Knowledge

In the world we live in, pipeline systems are everywhere, from the water supply and drainage pipes in our homes to the oil and natural gas transmission pipelines in the industrial sector, and to the heating and gas supply pipelines in cities. They are like the blood vessels in the human body, transporting the "blood" for the normal operation of various fields.

 

Among these piping systems, there is a group of "little giants" that play a crucial yet often overlooked role - pipe fittings. Despite their seemingly ordinary appearance, they undertake vital tasks such as connection, control, direction change, and flow diversion, being the key to ensuring the stable operation of the piping system.

Today, let's delve into the world of pipe fittings, explore their classification and applications, and uncover the magic of these "little giants".

 

There are various classification methods for pipe fittings, just like a large family where each member has its unique identity. Below, we will delve into the classification of pipe fittings from three main aspects: application, connection method, and material.

 

I. Classification by Use

 

1. Connecting Fitting: Pipe fittings act as the "bridges" in the world of piping, responsible for connecting different pipes together to ensure the integrity of the piping system. Common pipe fittings include flanges, unions, clamps, hose clamps, ferrules, and U-clamps. Among them, flange connections involve fixing each of the two pipes or pipe fittings onto a flange plate, adding a flange gasket between the two flange plates, and then tightening the two flange plates with bolts to make them closely combined. This connection method has good strength and tightness, and is applicable to a wide range of sizes. It can be used on both equipment and pipes, often at the connection points of main pipelines with valves, check valves, water meters, pumps, etc., as well as on sections that require frequent disassembly and maintenance. Pipe clamps are used to connect two pipe sections and have internal threads or sockets. The operation is relatively simple and is often used in situations where the connection strength requirements are not particularly high.

 

2. Elbow Fittings: When a pipeline needs to change direction, elbow fittings come into play. Elbows and bends are the most common types of elbow fittings, allowing pipelines to turn as per design requirements to adapt to different spatial layouts and process flows. Elbows come in various types, classified by angle into 45° elbows, 90° elbows, and 180° elbows. Among them, 90° elbows are widely used in building and industrial pipelines, such as in the drainage systems of household kitchens and bathrooms, where 90° elbows are frequently employed to achieve pipeline turns. They can also be categorized by curvature radius into long radius elbows (R=1.5D) and short radius elbows (R=D). Long radius elbows can reduce the impact of fluid on the inner wall of the elbow and lower pressure loss when transporting fluids. Therefore, they are more commonly used in pipeline systems with higher fluid transportation requirements, such as oil and natural gas pipelines.

 

3. Reducing Fittings: In pipeline systems, there are occasions where pipes of different diameters need to be connected, and this is where reducing fittings come into play. Also known as reducers, they are divided into concentric reducers and eccentric reducers. Concentric reducers have coincident centerlines and are mainly used for reducing connections in vertical pipes; eccentric reducers have non-coincident centerlines with one side being straight, and are often used for reducing in horizontal pipes. This can prevent the formation of air pockets or liquid pockets at the reducing point, which could affect the normal operation of the pipeline. For instance, in heating systems, when pipes branch off from the main pipe to the branch pipes, eccentric reducers are frequently used to achieve the change in pipe diameter.

 

4. Branch pipe fittings: To enable a piping system to branch out and increase the number of pipe branches, branch pipe fittings are indispensable. Elbows and tees are typical branch pipe fittings. A tee can connect three pipes in different directions, taking the shape of a T or Y. When a main pipe needs to branch off into a secondary pipe, a tee fitting can be used. In building water supply and drainage systems, the connection of secondary pipes that supply water from the main pipe to various water usage points often requires the use of tees. A cross, on the other hand, can connect four pipes in different directions, taking the shape of a cross. It is commonly used in complex piping networks, such as the ventilation duct systems in large shopping malls or office buildings. Cross fittings allow ventilation ducts to branch off in different directions to meet the ventilation needs of various areas.

 

5. Sealing pipe fittings: Sealing pipe fittings are the key defense line to ensure that the pipeline system does not leak. Common sealing pipe fittings include gaskets, PTFE tape, hemp thread, flange blind plates, pipe plugs, blind plates, end caps, and welded plugs. Gaskets are usually placed between two connection surfaces to provide sealing and buffering. Different materials of gaskets are suitable for different media and working conditions. For example, rubber gaskets are often used for sealing general media such as water and air, while metal gaskets are suitable for harsh environments with high temperatures, high pressures, and strong corrosions. PTFE tape is a common sealing material with good sealing and corrosion resistance. It is often wound around the threads in threaded pipe connections to enhance the sealing effect. PTFE tape is frequently used in the installation of water pipes in households.

