The piping equipment used in petrochemical plants generally includes pipes, fittings, valves, flanges, gaskets and fasteners, and other piping components, such as filters, separators, flame arresters, and compensators, etc.

1. Tube

There are many classification methods for pipes, which can be divided into metal pipes, non-metallic pipes and steel-lined non-metallic composite pipes according to material classification. Non-metallic pipes mainly include rubber pipes, plastic pipes, asbestos cement pipes, graphite pipes, glass steel pipes, etc. The use of non-metallic pipes is smaller than that of metal pipes, while metal pipes account for most of the petrochemical plants. To more than 85 percent of all process piping installations, this section focuses on metal piping.

(1) Welded steel pipe

Welded steel pipes, also known as seamed steel pipes, are generally formed by coil welding of steel plates or steel strips. According to the surface treatment of the pipe, it is divided into two types: galvanized and non-galvanized. The galvanized surface is whitish, also known as white iron pipe or galvanized steel pipe; the ungalvanized surface is ordinary welded steel pipe, also known as black iron pipe. Galvanized welded steel pipes are often used to transport pipelines that require relatively clean media, such as domestic water, purified air, instrument air, etc.; non-galvanized welded steel pipes can be used to transport steam, gas, compressed air and condensed water.

According to user requirements, welded steel pipes can be divided into two types when they leave the factory, one is threaded at the end of the pipe, and the other is unthreaded at the end of the pipe. The length of each pipe is 4 to 9m for welded steel pipes with threaded ends, and the length of each pipe for welded steel pipes without threads is 4 to 12m.

Welded steel pipes are divided into thin-walled steel pipes, thickened steel pipes and ordinary steel pipes according to the thickness of the pipe wall. The most used steel pipe is the ordinary steel pipe, and its test pressure is 2.0MPa. The test pressure of the thickened steel pipe is 3.0MPa.

There are many connection methods for welded steel pipes, including threaded connection, flange connection and welding. The flange connection is divided into threaded flange connection and welded flange connection, and the welding method is divided into gas welding and arc welding.

The specifications of commonly used welded steel pipes range from 6 to 150 mm in nominal diameter.

(2) Seamless steel pipe

Seamless steel pipes are the pipes with the largest amount and the largest variety of specifications in industrial pipelines. They are basically divided into two categories: seamless steel pipes for fluid transportation and special seamless steel pipes. The former is commonly used in process pipes. Such as boiler special steel pipe, cracking furnace pipe and heat exchanger steel pipe. The material, it can be divided into carbon seamless steel pipe, chrome-molybdenum seamless steel pipe and stainless steel and acid-resistant seamless steel pipe. Nominal pressure, it can be divided into three categories: low pressure (0≤1.0MPa), medium pressure (1.0<10MPa=, and high pressure (≥10MPa). Process pipelines are commonly used seamless steel pipes for fluid transportation.

1. Carbon seamless steel pipe, the commonly used manufacturing materials are No. 10, No. 20, and 16Mn steel, and its specification range is: hot-rolled outer diameter φ32~630mm, cold-drawn outer diameter φ6~200mm, single tube length 4~12m, allowable The operating temperature is -40~450℃, and it is widely used for conveying various media that are not corrosive to steel, such as conveying steam, oxygen, compressed air, oil and oil and gas.

2. Low-alloy steel seamless steel pipe refers to an alloy steel pipe containing a certain proportion of alloying elements. Usually divided into two types, one is low-alloy steel pipe containing manganese element, called ordinary low-alloy steel pipe, such as 16Mn, 15MnV, etc.; the other is low-alloy steel pipe containing chromium, molybdenum and other elements, called chrome-molybdenum steel pipe. Commonly used are 12CrMo, 15CrMo, 12Cr2Mo, 1Cr5Mo, etc. The specifications range from φ10 to φ273mm in outer diameter, and the length of a single pipe is 4 to 12m. The applicable temperature range of chrome molybdenum steel pipe is -40 to 550 °C. Low-alloy seamless steel pipes are mostly used to transport various high-temperature oil products, oil and gas, less corrosive brine, and low-concentration organic acids.

3. Stainless and acid-resistant seamless steel pipes have many varieties according to the different contents of chromium, nickel and titanium, including Cr13, 00Cr17Ni14Mo2, 1Cr18Ni12Mo2Ti, 1Cr18Ni9Ti and so on. Among these steel grades, the most used is 1Cr18Ni9Ti, which is usually represented by the simplified material code 18-8 on the construction drawing. The applicable temperature range is -196~700℃. Media such as nitric acid, acetic acid and urea etc.

