Advance in Pipes and Connections in

Pipes and connections of chemical equipment have progressed in bellows made of ethylene or polypropylene films, spring tubes lined with PTFE or polypropylene films, and PTFE short-circuits. Pipeline connection methods include flange connection, pipe thread connection and pipe joint connection. Pipe joints include unions, quick joints, clamp joints, etc. Familiar with the advantages and disadvantages of various pipes and connection methods, the simplest and fastest connection method will be adopted to better serve chemical production.

1 Connecting pipelines Pipes are classified according to flexibility and can be divided into rigid pipelines and flexible pipelines, namely straight pipelines and bendable pipelines. Straight pipelines include metal pipelines, enamel pipelines, glass pipelines, plastic pipelines, lined pipelines, etc .; flexible pipelines include corrugated pipes, tightly lined spiral pipes, and PTFE shorting.

Commonly used metal pipeline materials are stainless steel, carbon steel, titanium, etc., which are widely used in the connection of pipelines in chemical production. Other materials include copper, aluminum, and lead. They are rarely used and are often selected for special purposes. . The choice of metal materials includes factors such as corrosion, strength, price, and applicable temperature. Some manuals have detailed the characteristics and applications of different materials. Stainless steel material is not resistant to strong acid materials.

In addition to being too thin in diameter, such as stainless steel pipes under 8 and other metal pipes and soft metal pipes such as copper and aluminum are flexible, metal pipes are generally hard connections.

In chemical production, there are often problems with equipment and pipes and the connection between pipes. Especially in the production process of high value-added products characterized by multiple varieties and small batches, a reactor is often required to produce multiple products. For different products, different production processes are required, and the same connection method may not meet the requirements. This requires the temporary addition of equipment and the temporary construction of pipelines to meet different production requirements. As new materials continue to be applied and new designs emerge one after another, the connection of chemical equipment has also undergone new developments. New commercialized pipes without materials and new types of connecting pipes have played a great role in chemical production and greatly facilitated the production. demand.

In order to understand the materials used for the connection in more detail, this article will elaborate separately according to the connection pipe and the connection joint. The connection pipes are classified according to flexibility, and can be divided into soft connections and hard connections; according to the material classification, there are metal pipes, enamel pipes, glass pipes, plastic pipes, stainless steel corrugated pipes, corrugated with tetrafluoroethylene or polypropylene membrane Tube, spring tube lined with PTFE or polypropylene film, PTFE short circuit, etc. The connection joints are classified according to the connection form, including flange connection, threaded connection, quick joint, clamp joint, etc.

The connection form of metal materials is usually mainly flanges and threads, and the connection forms of thin pipes and ferrules are already widely used. This article will not expand the description.

1.2 Enameled pipes For acidic materials that are not resistant to corrosion by stainless steel, enamel pipes can be used. Enameled pipes can be purchased or customized from manufacturers producing enamel kettles, generally flanged connections, or existing pipes can be sent to enamel factories to apply porcelain as required.

1.3 Glass pipes Glass pipes are rarely used alone, and are generally connected to glass equipment such as glass condensers and glass reactors. However, for some places that require transparency and can not install pipeline sight glass, the use of glass pipelines can be considered for the transportation of high-temperature and highly corrosive materials and condensed materials.

The acid resistance, alkali resistance and heat resistance of glass are very good, but the disadvantage is that it is fragile. The stress state of the glass pipe must be considered, and the glass pipe is always kept in a safe state.

The glass pipe is generally connected with a loose flange. The loose flange squeezes the 0-ring, and the 0-ring squeezes the expansion opening of the glass pipe, through the PTFE-lined rubber gasket, and then with the other end of the glass pipe or Material flange connection. The material of flanges of other materials can be stainless steel, carbon steel, ABS, polyvinyl chloride, polypropylene and polytetrafluoroethylene, etc., which completes the connection between glass and pipes of other materials.

1.4 Plastic Pipes There are many plastic pipes. Common ones include ABS, polyethylene, polypropylene, polyvinyl chloride, and polytetrafluoroethylene. This article mainly introduces polypropylene materials with good solvent resistance, temperature resistance and low price.

