Summary of various pipeline connection methods

What is a pipe connection?

Pipe connection refers to connecting the processed and prefabricated pipe sections into a complete system according to the requirements of the design drawing. During construction, different pipe connection methods shall be selected according to the material of the pipes used. Common steel pipes have thread connection, flange connection, welding connection, socket connection, pipe bonding connection and other methods.

T1T4b By T1RCvBVdK - Summary of various pipeline connection methods

Pipe thread connection (galvanized steel pipe, plastic lined galvanized steel pipe)

1. Pipe break: according to the site mapping sketch, draw lines on the selected pipe and cut off the pipe according to the line.

  • A. to cut off the pipe with grinding wheel, put the pipe on the caliper of the grinding wheel saw, align with the drawing line and clamp firmly to break the pipe. When breaking the pipe, press the handle evenly and do not use too much force. After the pipe is broken, the iron film and burr on the cross section of the pipe mouth shall be removed.
  • B. when the pipe is cut by hand saw, the pipe should be fixed in the pressure clamp of the pressure table. The saw blade should be aligned with the drawing line and pushed with both hands. The saw blade should be kept perpendicular to the axis of the pipe. The force of the push-pull saw should be uniform. The saw mouth should be sawed to the bottom. It is not allowed to twist or break, so as to prevent the deformation of the pipe mouth section.

2. Threading: thread the broken pipe by stages according to the pipe diameter. Generally, the pipe with diameter of 15-32mm should be threaded twice, 40-50mm should be threaded three times, and the pipe with diameter above 70mm should be threaded 3-4 times.

  • A. thread the pipe with a threading machine, clamp the pipe on the chuck of the threading machine, set aside an appropriate length to clamp the chuck, align the plate sleeve number, install the die, align the appropriate position of the scale according to the pipe diameter, tightly hold the fixed trigger, align the lubricant pipe with the thread head, start the push plate, and gently release the trigger when the screw thread reaches the appropriate length.
  • B. use manual threading plate to thread. First, loosen the fixed trigger, set the plate back to zero degree, align the plate with the required scale, tighten the fixed trigger, put the pipe in the pressure clamp of pressure table, set aside an appropriate length for clamping, gently put the threading plate into the pipe to make it moderately tight, then push the threading plate with two hands, take 2-3 buckles, and then stand on the side to pull the threading plate, The force should be even. When the screw thread is about to be set, gently release the trigger, turn on the machine and withdraw the plate, and keep the screw thread taper.

3. Fitting pipe fittings: according to the on-site surveying and mapping sketch, the pipe fittings with thread are assembled.

  • A. when assembling the pipe fittings, the required pipe fittings should be brought into the pipe thread, and the tightness should be tested (generally, 3 screws should be brought in by hand). Lead oil should be applied at the screw thread and hemp should be wrapped. Then, the pipe fittings should be tightened with pipe tongs to make the screw thread exposed by 2-3 threads. Remove the hemp head, wipe the lead oil, and put the number in the appropriate position for alignment.
  • B. select appropriate pipe tongs according to the pipe diameter of the pipe fitting.

4. Pipe section alignment: straighten the pipe section with pipe fittings installed before installation.

  • A. lead oil shall be applied at the screw thread of the pipe section to connect two or more sections. During connection, the direction of the reserved opening shall not be taken into account, but the bending degree of the pipe shall be taken into consideration. After mutual alignment, the direction of the reserved opening shall be turned to the appropriate position and kept upright.
  • B. After the pipe section B is connected, the pipe diameter, reserved opening direction and diameter changing part must be checked according to the design drawings before alignment.
  • C. the straightening of the pipe section shall be placed on the pipe rack or the pipe platform. Generally, two people shall operate. One person shall visually inspect the end of the pipe section, and the other person shall knock and observe at the bending point until the straightening pipe section is free of bending. Mark the connection point of the two pipe sections, remove one or more sections, and then connect another section or several sections until the adjustment is completed.
  • D. for the pipe with dead bending or large diameter at the connection point of the pipe section, when it is heated to 600-800 ℃ (fire red) by oven or gas welding, the pipe shall be kept rotating on the pipe rack, and the pipe shall be made straight by the self weight of the pipe, or the wood block pad shall be used to straighten the heating place with a hammer. After straightening, the pipe shall rotate continuously before cooling, and oil shall be applied at the heating place when the temperature is appropriate. All the threads that have been heated and straightened must be marked with marks, removed, re coated with lead oil and wrapped with hemp, and then the pipe section is aligned with the mark and tightened.
  • E. when assembling the pipe section of the valve, the valve cover should be removed first, and the valve should be padded and then knocked to prevent the valve body from cracking.
  • F. galvanized carbon steel pipe shall not be straightened by heating method.
  • G. the pipe section shall not be damaged when straightening.

