Brief Introduction of The Gaskets And Bolts And Nuts
Gasket types (rubber, metal, spiral-wound) and bolt materials (steel, alloy) ensure flange sealing under varied temperatures/pressures. Proper selection prevents leaks and enhances pipeline safety.
1. Flange gaskets
In pipeline flange connections, flange gaskets play a crucial role as seals between two flanges. Due to the fact that flange failure usually manifests as leakage, the main task of gaskets is to fill gaps, prevent medium leakage, and thus ensure the safety and stability of pipeline systems. There are various types of gaskets, including rubber gaskets, asbestos rubber gaskets, metal gaskets, etc.
Each type is suitable for specific media, temperature, and pressure conditions. For example, rubber asbestos pads are suitable for various media such as steam, gas, etc., while high-temperature oil resistant rubber asbestos pads can withstand high temperatures of 350-380 ℃. In addition, rubber pads are also commonly used in pipeline connections for low-pressure water, acid, alkali and other media, and are highly favored for their good elasticity and sealing effect.
Rubber gaskets perform particularly well in low-pressure and vacuum environments, and are particularly suitable for pipeline systems containing organic solvents such as benzene, ketones, and ethers. However, it is necessary to be vigilant about the possible swelling, weight gain, softening, and sticking phenomena that may occur in high temperatures or certain media, which may lead to seal failure.
Next, we will introduce the spiral wound gasket, which is made by winding metal steel strips and non-metal filler strips, and is particularly suitable for concave convex flange sealing surfaces. It is suitable for medium pressure valves at higher temperatures and has the advantages of simple manufacturing, low cost, full utilization of materials, and good sealing performance. Therefore, it is widely used in petrochemical process pipelines.
In addition, a toothed gasket is also a commonly used sealing gasket. It is made of various metals, such as ordinary carbon steel, low-alloy steel, and stainless acid resistant steel, with a thickness of 3 to 5mm. It uses concentric circular tooth patterns to contact the flange sealing surface, forming multiple seals and thus having excellent sealing performance.
For high-temperature and high-pressure valves, metal gaskets are an ideal choice. The processing accuracy and surface roughness requirements for its sealing surface are strict. In addition, metal coated graphite gaskets are also suitable for valves with higher temperatures and pressures.
There are various types of metal washers, including flat metal washers, elliptical cross-sectional area washers, octagonal metal washers, and lens type washers according to their shapes. According to the manufacturing materials, there are low-carbon steel, stainless acid resistant steel, copper, aluminum, and lead. Among them, metal flat washers are mostly used for smooth surface flat welding flanges, which can withstand relatively low temperatures and pressures.
Elliptical and octagonal metal gaskets are commonly used for trapezoidal groove welded flanges, with a nominal pressure range of 6.4 to 22.0 MPa. Although this type of gaskets has superior sealing performance, the manufacturing process is complex and requires high precision.
Lens pads, named after their unique cross-sectional shape, also have good sealing performance. In petrochemical production, this type of gaskets is widely used for flange connections of high-temperature and high-pressure pipelines, with a commonly used nominal pressure range of 16.0 to 32.0MPa.
When selecting metal gaskets, one principle should be followed: the hardness of the gasket surface should not be higher than the hardness of the flange sealing surface. The final selection of gaskets requires comprehensive consideration of the temperature, pressure, corrosiveness of the medium inside the pipeline, as well as the sealing method of the connecting flange. For high-pressure flange connections, specialized gaskets such as lens pads are particularly suitable.
In addition, bolts connecting flanges are also an indispensable part of flange connections. The commonly used types of bolts include single headed bolts and double-headed bolts, with threads typically using triangular metric coarse threads. Single head bolts, also known as hexagonal bolts, are divided into two types: semi-refined and refined. The use of semi-refined single head bolts is most common in medium-pressure and low-pressure process pipelines. There are various materials for manufacturing single head bolts, including Q235A, 35 steel, and 25Cr2MoVA, and their applicable temperatures depend on the specific material of the bolt. For example, bolts made of 35 steel can work in environments below 350 ℃, while bolts made of 25Cr2MoVA steel can remain stable at temperatures up to 570 ℃.
2. Double-headed bolts
In process pipelines, double headed bolts are usually selected as equally long double-headed refined bolts, which are particularly suitable for flange connections under high temperature and pressure. These bolts come in a variety of materials, including 35 steel, 30CrMoA, 35CrMoA, 25Cr2MoVA, 0Cr19Ni9, 0Cr15Ni25Ti2MoAlVB, and 37SiMn2MoVA. They have a nominal pressure range of 1.6 to 32.0MPa and can operate stably at temperatures up to 700 ℃.
3. Nuts
A nut is a fixing tool with a hole in the center and threads on the inside of the hole. Nuts are often used in conjunction with screws or bolts of corresponding sizes to ensure the stability of the relevant joint parts. Through the internal thread design, the nut can be tightly connected to bolts that meet the specifications. In various mechanical manufacturing processes, nuts are indispensable and important components.
Nuts, a fixing tool, can be divided into multiple categories based on its material differences, such as carbon steel, stainless steel, and non-ferrous metals (such as copper). Its structure is usually a flat and hollow multi-faceted cylinder. Common specifications on the market include M10, M12, M16, etc., where "M" represents metric threads and numbers refer to the diameter of the threads. In addition, nuts also have various special types, such as square nuts and rolled thin nuts, which can flexibly adapt to various environments and application needs.
There are two types of manufacturing processes for nuts: semi-refined and refined. Meanwhile, according to their structural form, nuts can be divided into type A and type B. Usually, semi-refined single head bolts are used with A-type nuts, while refined double head bolts are often combined with B-type nuts. It is worth noting that the matching use of nuts and bolts is crucial, but the hardness of the nut manufacturing material must be controlled within a range that does not exceed the hardness of the bolt material.