At present, polypropylene pipes and fittings have been widely used in water treatment, pharmaceutical industry and chemical production. Its small products include pipe fittings, valves, sight glasses, etc., and large ones include storage tanks, storage tanks, and suction walls (large cloth Funnel), water spray chestnut, etc., because of its acid resistance, alkali resistance, solvent resistance, light weight, elasticity and low price, it has replaced metal products in some fields. Because polypropylene is difficult to bond with adhesives, the connection between polypropylene pipes and pipe fittings is generally flanged or welded, so the corresponding pipe fittings use flanges and sockets.

The connection of polypropylene pipes is easier to cut and weld than metal pipes, and because polypropylene pipes have rich fittings such as reducing, elbows, tees, etc., even without welding, they can be plugged and used without internal pressure, as long as Just wrap some PTFE tape around the connection. Elasticity is also a major advantage of polypropylene pipes. Unlike stainless steel pipes, the fixed angle and size are not too flexible. Polypropylene pipes can use their own elastic range to overcome errors in size and angle and facilitate connection.

Polypropylene pipes are resistant to acids, alkalis, and solvents, and have better heat resistance than ABS, polyethylene, and polyvinyl chloride, but they are not easy to operate at temperatures above 100T for a long time to prevent the polypropylene pipes from undergoing thermal deformation.

The connection of polypropylene pipes is mainly through flange connection. Of course, it can also be made of polypropylene, which is soft and easy to process, processed into threads, and connected with threaded pipes or pipes.

1.5 Straight lined pipe At present, PTFE-lined pipes are already available on the market, that is, the inner wall of the pipe including both ends of the pipe are lined with Teflon membrane to avoid corrosion of the pipe. In this way, PVC-lined pipes can be used in most chemical production. It is worth mentioning that the PTFE push (squeeze) pressure tube is tightly lined with the straight tube. The preparation method is to push (squeeze) powder such as polytetrafluoroethylene into a tube, and then force it into a seamless steel tube to form a tight liner without gaps, and then undergo high temperature and constant temperature treatment to eliminate stress. The tight lined straight pipe prepared in this way has the ability of corrosion resistance, positive pressure resistance and negative pressure resistance.

The above introduces the hard-connected connection pipes. For soft connections, you can also select the corresponding connection pipes. Among hoses, bellows and spring tubes are commonly used. The following are introduced separately.

1.6 Bellows Bellows are classified according to materials and can be divided into metal bellows, plastic bellows and composite bellows. Metal bellows are mainly made of copper, carbon steel and stainless steel. Plastic bellows are generally used for jackets of wire harnesses and cables. They can also be used for the transportation of water or aqueous solutions. Bellows for chemical transportation include High-density polyethylene (HDPE) double-wall corrugated pipes, reinforced polyvinyl chloride (PVC-U), polyethylene (PE), polypropylene (PP) corrugated pipes, etc., are currently mainly used in construction projects, and are really used in chemical It is still rare. It has been reported that bellows made of tetrafluoroethylene have been produced and will have great applications in chemical production.

Stainless steel corrugated pipe is mainly composed of corrugated flexible pipe, net sleeve and joint. Its inner tube is a stainless steel corrugated tube with a spiral or ring shape. The outer layer of the corrugated tube is a mesh sleeve woven from stainless steel wire or steel belt according to certain parameters to protect the inner tube. The ends of the hose are flanges or joints. The joints can be quick joints, clamp joints and threaded joints. The height, width, and shape of the stainless steel bellows determine the different strength and flexibility of the bellows, which can be bent to the desired angle in various directions. The hose pitch is flexible, has good scalability, and the internal strength of the pipe Very high, can withstand vacuum and low pressure, can be applied to complex pipeline connections.

Since the inner surface is a corrugated tube, the unevenness makes cleaning relatively cumbersome. Stainless steel bellows is suitable for connections of indefinite size and soft connections requiring strength, such as vacuum feed, low external pressure discharge, centrifuge outlet, etc.

The sealing forms of the joints at both ends of the metal bellows can be loose nut seals, quick connection seals, and flange seals. The loose nut seal is a flat surface, a conical surface, a tenon groove surface or a spherical surface on the loose nut of the bellows and the sealing surface corresponding to the connecting part is pressed with a screw to form a seal. The quick-connect seal is usually an eccentric groove seal with a quick-release lever.