Pipe flange connection (need to be disassembled, connected with equipment valve, etc.)

If the pipe section is connected with flange or the pipe section is connected with flange valve, the standard flange must be selected according to the design requirements and working pressure.

The diameter and length of the connecting bolts of the flange shall meet the requirements of the specification. When tightening the bolts of the flange, they shall be tightened symmetrically. The exposed thread buckle of the tightened bolts shall be 2-3 buckles, which shall not be greater than half of the bolt diameter.

For flange connection gasket, rubber gasket with thickness of 3mm shall be used for water supply (cold water) and asbestos rubber gasket with thickness of 3mm shall be used for heat supply, steam and domestic hot water pipeline. The gasket should be concentric with the pipe diameter and should not be deviated.

Pipe welding

According to the design requirements, the steam pipe with working pressure above 0.1MPa, heating pipe with general diameter more than 32mm and fire pipe of high-rise building can be connected by electric and gas welding.

Wind proof, rain proof and snow proof measures shall be taken during pipeline welding. The ambient temperature of welding area shall be lower than – 20 ℃, and the welding joint shall be preheated with preheating temperature of 100-200 ℃ and preheating length of 200-250mm.

The general pipeline welding is butt joint form and assembly.

Before welding, the axes of the two pipes should be aligned, and the end points of the two pipes should be welded firmly. Three points can be spot welded if the pipe diameter is less than 100 mm, and four points should be spot welded if the pipe diameter is more than 150 mm.

If the pipe wall thickness is more than 5mm, the groove shall be cut at the welding junction of the pipe end. If the pipe groove is processed by gas welding, the oxide skin on the groove surface must be removed, and the uneven parts affecting the welding quality shall be polished.

For the welding of pipe and flange, the pipe shall be inserted into the flange first, spot weld 2-3 points, and then the angle square shall be used for alignment and leveling before welding. The flange shall be welded on both sides, and the inner Korean seam shall not protrude from the sealing surface of flange.

Pipe socket connection

Cement twist: generally used for socket connection of indoor and outdoor cast iron drainage pipes

  • A. in order to reduce the fixed ash mouth, some pipes and pipe fittings can be twisted in advance. Before twisting, check whether there are cracks, sand holes and other defects in the pipes and fittings, and pre arrange the pipes and fittings to check whether the size is correct, and whether the circular gap of the socket and spigot is qualified.
  • B. when the pipe and pipe fittings are connected, they can be on the temporary fixed bracket. The socket of the pipe and the pipe fitting shall be inserted in the direction of upward and downward according to the requirements of the drawing, and the mortar mouth shall be twisted.
  • C. when twisting the mortar joint, first use the hemp drill rod to drill the tightly tightened green hemp or binding rope which is slightly thicker than the ring gap of the socket. Generally, it is better to make two circles (about one third of the socket depth). The length of the lap joint of the green hemp should be greater than 30mm. Then, the hemp should be compacted, aligned and leveled while drilling.
  • D. after the hemp is finished, the mortar (water cement weight ratio 1:9) can be filled into the annular gap of the socket in layers. First, use a thin twist chisel, fill the ash with one hand, tamp it with the other hand, and then tamp it with a hand hammer and twist chisel layer by layer until the ash mouth is filled up. The mortar mouth is compacted and leveled with a twist chisel with the thickness corresponding to the size of the circular gap of the socket, until the twist chisel has a rebound feeling on the ash mouth, it is qualified.
  • E. mixing twist mouth ash should be used as soon as mixing. The mixed ash should be controlled to be used up within one and a half hours. At the same time, the water consumption should be adjusted according to the climate.
  • F. when prefabricating two sections of pipes or more than two pipe fittings, the pipes or pipe fittings with the ash mouth twisted first shall be arranged at the upper part, and then the lower part shall be twisted to reduce the vibration. After twisting the last ash hole, check whether the rest of the ash mouth is loose, if any, handle it in time. G. prefabricated pipe sections and pipe fittings shall be stacked in a flat place, placed flat and padded, wrapped with wet hemp rope, watered and maintained wet. Generally, it can be transported to the site for installation after 48 hours at normal temperature.
  • H. effective anti freezing measures shall be taken for the mortar twist joint in winter. Proper amount of salt water can be added to plastering water. It is strictly forbidden to freeze the twisted mortar joint. The storage environment temperature should be kept above 5 ℃ and steam curing can be adopted if conditions permit.

