gaskets. It is suitable for pipeline systems in the chemical, petroleum, and natural gas industries that require higher sealing requirements.
5. Ring Type Joint (RTJ) Flange
The ring-type joint (RTJ) flange has a sealing surface with a circular groove that holds a metal ring gasket. The gasket is usually oval or octagonal in cross-section and made from hard metals like stainless steel or nickel alloy to ensure strength and sealing performance under high pressure. This type of flange is suitable for pipelines requiring very high sealing performance.
Specialty Flanges:
When conventional flanges cannot meet your unique needs, special flanges need to be designed and customized according to specific design standards to ensure that they can meet the expected application in terms of material selection, pressure rating, and dimensional tolerance.These specialty flanges include:
Orifice Flanges: Used for measuring fluid flow in pipelines.
Spectacle Blinds: Safety devices for isolating sections of a pipeline.
Anchor Flanges: Used to restrict pipe movement and absorb forces.
Expander and Reducer Flanges: These increase or decrease pipe size.
Swivel Flanges: Allow for rotational adjustment to align bolt holes during installation.
Nipoflange and Weldoflange: Simplify branch pipeline connections through welding or socket connections.
Long Weld Neck Flanges are similar in appearance to weld neck flanges but with a longer neck, providing additional reinforcement.
These flanges are designed to meet specific needs in various industries, ensuring reliable performance in their applications.
Industry-Specific Flanges:
1. ASME Flange
ASME/ANSI B16.5: Applicable to pipe flanges and flange fittings with nominal diameters ranging from NPS 1/2 to NPS 24.
ASME B16.47: Applicable to large diameter flanges, divided into Series A and Series B, with diameters ranging from NPS 26 to NPS 60.
2. DIN Flange
Din 2633: Applicable to steel pipe flanges with a nominal pressure of PN 16.
Din 2634: Applicable to steel pipe flanges with a nominal pressure of PN 25.
3. EN Flange
EN 1092-1: Applicable to steel pipe flanges with nominal pressures ranging from PN 2.5 to PN 400 and sizes from DN 10 to DN 4000.
4.JIS Flange
5.GB/T Flange
GB/T 9112: Applicable to steel pipe flanges with nominal pressures ranging from PN 2.5 to PN 40 and sizes from DN 10 to DN 4000.
6. API Flange
API 6A: Applicable to wellhead and Christmas tree equipment in the oil and gas industry, including flanges, fittings, valves, and related equipment, with pressure ratings ranging from 2000 to 20000 psi.
7.AWWA Flange
AWWA C207: Applies to steel and plate flanges, including weld neck flanges, slip-on flanges, and lap joint flanges, with pressure ratings of Class B, D, E, and F. It is primarily used for water systems.
Flange Dimensions & Weights
Flanges are typically produced according to relevant standards, but custom flanges can also be made based on specific drawings. The following data are essential: the flange’s outside diameter, bolt circle diameter, bolt hole diameter, flange thickness, raised face height, bore diameter, and the number and size of bolts. The weight of a flange can be determined by its dimensions and the material used (density). Usually, flanges have standard weights for corresponding sizes and pressure ratings. You should note that in most cases, manufacturers set prices based on the flange’s material weight and processing difficulty.
Selection Criteria
When selecting a flange, you should consider its pressure rating in addition to the flange dimensions mentioned earlier. By referring to ASME, EN, and DIN standards, pressure ratings and dimensions can be determined. Other parameters to consider include the type of sealing face and the material. The choice of material mainly depends on the specific application and environmental conditions.
Flange Measurement
When measuring flanges, it’s essential to use appropriate tools to ensure accuracy and precision. The tools you will use most often include:
Caliper: Used to measure diameters, thickness, and heights.
Tape Measure: Suitable for measuring larger outer diameters and bolt circle diameters.
Inside Micrometer: Used to measure bore diameters.
Thickness Gauge: Used to measure flange thickness and raised face height.
Before using measuring tools, ensure they are calibrated. Repeat measurements multiple times to obtain accurate data and adhere to relevant standards and regulations to ensure measurements fall within specified tolerances.
Follow these testing steps according to the corresponding specifications and drawing requirements:
Step 1: Use a caliper or tape measure to measure the maximum outer diameter of the flange.
Step 2: Use a caliper or tape measure to Measure the bolt circle diameter.
Step 3: Measure the diameter of individual bolt holes using a caliper.
Step 4: Measure the thickness of the flange using a caliper.
Step 5: Measure the height difference between the flange sealing face and the main flange surface.
Step 6: Measure the diameter of the flange’s intermediate holes using a caliper or inside micrometer.
Step 7: Record the number of bolt holes and measure the diameter and length of bolts to determine the appropriate bolt specifications.
Suppose you need to check the elemental composition and hardness of materials on-site. In that case, you can use a spectrometer and portable hardness tester. For more precise identification, sampling on-site and sending samples to a laboratory for testing is necessary to obtain the corresponding test reports.