Among the composite bellows, bellows lined with tetrafluoroethylene or polypropylene membrane are widely used. Its structure is similar to stainless steel bellows, the difference is that it is lined with tetrafluoroethylene or polypropylene film, which can resist acid and alkali. Since the inner surface is made of tetrafluoroethylene or polypropylene membrane, the inner wall of the pipe is smooth and relatively easy to clean. Its connection is the same as stainless steel bellows.

1.7 Tightly lined spiral pipe Tightly lined spiral pipe is a long stainless steel spring as a pipe support, the outer lining or the inner and outer double lining of Teflon or polypropylene membrane to form a pipeline. The preparation method of Teflon tight-lined spiral tube is: first wrap the Teflon film on the mold, wind the steel wire, and then wrap the Teflon film outside the steel wire, and finally deal with the high temperature to eliminate the stress. Since the wound steel wire has a certain strength, it can be used under vacuum and positive pressure. The connecting piece can be a quick joint, and the length of the tightly lined spiral pipe can be cut as needed, but cannot be spliced.

1.8 PTFE short-circuit PTFE short-circuit is to use a lathe to turn the PTFE rod into a spring shape, and the expansion ports at both ends can be connected with a loose flange. Use the flexibility of PTFE to produce tensile elasticity of PTFE short circuit. It is generally used as a commonly used soft connection for glass reactors, condensers and other glass pipes. Because it has a certain degree of expansion and bending performance, it is also a universal flange connection and can be connected to other pipes and equipment. Make up for errors in size and angle.

2Pipe connection form The connection form of pipe includes flange, thread and pipe joint connection. There are many types of pipe joints, which have received widespread attention in the world. A large number of patents are issued every year, covering all aspects of fluids, machinery, and electricity. Therefore, different connection forms should be selected for different pipe connection requirements.

Flange connection Flange connection is the most traditional and safest connection form, and it is also the main form of pipe connection of different materials. Such as the connection of the upper mouth of the kettle to stainless steel pipes, glass pipes, polypropylene pipes, the connection of stainless steel pipes to glass pipes, polypropylene pipes, and the connection between plastic pipes such as polypropylene and polyvinyl chloride pipes that cannot be welded to each other. Flange connection.

2.2 Threaded connection Threaded connection is also called screw connection. It uses the external thread on the pipe and the internal thread on the loose nut on the pipe to connect with each other to achieve sealing. Such a connection can connect materials of different materials. Threaded pipe or pipe fittings can be connected to other threaded pipes or pipe fittings by threads. In this way, the connection between the pipe and the corrugated pipe with a threaded loose nut can be completed, or the connection between the stainless steel pipe and the plastic pipe can be completed, or the diameter can be reduced through the thread, and the pipe with the flange and the thread can be connected Thread and flange connection.

According to different standards of thread, it can be divided into English system and American system. According to the taper, there are sealed conical pipe thread and non-threaded sealed pipe thread. NPT is the abbreviation of National (American) PipeThread, which belongs to the American standard 60 degree tapered pipe thread. G is a 55-degree non-threaded sealed pipe thread, belonging to the Wyeth thread family, marked as G representing cylindrical thread 151.3. 2.3 union union union union, the English name union, also known as union, by another, by order, is another kind Commonly used thread connection. Union consists of two pipe parts with upper and lower sealing surfaces and internal threads connected by threads. The sealing surfaces are in contact and the threads are clamped to form a seal. The internal threads at both ends are connected to different pipelines. The pipeline can be separated without moving the pipeline. Easy to overhaul. The internal sealing surface has a flat surface, a spherical surface, a conical surface, etc., and the connection methods with the pipeline include butt welding, socket welding, screw thread, etc.

Some union pipe fittings have three protruding parts, which can be locked by hammering or related wrenches. They are called hammerunion and are widely used in oil field pipelines. They are also called hammer unions and three claws. The QS airfoil union has a color mark for quick identification. The material meets ASTM and AISI standards, and is suitable for the connection of threaded ends, butt welded ends, and pressure-free sealed ends. There are corresponding standards abroad 6.2.4 quick connector and eccentric groove type quick connector. Among them, the steel ball locking quick joint can carry higher pressure and transport gas and liquid. The eccentric groove quick joint has a lower bearing pressure, which is often called the handle quick joint.