4. The high-pressure seamless steel pipe is basically the same as the above-mentioned seamless steel pipe, except that the pipe wall is thicker than the medium and low-pressure seamless steel pipe, and the thickest pipe wall is 40mm. For example, the specifications of high-pressure seamless steel pipes for fertilizer equipment are φ14×4(mm)~273×40(mm), the length of a single pipe is 4~12m, the applicable pressure range is 10~32MPa, and the working temperature is -40~400℃. In petrochemical plants, the above high-pressure seamless steel pipes are used to transport raw material gas, hydrogen nitrogen, synthesis gas, water vapor, high-pressure condensed water and other media.

In addition to the above, there are also low-temperature steel pipes, which are used in the cold area of ​​the imported projects. Pipe, at present, there is no mass production of steel pipes corresponding to this standard in China. Low-temperature steel pipes are divided into two types: seamless steel pipes and seamed steel pipes. The nominal diameter of seamless low-temperature steel pipes is 15-400mm, and the wall thickness is the same as that of carbon steel pipes; The standard length of the root canal is 6m.

(3) Steel plate coil tube

Coiled steel pipes are made of steel coils and welded, and are divided into two types: straight seam welded steel pipes and spiral seam welded steel pipes.

Most of the straight seam welded steel pipes are manufactured on the construction site or commissioned by processing plants, and professional steel pipe factories do not produce them. The steel plate materials include Q235A, No. 10, No. 20, 16Mn, 20g, etc. The specification range is 200-3000mm in nominal diameter, the largest is 4000mm, and the wall thickness is generally 4-16mm. The length of a single tube with a nominal diameter of 200 to 900mm is 6.4m; that of a nominal diameter of 1000 to 3000mm is 4.8m. Applicable working temperature: Q235A is -15~300℃, No.10, No.20, 16Mn, 20g is -40~450℃, all suitable for low-pressure range.

Spiral seam coil welded steel pipe, produced by the steel pipe manufacturer, the material is Q235A, 16Mn. Its specifications range from 200 to 700 mm in nominal diameter, 7 to 10 mm in wall thickness, and 8 to 18 m in length for a single tube. Applicable working temperature: Q235A is -15~300℃, 16Mn is -40~450℃, operating pressure: Q235A is 2.5MPa, 16Mn is 4MPa.

The straight seam welded steel pipe and the spiral seam welded steel pipe are mostly used for conveying medium at normal temperature and low pressure with low corrosiveness, such as low-pressure steam, underground circulating water, gas and oil and gas. The spiral seam welded steel pipe has a long single pipe, which is especially suitable for long-distance transportation pipelines.

According to the needs of the project, there are also straight seam stainless steel coil welded pipes, which are all rolled at the construction site and not produced by the manufacturer. The material used is mostly 1Cr18Ni9Ti steel plate. Its specification range has a nominal diameter of 200 to 1000mm, a wall thickness of 4mm for a nominal diameter of 200 to 400mm, a wall thickness of 6 to 8mm for a nominal diameter of 700 to 1000mm, and a single tube length of 4.5m. The applicable temperature and the range of the medium conveyed are the same as those of the low-pressure stainless steel pipe.

(4) Copper tube

Copper tubes are divided into two types: copper tubes and brass tubes. The material grades used in the manufacture of red copper pipes are T2, T3, T4 and TUP, etc., with a high copper content, accounting for more than 99.7%; the material grades of brass pipes are H62, H68, etc., which are alloys of zinc and copper. Such as H62 brass tube, the material composition of copper is 60.5% to 63.5%, zinc is 39.6%, and other impurities are less than 0.5%.

The manufacturing methods of copper pipes are divided into two types: drawing and extrusion. The outer diameter of the drawn copper tube is φ3~φ200mm, the outer diameter of the extruded copper tube is φ32~φ280mm, and the wall thickness is 1.5~5mm; And two kinds into a plate.

The applicable working temperature of copper pipe is below 250 ℃, and it is mostly used in oil pipelines, thermal insulation accompanying pipe and air separation oxygen pipelines.

