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Flange and pipe assembly connection

1. Flange and pipe assembly connection

The assembly quality of the flange and the pipe not only affects the strength and density of the pipe joint, but also affects the eccentricity of the entire pipeline. Therefore, in assembling the flange to the pipe, the following basic requirements must be met.

Flange and pipe assembly connection

The center of the flange should be in line with the center of the tube. The flange sealing surface should be perpendicular to the center of the tube.
The position of the screw hole on the flange of the pipe shall be consistent with the position of the flange screw hole on the matching equipment or pipe fitting. The screw hole positions of the flanges at both ends of the same pipe shall be consistent.

Flat welding flange and pipe assembly

When assembling the flat welding flange and the pipe, first insert the flange into the pipe end, and a certain distance (usually 1.5 times the pipe wall thickness) should be left between the pipe mouth and the flange sealing surface. At this time, spot welding can be performed on either side of the pipe, and then the flange is bent or squared on the opposite side of the spot welding, and then spot welding is performed at the curved rule. Rotate the pipe at an angle of 90° so that the spot welding position is placed above and below. At this time, use the curved ruler to align on either side of the pipe, and then spot weld on the left and right sides. When PN<1.6Mpa, only the outer port is welded; Internal and external welding is possible when PN ≥ 1.6Mpa.

Welding flange and pipe assembly

The welding flange and the pipe are assembled by butt welding. The welding method and requirements are the same as the welding method of the pipe.
2. Flange gasket
The gasket acts as a seal in the flange connection and is in contact with the medium being sealed, directly affected by the physical properties, temperature and pressure of the medium.
In general, flanges of the same pressure class should be used on the same pipeline for the same type of gaskets for interchangeability.
For water pipelines, medium-pressure asbestos rubber sheets are generally used. Due to the long service life of rubber, rubber gaskets should be used for infrequent disassembly and long service life.
The correct choice of gaskets, in order to ensure that the gasket will not be crushed, in order to reduce the excessive bolt tightening force, it is a principle to take a small width gasket. 3. Flange connection
3. Check and handle flanges, bolts and gaskets before installation:
First, the flange dimensions should be checked, including the outer diameter, inner diameter, groove, bolt hole center distance, flange height, etc., which should meet the design requirements.
The flange sealing surface should be smooth and smooth, without burrs and radial grooves.
The threaded portion of the threaded flange shall be intact and free of damage; the convex and concave flanges shall be naturally fitted, and the height of the convex surface shall not be lower than the depth of the groove.
Rubber asbestos board, rubber sheet, plastic and other hose gaskets should be flexible, without aging deterioration and delamination; the surface should not have defects such as defects and wrinkles. The material should match the design selected.
The processing dimensions, precision, surface roughness and hardness of the metal gasket shall meet the requirements, and the surface shall be free of defects such as cracks, burrs, grooves, radial scratches and rust spots.
Metal wound gaskets should not have defects such as radial scratches, looseness, warpage, and the like.
Before the flange is assembled, the rust, oil and other debris on the surface and the sealing surface must be removed until the metallic luster is exposed. The sealing line of the flange sealing surface must be clearly clarified.
Flange assembly
When installing the flat flange, the end of the tube should be inserted into the flange 2/3. Since the flat welding flange is subjected to mechanical stress and thermal stress, the entire joint is suddenly broken at the time of fracture. Therefore, the flat welding flange should adopt the reinforced welding method on both the inner and outer sides under the condition of condition. After welding, the slag should be cleaned, the inner hole should be smooth, and the flange surface should be free of spatter.
The flange face must be perpendicular to the pipe centerline. The skewness is allowed to be 1 mm when DN < 300 mm and 2 mm when DN > 300 mm.
The flange connection should be kept coaxial, and the center deviation of the bolt hole should generally not exceed 5% of the hole diameter, and the bolt should be allowed to penetrate freely.
The flange connection should be the same size bolts, the installation direction is the same, that is, the nuts should be on the same side. The bolts and nuts that connect the valves should generally be placed on the side of the valve. When tightening the bolts, it should be symmetrical and evenly elastic. The tightened bolts shall not exceed 5mm or 2~3 buckles outside the exposed nut.
Bolt hole position on the flange: The bolt hole of the horizontal pipe, the uppermost two should be kept horizontal; the bolt hole on the vertical pipe, the two holes closest to the wall should be parallel to the wall. At the same time, the two connecting flanges should be parallel and natural, and the parallelism deviation should be no more than 2mm.
The flange on the branch pipe is 100mm or more from the outer wall of the riser, or the bolt can be worn. For ease of disassembly, the distance between the flange and the edge of the bracket or building should be more than 200mm.
Source: China Flanges Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

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