2.4.1 Self-locking rotary quick coupling Self-locking rotary quick coupling English Self-LockingSwivelQuickCoupler, also known as steel ball locking quick coupling. There are many classification methods, according to the transmission medium, it can be divided into pneumatic quick couplings (airquickcoupler self-locking rotary quick couplings are small in volume, composed of plug body and socket body, with internal steel balls, gaskets and other parts, relying on the outer casing Push and pull, compress the steel ball, the steel ball is caught in the groove of the socket body, so that the plug body and the socket body are connected together. Sealing forms include sealing surface seal, non-metallic 0-ring seal, rubber ring seal, thread connection seal There are many types of these joints, each of which is aimed at different uses. When selecting, it is necessary to consider the nature of the medium to be transferred, but also to consider the pressure of the medium, the flow or static pressure, the corrosiveness, the sealing method, and the way of taking over. In this paper, the improved design of the hydraulic quick connector is applied to the hydraulic connection. The finite element analysis of the hydraulic quick connector is performed using ANSYS software. The contact stress between the male and female heads is calculated, and the contact coordination between the male and female heads is calculated. Optimized, the finite element analysis of the sealing ring was carried out in the paper, and the key to the improved part of the fast hydraulic joint after the improved design was determined Inch 17 self-locking rotary quick couplings can be provided with check valves at both ends, and form a single self-closed type and a double self-closed type. The ones without valves are straight-through. They are suitable for the transportation of gas and fluids with small flow rates. Yi et al. Established a two-way self-sealing quick coupling split dynamics model and calculated the maximum operating thrust, maximum door opening torque, maximum door closing torque and maximum operating tension The Chinese meaning is eccentric-groove quick connector, eccentric lock quick connector. It uses the outer wall of the female head to press the eccentric wheel of the shaft end and the groove, and the sealing surface is at the connection between the inner wall of the female head and the male head. Different materials can choose different quick joint materials and gasket materials. According to different connection methods, it can be divided into thread quick joints, flange quick joints, butt welding quick joints, mainly used for quick connection between mobile equipment and fixed devices , Convenient and fast. It is a kind of pipe joint that can be quickly disassembled without other tools, with compact structure, small size, light weight and high pressure resistance , Interchangeable and other advantages. It can also be used in the transportation of chemical production liquids, this connection can be installed on a variety of soft and hard tube metals, can also withstand higher pressure. Liu Ruihe proposed this type of lever type fast The detailed and reasonable design parameters of the lug compression circle radius, eccentricity and groove radius of the joint.

Micromold manufactures quick couplings made of polyvinyl chloride. The O-ring used for sealing is Teflon hexafluoropropylene encapsulated silicone material. It is suitable for pharmaceuticals, semiconductors, water treatment, etc. 2.5 clamp joints Through the circular convex surface of the clamp, the inner chuck is tightened to form a sealed joint form. According to the form of the clamp, it can be divided into precision cast clamp joints, stamping clamps, high-pressure clamps, copy-lin clamps, three-piece clamps, dual spare clamps, safety clamps, etc. According to different standards, it can be divided into ISO, DIN, 3A, SMS, IDF, RT and other models. The structure of different types of clamp joints is similar. There are four components, including two chucks with short tubes, a silicone or PTFE gasket and a heavy-duty clamp shell. When the clamp is tightened, the circular rings composed of the protruding parts at both ends of the clamp shell press the tapered surfaces of the upper and lower chucks, and the gasket is pressed to complete the seal. The clamp joint adopts a flat mouth design, and the joint gap between the joint key shoulder and the pipeline is used to achieve the requirement of flexibility. Under the premise of ensuring the strength of this structure, the joint does not completely clamp the pipeline, allowing some axial and radial displacements, resulting in a small amount of flexibility. Because the clamp type joint is widely used, the country has specified the clamp type pipe joint in detail.

2.5.2 Three-section clamp Three-section clamp is also called three-lobe clamp, and its form is slightly more complicated than the above calculation method.

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