(5) Titanium tube

Titanium pipe is a new type of pipe material in recent years. Because of its lightweight, high strength, strong corrosion resistance and low-temperature resistance, it is often used in process parts where other pipes are not competent. Titanium tube is made of TA1, TA2 industrial pure titanium, the applicable temperature range is -140 ~ 250 ℃, when the temperature exceeds 250 ℃, its mechanical properties will decline. Commonly used titanium tube specifications range from 20 to 400 mm in nominal diameter. It is suitable for low and medium pressure, the wall thickness of the low-pressure pipe is 2.8~12.7mm, and the wall thickness of medium pressure pipe is 3.7~21.4mm. Although titanium tube has many advantages, it has not been widely used due to its high price and difficulty in welding.

2. Pipe fittings

Pipe fittings are required to change the direction, elevation or pipe diameter in the piping system, and to lead out branch pipes from the main pipe. Due to the different shapes of the piping system, simple and complex, there are many types of pipe fittings. Commonly used pipe fittings are elbows, tees, reducers, pipe joints, pipe caps, etc.

(1) Elbow

Elbow is used to change the direction of the pipe. The bending angles of commonly used elbows are 90°, 45° and 180°. 180° elbows are also called U-shaped elbows. There are also elbows with special angles, but there are very few.

1. Malleable steel elbow

Malleable steel elbow, also known as malleable iron elbow, is the most common threaded elbow. This kind of malleable steel pipe fittings is mainly used for heating, upper and lower water pipes and gas pipes. In the process, except for low-pressure pipelines that need to be dismantled frequently, other material pipelines are rarely used. The specifications of malleable steel elbows are relatively small, and the commonly used specifications range from 1/2 to 4 inches. According to their different surface treatments, they are divided into two types: galvanized and non-galvanized.

2. pressed elbow

Pressed elbows, also known as stamped elbows or seamless elbows, are made of high-quality carbon steel, stainless acid-resistant steel and low-alloy steel seamless pipes, etc., and are pressed and formed in a special mold. Its bending radius is one and a half times the nominal diameter (R=1.5DN). In special occasions, an elbow with a bending radius equal to the nominal diameter (R=1DN) can also be used. Its specification range is within DN20~600mm. Its wall thickness range is consistent with the table number of seamless steel pipes. Pressed elbows are generally stamped and processed by professional manufacturers or processing plants with standard seamless steel pipes, and both ends of the elbows should be beveled when leaving the factory.

3. Stamped Welded Elbow

Stamping and welding elbows are formed by stamping a half-ring elbow from a plate through a die, and then welding the two half-ring elbows together. Its bending radius is the same as that of seamless pipe elbow, and its specification range is more than 200mm in nominal diameter.

4. Welding elbow

Welded elbow, also known as shrimp waist or shrimp body elbow. There are two production methods. One is to cut the steel plate in the processing plant, cut it, roll it and weld it, and most of it is used for the matching of the steel plate coil. The other is to use pipe blanking, which is formed by group butt welding, and its specifications are generally above 200mm. The use temperature cannot be higher than 200℃, and it can generally be produced on the construction site.

5. High-pressure elbow

High-pressure elbows are forged from high-quality carbon steel or low-alloy steel. According to the connection form of the pipe, the two ends of the elbow are processed into threads or grooves, and the processing precision is very high. It is required that the thread of the pipe mouth and the thread of the flange mouth can be tightly matched and screwed in freely without loosening. For petrochemical pipelines, the commonly used specifications range from DN6 to 200mm.

(2) Tee

The tee is a pipe fitting that connects the main pipe and the branch pipe. According to the different materials and uses, it is divided into many types. In terms of specifications, it can be divided into the same diameter tee and different diameter tee. The same diameter tee is also called an equal diameter tee; the same diameter tee means that the pipe diameter of the branch pipe is the same as the pipe diameter of the main pipe; the different diameter tee means that the pipe diameter of the branch pipe is smaller than that of the main pipe, so it is also called unequal diameter tee, and the amount of reducing tee is more.

1. Malleable Steel Tee

The manufacturing material and specification range of the malleable steel tee are the same as those of the malleable steel elbow.

