蜜桃传媒

Chemical pipelines and valves are an indispensable part of chemical production and are the link between various chemical equipment. How do the 5 most common valves in chemical pipelines work? What are their main uses? What are the chemical pipes and pipe fittings valves? (11 types of pipes + 4 types of pipe fittings + 11 large valves) All these things about chemical pipelines, master them in one article!

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Chemical pipes and pipe fittings valves

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11 types of chemical pipes

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Chemical pipes are divided into metal pipes听and non-metal pipes听according to their materials

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Metal pipes

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Cast iron pipes, seamed steel pipes, seamless steel pipes, copper pipes, aluminum pipes, and lead pipes.

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鈶犔�Cast iron pipes:

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Cast iron pipes are one of the commonly used pipes in chemical pipelines.

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Due to their brittleness and poor connection tightness, they are only suitable for conveying low-pressure media, and are not suitable for conveying high-temperature and high-pressure steam and toxic and explosive substances. Commonly used in underground water supply pipes, gas mains and sewer pipes. The specifications of cast iron pipes are expressed in 肖 inner diameter 脳 wall thickness (mm).

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鈶√�Seamless steel pipes:

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Seamless steel pipes are divided into ordinary water and gas pipes (pressure resistance 0.1~1.0MPa) and thickened pipes (pressure resistance 1.0~0.5MPa) according to the use pressure.

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Generally used to transport pressure fluids such as water, gas, heating steam, compressed air, and oil. Galvanized ones are called white iron pipes or galvanized pipes. Ungalvanized ones are called black iron pipes. Its specifications are expressed in nominal diameter. The minimum nominal diameter is 6mm and the maximum nominal diameter is 150mm.

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鈶⑻�Seamless steel pipes:

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The advantages of seamless steel pipes are uniform quality and high strength.

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Its materials include carbon steel, high-quality steel, low-alloy steel, stainless steel, and heat-resistant steel. Due to different manufacturing methods, they are divided into hot-rolled seamless steel pipes and cold-drawn seamless steel pipes. In pipeline projects, when the pipe diameter exceeds 57mm, hot-rolled pipes are often used, and when it is less than 57mm, cold-drawn pipes are often used.

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Seamless steel pipes are often used to transport various pressurized gases, steam and liquids, and can withstand higher temperatures (about 435掳C). Alloy steel pipes are used to transport corrosive media, among which heat-resistant alloy pipes can withstand temperatures of up to 900-950掳C. The specifications of seamless steel pipes are expressed as 肖 inner diameter 脳 wall thickness (mm).

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The maximum outer diameter of cold-drawn pipes is 200mm, and the maximum outer diameter of hot-rolled pipes is 630mm. Seamless steel pipes are divided into general seamless pipes and special seamless pipes according to their uses, such as petroleum cracking seamless pipes, boiler seamless pipes, fertilizer seamless pipes, etc.

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鈶� Copper pipes:

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Copper pipes have good heat transfer effects.

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Mainly used in pipelines of heat exchange equipment and deep cooling devices, instrument pressure measuring pipes or conveying pressurized fluids, but when the temperature is higher than 250掳C, it is not suitable for use under pressure. Because of its high price, it is generally used in important places.

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鈶� Aluminum pipes:

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Aluminum has good corrosion resistance.

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Aluminum pipes are often used to transport media such as concentrated sulfuric acid, acetic acid, hydrogen sulfide and carbon dioxide, and are also commonly used in heat exchangers. Aluminum tubes are not alkali-resistant and cannot be used to transport alkaline solutions and solutions containing chloride ions.

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Since the mechanical strength of aluminum tubes decreases significantly with the increase of temperature, the operating temperature of aluminum tubes cannot exceed 200掳C. For pressurized pipelines, the operating temperature will be lower. Aluminum has good mechanical properties at low temperatures, so aluminum and aluminum alloy tubes are mostly used in air separation units.

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鈶� Lead pipes:

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Lead pipes are often used as pipelines for transporting acidic media. They can transport 0.5% to 15% sulfuric acid, carbon dioxide, 60% hydrofluoric acid, and acetic acid with a concentration of less than 80%. It is not suitable for transporting nitric acid, hypochlorous acid and other media. The maximum operating temperature of lead pipes is 200掳C.

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Non-metallic pipes

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Plastic pipes, plastic pipes, glass pipes, ceramic pipes, cement pipes.