Flange Classification & Service Ratings
The ASME standard system includes common pressure ratings, including Class 150, Class 300, Class 600, Class 900, Class 1500, and Class 2500.
Flange Standards & Markings
Once flange production is completed and passes inspection, it is typically marked according to relevant standards to facilitate identification and usage during subsequent operations. Flange markings commonly include the following essential information:
Standard specification (e.g., ASME B16.5)
Pressure rating (e.g., Class 150)
Material grade (e.g., ASTM A105, ASTM A182 F316)
Manufacturer’s name or logo
Size (nominal pipe size or diameter)
Heat number or batch number for traceability
Flange Materials
The material for flanges needs to be selected based on characteristics such as operating environment, pressure, temperature, and the nature of the medium. Apart from aluminum, copper alloys, plastics, and composite materials, commonly used metallic materials include carbon steel, stainless steel, alloy steel, and nickel-based alloys. You can learn about the common alloy grades and their applications. For more details, please refer to:
Carbon Steel Flange
Carbon steel flanges commonly use materials such as ASTM A105 and, for low-temperature applications, ASTM A350 LF2. They are frequently employed in the petroleum, natural gas, and chemical industries. Due to their high material strength, they are suitable for high-pressure applications. However, their corrosion resistance is average, often requiring coatings or galvanization treatments.
Stainless Steel Flange
The commonly used grades for stainless steel flanges are ASTM A182, F304, and F316. Due to its high chromium content (at least 11% chromium), stainless steel forms a stable chromium oxide layer that prevents further oxidation and corrosion. Therefore, stainless steel exhibits excellent corrosion resistance. Flanges made from this material are commonly used in the chemical, pharmaceutical, and water treatment industries, where corrosion resistance is required for pipeline systems.
Alloy Steel Flange
Joint chromium-molybdenum alloy steel flanges, such as ASTM A182 F11 and F22, contain chromium and molybdenum elements that enhance the material’s resistance to high temperatures and oxidation. Therefore, chromium-molybdenum alloy flanges are commonly used in pipelines and equipment under high temperature and high-pressure conditions, such as in chemical and power industries.
Nickel Alloy Steel Flange
Nickel-based alloy flanges include Inconel (corrosion and high-temperature resistant Inconel 600 / corrosion and fatigue resistant Inconel 625), Incoloy (high-temperature and oxidation resistant Incoloy 800 / corrosion resistant Incoloy 825), Hastelloy (corrosion-resistant Hastelloy C276), Monel (Monel 400), and acid-resistant Alloy 20. Due to their unique resistance to high temperatures, high pressures, and corrosive environments, nickel alloy steel flanges are widely used in various industrial applications.
Flange gaskets and nuts
Flange sealing relies on the flange gasket, nuts, and bolts. These components are crucial to the flange connection system. Selecting the correct ones when using flanges ensures optimal sealing performance.
The flange gasket is a sealing material placed between flange faces. As mentioned in the section on flange sealing face classifications, its primary function is to fill the gaps between the flange faces and prevent leaks.
Standard flange gaskets are categorized by material into non-metallic, semi-metallic, and metallic types. They are used in different applications: low-temperature and low-pressure systems, medium to high-pressure and high-temperature environments, and applications requiring high temperature, high pressure, mechanical strength, and corrosion resistance.
Non-metallic materials include rubber, flexible graphite, PTFE (polytetrafluoroethylene), and fibers. Semi-metallic materials include spiral wound gaskets and metal composite gaskets. Metallic materials include aluminum, stainless steel, and copper.
Flange nuts are used to secure bolts in flange connections. When selecting nuts, you should choose based on the application. Incorrect selection can lead to seal failure or reduced durability. Common types of nuts include:
Hex nuts are the most common type and are suitable for various flanges. Heavy hex nuts are used for high-load connections and high-strength bolts. Lock nuts, designed with anti-loosening features, are ideal for flange connections in vibrating environments.
Production, Installation, and Maintenance of Flanges
The above description covers the types of flanges, size standards, materials, and their corresponding applications. It would help if you now had a basic understanding of flanges. Next, we will provide further details on their production, installation, and maintenance.
Manufacturing Processes
Joint flange forming processes mainly include forging, casting, and rolling, each used in different scenarios:
Forged flanges are commonly used in high-pressure and high-temperature environments such as oil and gas, chemical processing, and power generation.
Cast flanges are typically used in applications without high strength, such as water treatment and HVAC systems.
Rolled flanges are usually used to manufacture large-diameter flanges. They are often found in low to medium-pressure pipeline projects.
No matter which forming process is used, the following production steps must be followed:
Step 1: Material Selection
Select materials according to requirements. After the raw materials pass inspection, cut them into sizes and shapes suitable for processing.
Step 2: Forming
Forging: Heat the raw material and use forging equipment and molds to press it into shape.
Casting: The raw material of metal is melted, poured into molds, and cooled to form. This method can produce flanges with complex shapes.
Rolling: Roll the metal into a specific shape, then cut it to form.