2. steel tee

Before the 1970s, the development speed of my country’s industrial production technology was relatively slow, and the engineering technology of process piping was relatively backward. In the design of various medium and low-pressure steel pipes, when the pipes need to use three-way pipe fittings, they are generally solved by the method of digging holes for connecting pipes. Weld the branch pipe. This method has many disadvantages. The welding quality is not easy to guarantee, the pipeline is easily deformed after welding, and impurities are easy to enter the main pipe. In the late 1970s, with the introduction of large-scale modern production equipment such as metallurgy and the petrochemical industry, the development of process pipeline engineering technology was promoted. At present, my country has been able to produce medium and low-pressure pipeline steel custom-made tee, and has formed a series of products, seamless The specification of the tee is DN20~600mm, and the specification of the welded steel tee is DN150~1500mm.

The production of the stereotyped tee is made of the high-quality pipe as raw material, after cutting, digging, heating and drawing with a mold, and then machined to become a stereotyped finished tee. The tees of medium and low-pressure steel products are all welded on site. There are two cases for the tee used for steel coil pipe, one is to use steel plate blanking in the processing plant, and it is formed by rolling and welding; the other is to cut the hole to take over at the installation site.

3. High-pressure tee

There are two commonly used high-pressure tee, one is welded high-pressure tee, and the other is an integral forged high-pressure tee.

The high-pressure tee is welded, and a high-quality high-pressure steel pipe is selected as the material. The manufacturing method is similar to the digging pipe. The hole opened on the main pipe should be consistent with the diameter of the connected branch pipe. Welding quality requirements are strict, and usually require preheating before welding and heat treatment after welding. Its specifications range from DN16 to 200mm, and the pressure is 22MPa and 32MPa.

The integral forged high-pressure tee is generally connected by a threaded flange. Its specification range is table number SCH160, DN15~600mm, the table number is added with “XXS”, and its pipe diameter range is DN15~300mm.

(3) Reducer

The function of the reducer is to reduce the diameter of the pipe. From the direction of fluid movement, most of them change from large to small, and some from small to large. For example, the reducer of steam return pipes and sewer pipes changes from small to large. The reducer is commonly known as the size head.

1. Malleable steel reducer

Malleable steel reducers are generally divided into two types, one is an internal thread reducer, also known as an external joint; the other is a pipe fitting combined with an internal thread and an external thread, called a core, although it is not called a reducer, But it acts as a reducer.

2. steel reducer

The steel reducer is divided into two types: seamless and seamed. . Both types of reducers are available in both concentric and eccentric specifications. The bottom of the eccentric reducer has a straight edge, which can make the bottom of the pipe into a horizontal plane when in use, which is convenient for discharging the materials in the pipe during shutdown and maintenance.

The specification range of seamless reducer is DN25~600mm, and the specification range of seam welded reducer is DN200~1500mm.

Steel reducers, as finished pipe fittings on pipelines, have only been available since the 1970s. Most of the reducers on early process pipelines were made on site. If the diameter of the pipe changes greatly, the pipe end is drawn and welded, and it is directly processed into a reducer; if the pipe diameter does not change much, the pipe end is heated directly.

Made by smashing. The production of reducers by drawing and welding requires a lot of labor, many welds, and it is not easy to guarantee the welding quality. At present, this method has been banned for process pipes with high welding quality requirements.

(4) Other pipe fittings
1. head
The head is a plug used to seal the pipe end. Commonly used heads are oval and flat.
The oval head is also called the pipe cap, and its specifications range from DN25 to 600mm, and it is mostly used in medium and low-pressure pipelines. The flat cover head is divided into two types according to its installation position. One is that the flat cover head is slightly larger than the outer diameter of the pipe and is welded outside the pipe. The other is that the flat cover head is slightly smaller than the inner diameter of the tube, and the head plate is put into the tube for welding. The commonly used specifications range from DN15 to 200mm, and this type of head is mostly used on pipelines with lower pressure.
2. boss
The boss, also known as the nozzle, is a one-time component of the automatic control instrument professional on the processing pipeline. It is installed by the processing pipeline professional, so the boss is also listed as a pipe fitting. The single-sided pipe joints used in process pipelines also belong to this category. One end is welded to the main pipe, and the other end is either installed with other components or is connected to another pipe.
3. blind plate
A blind plate, whose function is to cut off the medium in the pipeline, is divided into the following types according to the operating pressure and the form of the flange sealing surface:
(1) The smooth surface blind plate is used in conjunction with the smooth sealing surface flange, and its applicable pressure range is 1.0 ~ 2.5MPa.
(2) Convex blind plate, which has a convex surface on one side and a concave surface on the other side, is used in conjunction with the flange of the concave-convex sealing surface. The working pressure is 4.0MPa, and the specification range is DN25~400mm.
(3) The trapezoidal groove face blind plate is used in conjunction with the trapezoidal groove sealing face flange, and the operating pressure range is 6.4 ~ 16.0MPa. The specification range is DN25~300mm.
(4) The “8” blind plate is also divided into three types: smooth surface, concave-convex surface and trapezoidal groove surface. The use pressure is the same as the above three blind plates. The purpose is combined on one component, that is, the blind plate and the gasket are connected and fixed together. When the flange is inserted into the blind plate, the gasket exposed on the outside serves as a visual sign of whether the pipeline is cut off.
There are many kinds of manufacturing materials for the “8” blind plate, which are selected according to the temperature and pressure of the medium to be conveyed. For general low-pressure pipelines, when the temperature does not exceed 450 °C, the materials used are Q235A, No. 20 steel and No. 25 steel; when the temperature is 450 to 550 °C, the materials used are 15CrMo and 1Cr5Mo. When the pressure is between 4.0 and 16.0MPa and the temperature is greater than 550℃, stainless steel is used.
3. Flanges, gaskets, and bolts

