Pipe Flanges Overview

Figure 1: Threaded pipe flange

For more information, please visit our website.

Pipe flanges serve as essential connection components in piping systems, uniting pipes with equipment like valves and vessels. Each connection comprises three primary elements: the flange itself, a gasket to create a seal, and bolting to secure the parts together. With applications spanning a wide range of industries and pressure classes, these connections ensure a continuous flow without any drop in pressure. This piece delves into various pipe flange types, their respective uses, and the applications most suited to them.

How do pipe flanges work?

Pipe flanges facilitate the connection of different piping components—such as pipes, valves, and pressure vessels—through bolted joints. At the core of this process are bolts that secure two components together, while a gasket guarantees a tight, leak-proof seal. Various methods of joining piping to flanges exist, including threaded connections, welding (illustrated in Figure 2), and stub-end connections.

Figure 2: The components of a pipe flange connection: pipe (A), flange (B), gasket (C), bolting (D), and weld (E).

Standard types of pipe flanges

Threaded Flange

Threaded flanges utilize male and female threads for attachment, typically not requiring welding. However, adding a weld can enhance the connection's integrity. Threaded flanges are commonly employed in lower pressure and temperature settings, such as water or compressed air systems. They are particularly vital in environments prone to explosions, like gas stations, where welding creates safety hazards.

Figure 3: Threaded flange

Welding Neck Flange

A welding neck flange features a long, tapered hub that is designed for welding onto pipes. This flange type is well-suited for high-pressure applications at varying temperatures, offering a smooth passage for the media. By eliminating flow restrictions, issues such as turbulence and corrosion at the joints are minimized. A full penetration butt weld is typically made between the pipe and the flange to achieve maximum strength.

Figure 4: An example of a welding neck flange connection. Pipe to flange V-shaped butt weld (A), pipe (B), flange (C), and bolting (D).

Long Welding Neck

Similar to weld neck flanges, long welding neck flanges have an extended neck that serves as a bore extension. They are often utilized in high-pressure and high-temperature scenarios, maintaining the same bore size as the pipes in the system or adjusted as necessary. These flanges are mainly found in industries such as oil, gas, and petrochemicals and can replace pipe sections while also acting as nozzles. A butt weld connects these flanges, ensuring structural integrity in high-pressure applications, such as drilling rig standpipes.

Figure 5: Welding neck flanges

Slip-On Flanges

Physically resembling threaded flanges, slip-on flanges do not include interior threads. Instead, they secure the pipe using two fillet welds—one inside and one outside the flange. Also referred to as tee joints, the internal diameter of the flange is slightly larger than the corresponding pipe's outer diameter, allowing a snug fit before welding.

Figure 6: Slip-on flange

Socket Weld Flange

Primarily designed for small-diameter, high-pressure applications, socket weld flanges involve inserting the pipe into the flange and securing it with a fillet weld around the outer part of the socket. An expansion gap should be left between the pipe shoulder and the socket's shoulder; however, these flanges are not advisable in highly corrosive environments due to potential crevice corrosion at the expansion gap.

Figure 7: Socket weld flange pipe

Lap Joint Flange

Lap joint flanges provide a cost-effective connection solution in stainless steel or nickel alloy piping systems. Typically paired with stub ends, this design allows the flap joint itself to be made from lower-cost materials like carbon steel while the stub end matches the piping material. For additional strength, a butt weld can secure the pipe in place.

Figure 8: Components of a lap joint flange connection (left) and a lap joint flange (right). The pipe is welded with a butt weld on the back of the stub end (B), while the lap joint flange (A) slides over the pipe (C) and is secured by the pressure from the bolts.

Blind Flange

Blind flanges play an integral role in sealing off pipelines to halt fluid flow. They allow easy access when unbolted, enabling operators to manage tasks at the terminal end of the pipeline. These flanges are designed to mount against flat face-type joints.

Figure 9: Blind flange

Other flange types

A range of specialized flanges has been created for unique applications that extend beyond common types. Below, we spotlight some specific variations:

Nipoflange

Nipoflanges are engineered to create a 90-degree branch in pipelines, combining a welding neck flange with a forged Nipolet. Their installation involves welding the Nipolet section onto the run pipe while bolting the flanged part to the branch pipe.

Weldoflange

Weldoflange combines a weld neck flange with a branch fitting connection termed a Weldolet, all produced from a single piece of forged steel.

Swivel Flange

Swivel ring flanges facilitate swift alignment of bolt holes on adjacent flanges. This function is particularly useful in large pipeline installations, especially offshore installations transporting oil and gas, where quick adjustments are necessary.

Expander Flange

Expander flanges serve the purpose of increasing the bore size within a pipeline or connecting pipes with varying diameters to other mechanical devices like pumps and valves. While they can increase the bore by a maximum of two sizes, a standard flange should be used for more substantial increases.

