Ways to Connect Pipes

Pipeline connection is a very important part of water supply and drainage engineering construction, which is directly related to the quality of the project. With the rapid development of the pipeline industry, there are more and more ways to connect pipes, but different pipes have their own advantages and disadvantages, and have different uses. The correct choice of connection method is a skill that engineers must have. This article sorts out 12 connection methods for your reference and understanding.

Ⅰ. Threaded connection

It is called threaded connection. It connects pipes with pipes and pipes with valves through internal and external threads. This connection is mainly used for the connection of steel pipes, copper pipes and high-pressure pipes.

Selection of threaded fastener types

Type: bolt connection

Features and applications: used to connect two thinner parts. A through hole is opened on the connected part. There is a gap between the rod and the hole of the ordinary bolt. The processing requirements of the through hole are low, the structure is simple, the assembly and disassembly are convenient, and it is widely used. The hole and the screw of the reamed hole bolt (GB/T 27) often adopt transition fits such as H7/m6 and H7/n6. This connection can accurately fix the relative position of the connected parts. Suitable for bearing lateral loads, but the hole processing accuracy requirements are high, and drilling and reaming are often used

Type: Stud bolt connection

Features and applications: Used in situations where one of the connected parts is thicker and not suitable for bolt connection, the thicker connected part has poor strength, and needs to be disassembled frequently. Threaded holes are machined on thick parts, and light holes are machined on thin parts. Bolts are screwed into the threaded holes, and nuts are used to tighten the thin parts. When disassembling, only the nuts need to be unscrewed without removing the stud bolts. Damage to the threaded holes on large connected parts can be avoided

Type: Screw connection

Features and applications: Bolts (or screws) are directly screwed into the threaded holes of the connected parts without nuts. The structure is simpler and more compact than stud bolts. Used in situations where one of the two connected parts is thicker, but does not need to be disassembled frequently to avoid damage to the threaded holes

Type: Set screw connection

Features and applications: The end of the thread screwed into the threaded hole of the part is used to press against the surface of the other part or into the pit on the other part to fix the relative position of the two parts. This connection method has a simple structure, and some parts can be arbitrarily changed in the circumferential or axial position for adjustment, such as the fixing of electrical switch knobs

Type: countersunk screw

Features and applications: used in places where strength requirements are not high and the thread diameter is less than 10mm. The head or part of the screw is sunk into the connected part. This structure is mostly used in places where the outer surface is required to be flat, such as instrument panels

Type: self-tapping screw

Features and applications: used in places where connection strength requirements are not high. However, the bottom hole should generally be pre-made first. If a self-drilling self-tapping screw with a drill bit is used, the bottom hole does not need to be pre-made. It is used for non-ferrous metals, wood, etc.

Type: wood screw connection

Features and applications: generally used for the connection of wooden structures. Depending on the hardness of the material and the length of the wood screw, the wooden part can be pre-made without or with a certain size and depth of pre-made holes

Type: self-tapping locking screw connection

Features and applications: Its thread is an arc-shaped triangular interface. The screw is surface hardened and can be screwed into the pre-made hole of the metal material to form an internal thread by extrusion. The internal thread formed by extrusion increases the strength by more than 30% compared with the cut one. The minimum tensile strength of the screw is 800MPa. Self-tapping locking screws have low tightening torque and high locking performance, and have been widely used in household appliances, electrical and automotive industries.

Type: Fastener-assembly connection

Features and applications: Washers and external threaded fasteners are assembled and supplied as a set after being produced by standard professional factories. my country issued 23 fastener assembly production standards in 1988. This type of connector is easy to use, time-saving, safe and reliable, and is often used in places where fasteners are tightly connected, such as the terminal of an electrical cabinet.

Advantages: Simple manufacturing and use, reliable connection, easy use, good versatility, can be assembled and disassembled and reused, etc.

Disadvantages: Low pressure bearing, easy to rot and leak at the thread.

Ⅱ. Welding connection

As the most traditional connection method, welding connection is also the most commonly used connection method in daily life. Its main characteristics are firm and durable interfaces, high sealing at the interfaces, and no frequent maintenance.

