How to Choose Pipe Flange Materials

Pipe flange is an important connecting pipe fitting in the pipeline system, and its material selection is particularly important. The material selection of the pipe flange needs to be comprehensively considered based on the media characteristics (corrosion resistance), working environment, price, etc. Commonly used materials include carbon steel, stainless steel, alloy steel, cast iron, special alloys, etc. Different materials are suitable for different environmental conditions, and the selection needs to be judged based on the specific situation.

What are the principles for selecting flanges?

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

Flange usage standards

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.

What are the different types of flange materials?

Pipes and flanges must be durable enough to withstand heat, pressure, vibrations, and corrosion, while still providing a leak proof seal. Flange class helps determine bolt hole alignment, pressure and temperature rating, and dimensional standards, however, flange material specifications must also be considered based on your application:

• Steel is the most common flange material and has higher carbon content for applications requiring superior strength
• Stainless Steel is used when high durability and corrosion resistance is required
• Aluminum flanges are used for applications where corrosion resistance is important, and a light weight material is required like in irrigation
• Ductile Ironoffers a higher yield strength and is lower cost than steel, so preferred for instances where the flange doesn’t come in contact with the medium (like with backing flanges) and cost is an important consideration

The manufacturing method is also important to understand. There are typically three methods used:

• Aluminum flanges are used for applications where corrosion resistance is important, and a light weight material is required like in irrigation
• Plate flanges are manufactured when metal slabs are sent through rollers until they reach the desired thickness. A plate flange typically costs less, but doesn’t offer the same strength or variety of material and sizes that other manufacturing methods do.
• Aluminum flanges are used for applications where corrosion resistance is important, and a light weight material is required like in irrigation
• Cast flanges are manufactured by pouring molten metal into a flange mold. The metal cools and hardens, and then the flange is removed from the mold and machined to the appropriate specifications. This lower-cost option offers plenty of flexibility, but does not produce the highest strength flanges.
• Forged flanges are made through a process of heating and forming the material, and then machining the part to the proper specifications. This creates the highest strength flange, but comes at a higher cost.

Consider the Intended Application

Choose the right flange material based on its intended use and the requirements specific to that application. Generally, your flange material will match your pipe material, but this is not always the case. Consider the strengths and weaknesses of each material when designing a piping system; the material should suit the application requirements or it may fail prematurely.

Pipe material is chosen based on variables associated with an application, including:

• What flows through the pipes (fluids, air, etc.)
• Expected high or low temperature
• Pressure conditions
• Maintenance requirements
• Environment
• Budget considerations

Certain fluids, for example, fuel or corrosive liquids, require pipes and flanges manufactured of stainless steel, alloy, or other corrosion resistant materials. Pipes and flanges used for air or other non-corrosive applications may not require the same corrosion resistant material as acidic or caustic liquids.

Consult Flange Requirements and Standards

The standards dictate the chemical composition, dimensions, and other specifications for flanges. Generally, your flange and pipe material should meet the same standards.

American Society for Testing and Materials (ASTM) standards—displayed as the “grade” of the material used to manufacture the flange—is determined by the metal’s chemical composition. More specifically, this standard dictates how much carbon and other chemical elements are allowed to make up the raw material.

• ASTM A36 is a low-carbon steel favored for its welding properties and is suitable for machining, making it a common material for steel flanges.
• ASTM A105 is the standard for carbon steel piping components, particularly for high-temperature applications.
• ASTM A182 is the standard for alloy and stainless steel piping flanges and fittings. Alloy steel flanges are produced with more chrome and molybdenum, so they are sometimes preferred for corrosion resistance and can better withstand high temperatures and high pressure.
• ASTM A240 is stainless steel plate that offers strength at high temperatures, and high corrosion resistance. While ASTM A182 and ASTM A240 have similar chemical properties, the production method differs: A240 is plate; A182 is forged, which may affect materials choice.
• ASTM A536 covers ductile iron, which is used for backing flanges.

Guobiao (GB) standards are issued by the Standardization Administration of China (SAC) and include:

• Q235B is a low-carbon steel manufactured in China. The structure allows adequate welding and bolt connection. This steel exceeds AWWA strength requirements and is considered the China comparable material to DIN EN S235JR and ASTM A36 standards (but with slightly lower strengths).

American Water Works Association (AWWA) standards include specifications for steel and stainless steel. AWWA flanges include:

• AWWA C207 is the specification for steel ring or slip-on flanges and blind flanges
• AWWA C228 is the specification for stainless steel and may use 304L or 316L stainless steel. 304L contains more chromium and less nickel than 316L. The 316L material also includes molybdenum for improved corrosion resistance.

American National Standards Institute (ANSI) and American Society of Mechanical Engineers (ASME) are the industry standards for pipeline flanges in the United States. These standards include B16.1, B16.5, and B16.47 and cover steel, forged, or cast flanges.

Deutsches Institut für Normung (DIN, German Institute of Standardization) is an international standard that applies to steel and stainless steel metric flanges and commonly in maritime applications.

Factors to note when selecting flanges

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: 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 for all country 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. For this reason we are at your service for any clarification
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 9001, which aims to help enterprises establish and improve management systems, improve the quality of products and services, and increase customer satisfaction. After obtaining ISO 9001 certification, the management level and production quality of the enterprise can meet certain 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 requirement: 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.