Reducer Flange

The role of reducer flanges is to facilitate a reduction in pipeline bore. While they are safe to reduce by one or two sizes, larger reductions necessitate using both a buttweld reducer and a standard flange.

Storz Flange

Commonly used as fire hose couplings, Storz couplings have a wide range of applications across industries like refineries, agriculture, construction, maritime safety, and military sectors due to their excellent corrosion and acid resistance. The Storz flange features a storz coupling on one end and a flat face on the opposite side.

Pipe flange face variants

The choice of flange face is crucial for its performance and longevity, as it affects the required gasket type and the sealing properties created. Below is a summary of the common face types.

Figure 10: Face variants: Flat face (FF), raised face (RF), lap joint (LJ), ring joint (RTJ), male and female (M&F)

• Flat Face (FF): Features an even surface with a full-face gasket extending over much of the flange area.
• Raised Face (RF): Contains a raised ring around the bore with a gasket inside the bore circle.
• Lap Joint (LJ): Features stub end and flange face alignment, similar to raised face designs.
• Ring Joint Face (RTJ): Characterized by grooves and raised sections which provide a reservoir for gasket adhesive.
• Male & Female (M&F): By utilizing matching grooves, these flanges secure the gasket and ensure accurate positioning.
• Seal finish: Various finishes such as serrated or smooth impact gasket compatibility and seal reliability, with metallic gaskets favoring smooth surfaces and soft gaskets working optimally with serrated finishes.

Common pipe flange materials

Pipe flanges are commonly crafted from materials like carbon steel, high-yield carbon steel, alloy steel, and various grades of stainless steel, including duplex and super duplex steel. Nickel alloy grades like Inconel, Incoloy, and Hastelloy find specialized use in certain applications. For a detailed analysis of the chemical properties of these materials, check our chemical resistance page.

Link to Ziheng

Explore more:
How to Choose custom precision metal stamping?

Carbon Steel

Carbon steel flanges exhibit excellent chemical and mechanical traits such as high fatigue strength and resistance to stress corrosion cracking, making them ideal for pipe connections.

Alloy Steel

Alloy steel incorporates more chromium and molybdenum compared to carbon steel, thus proving effective in applications involving high pressures and temperatures, with better corrosion resistance.

Duplex Steel

Combining austenite and ferrite phases, duplex steel offers rigidity and outstanding corrosion resistance, particularly in chloride and sulfur environments, making it adaptable for numerous industrial uses.

Stainless Steel

Stainless steel features nickel, chrome, and molybdenum for enhanced corrosion resistance and is versatile enough to create all types and sizes of pipe flanges. Consider consulting our comparison for 304 vs. 316 stainless steel for further information.

Pipe flange classification and pressure rating

The pressure rating, often referred to as the class, denotes the maximum pressure a flange can endure at specified temperatures. The ANSI/ASME B16.5 classification distinguishes seven ratings: 150, 300, 400, 600, 900, and beyond.

This classification aids in selecting the appropriate flange for specific applications. For example, comparing two flanges with an identical bore size of 10 inches and made from carbon steel but with different pressure ratings, say 300# and #, highlights key differences:

• The lower-rated flange is generally less robust, smaller, and lighter.
• The higher-rated flange is stronger, larger, and heavier.
• A 300# is rated at 50.1 bar at 50°C.
• Conversely, the # flange is rated at 250.6 bar at the same temperature.

Guide to Flanges

This document pertains to flanges, covering various types and attachment methods, aiding users in choosing the best flanges for different applications, along with an overview of pertinent pressure ratings and temperature standards that apply to separate piping systems.

What Are Flanges and How Do They Work?

A flange is a protruding edge or rim designed to offer reinforcement or a fastening method to connect pipes, valves, and other equipment within piping systems, while also allowing easy access for inspections or modifications.

Flange Attachment Methods and Purposes

Flanges can be attached through welding or screwing, which is dictated by the flange type and system needs. Key factors when selecting a flange include pressure capacity, pipe size, and intended functionality.

• Ring or slip-on flanges are characterized by a center hole and are slid onto the pipe end. Their flange face extends past the pipe to allow for welding.
• Lap-joint flanges work in tandem with stub ends, facilitating alignment as they can rotate freely, eliminating the need for welding.
• Threaded flanges do not require welding, making them suitable for smaller sizes where space restricts options, though they are unsuitable for thin-walled piping systems.
• Socket weld flanges are preferred for small high-pressure setups; the pipe end is inserted then retracts to create an expansion gap before applying a fillet weld, allowing smooth fluid flow.
• Weld neck flanges feature a long, tapered attachment that binds to pipes, optimizing distribution of system stress for applications with varying pressure and temperature.
• Blind flanges are solid with no openings, finishing off systems and sealing them when paired with a gasket.

Common Flange Materials

The material of flanges affects connection methods and rating capabilities, making it vital for selection. Common options include:

• Steel for its prevalent strength.
• Stainless Steel for its superior rust and corrosion resistance.
• Aluminum, a lightweight option ideal for resisting corrosion.
• Ductile Iron, a cost-effective alternative less involved in direct medium contact.