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鈶犔�Plastic pipes:

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The advantages of plastic pipes are good corrosion resistance, light weight, convenient molding, and easy processing.

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The disadvantages are low strength and poor heat resistance.

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At present, the most commonly used plastic pipes are hard polyvinyl chloride pipes, soft polyvinyl chloride pipes, polyethylene pipes, polypropylene pipes, and metal pipes sprayed with polyolefins and polytrifluoroethylene.

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鈶√�Rubber pipes:

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Rubber pipes have good corrosion resistance, light weight, good plasticity, and are flexible and convenient to install and disassemble.

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Commonly used rubber pipes are generally made of natural rubber or synthetic rubber, suitable for occasions where pressure requirements are not high.

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鈶⑻�Glass pipes:

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Glass pipes have the advantages of corrosion resistance, transparency, easy cleaning, low resistance, and low price. The disadvantages are brittleness and non-pressure resistance.

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Commonly used in testing or experimental work occasions.

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鈶Ｌ�Ceramic pipes:

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Chemical ceramics are similar to glass and have good corrosion resistance. Except for hydrofluoric acid, fluorosilicic acid and strong alkali, they can withstand corrosion from various concentrations of inorganic acids, organic acids and organic solvents.

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Due to low strength and brittleness, they are generally used in sewers and ventilation ducts to remove corrosive media.

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鈶ぬ�Cement pipe:

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Mainly used in places with low pressure requirements and low sealing of pipes, such as underground sewage and drainage pipes.

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4 types of pipe fittings

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In addition to pipes, there are many other components in the pipeline, such as short pipes, elbows, tees, reducers, flanges, blind plates, etc., to meet the needs of process production and installation and maintenance.

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We usually call these components pipeline accessories for short pipe fittings. Pipe fittings are an indispensable part of the pipeline. Here are some common pipe fittings.

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鈶犔�Elbow

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Elbows are mainly used to change the direction of the pipeline. They can be classified according to the degree of bending of the elbow. Common ones are 90掳, 45掳, 180掳, and 360掳 elbows. 180掳and 360掳elbows are also called "U" elbows.

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In addition, there are elbows with specific angles required for process piping. Elbows can be made by bending straight pipes or welding pipes, or by welding after molding, or by casting and forging. For example, elbows in high-pressure pipelines are mostly forged from high-quality carbon steel or alloy steel.

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鈶Ｌ�Tee

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When two pipelines are interconnected or bypass diversion is required, the pipe fittings at the joint are called tees.

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Depending on the angle of the access pipe, there are vertically connected straight tees and beveled tees. Beveled tees are named according to the bevel angle, such as 45掳beveled tees.

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In addition, they are named according to the size of the inlet and outlet, such as equal-diameter tees. In addition to the common three-way pipe fittings, they are often called by the number of interfaces, such as four-way, five-way, beveled five-way, etc. In addition to pipe welding, common three-way pipe fittings are also made by molding, welding, casting and forging.

Tee

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鈶ぬ�Short pipe and reducer

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When a short section is missing in the pipeline assembly, or a small detachable pipe section needs to be placed in the pipeline for maintenance, a short pipe is often used.

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Short pipes have connectors (such as flanges, threads, etc.), or are just short pipes, also known as pipe pads.

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Pipe fittings that connect two pipe openings of unequal diameters are called reducers. Usually called reducers. This type of pipe fittings include cast reducers, pipe cutting and welding, or steel plate rolling and welding. Reducers in high-pressure pipelines are made of forgings or high-pressure seamless steel pipes.

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鈶ヌ�Flanges and blind plates

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For ease of installation and maintenance, detachable connections are often used in pipelines, and flanges are a commonly used connection part.

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For cleaning and inspection, it is necessary to set a hand hole blind plate on the pipeline or install a blind plate at the pipe end. Blind plates can also be used to temporarily close a certain interface of the pipeline or disconnect a certain section of the pipeline from the system.

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In general medium and low pressure pipelines, the shape of the blind plate is the same as that of the solid flange, so this blind plate is also called a flange cover. This blind plate is standardized like the flange, and the specific size can be found in the relevant manual.

