How to choose the right flange for the pipeline

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How to choose the right

flange

Flange, a part, can be used with gaskets and bolts in the pipeline system. It can be used to connect the pipe ends or the two devices. There are many types of flanges, including threaded flanges, butt-welded flanges, necked flat-welded flanges, necked socket-welded flanges, flat-welded ring-plate loose-fitting flanges, flanged ring-plate loose-fitting flanges, etc. So, how should we choose the right flange? 

What are the principles for selecting flanges?

1. The selection of flanges should be determined based on the parameters of the flanges.

When using flanges, the flange size must be determined first, and to determine the flange size, the nominal diameter and nominal pressure of the flange must be known first. The nominal diameter of the pressure vessel flange and the nominal diameter of the pressure vessel take the same series of values; the determination of the nominal pressure of the flange is related to the maximum operating pressure, operating temperature and flange material of the flange. The flange materials specified in the pressure vessel flange standard are low carbon steel, ordinary low steel and stainless steel. At different temperatures, their nominal pressure and maximum allowable working pressure are different.

In addition to flat welding and butt welding flanges, pipe flanges also include cast steel flanges, cast iron flanges, slip-on flanges, threaded flanges, etc. In addition to national standards, pipe flange standards also include the Ministry of Chemical Industry standards and Sinopec standards. Among them, the Ministry of Chemical Industry standards are divided into European systems and American systems. The European system is commonly used in my country. It is worth noting that the nominal diameter of the container cylinder and the nominal diameter of the pipe represent different specific sizes. Therefore, the container flange and pipe flange of the same nominal diameter have different sizes and cannot be used interchangeably.

2. The flange selection should be based on the actual usage.

For example, the groove or concave surface of the equipment flange of a vertical container should face upward, and the groove or concave surface of a horizontal container should be located on the cylinder. Therefore, we can choose a flat-welded flange with a neck for the equipment flange. After all, it belongs to the national standard flange system. Its advantage is that it is more convenient to install on site, and the process of beating and rubbing the weld can be omitted. It is one of the commonly used flanges on equipment or pipelines; you can also choose a flat-welded flange with a neck. Its connection is not easy to deform, has a good sealing effect, and is widely used. It is suitable for pipelines with large fluctuations in temperature or pressure or high temperature, high pressure and low temperature pipelines. It is also used for pipelines that transport expensive media, flammable and explosive media, and toxic gases.

Integral flanges are represented by IF in various domestic standards. They are generally raised faces (RF) and are mostly used in pipelines with higher pressures. If they are used in flammable, explosive, high and extremely hazardous conditions, you can choose sealing surfaces of convex and concave surfaces (MFM) and tongue and groove surfaces (TG) in addition to RF surfaces.

Flanges are one of the important components for connecting pipeline equipment and accessories. Their use must be strictly in accordance with the corresponding standards. The following are common flange usage standards:

1. International standards: ISO, ANSI, DIN, JIS, etc.

2. National standards: GB, HG, JB, etc.

3. Enterprise standards: such as standards for chemical, petrochemical, power and other industries.

According to the needs of different industries, the standards of flanges will also be different. Therefore, when selecting, you must first understand the corresponding industry standards in order to correctly select the appropriate flange.

1. Material

The material of the flange is the first factor to consider. Common flange materials include carbon steel, stainless steel, alloy steel, PVC, PP, PE, etc. Different materials will have different choices depending on the nature of the medium and the use environment. For example, if the medium is acidic, stainless steel flanges are the best choice.

2. Temperature

Flanges used in high or low temperature environments also have different choices. For example, for high temperature media, alloy steel flanges are usually the best solution.

(1) Material expansion: When the temperature rises, the material expands. This also applies to flange materials. If the flange material cannot withstand temperature changes, it will cause the shape of the flange to change or distort, making it unable to effectively connect with other components. Therefore, suitable flange materials should be able to expand or contract on their own when the temperature changes to maintain their required shape and size.