(1) Flange
A flange is a part of the processing pipeline that acts as a connection. This form of connection has a very wide range of applications, such as the connection of pipelines and process equipment, the connection of flanged valves and accessories on pipelines. The use of flange connection not only has the flexibility of installation and disassembly but also has reliable sealing.
The standardization of flanges has not yet been unified in China. The earliest is the pipe flange standard issued by the former Ministry of Chemical Industry in 1958, which was formulated with reference to the standards of the Soviet Union in the 1950s; in 1959, the former Ministry of Machinery issued a set of pipe flange standards; With the rapid development of the industry, the former Ministry of Petroleum also issued a set of flange standards in 1964. These flange standards have commonalities and their own particularities. The flange standards of the former Ministry of Machinery and the Ministry of Chemical Industry, the inner diameter of the flat welding flange and the outer diameter of the butt welding flange neck, are mostly based on the small outer diameter of the pipe; the original Ministry of Petroleum flange standards are mostly based on It is based on the large outer diameter of the tube. Therefore, various standard flanges are not the same in some local dimensions.
The medium conveyed by the processing pipeline is of various types, and the temperature and pressure are also different, so different requirements are put forward for the strength and sealing of the flange. In order to meet the needs of process pipeline installation projects, there are many kinds of flanges with different structures and pressures. The following is a brief introduction to various flanges:
1. Flat welding flange
Flat welded steel flanges are the most commonly used type of medium and low-pressure process pipelines. This form of fixing the flange and the pipe is to put the flange on the pipe end, and weld the inner and outer ports of the flange to fix the flange, and the applicable nominal pressure does not exceed 2.5MPa. Flat welding flanges used for carbon steel pipeline connections are generally made of Q235A and No. 20 steel plates; flat welding flanges used on stainless acid-resistant steel pipes are made of stainless acid-resistant steel plates of the same material as the pipes. The sealing surface of flat welded steel flanges is generally smooth, and the sealing surface is machined with shallow grooves. Often called a waterline.
The specification range of flat welded steel flanges is as follows:
Nominal pressure PN0.25, 0.6MPa is DN10 ~ 2000mm; PN1.0 ~ 2.5MPa is DN10 ~ 600mm.
2. Butt welding flange
Butt welding steel flange, also known as high neck flange or big tail flange. It has high strength and is not easily deformed, and has good sealing performance. It has various forms of sealing surfaces and is suitable for a wide range of pressures.
For smooth facing welding flange, the nominal pressure is below PN2.5MPa, the specification range is DN10~2000mm, the nominal pressure is PN2.5MPa, the specification range is DN10~1000mm, the nominal pressure is PN4.0MPa, and the specification range is DN10~600mm.
The concave-convex seal faces the welding flange. Due to the tightness of the concave-convex sealing surface, the pressure is large. The sealing surface of each flange must be concave and convex. The commonly used nominal pressure range is PN1.6~4.0MPa, and the specification range is DN10~600mm.
The tongue and groove seal faces the welding flange. This kind of flange has good sealing performance, and the structure is similar to the concave-convex sealing face flange. It is also a pair of flanges that must be used together. The nominal pressure range is PN1.6~4.0MPa, and the specification range is DN10~600mm; PN6.4~10MPa, the specification range is DN10~400mm.
The trapezoidal groove seal faces the welding flange. This kind of flange is commonly used in the petroleum industry pipeline and bears high pressure. The commonly used nominal pressure is PN6.4, 10.0MPa, and the specification range is DN10~400mm; PN16MPa, the specification range is DN10~300mm .
The above-mentioned various butt welding flanges are only distinguished according to the form of their sealing surfaces. From the point of view of the installation, no matter what kind of butt welding flange, the connection method is the same, so the labor, materials and mechanical shifts consumed are basically the same. However, due to the different forms of sealing surfaces, the processing and manufacturing costs of flanges vary greatly. Therefore, special attention should be paid to the price of the flange itself when preparing the budget (budget).