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In addition, in the maintenance of chemical equipment and pipelines, in order to ensure safety, a solid disc made of steel plate is often inserted between two flanges to temporarily isolate the equipment or pipeline from the production system. This blind plate is usually called an inserted blind plate. The size of the inserted blind plate can be the same as the outer diameter of the sealing surface of the flange at the insertion point.

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11 Large valves

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The device used to control the flow of fluid in the pipeline is called a valve. Its main functions are:

• Opening and closing function - cutting off or communicating the flow of fluid in the pipeline.
• Regulating function - regulating the flow rate and flow of fluid in the pipeline.
• Throttling function - after the fluid flows through the valve, a large pressure drop is generated.

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Classification:

• 听According to the different functions of valves in pipelines, they can be divided into cut-off valves (also known as stop valves), throttle valves, check valves, safety valves, etc.;
• According to the different structural forms of valves, they can be divided into gate valves, plug valves (often called cocks), ball valves, butterfly valves, diaphragm valves, lined valves, etc.
• In addition, according to the different materials used to make valves, they are divided into stainless steel valves, cast steel valves, cast iron valves, plastic valves, ceramic valves, etc.

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The selection of various valves can be found in relevant manuals and samples. Here we only introduce the most common types of valves.

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鈶� Stop valve

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Due to its simple structure and convenient manufacturing and maintenance, it is widely used in medium and low pressure pipelines. It uses the circular valve disc (valve head) installed under the valve stem to cooperate with the flange part (valve seat) in the valve body to achieve the purpose of cutting off the flow of fluid.

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The valve stem can adjust the degree of opening of the valve by lifting and lowering the thread, which plays a certain role in regulation. Since the valve's shutoff function relies on the contact and sealing between the valve head and the valve seat plane, it is not suitable for pipelines containing solid particle fluids.

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The stop valve can select the appropriate materials for the valve head, valve seat and shell according to the characteristics of the medium used. For valves that are not well sealed or the valve head, valve seat and other parts are damaged during use, they can be repaired by polishing, grinding, surfacing and sleeve inserting to extend the service life of the valve.

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鈶� Gate valve

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It relies on one or two flat plates perpendicular to the flow direction of the medium, which cooperate with the sealing surface of the valve body to achieve the purpose of sealing. The rise of the valve plate opens the valve.

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The plate rises and falls with the rotation of the valve stem, and the flow rate of the fluid is adjusted by the size of the opening. This kind of valve has low resistance, good sealing performance, and labor-saving switching. It is particularly suitable for large-diameter pipelines, but the structure of the gate valve is relatively complex and there are many types.

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According to the different valve stem structures, there are open stems and dark stems; according to the structural form of the valve plate, it is divided into wedge type, parallel type, etc.

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Generally, the wedge type valve plate is a single valve plate, and the parallel type uses two valve plates. The parallel type is easier to manufacture and repair than the wedge type, and is not easy to deform during use, but it is not suitable for conveying fluid pipelines containing impurities. It is mostly used for conveying water, clean gas, oil and other pipelines.

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鈶� Plug valve

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The plug is commonly known as cock. It uses a conical plug with a central hole inserted into the valve body to open and close the pipeline.

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According to the different sealing forms, the plug can be divided into packing plug, oil-sealed plug and unpacked plug. The plug has a simple structure, small size, fast opening and closing, easy operation, small fluid resistance, and is easy to make a three-way or four-way distribution or switching valve.

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The sealing surface of the plug is large, easy to wear, laborious when opening and closing, and difficult to adjust the flow, but it is cut off quickly. The plug can be used in fluid pipelines with low pressure and temperature or containing solid particles in the medium, but it is not suitable for high pressure, high temperature or steam pipelines.

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鈶� Throttle valve

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It is a kind of stop valve. The shape of the valve head is conical or streamlined, which can better control and adjust the flow rate of the fluid or perform throttling and pressure regulation. The valve has high manufacturing precision requirements and good sealing performance.

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It is mainly used in pipelines such as instrument control or sampling, but it is not suitable for pipelines with high viscosity and solid particle media.

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鈶� Ball valve

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Also known as ball-core valve, it is a valve that has developed rapidly in recent years. It uses a sphere with a hole in the middle as the valve core and relies on the rotation of the sphere to control the opening or closing of the valve.

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It is similar to the plug, but has a smaller sealing surface than the plug, a compact structure, and labor-saving switching, and is far more widely used than the plug.