(2) Sealing issues: When the temperature rises, the sealing material will also expand. This may cause the sealing material on the flange to lose its sealing performance, resulting in leakage. Suitable flange sealing materials should be able to support high temperatures and maintain stable pressure and sealing.

(3) Corrosion resistance: Certain high temperature conditions may cause the material to corrode, which may reduce the strength and stability of the flange. Therefore, it is important to choose a corrosion-resistant flange material that can maintain stability and strength at high temperatures. 

(4) Reliability: Temperature changes will also affect the life of the flange. If the flange material cannot withstand temperature changes, its life may be greatly reduced. Therefore, it is important to choose the right flange material to ensure that the flange can be stable and reliable in long-term use. 

3. Structural type

Different structural types also have their own applicable scenarios. For example, blind flanges are suitable for scenarios where pipelines need to be closed or communicated, while socket flanges can be selected for scenarios with higher rigidity requirements. 

4. Medium characteristics

Different media also have different requirements for flange connection methods. Liquids, gases, corrosive media or flammable media may all have special requirements for flange material selection and sealing performance. When choosing a flange connection method, factors such as the temperature, pressure, corrosive properties and fluid properties of the medium need to be considered. 

5. Flange type

Link to Ziheng

Common flange types include plate flanges, flange pairs, bolt flanges, union flanges, flange sleeves, etc. Choose the appropriate flange type for different usage scenarios.

6. Flange specifications

The specifications of flanges include diameter, number of faces, number of bolt holes, etc., which must match the pipeline connection equipment and accessories to operate safely and stably.

 7. Quality certification

(1) Production license

A production license is one of the qualifications that flange suppliers must have. According to the "Regulations on the Administration of Production Licenses of the People's Republic of China", enterprises that produce flammable, explosive, toxic, radioactive and other special items must obtain a production license before they can carry out production and business activities. Flanges are flammable and explosive items, so flange suppliers must obtain a production license to ensure the quality and safety of their products. 

(2) Quality management system certification certificate

In order to ensure the quality of flange products, flange suppliers also need to obtain a quality management system certification certificate. The most commonly used quality management system certification standard in the world is ISO , which aims to help enterprises establish and improve management systems, improve the quality of products and services, and increase customer satisfaction. After obtaining ISO certification, the management level and production quality of the enterprise can meet certain standards. 

(3) Tax registration certificate

The tax registration certificate is a certificate that flange suppliers must have during production and operation. After obtaining the tax registration certificate, the enterprise can pay taxes according to law, comply with tax laws and regulations, ensure tax security, and avoid illegal risks. In addition, flange suppliers must comply with the requirements of relevant laws and regulations during the production process, such as the "Product Quality Law of the People's Republic of China" and the "Safety Production Law of the People's Republic of China". At the same time, enterprises must also have professional technical personnel, production equipment and complete production process to ensure that the flange products produced meet relevant national standards and industry standards.

8. Price and delivery cycle

On the premise of meeting technical requirements, choose flange products with reasonable prices and short delivery cycles to save costs and ensure production progress. 

9. Pressure level

When using flanges, pressure level is an important consideration. Depending on the pressure level, the size of the flange connection bolts and gaskets will also change. The pressure level of the flange connection is related to the design pressure of the pipeline system. It is crucial to select the appropriate flange level according to the system design pressure level and fluid medium. Generally, systems with lower pressure levels can choose smaller flanges, while high-pressure systems require flanges with larger sizes and higher pressure levels. 

10. Pipe size

The pipe size also affects the choice of flange connection method. Small-diameter pipes are usually connected with bolted flanges, while large-diameter steel pipe may be connected with welded flanges. In addition, the pipe wall thickness will also affect the choice of flanges. Pipes with thicker walls may require stronger connections.