3. Loose Steel Pipe Flanges
This kind of flange and the pipe are not directly welded together, but the flange of the pipe or the welding ring is used as the sealing contact surface, and the loose flange is used for fastening. It is mostly used for non-ferrous metals such as copper, aluminum and lead, and stainless and acid-resistant on steel pipes. Its biggest advantage is that because the flange can move freely, it is very convenient for the flange to wear bolts. The welding ring loose sleeve steel pipe flange is suitable for the pressure PN0.6~2.50MPa, and its specification range is DN10~600mm; the pressure PN4.0MPa, the specification range is DN10~300mm, the flat welding ring loose sleeve steel pipe flange is only suitable for more Low pressure, PN0.6~1.6MPa, its specification range is DN10~600mm. The nozzle flanging looper method is only applicable to PN06MPa and below.
4. Threaded flange
Threaded flange is a flange connected with a threaded flange and a pipe end thread. There are two types of high pressure and low pressure.
Low-pressure threaded flanges, including steel and cast iron, were widely used in the early days of the founding of the People’s Republic of China with poor welding technology. With the development of industry, low-pressure threaded flanges have been replaced by flat-welded flanges, which are basically not used except in special cases.
High-pressure threaded flanges are widely used in the connection of modern industrial pipelines. The seal is formed by the tube end and the lens washer, which requires high precision machining of the contact surface between the thread and the tube end washer. The characteristic of this kind of flange is that the flange does not contact the medium in the pipe, and the installation is more convenient. The applicable pressure is PN22.0 and PN32.0MPa, and its specification range is DN6~250mm.
5. Flange cover
The flange cover is a component used in conjunction with the flange. It acts as a seal at the end of the pipe like the head. The sealing surface has a smooth type and convex and concave type, and its specification and applicable pressure range are consistent with the matching flange.
(2) Flange gasket
Leakage is the main form of failure of pipe flanges, and it is related to many factors such as the type of seal structure, the stiffness of the connected parts, the performance, operation and installation of the seal. The gasket is the main seal of the flange connection, so the correct selection of gasket is also the key to ensuring flange connection does not leak. There are many kinds of flange gaskets according to the corrosiveness, temperature, pressure and the form of flange sealing surface of the medium conveyed by the pipeline. Pipe flange gaskets include non-metallic gaskets, semi-metallic gaskets and metal gaskets.
1. Rubber asbestos pad
Rubber asbestos gasket is the gasket with the largest amount of flange connection, and can be applied to many media, such as steam, gas, air, salt water, acid and alkali. The thickness of rubber asbestos pads is not uniform in various professions, usually 3mm thick. For flanges with a nominal diameter of less than 100mm, the gasket thickness should not exceed 2.5mm.
The working pressure of the gasket shall not exceed 2.5MPa when it is used for flange connection with smooth sealing surface. There are two types of rubber asbestos pads commonly used in the oil refining industry. One is oil-resistant rubber asbestos pads, which are suitable for transporting general oil products, liquefied hydrocarbons, propane and acetone and other media at temperatures below 200°C and nominal pressure below 2.5MPa. High-temperature oil resistant rubber asbestos pad, the operating temperature can reach 350 ~ 380 ℃. The other is a medium pressure rubber asbestos pad, which can be used in steam, condensed water, water, air and other media at 200 ° C and below PN 2.5MPa.
2. Rubber mat
Rubber gasket is a gasket made of rubber sheet. It has certain corrosion resistance. It is often used for flange connection of pipelines where the temperature is below 60°C and the pressure does not exceed 1.0MPa, which transports low-pressure water, acid and alkali and other media. The characteristic of this kind of gasket is to use the elasticity of rubber to achieve a better sealing effect, so it is also often used in the installation of cast iron flange valves.
3. Spiral wound gasket