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With the improvement of ball valve manufacturing precision, ball valves are not only used in medium and low pressure pipelines, but also in high pressure pipelines. However, due to the limitation of sealing materials, it is not suitable for high temperature pipelines at present.

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鈶� Diaphragm valve

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Common ones are film valves. The opening and closing of this valve is a special rubber diaphragm, which is sandwiched between the valve body and the valve cover. When closed, the disc under the valve stem presses the diaphragm against the valve body to achieve sealing.

This valve has a simple structure, reliable sealing, easy maintenance, and low fluid resistance. It is suitable for pipelines that transport acidic media and fluids with suspended matter, but it is generally not suitable for pipelines with higher pressure or temperature above 60掳C, and it is not suitable for pipelines that transport organic solvents and strong oxidizing media.

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鈶� Check valve

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Also known as a check valve or a one-way valve. It is installed in the pipeline so that the fluid can only flow in one direction and does not allow reverse flow.

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It is an automatic closing valve with a valve disc or a rocker plate in the valve body. When the medium flows downstream, the fluid automatically pushes the valve disc open; when the fluid flows backward, the fluid (or spring force) automatically closes the valve disc. According to the different structures of the check valve, it is divided into two types: lifting type and swing type.

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The lift check valve flap moves vertically to the valve body channel and is generally used on horizontal or vertical pipes; the valve flap of the swing check valve is often called a rocking plate, one side of which is connected to the shaft and can rotate around the shaft. The swing check valve is generally installed on a horizontal pipe. For small-diameter ones, it can also be installed on a vertical pipe, but it should be noted that the flow rate should not be too large.

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Check valves are generally suitable for pipelines with clean media, and should not be used in pipelines containing solid particles and media with high viscosity. The lifting check valve has better closing performance than the swing check valve, but the fluid resistance of the swing check valve is smaller than that of the lifting check valve. In general, the swing check valve is suitable for large-diameter pipelines.

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鈶� Butterfly valve

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It relies on a rotatable disc (or elliptical disc) in the pipe to control the opening and closing of the pipeline. It has a simple structure and small dimensions.

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Due to the sealing structure and material problems, the valve has poor closing performance and is only suitable for regulation in low-pressure and large-diameter pipelines. It is often used in pipelines that transport media such as water, air, and gas.

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鈶� Pressure reducing valve

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It is an automatic valve that reduces the medium pressure to a certain value. Generally, the pressure after the valve is less than 50% of the pressure before the valve. It mainly relies on diaphragms, springs, pistons and other parts to use the pressure difference of the medium to control the gap between the valve disc and the valve seat to achieve the purpose of pressure reduction.

There are many types of pressure reducing valves, the most common of which are piston type and film type.

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鈶� Lined valve

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To prevent corrosion of the medium, some valves need to be lined with corrosion-resistant materials (such as lead, rubber, enamel, etc.) on the valve body and valve head. The lining material should be selected according to the properties of the medium.

For the convenience of lining, lined valves are mostly made into right-angle or direct current types.

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鈶� Safety valve

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To ensure the safety of chemical production, a safety device is often installed in a pressurized pipeline system, that is, a metal sheet of a certain thickness is selected and installed on the end of the pipeline or the three-way interface like a blind plate.

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When the pressure in the pipeline increases, the sheet is broken to achieve the purpose of pressure relief. Bursting plates are generally used in low-pressure, large-diameter pipelines, but safety valves are used in most chemical pipelines. There are many types of safety valves, which can be roughly divided into two categories, namely spring type and lever type.

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Spring type safety valves mainly rely on the force of the spring to achieve sealing. When the pressure in the pipe exceeds the elastic force of the spring, the valve is pushed open by the medium, and the fluid in the pipe is discharged to reduce the pressure.

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Once the pressure in the pipe drops below the elastic force of the spring, the valve closes again. The lever type safety valve mainly relies on the force of the heavy hammer on the lever to achieve sealing, and the working principle is the same as the spring type. The selection of safety valves is based on the working pressure and working temperature to determine the level of nominal pressure, and its caliber can be calculated and determined by referring to relevant regulations.

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The structural type of the safety valve and the material of the valve should be selected according to the nature of the medium and the working conditions. There are special regulations for the starting pressure, test and acceptance of the safety valve, which are regularly checked and sealed by the safety department. It shall not be adjusted arbitrarily during use to ensure safety.