What Are the Different Methods for Duct Installation?

Pipe connection refers to connecting prefabricated pipe sections into a complete system according to the requirements of the design drawing. In construction, different connection methods should be selected according to the material of the pipe used. Ordinary steel pipe has methods such as thread connection, flange connection, welding connection, socket connection, pipe adhesive connection and so on. ^[1]

In pipeline engineering construction, different connection methods should be selected according to the material of the pipe used. ordinary

There are three ways to connect pipe threads: cylindrical internal thread is inserted into cylindrical external thread, cylindrical internal thread is inserted into conical external thread and conical internal thread is inserted into conical external thread, as shown in the figure below. Among them, the latter two methods are more closely connected and are commonly used.

Flange connection is to connect two pipes, fittings or equipment. It is a detachable joint that is fixed on a flange plate first, then a flange pad is added between the two flange plates, and the two flange plates are tightened with bolts to tightly combine them.

This connection is mainly used for the connection of cast iron pipes, rubber-lined pipes, non-ferrous metal pipes and flange valves. The connection of process equipment and flanges also uses flange connections.

The parts to be dismantled for the flange connection of steel pipes are related to the flanged valves, equipment, instruments, etc. Flange is available in cast iron and steel. There are three types of flange and pipe connections: flanged loose sleeves, threaded connections, and welded connections. In pipeline installation, flat welded steel flange connection methods are commonly used.

Flanged flange connection. Flanged loose sleeve flanges are generally used for pipes of similar materials such as copper pipes, lead pipes, plastic pipes, etc. When flanging, different operating methods are selected according to different materials.

Threaded flange connection. The flange with internal thread is used to connect with the steel pipe with external thread. This flange is mostly cast iron and can be used for the connection of low-pressure pipelines.

Welded flange connection. The flange and steel pipe are welded. This flange connection is widely used. The welding method is: select a pair of flanges, and install them on the two pipe ends that are connected. If the equipment already has a flange, choose a flange of the same specification to wait for the spot. Correct the perpendicularity, and finally weld the flange and the pipe firmly. The inner and outer sides of the flat welding flange must be welded to the pipe.

Features of pipe connections

The joint is firm and tight, and the strength of the weld generally reaches more than 85% of the strength of the pipe, and even exceeds the strength of the base metal.

The welded connection is a direct connection between the pipe sections. The structure is simple, the pipeline is beautiful and neat, and a large number of shaped pipes are saved.

Tight connection, no packing, can reduce maintenance work.

The interface is not limited by the pipe diameter and the operation speed is fast.

The welding connection interface is a fixed interface, which is difficult to connect and disassemble. If maintenance or cleaning is required, the pipeline must be cut off.

Pipe connection metal pipe welding

Welding connection is mainly used for butt joint of water supply steel pipe, welding flange and other flexible mouths. Welding methods usually include gas welding, manual electric welding and automatic arc welding, contact welding and so on. Pipes should be thoroughly cleaned and inspected before welding.

When steel pipes are aligned, the longitudinal welds shall be staggered from each other by more than 100 mm arc length, there shall be no cross-shaped welds; the welds shall not be placed in the walls of buildings, structures, etc.

When steel pipe is rolled, the longitudinal welds of each pipe cannot be arranged on the same straight line. The distance between the longitudinal welds of two adjacent pipes should be greater than 3 times the wall thickness and not less than 100 mm; The distance between two adjacent longitudinal welds shall not be less than 300 mm.

There must be no welding seam in the bending part of the pipeline, and the distance from the starting point of the butt welding seam must not be less than the outer diameter of the pipe and not less than 100 mm (except for welding elbow). There shall be no circular welds at the pipe support. ^[2]