Spiral wound gaskets are referred to as wound gaskets, which are wound with metal steel strips and non-metallic packing strips. This gasket has the advantages of simple manufacture, low price, fully utilized materials and good sealing performance, and is widely used in petrochemical process pipelines. The applicable nominal pressure is below 4.0MPa, the applicable temperature range, the temperature of No. 08 steel can reach 450℃, and the temperature of the wound pad made of 0Cr13 steel strip can reach 540℃. Most of these gaskets are used for smooth surface flange connections, and their sealing surfaces do not use vehicle water lines. Some wound gaskets also have a positioning ring to prevent the gasket from deviating from the center of the flange. The thickness of the gasket is generally 4.5mm, and when the diameter is greater than 1000mm, the thickness of the gasket is 6-7mm. The thickness of the positioning ring is about 3mm. Metal steel strips are made of No. 08 steel, 0Cr13 steel and 1Cr18Ni9Ti steel; non-metallic strips are made of asbestos, flexible graphite, PTFE, etc.
4. Tooth pad
The toothed pads are made of various metals, such as ordinary carbon steel, low-alloy steel and stainless acid-resistant steel, and the thickness is 3-5mm. It uses the concentric toothed dense pattern to contact the flange sealing surface to form a multi-channel seal, so the sealing performance is better, and it is often used for the connection of concave-convex sealing surface flanges. The highest nominal pressure can reach 16.0MPa, which is suitable for parts with high working temperatures.
5. metal washers
There are many types of metal washers, which are divided into metal flat washers according to their shapes, and their cross-sectional areas are oval, octagonal, and lens washers. The manufacturing material, there are low carbon steel, stainless acid-resistant steel, red copper, aluminum and lead, etc.
Metal flat washers, mostly used for flat welding flanges with smooth surfaces, bear low temperature and pressure.
Oval and octagonal metal gaskets are mostly used for trapezoidal groove butt welding flanges, with a nominal pressure range of 6.4 to 22.0 MPa. Although this gasket has good sealing performance, it is complicated to manufacture and requires high precision.
The lens pad, named for its cross-sectional shape resembling a lens, has good sealing performance. In petrochemical production, the flange connection of various high-temperature and high-pressure pipelines is widely used. The common nominal pressure range is 16.0 ~ 32.0MPa.
There is a rule for the use of metal gaskets, that is, the hardness of the gasket surface must be lower than the hardness of the flange sealing surface.
The selection of gaskets should be determined according to the temperature, pressure, corrosiveness of the medium transported by the pipeline and the sealing form of the connecting flange. Specialized gaskets, such as lens gaskets, are suitable for high-pressure flange connections.
(3) Bolts for flanges
There are two types of bolts used to connect flanges: single-headed bolts and double-headed bolts, and their threads are generally triangular metric coarse threads.
1. single head bolt
Single head bolts are also called hexagon head bolts, as shown in Figure 12-2-8. Single-head bolts are divided into two types: semi-refined and refined. In medium and low-pressure process pipelines, semi-refined single-head bolts are the most used.
The materials commonly used in the manufacture of single-head bolts are Q235A, 35 steel and 25Cr2MoVA. Commonly used for flange connections with nominal pressure below 2.5MPa. The applicable temperature depends on the material of the bolt. For example, the applicable temperature of bolts made of No. 35 steel can reach 350℃; the applicable temperature of bolts made of 25Cr2MoVA steel can reach 570℃.
2. Stud
Most of the stud bolts used on the processing pipeline are made of equal-length stud bolts, as shown in Figure 12-2-9. Suitable for flanged connections with high temperature and pressure. The materials are 35# steel, 30CrMoA, 35CrMoA, 25Cr2MoVA, 0Cr19Ni9, 0Cr15Ni25Ti2MoAlVB and 37SiMn2MoVA, etc. The nominal pressure range is 1.6~32.0MPa, and the applicable temperature can reach 700℃.
3. nut
Nuts are collectively referred to as hex nuts. Divided into semi-refined and refined two. According to the nut structure, it can also be divided into A type and B type, as shown in Figure 12-2-10.
Semi-refined single-head bolts mostly use A-type nuts; refined stud bolts mostly use B-type nuts. Nuts and bolts should be used together, but the hardness of the nut manufacturing material cannot exceed the hardness of the bolt material.

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