WHAT IS A FLANGE?
A flange is a component that is used to connect two pieces of pipe, valve, or other equipment together. It is essentially a flat or raised ring that has holes for bolts or screws to secure it to the connecting part. Flanges are typically made of steel, stainless steel, or other materials that offer high strength and corrosion resistance.
- The nominal size of a flange should match the bore size of the connecting pipe.
- Flange rating indicates the pressure and temperature performance of the flange.
- Flange ratings range from 150# to 2500#.
- Welding neck flanges require a schedule that matches the pipe schedule.
FLANGES IN PIPING
There are multiple types of pipe flanges available, including the standard types such as welding neck, blind, socket weld, lap joint, and threaded flanges, among others. Additionally, there are some special types of flanges, such as swivel flanges, expander/reducer flanges, Nipoflange/Weldoflange, and orifice flanges.
In general, welding neck, slip-on, and socket weld flanges are suitable for high-pressure applications that require long-lasting flanged joints. Threaded flanges are typically used in lower pressure piping systems, as long as vibrations are not present.
Lap joint flanges are often used in combination with stub ends to align the bolts of the two mating flanges or to reduce the cost of using high-grade materials in flanged joints. For instance, in an Inconel piping system, the stub end connected to the pipe can be made of Inconel, while the lap joint flange can be of a lower grade material, thus saving on the overall weight and cost of expensive Inconel material.
What are the different types of flange materials?
Pipes and flanges are required to withstand high temperatures, pressure, vibrations, and corrosion, while providing an effective seal to prevent leaks. The flange class is important in determining factors such as bolt hole alignment, pressure and temperature ratings, and dimensional standards. However, it’s also crucial to consider the material specifications of the flange based on the specific application to ensure durability and reliability.
Steel is commonly used in flanges for high-stress applications.
- Stainless Steel is preferred for applications requiring high durability and corrosion resistance.
- Aluminum flanges are used when lightweight materials with good corrosion resistance are required, such as in irrigation.
- Ductile Iron is a cost-effective alternative to steel, offering higher yield strength and is preferred in instances where the flange doesn’t come in contact with the medium, such as with backing flanges.
The manufacturing method is also important to understand. There are typically three methods used:
- Plate flanges are made by rolling metal slabs to the desired thickness, making them relatively inexpensive. However, plate flanges may not have the same level of strength or material variety as other manufacturing methods.
- Cast flanges are created by pouring molten metal into a flange mold, offering good flexibility at a lower cost. However, cast flanges may not provide the highest strength compared to other manufacturing methods.
- Forged flanges are produced by heating and shaping the material before machining it to specifications, resulting in the strongest flanges. However, forged flanges come at a higher cost than other manufacturing methods.
Consider the Intended Application
The selection of flange material depends on various factors such as pressure, temperature, medium, and service conditions. While matching the pipe and flange materials is recommended, it’s not always practical or cost-effective. Thus, it’s important to evaluate the properties and limitations of each material and choose the one that meets the requirements of your piping system. A wrong material choice can lead to premature failure, leaks, or other issues.
Pipe material is chosen based on variables associated with an application, including:
- What will be conveyed through the pipes (fluids, air, etc.)
- Anticipated high or low temperature
- Pressure conditions (high or low pressure)
- Maintenance requirements (how often maintenance is needed)
- Environmental factors (exposure to corrosive substances, weather conditions, etc.)
- Budget constraints (cost of the materials used in the flange and pipe system)
The material used for pipes and flanges depends on the type of fluid or substance being transported. Corrosive liquids, such as fuel or acidic substances, require pipes and flanges made of stainless steel, alloys, or other corrosion-resistant materials. On the other hand, pipes and flanges used for non-corrosive substances like air may not require the same level of corrosion resistance.
Consult Flange Standards & Requirements
Flange standards determine the chemical composition, dimensions, and other specifications required for flanges. It is recommended that the material used for flanges and pipes comply with the same standards.
The ASTM standards determine the grade of the flange material based on its chemical composition. This grade is determined by the allowable amount of carbon and other chemical elements in the raw material.
- ASTM A36 is a low-carbon steel that is commonly used for steel flanges due to its welding properties and machinability.
- ASTM A105 is the standard for carbon steel piping components and is preferred 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, making them suitable for corrosion resistance and high temperature and pressure applications.
- ASTM A240 is a stainless steel plate that offers high strength at high temperatures and high resistance to corrosion. It is similar in chemical properties to ASTM A182, but differs in production method – A240 is plate while A182 is forged.
- ASTM A536 covers ductile iron, which is commonly used for backing flanges.
Guobiao (GB) standards are issued by the Standardization Administration of China (SAC) and include:
- Q235B is a type of low-carbon steel that is produced in China. Its structure is designed to facilitate proper welding and bolt connection. This particular steel meets or exceeds the strength requirements set by AWWA (American Water Works Association). Although it has slightly lower strengths than comparable materials like DIN EN S235JR and ASTM A36, Q235B is widely considered the equivalent in China.
American Water Works Association (AWWA) standards include specifications for steel and stainless steel. AWWA flanges include:
AWWA C207 specifies steel ring or slip-on flanges and blind flanges.
- AWWA C228 specifies the use of stainless steel and allows for the use of 304L or 316L stainless steel.
- 304L stainless steel has more chromium and less nickel than 316L stainless steel.
- 316L stainless steel includes molybdenum for enhanced corrosion resistance.
ANSI and ASME are two industry standards for pipeline flanges in the United States. These standards cover steel, forged, or cast flanges and include B16.1, B16.5, and B16.47.
Flange Material Source
When selecting flange material, it’s important to take into account where it is sourced from. While it may be acceptable to use imported materials for some applications to save on costs, there are cases where Buy America or Domestic materials may be required.
The Buy America standard was created for government-funded transportation projects to give preference to domestically produced materials. However, there are provisions that allow materials to be sourced from approved countries if it makes up a small enough part of the total contract and domestic product availability is low or the price is too high.
Domestic flanges meet the American Iron & Steel (AIS) standard, which permits the use of imported raw metal components but requires that the flange material is melted and manufactured in the United States.
For Buy America applications, domestic flanges can be substituted, and for applications where imported flanges are acceptable, Buy America flanges can be substituted. However, flanges can’t be substituted in the opposite direction.
Other Factors for Choosing Flanges
To determine the appropriate flange material, several factors should be considered, such as the pipe material, pressure and temperature ratings, flange dimensions, and tolerances. ANSI ratings provide vital information on pressure and heat tolerances that must be taken into account.
Another significant consideration is the fitting type. If welding is required, the material chosen must be weldable. However, for non-welded styles like lap joint or threaded flanges, weldability is less important than other requirements.
To select the ideal flange material, one should refer to the standards required for their intended application, consider the pipe material that will connect to the flange, and ensure that the chosen flange material can withstand the temperature and pressure required. Newzel Industries can be contacted for assistance with standard fittings or custom machined parts, or for further information.