Asbestos cement interface: generally, asbestos cement is used for laying indoor and outdoor cast iron water supply pipes, that is, mixing appropriate amount of asbestos wool into the cement.

Lead connection: it is generally used for laying of cast iron water supply pipe in industrial workshop. If there are special design requirements or emergency repair of outdoor cast iron water supply pipe, lead connection can be used in case of pipeline meeting and water supply

Rubber ring interface: it is generally used for laying and installation of outdoor cast iron water supply pipe. Pipes and fittings still need asbestos cement

Pipe bonding connection: (UPVC pipe, ABS pipe)

The pipe bonding should not be carried out in the environment with high humidity, and the operation site should be far away from the fire source to prevent impact, and it should be conducted at – 20.

Before bonding, clean cotton yarn or dry cloth shall be used to wipe the inside and outside of socket and keep the bonding surface clean. If the surface is stained with oil, it should be cleaned with cotton yarn dipped in acetone and other cleaning agents.

When applying the adhesive with oil brush, the inner side of socket shall be painted first, and then the outside of socket. When coating the socket, it should spit evenly and appropriately from the inside to the outside along the axial direction, and should not be omitted or coated too thick.

After the socket is coated with adhesive, it is advisable to insert it continuously once at a time in alignment with the axis within 20s. The depth of the pipe end inserted into the socket shall be marked on the surface of the inserted pipe according to the measured socket depth, and the pipe shall be rotated 90 ° after insertion.

After inserting, wipe the adhesive extruded from the outside of the joint immediately. Stress should be avoided, and the installation can be continued after the joint is firm.

The bonding joint should not be operated under the ambient temperature of 0 ℃, and the adhesive should be prevented from freezing. Do not use open fire or electric furnace to heat adhesive.

Ferrule connection of pipe (aluminum plastic composite pipe)

  • Cut off the pipeline according to the pipe diameter required by the design and the length of the pipe section after site review. Check the pipe orifice and correct it if there is burr, irregularity or the end face is not perpendicular to the pipe axis;
  • Use a special scraper to cut the groove of polyethylene inner layer at the pipe mouth, with the slope angle of 20-30 ° and the depth of 1.0-1.5mm, and clean the groove debris with clean paper or cloth;
  • Round the pipe orifice with a rounder;
  • Put the locking nut and C-type Hoop Ring on the pipe, and insert the pipe core into the pipe until the pipe orifice reaches the root of the pipe core; 6.5 move the C-type clamp ring to 0.5-1.5mm away from the pipe orifice, and then tighten the locking nut and the pipe fitting body.

Hot melt connection of pipeline (at present, it is mostly used for the installation of PP-R pipe and PB pipe for indoor domestic water supply)

  • The hot-melt tools can be operated only when the working temperature indicator is on after the power is turned on;
  • When cutting the pipe, the end face must be perpendicular to the pipe axis. Generally, pipe shears or pipe cutting machines are used for pipe cutting. If necessary, sharp hacksaw can be used. However, burr and burr should be removed from the section of pipe after cutting;
  • The connecting end face of pipe and pipe fitting must be clean, dry and oil-free;
  • Measure and plot the hot melt depth at the pipe end with a caliper and a suitable pen.
  • When welding elbows or tees, pay attention to the direction according to the requirements of the design drawings, and mark their positions with auxiliary signs in the straight direction of pipe fittings and pipes;
  • During connection, the pipe end shall be led into the heat jacket without rotation and inserted into the marked depth. Meanwhile, the pipe fitting without rotation shall be pushed onto the heating head to reach the specified mark. The heating time shall meet the requirements of the above table (or the regulations of the hot melt tool manufacturer);
  • After the heating time is reached, immediately remove the pipe and pipe fittings from the heating sleeve and the heating head at the same time, and quickly insert the straight line without rotation into the marked depth to form a uniform flange at the joint;
  • Within the processing time specified in the table above, the newly welded joint can be corrected, but rotation is strictly prohibited.