 

6. Fixed pipe fittings: To ensure the stability of pipelines during operation, fixed pipe fittings play an important role in supporting and fixing. Examples of fixed pipe fittings include clamps, drag hooks, lifting rings, supports, brackets, and pipe clamps. Pipe clamps are one of the most common fixed pipe fittings. They can firmly fix pipes to walls, floors, or supports, preventing pipes from shaking or moving. In building decoration, the installation of water pipes and electrical conduits cannot do without the fixation of pipe clamps. Supports and brackets are used to support longer or heavier pipes. According to the weight, diameter, and installation environment of the pipes, appropriate types of supports and brackets should be selected to ensure the safe operation of the pipeline system. In industrial plants, large steam pipes usually require the installation of sturdy supports to bear their weight and the stress caused by thermal expansion and contraction.

 

II. Classification by Connection Method

 

1. Welded pipe fittings: Welding connection is one of the most widely used connection methods in pipeline engineering. Welded pipe fittings are connected to pipes as a whole through fusion welding or brazing. The advantages of this connection method are that the interface is firm and durable, not easy to leak, and the joint strength and tightness are high. After use, it does not require frequent management and is particularly suitable for long pipelines. However, the welded joint is prone to large welding deformation and residual welding stress, which affects the bearing capacity of the joint. At the same time, stress concentration is easy to occur at the junction of the weld and the pipe (heat-affected zone), which has a significant impact on the fatigue fracture of the joint. Common welded pipe fittings include elbows, flanges, tees, reducers, and heads. In the pipeline systems of the petrochemical and power industries, due to the extremely high requirements for the sealing and strength of pipelines, welded pipe fittings have been widely applied.

 

2. Threaded pipe fittings: Threaded connection, also known as screw connection, connects pipes to pipes or pipes to valves through internal and external threads. This connection method is simple to manufacture and use, reliable in connection, convenient to use, has good versatility, and can be disassembled and reused. It is mainly used for the connection of steel pipes, copper pipes and high-pressure pipes. However, it has a relatively low pressure resistance, and the threaded part is prone to corrosion and leakage, so it is mostly used for exposed pipes. In home decoration, some water pipes and heating pipes are connected with threaded pipe fittings, which are convenient for installation and maintenance.

 

3. Ferrule fittings: Ferrule connections are often used for joining pipes of different materials and for temporary pipe connections. The principle is to tightly press the pipe onto the fitting through the lock nut and the open compression ring. The sealing surface is short, the installation is convenient and simple, no special tools are required, and it can be disassembled. This connection method is generally suitable for small-sized water supply and gas systems, but the safety factor is relatively low.

 

4. Clamp pipe fittings: Groove connection (clamp connection) is a type of quick coupling composed of a sleeve, rubber sealing rings and fasteners, etc., which is formed by processing a circular groove at the pipe joint and other parts. During installation, after putting the special-shaped rubber sealing ring on the adjacent pipe end, the pipe is connected with the split clamp fitting. The inner edge of the clamp fitting is positioned in the groove and fastened with fasteners, ensuring the sealing performance of the pipe. This connection method has the advantages of not damaging the galvanized layer of the steel pipe, quick installation, good sealing performance and easy disassembly. It can be used in building water supply, fire protection water supply, production water supply and other pipeline projects. In the fire protection pipeline systems of some large buildings, clamp pipe fittings are widely used, which can quickly achieve the connection and installation of pipes and improve the construction efficiency.

 

5. Socket pipe fittings: Socket connection is mainly used for cast iron pipes, ceramic pipes, plastic pipes, etc., and is mainly applied in water supply and drainage pipelines with low pressure. Socket connection is divided into mechanical interface and non-mechanical interface. The mechanical interface uses a pressure ring to connect with the flange at the end of the pipe, pressing the rubber sealing ring tightly into the gap of the cast iron socket, compressing the rubber ring to closely adhere to the pipe wall to form a seal. Non-mechanical interfaces are classified into asbestos cement interface, self-stressing cement interface, lead interface, rubber ring interface, etc., depending on the different fillers. In some old residential areas' water supply and drainage renovation projects, socket cast iron pipe fittings can often be seen. Although they have a simple appearance, they can work stably for many years.

 

6. Adhesive pipe fittings: Adhesive connection uses adhesive as the bonding filler to bond the same type of pipes and pipe fittings together, thereby achieving a sealing effect. Adhesive connection has advantages such as simple construction and fast curing speed, and is widely used in drainage systems. However, the peel strength, non-uniform tensile strength and impact strength of the adhesive layer are relatively low, and the general adhesives have poor heat resistance and aging resistance. For example, the PVC drainage pipes in household bathrooms are usually connected through adhesive pipe fittings, which is simple to construct and has a low cost.

 

7. Hot-melt pipe fittings: Hot-melt connection is mainly used for the connection of domestic water pipes, such as PPR and PE pipes. This connection method involves heating and melting the pipe ends with a hot-melt machine and then quickly joining them to form a stable connection. Due to its high requirements for the construction skills of workers, tools, pipe materials, and construction temperature, it is the most widely used in home water supply systems, featuring a firm and durable connection that is less prone to leakage. In home decoration, the hot-melt connection of PPR pipes is a key technology, and construction personnel must strictly follow the operation procedures to ensure the connection quality.

