The Role of Flange Bolts in Gas Equipment

Flange bolts consist of a hexagonal head and a flange plate, with the gasket positioned beneath the hexagonal head, creating an integral unit. The bolts include screw threads, typically a cylinder with external threading, and require a nut for fastening. These bolts serve as components connecting two through holes.

Flange Types

50. Structural Types: Based on their connection method with the pipe, pipe flanges are categorized into various basic types, including flat welding, butt welding, socket welding, loose sleeve, threaded flange, integral flange, and more.
50. Types of Sealing Surfaces: Flange sealing surfaces come in various forms, including whole plane, boss surface, concave-convex surface, ring groove surface, tenon groove surface, and others.
50. Codes: Several codes (representation methods) are commonly used in flanges. Although different standards may have slightly different names and codes for sealing surfaces and types of flanges, they generally adhere to similar principles.

Application of Structural Types

50. Flat Welding Flange: Primarily used in public infrastructure pipelines, designed for low-pressure environments with fluctuations in pressure, temperature, and vibration. Its strength level is lower than that of equivalent butt-welding flanges.
50. Butt-Welding Flange: Also known as the stiff flange, it is widely utilized in industrial processes. It features a long and inclined neck where the flange connects with the pipe, enhancing its strength. It is suitable for high—and low-temperature environments, particularly in rigorous high-level settings.
50. Loose Flanges: Offer an economical solution for systems handling precious materials. They allow using different materials in pipe joints and flanges, optimizing cost-effectiveness without compromising performance.
50. Threaded and Socket Connections: Present distinct options for joining flanges and pipes, with the choice of connection form on the flange surface varying based on specific sealing requirements.

Application of Sealing Surface Types

50. Full-Plane Sealing Surfaces: Commonly employed in applications with low operating conditions, particularly suitable for cast iron and steel flanges when operating pressures are ≤0.1 MPa.
50. Boss Surface Sealing Surfaces: Extensively utilized in PN2.0 MPa, PN5.0 MPa, and PN1.6 MPa pressure grades.
50. Concave-Convex Sealing Surfaces: Commonly employed in the PN4.0 MPa grade; however, they pose challenges in gasket replacement due to their design.
50. Ring Groove Sealing Surface: Typically paired with butt welding connections, predominantly utilized in high-temperature, high-pressure environments such as PN10.0 MPa, PN25.0 MPa, PN32.0 MPa, and other elevated pressure levels.

Gaskets

Gaskets undergo compression within the flange under the load of the bolts, leading to elastic and plastic deformation. This process fills the micro-geometric gaps between the flange sealing surface and the gasket, effectively reducing medium leakage. The sealing effectiveness is significantly influenced by the performance and suitable selection of gaskets. Commonly used gaskets include non-metallic, semi-metallic, and metallic gaskets.

50. Non-Metallic Gaskets: These are compressed by adding various additives to asbestos. They are suitable for temperatures up to 260°C and pressure levels up to PN2.0 MPa and are applicable to water, air, alkali, oil, and other media.
50. Polytetrafluoroethylene (PTFE) Gaskets: Suitable for temperatures ranging from -18°C to 200°C and pressure levels up to PN4.0 MPa. Frequently employed in low-temperature environments or when cleaning is necessary.
50. Semi-Metallic Gaskets: Comprise three categories: spiral wound gaskets, metal-clad gaskets, and flexible graphite spiral wound gaskets. The spiral wound gasket is the most ideal and commonly used type among semi-metallic gaskets, distinguished by its excellent compression surface elasticity and high strength. It maintains reliable sealing performance even under high and low-temperature vibration conditions.
50. Metal Gaskets: Frequently employed on high-pressure flanges due to their ability to withstand relatively high sealing pressures. Common types include flat, octagonal, and oval gaskets, typically paired with flanges featuring concave-convex surfaces, convex table surfaces, and tenon-groove surfaces.

Bolts and Nuts

When choosing the fastener material for a flange connection, factors such as the pipeline's operating pressure and temperature, the type of medium being conveyed, and the type of gasket used concurrently must be considered.

50. Alloy Steel Bolts: Crafted from high-grade, high-quality steel, with the letter "A" typically added after the material grade, as seen in commonly used examples like 35CrMoA and 25CrMoVA.
50. Hexagon Head Bolts： These bolts are commonly used with flat welding flanges and non-metallic gaskets for less demanding applications. They are typically made from Q235B material.
50. Stud Bolts: Frequently paired with butt welding flanges in demanding conditions. Typically, the material for the nut is selected based on the matching bolt material, often grade 8.8 and above.

To achieve optimal sealing performance, beyond selecting appropriate flanges and gaskets, as mentioned earlier, it's crucial to ensure the cleanliness of the flange sealing surface and the alignment of flange welding. During installation, adhere strictly to operating procedures when tightening bolts and sealing gaskets to prevent misalignment. Additionally, ensure regular maintenance during operation to maintain proper lubrication of bolts and nut fasteners.

In summary, only a well-matched sealing pair can guarantee the safe and efficient operation of the pressure-regulating station (or pressure-regulating device) or gas equipment. If you're searching for high-strength flange bolt factories or hex flange bolt manufacturers in China, we aim to be your top choice.