Connection of copper pipe

Copper pipe is used in building water supply system, and its connection mode mainly includes two types: ferrule type and welding type.

(1) The ferrule connection is easy to operate and simple. Choosing the right accessories can make the connection close without leakage and bear enough pressure.

There are two types of ferrule connection: type A of non operational joint and type B of operable joint

A-joint connection: the installation process includes selecting the sleeve that meets the pipe specification, cutting the pipe according to the correct length, removing all burrs, checking whether the pipe end is clean and whether there are deep scratches or other defects. If the pipe end is elliptical, use a suitable tool to make it round, and then insert the pipe into the casing until it does not change to the gear ring. Tighten the nut with hand and a wrench until the pressure ring clamps the pipe. At this time, the nut on the sleeve cannot be turned by hand. Now use two spanners to tighten the nut to 1 / 3 to 2 / 3 turn. This allows the pressure ring to bite into the tube and deform the tube slightly.

Operational joint type B: the joint can clamp the internal and external surfaces of the pipe at the same time, so that the joint can support and tightly clamp the copper pipe.

The connection method includes confirming that the specification of the pipe and the casing used are correct, and then cutting the pipe to the required length with a fine tooth saw, cleaning the internal and external burr, inserting the compression nut and pressing ring into the pipe end, knocking the corresponding expanding tool or punch into the pipe end to enlarge the pipe orifice, and then correctly placing the stereoscopic pipe into the pipe end and casing, and tightening the compression nut. First screw it by hand, and then tighten it with a spanner for about a week, then a firm and tight joint can be made.

(2) There are two main welding methods, tin welding and copper welding

The difference between the two mainly lies in the use of different metal filler, welding flux, application of different parts, the use of welding method requires professional personnel to operate.


  • 1. Before pipe connection, the specification and size of pipe and pipe fittings should be confirmed again whether they meet the connection requirements;
  • 2. According to the design drawings, the piping length is measured on site, and the blanking is accurate. Rotary pipe cutter or hacksaw or electric saw with no less than 13 teeth per centimeter can be used for vertical cutting. After cutting, the burr of pipe orifice shall be removed and the whole circle shall be made;
  • 3. The brazing strength is small, and the lap joint is generally used. When the outer diameter of the pipe is less than or equal to 28mm, the lap length is (1.2 1.5) d (mm);
  • 4. Before welding, the outer wall of copper pipe and the inner wall of pipe fitting should be rubbed with fine sandpaper, steel brush or cloth sandpaper containing other abrasives to remove oxide on the surface;
  • 5. Brush paste or liquid flux evenly on the cleaned outer surface of the pipe and the inner surface of the pipe fitting;5. Insert the copper pipe into the pipe fitting, check it to the bottom and rotate it properly to keep a uniform gap, and wipe off the excess flux from the extrusion joint;
  • 6. Heat the joint evenly with gas welding flame until it reaches the brazing temperature;When the temperature at the joint of copper pipe can melt rapidly, it means that the temperature at the joint has reached the brazing temperature. When the temperature is heated, the solder can be added until the brazing seam is full;
  • Remove the flame and make the joint cool and crystallize in the static state;
  • Clean up the residue at the joint.

Grooved connection

  • Cut the steel pipe according to the required length with the steel pipe cutting machine, and the incision should be flat, and the burr of the incision should be grinded with a grinder to make the end face smooth and smooth;
  • Use special grooving machine to press groove. The steel pipe to be machined is erected on the grooving machine and the tailstock of the grooving machine. The horizontal position of the tailstock of the grooving machine and the grooving machine and the steel pipe plate is adjusted with a level instrument, and the end face of the steel pipe is closely connected with the end face of the groove wheel baffle plate of the grooving machine; When pressing the groove, it should continue to increase gradually;
  • Check whether the rubber sealing ring is matched, apply lubricant, cover it at the end of one pipe section, cover the butt joint of another pipe section, and move the rubber ring to the center of the connecting section;
  • Put the clamp outside the rubber ring and clamp the edge into the groove;
  • Insert the bolt with deformation block into the bolt hole and tighten the nut.

Flexible drainage cast iron pipe connection

  • Type a socket rubber ring flange gland connection;
  • W-type stainless steel clamp with rubber ring lining.