Flanges come with various surface finishes influencing their roughness level. Options range from smooth to serrated finishes, depending on the use needed. While the AWWA standard provides beneficial serration options, others like mill finishes may be utilized when required.

Coatings can shield flanges from corrosion and damage throughout storage, transit, and operational use. Examples include:

• Light oil or rust-inhibitors
• Zinc
• Paint
• Epoxy
• Galvanized treatments

Flange sources also differ, encompassing categories such as:

• Import, valued for cost-effectiveness but may lack appropriateness in some applications.
• Buy America, a standard favoring local materials, with allowances for approved foreign materials in certain conditions.
• Domestic, aligning with AIS standards to confirm adherence to quality controls.

How Are the Most Common Flanges Used?

Selecting the right flange for specific applications necessitates considering various factors including size, attachment methods, manufacturing materials, pressure class ratings, and bolt specifications. Referencing flange dimensions, commonly cited by outside and inside diameters, bolt hole diameters and spacings, and thicknesses is essential in making informed decisions, with custom-machined fittings attainable if necessary.

Slip-On Flanges

Slip-on or ring flanges work best for high-temperature, low-pressure systems and accommodate higher flow rates. These flanges fit over the pipe end through a central hole, with welded securement. Available in elements adhering to ANSI and AWWA standards, slip-on flanges come in class ratings ranging from 150 upwards and can be flat or raised face designs.

Ring-type joint flanges, akin to slip-on designs, focus on better sealing through gasket use in high-pressure scenarios.

Lap-Joint Flanges

Lap-Joint flanges, also termed backup or backing flanges, feature stub or angle face rings. They slide over pipe ends without needing welding, offering a hassle-free connection, particularly in maintenance-intensive systems as alignment of bolt holes is simple.

Threaded Flanges

Threaded flanges attach directly to threaded pipes, providing an excellent alternate where welding is impossible to manage. These accessible options are suited for small-diameter pipe usages and high-pressure scenarios, but they lack fit in thin-walled systems. Available in various dimensions and materials, threaded flanges accommodate extensive specifications.

Blind Flanges

Blind flanges mimic thickness and bolt hole patterns of other types while remaining solid without a bore, serving to finish piped systems and create efficient seals alongside gaskets.

Weld-Neck Flanges

Weld-neck flanges possess long tapered hubs that are welded to the pipe itself. They are utilized in environments experiencing high pressure and varied temperature applications, distributing system stress while enhancing reinforcement.

Socket Weld Flanges

Offering superior fatigue endurance compared to their slip-on counterparts when applied to small-diameter high-pressure conditions, socket weld flanges rely on classes and ratings tied to pressures and pipe schedules. Assembly involves inserting piping, slightly retracting for expansion, and applying a fillet weld externally. This leads to consistent flow with no leaks.

Reducing Flanges

These flanges are vital for connecting differing pipe sizes in piping systems where expansions or reductions are stipulated, as they ensure a seamless fit between larger and smaller pipes. Reducing options are available across styles including weld-neck, slip-on, and threaded variants.

Flanged Pump Connectors

Featuring flanges at either end, flanged pump connectors are designed from flexible braided steel or stainless steel for absorbing pump vibrations, also aiding in minor alignment adjustments. They can be equipped with male X male threaded endings.

Overview of Flange Types and Benefits

Each flange type holds different benefits and uses classified under their pressure capacities. Understanding these details greatly assists in choosing the appropriate flange configurations for your system.

Common Piping and Flange Standards

Flange standards govern dimensions, material quality, maximum pressure, temperature tolerances, manufacturing protocols, and other technical criteria, directing proper selections for specific applications.

Several prevalent piping standards include:

• ANSI/ASME (American National Standards Institute and American Society of Mechanical Engineers), the predominant U.S. standard for pipeline flanges.
• MSS (Manufacturers Standardization Society) applies specifically for standards concerning steel pipeline systems.
• API (American Petroleum Institute) encompasses large diameter carbon steel flanges tailored for elevated pressure oilfield scenarios.
• AWWA (American Water Works Association), standards applicable for water supplies and treatment processes.
• DIN (Deutsches Institut für Normung) represents a European metric standard enjoying global use, often in maritime contexts.

ANSI Flange Temperature and Pressure Ratings

Flange evaluations are based on maximum pressure endurance at given temperatures, categorizing into seven key pressure ratings from #150 up to higher classifications. Overall flange performance relates to these specifications, typically reflecting that lower class numbers correspond with reduced pressure abilities.

AWWA Flange Standards, Ratings, and Size Range

The AWWA standard provides detailed classifications based on drilling patterns, PSI ratings, and size ranges, catering to specific requirement needs.

This information empowers clients seeking standard or custom options meeting the highest quality control standards. Comprehensive selections can be viewed here.