Advantages: Firm and durable interfaces, not easy to leak, high joint strength and tightness, and no frequent management after use. Welding has the advantages of saving metal materials, high production efficiency and good joint sealing.

Disadvantages: Welded joints are prone to large welding deformation and welding residual stress, which affects the bearing capacity, processing accuracy and dimensional stability of the joints. At the same time, stress concentration is produced at the junction of the weld and the pipe (heat-affected zone), which has a great impact on the fatigue fracture of the joint. Welding defects (cracks, pores, slag inclusions, incomplete fusion, incomplete penetration) are prone to occur in welded joints. The presence of these defects will reduce the strength of the welded joint, cause stress concentration, and damage the density of the weld.

III. Socket connection

In chemical pipelines, cast iron pipes used for water delivery are mostly connected by socket connection. Socket connection is suitable for cast iron pipes, ceramic pipes, plastic pipes, etc. It is mainly used in water supply and drainage pipelines with low pressure.

1. Blue lead interface Blue lead interface is the earliest interface form used for socket cast iron pipes. It has good elasticity, rigidity and seismic resistance, and does not require maintenance after construction. However, lead is a relatively precious metal, and the cost of large-scale consumption is too high. It is mainly used in places with large vibration, such as crossing railways, highways, riverbeds and emergency repairs.

Advantages: good interface quality, high strength, good seismic resistance, water can be passed or pressure tested immediately after operation, no maintenance is required, and if a small amount of leakage is found after water is passed, it can be repaired by twisting and chiseling.

Disadvantages: large amount of non-ferrous metals are consumed and the cost is high, so it can only be used when the engineering repair or pipeline seismic requirements are high.

2. Advantages of asbestos cement interface It has high strength and good seismic resistance, good water tightness and adhesion. Disadvantages High labor intensity.

3. Advantages of self-stressed cement interface It has low labor intensity in manufacturing and interface, and high work efficiency. Disadvantages It is only suitable for socket pipes with working pressure not exceeding 1.2MPa, poor seismic resistance, and is not suitable for places with soft soil and unstable foundation.

4. Socket connection of non-metallic pipes: The socket connection of rigid polyvinyl chloride is to connect pipes or pipe fittings by socket bonding, and no welding of the pipe mouth is required. FRP pipes are connected by socket connection, which generally requires a relatively large inner diameter of the pipe. The minimum inner diameter that can be seen on the market is not less than 300mm. If the inner diameter is too small, it is difficult to meet the design of the rubber ring groove on the plug from the manufacturing process because the wall thickness of the FRP pipe is thin. Most of the FRP sand-filled pipes used in municipal engineering water supply and drainage projects are connected by socket connection.

Advantages: simple and fast connection, time-saving, labor-saving, and low installation cost.

Disadvantages: In some silt areas with poor geological conditions, because the FRP pipe is a flexible connection, when the two adjacent pipes settle unevenly, it is easy to cause floating pipes and pipe connections to separate.

IV. Bonding connection

Bonding connection uses adhesives as bonding fillers to bond homogeneous pipes and pipe fittings together, thereby playing a sealing role. Bonding connection has the advantages of simple construction and fast curing speed, and is widely used in drainage systems.

Advantages: Uniform stress distribution at the bonding interface; Prevent electrochemical corrosion of metals; Ensure fatigue strength of structural components; Low investment in bonding process equipment, easy to use, fast, safe, and energy-saving; Strong adaptability, can meet special needs, such as thermal conductivity, electrical conductivity, oil resistance, etc.

Disadvantages: The peel strength, uneven tear strength and impact strength of the bonding layer are low. General adhesives have low heat resistance (generally 150°C, maximum 300°C), poor aging resistance, and lack of non-destructive testing methods for bonding quality.

V. Flange connection

Flange connection is to fix two pipes, pipe fittings or equipment on a flange plate, then add a flange gasket between the two flange plates, and finally tighten the two flange plates with bolts to make them tightly combined. A detachable joint.

Advantages: Flange connection has good strength and tightness, a wide range of applicable sizes, and can be used on equipment and pipelines, so it is the most commonly used.