Thin wall stainless steel pipe

Clamp connection

A kind of extrusion connection. With the help of autocratic quick hydraulic tong tool, the stainless steel hold down ring is deformed by external force to connect it with steel pipe tightly; Then put on the rubber seal ring, and tighten the stainless steel nut (the rubber seal ring, stainless steel nut and pipe fittings have been assembled in the factory) to connect with the pipe fittings. It is suitable for DN 15 and DN 20.

Bulging connection

The thin-walled stainless steel pipe is expanded into a hill shaped flange with a autocratic Bulger. A rubber sealing ring is set on one end of the flange, and the stainless steel nut is tightened to connect with the pipe fitting. It is suitable for DN25 – DN50.

Rubber sealing ring

According to the different requirements of conveying medium, silicone rubber, EPDM and other material sealing rings are selected as the sealing rings connecting thin-walled stainless steel pipes and pipe fittings.

Argon arc welding (butt welding) connection DN (15-100)

  • Two piping (or piping and pipe fittings) shall be welded by T1G girth.

HDPE buried drainage pipe heat shrinkable tape connection

Polyethylene pipe is required to bear certain pressure when transporting gas and water supply, and the service life is required to be at least 50 years, and to ensure absolute safety. The advantages and disadvantages of PE pipeline system connection technology are directly related to the operation effect and service life of the pipe network. Therefore, the requirements of connection technology are very strict.

Development of polyethylene pipe connection technology:

The main progress in welding technology of polyethylene gas pipeline is as follows

The development of electrofusion bonding technology in the 1990s is mainly reflected in the following aspects:

  • 1) The material of pipe fitting follows the development of pipe material. There are many manufacturers of melting pipe fittings in the world to develop and produce PE100 pipe fittings.
  • 2) After continuous development and improvement, the structure of electrofusion pipe fittings is becoming mature. It has wide welding zone, long insertion depth and cooling zone. In 1997, georgfisher company launched its modular design of electric melting saddle pipe fitting and transition pipe fitting system, which realized the combination of some basic components into required pipe fittings in workshop and construction site, reducing inventory and facilitating application.
  • 3) Electric fusion welding equipment has entered the third generation (multi-functional), which can control the welding quality on site and ensure the traceability of equipment and installation.
  • 4) The automatic identification system of electric melting pipe fittings enables the electric energy to be automatically transmitted to the electric melting pipe fittings in a certain way. In the late 1990s, the standardization was realized. There are three types: digital identification system, electromechanical identification system and self-regulation system. At present, most of the electrofusion pipe fittings adopt the digital identification system. The welding parameters and other information are recorded in the form of code on the barcode, magnetic card and other data carriers. The welding controller automatically controls the welding after reading the parameters from the above carriers.
  • 5) In recent years, the most important progress of electrofusion pipe forming technology is the automation of forming.

Development of hot melt bonding:

The development direction of hot melt butt welding equipment is full automation, which can not only eliminate human factors, but also achieve traceability. The British Gas Company first developed it, mainly for large diameter pipes, because problems have appeared when traditional machines are used for pipes with diameter greater than D315mm. Britain, Germany, Belgium, France and the United States have developed semi-automatic and fully automatic equipment.

The research on the hot-melt butt joint technology of polyethylene pipe is always in progress. At present, some main countries (such as the United Kingdom, Germany, Belgium, Finland, etc.) have different process parameters, and due to the continuous development of materials, the requirements of process changes are inevitable. German Welding Association (DVS) has issued a wide range of welding processes. Two parameters of DVS welding process were changed in Ghent University of Belgium: the temperature was increased from 215 ℃ to 225 ℃; The heating pressure is reduced by 50%. It is considered that the pressure can be further reduced. Swedish Plastics Pipe Quality Committee

(KP Council) according to the research of practical experience, the cooling time should be further extended, especially for thick walled pipes. In 1993, the British Water Research Center (WRC) proposed a “dual pressure” connection method for the connection of polyethylene pipes with wall thickness greater than 20 mm. The main difference between this method and the usual welding procedure is that the cooling pressure is reduced in the welding stage. The American Natural Gas Research Institute (GRI) has developed a new method for connecting and repairing polyethylene natural gas transmission and distribution pipelines. This method uses a new technology called “Smartheat”, which is self-adjusting and constant temperature heating. The technology has the advantages of good temperature control, low cost of connector and assembly.