 

III. Classification by Materials

 

1. Cast steel pipe fittings: Cast steel pipe fittings have relatively high strength and toughness, capable of withstanding significant pressure and impact forces. They are suitable for high-pressure and high-temperature piping systems, such as steam pipes and high-pressure water pipes in power plants and chemical plants. However, the corrosion resistance of cast steel pipe fittings is relatively poor, and special anti-corrosion treatment is required in environments with corrosive media.

 

2. Cast iron pipe fittings: Cast iron pipe fittings have good corrosion resistance and wear resistance, and are relatively low in price. They are widely used in building drainage, municipal sewage discharge and other fields. Common types include gray cast iron pipe fittings and ductile iron pipe fittings. Gray cast iron pipe fittings have lower strength but are also lower in cost, and are often used in general drainage pipes; ductile iron pipe fittings have higher strength and toughness, and are suitable for some occasions with higher requirements for pipe strength, such as urban water supply pipe systems. In the old residential areas of cities, many drainage pipes use cast iron pipe fittings. Although they have been in use for many years, they can still work normally.

 

3. Stainless steel pipe fittings: Stainless steel pipe fittings feature excellent corrosion resistance, high-temperature resistance, and high strength. They have a beautiful and clean surface and are widely used in industries such as food, medicine, chemical engineering, and architectural decoration. Based on chemical composition and performance characteristics, stainless steel pipe fittings are mainly classified into austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, and duplex stainless steel, etc. Austenitic stainless steel, such as 304 and 316 stainless steel pipes, has good corrosion resistance, formability, and weldability, is non-magnetic or weakly magnetic, and is widely used in food processing, medical equipment, and other fields. Ferritic stainless steel has a high chromium content, good corrosion resistance and oxidation resistance, is magnetic, and has high thermal conductivity, making it suitable for manufacturing cookware and other equipment with high thermal conductivity requirements. Martensitic stainless steel can have its hardness and strength altered through heat treatment and is often used in the manufacture of cutting tools, blades, and mechanical parts. Duplex stainless steel combines the advantages of austenitic and ferritic stainless steel, featuring high strength, good corrosion resistance, and weldability, and is suitable for applications in marine engineering, chemical equipment, and other fields with high material performance requirements. In the kitchen and bathroom piping systems of some high-end hotels, stainless steel pipe fittings are often used, which not only ensures the hygiene of water quality but also enhances the overall quality of the building.

 

4. Plastic pipe fittings: Plastic pipe fittings have the advantages of light weight, corrosion resistance, easy installation and low cost, and are widely used in home decoration and some low-pressure pipeline systems. Common plastic pipe fittings include PVC (polyvinyl chloride) pipe fittings, PPR (random copolymer polypropylene) pipe fittings, and PE (polyethylene) pipe fittings. PVC pipe fittings have good chemical corrosion resistance, self-extinguishing and flame-retardant properties, and are widely used in building drainage, municipal sewage and rainwater drainage, etc. PPR pipe fittings have good heat resistance and pressure resistance, are non-toxic and odorless, and are the preferred material for home water supply systems. PE pipe fittings can be widely used in gas transmission, water supply, sewage, agricultural irrigation, oil fields, mines and post and telecommunications, etc. In home decoration, PPR pipes and PVC pipes are the most common plastic pipes, and their connecting pipe fittings are also widely used.

 

5. Rubber pipe fittings: Rubber pipe fittings feature excellent flexibility, sealing performance and corrosion resistance. They are often used in scenarios that require buffering, sealing or transporting corrosive media, such as flexible connections in chemical pipelines and cooling water pipes in car engines. Different rubber materials can be selected based on various application requirements, including natural rubber, nitrile rubber and fluororubber. Natural rubber offers good elasticity and wear resistance but has poor oil resistance. Nitrile rubber has outstanding oil resistance and chemical corrosion resistance and is commonly used in pipelines transporting oil-based media. Fluororubber, on the other hand, boasts extremely high heat resistance, corrosion resistance and chemical resistance, making it suitable for extremely harsh working environments.

 

6. Graphite pipe fittings: Graphite pipe fittings possess excellent corrosion resistance, high-temperature resistance, and thermal conductivity, making them uniquely applicable in certain high-temperature and highly corrosive chemical production processes. For instance, in the transportation pipelines of strong acids, strong alkalis, and other corrosive media, graphite pipe fittings can demonstrate their outstanding corrosion resistance, ensuring the long-term stable operation of the pipelines. However, the strength of graphite pipe fittings is relatively low, and they are brittle in nature. Therefore, special care must be taken during installation and use to avoid impacts and excessive force.

 

Vigor produce both cast and forged pipe fittings. If you have any question and demand of products development or improve your supply chain, please feel free to contact us at info@castings-forging.com