Disadvantages: However, when flange connection is used, it cannot be assembled and disassembled quickly, and the manufacturing cost is high.

VI. Pipeline connector connection

The pipe connector is a new type of pipe connection device. It breaks through the traditional connection concept and uses stainless steel and rubber to make a component combination device to achieve the sealing and pressure-bearing function. There is no need to do any treatment on the pipe end during construction. Just put the connector on the two pipe ends to be connected and tighten the side bolts to make the clamping teeth bite the surface of the pipe end to achieve limit fixation, and the sealing sleeve is close to the pipe to achieve a locked state of sealing and firm connection.

Advantages: flexible connection, fast installation, no need for hot work, strong and durable, strong versatility, etc.

Disadvantages: The pressure resistance for some special purposes is not up to the task.

VII. Groove connection

The groove connection is a sleeve-type quick connector composed of a clamp, a rubber sealing ring and a fastener, etc., which is formed by processing an annular groove at the pipe joint and other parts.

During installation, after the adjacent pipe ends are covered with special-shaped rubber sealing rings, they are connected with a spliced clamp. The inner edge of the clamp is in place in the groove and fastened with a fastener to ensure the sealing performance of the pipeline. This connection method has the advantages of not destroying the galvanized layer of the steel pipe, fast construction, good sealing, and easy disassembly. It can be used for pipeline projects such as building water supply, fire water supply, and production water supply.

Advantages: simple operation, the original characteristics of the pipeline are not affected, which is conducive to construction safety, good system stability, convenient maintenance, and good economic benefits.

VIII. Card sleeve connection (aluminum-plastic composite pipe)

The connection method of pressing the pipe to the pipe fitting with a locking nut and an open clamping ring.

Features: The sealing surface of the card sleeve pipe fitting is short, the installation is convenient and simple, no special tools are required, and it can be disassembled. It is generally used in tap water and gas systems with specifications below 2632.

Advantages: reliable connection, high pressure resistance, temperature resistance, good sealing and reproducibility, convenient installation and maintenance, safe and reliable work, etc.

IX. Hot melt connection

Hot melt connection is widely used in the connection of new pipes and fittings such as PP-R pipes, PB pipes, and PE-RT pipes. The pipe interface is changed by heating, so that the travel between the pipe and the fitting is integrated, and it is formed after cooling. There are mainly hot-melt socket connection and hot-melt butt welding connection.

Advantages: simple connection, long service life, not easy to corrode, etc.

Ⅹ, electric fusion connection

Generally, it is to weld PE pipes. By heating the copper wire embedded in the inner wall of the pipe fittings, the plastic resin in the fusion zone undergoes phase change, and the polymer chain segments penetrate each other under a certain pressure, cross-strengthen, and recrystallize and arrange by cooling the material, so that the fusion part is combined into a whole.

Advantages: flexible construction, etc.

Disadvantages: high cost

Ⅺ, compression connection

The stainless steel compression pipe fitting connection technology replaces the traditional water supply pipeline connection technology such as threading, welding, and gluing. It has the characteristics of protecting water quality, strong corrosion resistance, and long service life. During construction, the socket pipe fittings with special sealing rings are connected to the pipeline, and the pipe mouth is compressed with special tools to play a sealing and tightening role.

Advantages: convenient installation, reliable connection and economic rationality, etc.

Ⅻ. Heat shrink tube connection

Heat shrink tube is a new insulating material. In recent years, it has been widely used in the fields of electronics, electricity and household appliances. It is a connection method that uses fiber-reinforced polyethylene heat shrink tape as the inner layer and heat shrink tube as the outer layer. The inner surface of the heat shrink tube is coated with hot melt adhesive. After heating, the adjacent pipe ends are tightly connected together. The construction environment temperature should generally be -20~60℃. If the ambient temperature is lower than 0℃, insulation measures should be taken; when connecting, the operation steps must be carried out in accordance with the process requirements of the heat shrink tube tape.

Advantages: high insulation performance, not easy to age and fall off, waterproof, etc.

Disadvantages: many construction steps and slightly higher cost.