Polyethylene connection mode:

PE pipe can not be connected with pipe fittings with soluble adhesive, and its best connection method is fusion welding. The development of welding technology has experienced a certain process. The early PE welding methods include hot melt butt joint connection, hot melt socket connection and saddle welding. Due to the shortcomings of the hot-melt socket connection, a new connection method, electrothermal fusion connection, has been developed through continuous research on the connection technology. Accordingly, the construction machines and tools used are electric fusion welding machine and hot melt butt welding machine, and the welding equipment shall meet the requirements of iso12176-1 or iso12176-2. Secondly, steel plastic transition joint is used to connect with metal pipe.  

Welding principle of polyethylene pipe:

The welding principle of polyethylene pipe is that polyethylene is usually melted in the range of 190 ℃ – 240 ℃ (the melting temperature of different raw materials is generally different). At this time, if the two melted parts of pipe (or pipe fitting) are fully contacted and proper pressure is applied (the pressure of electric fusion welding comes from the thermal expansion of polyethylene itself during welding), it can be firmly integrated after cooling. Due to the bulk fusion between polyethylene materials, the strength of the joint is the same as that of the pipe itself.  

Connection precautions:

Attention should be paid to the following matters when connecting PE pipes:

  • 1. Before taking up the post, the operator shall receive special training and pass the examination and technical evaluation before taking up the post.
  • 2. Before connecting the pipes, the appearance of the pipes and fittings should be inspected, and they can be used only if they meet the requirements of the product standards.
  • 3. When connecting in cold climate (- 5 ℃) and strong wind environment, protective measures or adjustment of construction technology should be taken.
  • 4. After the completion of each connection, the appearance quality inspection shall be carried out. If it does not meet the requirements, it must be cut and reworked, and the joint appearance quality inspection shall be conducted again after rework.

PE pipe connection technology:

The advantages and disadvantages of hot melt connection and electric fusion connection are as follows:

Electrofusion bonding

  • 1. Special electric welding machine is needed.
  • 2. Suitable for all sizes of pipe.
  • 3. It can be used for the connection of pipes of different brands and materials and between pipes and fittings.
  • 4. It is not easy to be affected by environment and human factors.
  • 5. Low equipment investment and low maintenance cost.
  • 6. The connection operation is simple and easy to master.

Hot melt bonding

  • 1. Special hot-melt welding machine is required.
  • 2. It is generally applicable to pipes with nominal diameter greater than 63mm.
  • 3. It is suitable for the connection of pipes and pipes of the same brand and material. The performance is similar, and the connection of different brands and materials of pipes and pipes and pipe fittings needs to be verified by experiments.
  • 4. Vulnerable to environmental and human factors.
  • 5. High equipment investment.
  • 6. Low connection cost.
  • 7. Operators need special training and experience.

Butt welding

Butt welding is often used for the connection of larger diameter pipes, which is generally larger than D63mm. Put the heating plate with a certain temperature between the two pipes or pipe fittings and heat it for a certain period of time. After pulling out the hot plate, the two ends to be welded are quickly butted together under a certain pressure and cooled for a certain period of time. The pressure chosen is such that the required force is generated at the contact surface regardless of friction pressure loss. When the butt welder has a hydraulic source, the force is usually expressed as the applied cylinder pressure. For such machines, a special comparison table should be provided to show the relationship between the actual contact pressure and the indicated pressure of the pressure gauge.

Electric fusion welding:

The key of electrofusion welding is to design advanced electrofusion pipe fittings. Its basic principles include heating, using Joule effect, resistance coil integrated on the inner surface of the pipe (welding surface), causing the material near the coil to melt, so that the pipe and pipe can be fused together. Electrofusion pipe fittings generally include sleeve, saddle, reducer, equal tee, reducing tee and elbow. It can be used to connect with trunk pipe, branch pipe or spigot pipe made of different types of polyethylene materials and different melt flow rate materials.


For changes in ambient temperature, as long as these changes are within the range specified by the continuous procedure, welding operations can be carried out without taking special precautions. If it is necessary to make some adjustments to the electrical energy output to the pipe fitting to suit the extreme ambient temperature requirements, appropriate electrofusion equipment should be used.

