What is a welded pipe? Definition of piping

Welded piping is a device for conveying gases, liquids or fluids with solid particles by coupling pipes, pipe couplings (fittings) and valves, etc. Usually, fluid is pressurized by blowers, compressors, pumps and boilers, etc., and flows from the high pressure of the pipe to the low pressure, or it can be transported by the fluid's own pressure or gravity. Pipelines are used in a wide range of applications, mainly in water supply, drainage, heating, gas supply, long-distance transportation of oil and gas, agricultural irrigation, hydraulic engineering and various industrial installations.

Basic Introduction

Pipeline is a device for transporting gases, liquids or fluids with solid particles connected with pipes, pipe couplings (fittings) and valves. Usually, fluids are pressurized by blowers, compressors, pumps and boilers, etc., and flow from the high pressure of the pipe to the low pressure, or they can be transported by the fluid's own pressure or gravity. The pipeline is widely used, mainly in water supply, drainage, heating, gas supply, long-distance transportation of oil and gas, agricultural irrigation, hydraulic engineering and various industrial installations.

1、Classification by material: metal pipeline and non-metal pipeline.

2、Classified by design pressure: vacuum piping, low pressure piping, high pressure piping, ultra-high pressure piping.

3、Classification by conveying temperature: low temperature pipeline, room temperature pipeline, medium and high temperature pipeline.

4、Classification by conveying medium: water supply and drainage pipeline, compressed air pipeline, hydrogen pipeline, oxygen pipeline, acetylene pipeline, heat pipeline, gas pipeline, fuel pipeline, highly toxic fluid pipeline, toxic fluid pipeline, acid and alkali pipeline, boiler pipeline, refrigeration pipeline, purified pure gas pipeline, pure water pipeline.

Piping - Determination of pipe diameter When the flow rate of the fluid is known, the size of the pipe diameter depends on the allowable flow rate or the allowable frictional resistance (pressure drop). The pipe diameter is small for high flow rates, but the pressure drop value increases. Therefore, when the flow rate is large, you can save investment in pipeline infrastructure, but the operating energy costs of power equipment such as pumps and compressors increase. In addition, if the flow rate is too large, there may bring some other unfavorable factors. Therefore, the pipe diameter should be decided according to the construction investment, operation cost and other technical factors.

Pipeline - pipe coupling pipe, pipe couplings, valves and equipment on the inlet and outlet between the connection method, the nature of the fluid, pressure and temperature, as well as the pipe material, size and installation site and other factors, mainly threaded coupling, flange coupling, socket coupling and welding and other four methods: ① threaded coupling: mainly applicable to small diameter pipeline. Coupling, generally in the threaded part of the connection to wrap the fluorine plastic sealing tape or coated with thick paint, around the wire and other sealing materials to prevent leakage. At pressures above 1.6 MPa, gaskets are generally added to the pipe end face to seal. This coupling method is simple and can be disassembled and reassembled, but a live joint must be installed in the appropriate place of the pipe to facilitate disassembly. ② Flange coupling: applicable to a larger range of diameters. The flange and gasket are selected according to the nature of the fluid, pressure and temperature, and the gasket is clamped with bolts to maintain the seal. In the need for frequent disassembly of the pipe section and pipe and equipment connected to the place where most of the use of flange coupling. ③ socket connection: for cast iron pipes, concrete pipes, terra cotta pipes and their couplings between the connection, only for water supply, drainage and gas pipelines working under low-pressure room temperature conditions. Coupling, generally in the socket groove first filled with hemp, cotton thread or asbestos rope, and then filled with asbestos cement or lead and other materials, but also in the socket filled with rubber sealing ring, so that it has good flexibility, allowing the pipe to have a small amount of movement. ④Welding coupling: This coupling has the best strength and sealing, and is suitable for all kinds of pipes, saving labor and materials, but the pipe and pipe coupling must be cut off when dismantling.

Pipeline - the laying of the pipeline The city's water supply, drainage, heating, gas supply pipeline trunk and long-distance oil and gas pipelines are mostly laid underground, while the process pipeline in the factory for easy operation and maintenance more laid on the ground. Pipeline passage, support, slope and exhaust, compensation, insulation and heating, corrosion and cleaning, identification and painting and safety, whether for above-ground or underground laying is an important issue.

Support issues

The pipeline may be subjected to many kinds of external forces, including its own weight (the weight of the pipe, valve, pipe coupling, insulation and fluid inside the pipe), the pressure of the fluid acting on the end of the pipe thrust, wind and snow load, soil pressure, thermal stress caused by thermal expansion and contraction, vibration load and earthquake disaster. In order to ensure the strength and stiffness of the pipe, it is necessary to set up various kinds of supports (hangers), such as movable brackets, fixed brackets, guide brackets and spring brackets. The setting of the bracket is decided according to the diameter, material, pipe wall thickness and load of the pipe. Fixed brackets are used to control the thermal elongation of the pipe in sections and make the expansion joint work evenly. Guided bracket makes the pipe move axially only.

Passage problems

Above-ground pipes should try to avoid crossings with roads, railroads and waterways. When crossings cannot be avoided, the height of the crossing should also enable safe passage of pedestrians and vehicles and vessels. Underground pipelines are generally laid along roads, and appropriate distances are maintained between various pipelines for installation and maintenance; heating pipelines with insulation on the surface, laid in trenches or protected pipes, should avoid being crushed by soil and enabling the pipes to expand and move.

Slope and drainage of liquid exhaust

In order to exclude condensate, steam and other gases containing water pipeline should have a certain slope, generally not less than two thousandths. For the use of gravity flow of underground drainage pipes, the slope is not less than five thousandths. Steam or other water-containing gas piping at the lowest point of the drain or trap, some gas piping is also equipped with a gas-water separator, in order to timely drain the water and liquid to prevent water strikes and obstruct the flow of gas. Water or other liquid piping is equipped with an exhaust device at the highest point to remove air or other gases accumulated in the piping in order to prevent air obstruction from causing malfunction in operation.