11. Application requirements

Different types of flange connections can also be selected according to specific application requirements, such as ease of disassembly, shock resistance requirements, wear resistance, etc. For example, if the pipeline system needs to be frequently disassembled and repaired, a flange connection with threads can be selected; if it needs to prevent vibration and impact, a flange connection with a rubber gasket can be selected.

Making the Connection: Flange Facing Types

Flange design is only the start when considering the ideal flange for your piping system. Face types are another characteristic that will have a major impact on the final performance and service life of your flanges.

Facing types determine both the gaskets needed to install the flange and characteristics related to the seal created.

Common face types include:

• Flat Face (FF): As the name suggests, flat face flanges feature a flat, even surface combined with a full face gasket that contacts most of the flange surface.
• Raised Face (RF): These flanges feature a small raised section around the bore with an inside bore circle gasket.
• Ring Joint Face (RTJ): Used in high-pressure and high-temperature processes, this face type features a groove in which a metal gasket sits to maintain the seal.
• Tongue and Groove (T&G): These flanges feature matching grooves and raised sections. This aids in installation as the design helps the flanges to self-align and provides a reservoir for gasket adhesive.
• Male & Female (M&F): Similar to tongue and groove flanges, these flanges use a matching pair of grooves and raised sections to secure the gasket. However, unlike tongue and groove flanges, these retain the gasket on the female face, providing more accurate placement and increased gasket material options.

Many face types also offer one of two finishes: serrated or smooth.

Choosing between the options is important as they will determine the optimal gasket for a reliable seal.

In general, smooth faces work best with metallic gaskets while serrated faces help to create stronger seals with soft material gaskets.

The Proper Fit: A Look at Flange Dimensions

Apart from the functional design of a flange, flange dimensions are the most likely factor to impact flange choices when designing, maintaining, or updating a piping system.

However, you must consider how the flange interfaces with the pipe and the gaskets in use to ensure proper sizing.

Common considerations include:

• Outside diameter: The distance between two opposing edges of the flange face
• Thickness: A measure of the thickness of the outer attaching rim
• Bolt circle diameter: The distance between opposing bolt holes when measured from centre to centre
• Pipe size: A designation of the pipe size with which the flange corresponds
• Nominal bore size: A measurement of the flange connectors inner diameter

Flange Classification & Service Ratings

Each of the above characteristics will have an influence on how the flange performs across a range of processes and environments.

So how can you tell which flanges are up to the task and which are not?

Flanges are often classified based on their ability to withstand temperatures and pressures.

This is designated using a number and either the &#;#&#;, &#;lb&#;, or &#;class&#; suffix. These suffixes are interchangeable but will differ based on the region or vendor.

Common classifications include:

• 150#
• 300#
• 600#
• 900#
• #
• #

Exact pressure and temperature tolerances will vary by materials used, flange design, and flange size. The only constant is that in all cases, pressure ratings decrease as temperatures rise.

Flange Standards and Markings

To help make comparison easier, flanges fall under global standards established by the American Society of Mechanical Engineers (ASME) -- ASME B16.5 & B16.47.

If you&#;re attempting to replace or verify existing parts, all flanges must include markers -- typically on their outer perimeter -- to aid in the process.

These markers also follow a strict order:

• Manufacturer logo or code
• ASTM material code
• Material Grade
• Service rating (Pressure-temperature Class)
• Size
• Thickness (Schedule)
• Heat Number
• Special designations, if any -- for example, QT for Quenched and tempered or W for repair by welding

This guide offers a solid foundation of the basics of flange design and how to choose the ideal flange for your piping system. However, with a wide range of stainless steel flanges and other flange materials available, it is impossible to list every configuration, detail, or consideration.

Should you have questions, the Technical Sales Experts at Unified Alloys are ready to help. Serving industries and businesses across North America and Canada for more than 40 years, we understand the complexities of alloy piping and the needs of your industry. Call us today for additional information and to find the ideal flange, piping, and components for your next project.

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