Step 3: Heat Treatment
To improve the material’s hardness, strength, and wear resistance, the formed flange blanks must undergo heat treatment according to specifications or design requirements, such as annealing, normalizing, quenching, and tempering.
Step 4: Machining
Finishing flanges requires specialized equipment, such as CNC lathes, milling machines, and grinders, to ensure dimensional accuracy and surface finish:
Turning and Milling: Used for machining the flange’s outer diameter, sealing surface, and bolt holes.
Drilling and Tapping: Used for machining bolt holes to ensure connection with pipes or equipment.
Grinding and Polishing: Used to optimize the surface finish and flatness of the flange.
Step 5: Inspection and Testing
After production and processing, flanges need to undergo rigorous quality inspection to be deemed qualified, including:
Dimensional Inspection: This has been mentioned earlier and includes detailed flange measurements.
Surface Quality Inspection: This mainly checks the surface finish, especially the sealing surface, and the overall appearance for any scratches or flatness issues that might affect quality.
Material Performance Testing: This includes hardness and tensile tests to verify that material performance meets the standards and design requirements. For example, low-temperature performance testing is also required for 350LF2 material.
Step 6: Marking and Packaging
After passing inspection, the flange needs to have necessary identification information printed on its surface, serving as its certification. Then, it should be securely packaged for transportation and storage. Particular attention should be given to protecting the sealing surface to prevent wear and impact during transportation, which could cause unnecessary damage.
Installation and Assembly
To ensure a flange performs well, you must follow the correct installation methods. Incorrect installation can lead to frequent failures and prevent the flange from meeting standard and design requirements.
Flange assembly primarily involves the following steps:
Step 1: Preparation
Before installation:
1.1 Inspect the flange and components to meet the drawing and standard requirements.
1.2 Clean all parts to remove dirt and grease.
Ensure the ends of the pipes or equipment align correctly with the flange face to avoid unnecessary stress during assembly.
Step 2: Installation Procedures
2.1 Gasket Placement: Center the gasket between the flange faces.
2.2 Bolt Installation: Insert the bolts into the flange bolt holes and tighten the nuts to hold the assembly in place.
2.3 Torque Tightening: Use a calibrated torque wrench to tighten the bolts. Tighten the bolts gradually in a star or crisscross pattern to ensure even pressure distribution and prevent gasket deformation due to uneven stress.
Tighten the bolts in three stages:
First, tighten each bolt to approximately 30% of the final torque value.
Second, tighten each bolt to approximately 60% of the final torque value.
Finally, tighten each bolt to the total specified torque value.
Though tightening flanges may seem tedious, this method dramatically enhances durability and prevents leakage issues.
Step 3: Final Inspection
For example, a final inspection is crucial in manufacturing processes to ensure proper installation.
Inspect for noticeable gaps, ensure the gasket is seated correctly, and confirm that bolts are tightened.
Conduct a leak test by pressurizing or introducing fluid to verify the integrity of the flange connection.
Maintenance and Inspection
Please note: To ensure safety, ensure the system is shut down and fully depressurized before performing any maintenance work. Maintenance should follow a systematic approach to avoid inefficiency and potential issues:
Step 1: Disassemble the Flange
This step is essentially the reverse of installing a flange. First, use a torque wrench or other suitable tools to gradually loosen the bolts in a star or cross pattern to release the pressure between the flanges evenly. Then, remove the old gasket, being careful not to damage the sealing surfaces of the flanges.
Step 2: Cleaning
Clean the sealing surfaces of the flanges, bolts, and nuts with an appropriate solvent and brush.
Step 3: Inspection and Repair
Check the sealing surfaces for scratches, dents, or other damages. If necessary, repair or replace them. Replace the old gasket with a new one, ensuring the material and specifications meet the requirements.
Step 4: Reinstallation and Testing
Follow the installation steps for reinstallation. This process is the same as the installation procedure, so refer to those steps for details.
Troubleshooting Guide
For all equipment to operate safely and correctly, “safety first, prevention foremost” should be followed. Reactive measures often result in significant losses, while scientific preventive measures can effectively address common issues in flange installation and maintenance, ensuring system safety and reliability. Understanding common issues during installation and maintenance allows for proactive response and proper preventive control.
Common installation issues:
Misalignment
Uneven bolt tightening
Improper gasket selection
Damage to the flange sealing surface
Common maintenance issues:
Lack of regular inspections
Loose or rusty bolts
Failure to follow prescribed procedures
Ignoring environmental impacts
Innovations and Trends
The above content provides a comprehensive introduction to the development, types, installation, and maintenance of flanges, giving you a thorough understanding of flanges.
The flange industry continues to evolve and develop with technological advancements and changing industrial demands.
For example, in terms of materials, in addition to metals, the application of high-polymer composite materials can enhance strength and adapt to harsher working environments. In manufacturing, automated forging increases efficiency and improves production precision. Embedding sensors in flanges allows for real-time monitoring and remote control. These innovations and trends drive the flange industry towards greater efficiency and safety.