Electric fusion welding equipment:

The electric fusion welding machine uses the power supply (generator or public power) to provide the correct welding parameters for pipe fittings. If necessary, the ambient temperature should also be considered. Welding parameters are applied voltage and / or current and welding time. If the generator is used as the power supply, it should be able to output the energy required by the pipe fittings and consider the electrical characteristics of the welding machine and generator. The generator shall be equipped with appropriate protection and safety devices to meet the requirements of relevant standards. In some cases, the welding machine and the generator may need to be combined as a whole. Electrofusion welding equipment shall comply with ISO 12176-2. When the working condition of welding equipment is not good, it is impossible to have high quality welding joint. Maintenance of welding equipment is very important and should be carried out regularly.

Electrofusion welding procedure:

The operation process of electric fusion welding is summarized below.

Fused fittings shall be packed and protected until they are ready to be connected to the tubes or Spigot fittings. Before welding, the welding surface shall be dry

Make sure that the fused fittings match the ambient temperature, pipe or spigot fitting series or SDR values.

For all types of electrofusion fittings, restoration and alignment fixtures are used to reduce out of roundness, offset and movement during connection and cooling stages.

Scrape off the outer welding surface of the pipe or spigot fitting to remove the oxidized material. Use a suitable tool, such as a manual or mechanical scraper, to do this. Mechanical scraper is recommended. Scraping shall be carried out along the entire outer circumference of the end of the pipe or spigot fitting. When using saddle or saddle tee, at least the welding area should be scraped. The shaving depth is about 0.2mm.

When the socket electric melting pipe fittings are connected, the plastic pipe cutter or the fine tooth saw with cutting guide device is used to cut off the pipe, and the end face is perpendicular to the pipe axis. Deburring the inner edge with a knife.

Make sure you can check the insertion depth (for example, mark the insertion depth). Slide the bell fitting into the spigot end and position it correctly.

If the through sleeve connection is adopted, push the electric melting sleeve part completely onto one of the pipe ends. After the two pipe ends are clamped, the electric melting sleeve is pushed back, so that both pipe ends are covered by pipe fittings. Check the insertion depth of the ends of the two tubes.

Fix the alignment fixture or positioning fixture and check whether the pipe ends are aligned.

Open the protective cap of pipe fittings, connect the wire of welding machine, and weld according to the given parameters.

After welding, check whether the material in the observation hole is ejected and whether there is material extrusion at the weld joint. The qualified weld joint shall be free from smoke (fire) and premature shutdown during electric fusion welding. There shall be material ejection from the observation hole and no material extrusion at the weld joint.

Steel plastic connection:

PE pipe is connected with steel pipe and valve by steel plastic transition joint and steel plastic flange connection. For small diameter PE gas pipe (DN ≤ 63), integral steel plastic transition joint is generally used; For large diameter PE gas pipe (DN > 63), steel plastic flange connection is generally used. At present, our company has successfully developed and produced large caliber steel plastic transition joint such as DN 315.

Steel plastic transition joint

  • ① The PE pipe end of steel plastic transition joint is connected with PE pipe according to hot melt and electric fusion connection methods.
  • ② The connection between steel pipe end of steel plastic transition joint and metal pipe shall comply with corresponding regulations on steel pipe welding, flange connection and mechanical connection.
  • ③ When the steel pipe end of steel plastic transition joint is welded with steel pipe, cooling measures should be taken.

Steel plastic flange connection

  • ① PE pipe end and corresponding plastic flange connection, hot melt and electric fusion connection.
  • ② The connection between steel pipe end and metal flange shall comply with corresponding regulations on steel pipe welding, flange connection and mechanical connection.
  • ③ Connect metal flange and plastic flange loop. The looper flange should be treated with anti-corrosion treatment to improve its service life.


The advantages and disadvantages of the connection technology is one of the important factors affecting the quality and service life of the pipeline. Reliable and advanced connection technology provides guarantee for the wide application of polyethylene pipeline. Therefore, it is necessary to understand and master various technologies of PE pipe connection to ensure the safety of PE pipe system. Give full play to the advantages of PE pipeline system.

Source: Network Arrangement – China Steel Pipelines Manufacturer – Yaang Pipe Industry Co., Limited (

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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Summary of various pipeline connection methods
Common pipe connection methods have thread connection, flange connection, welding connection, socket connection, pipe bonding connection and other methods.
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