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Standard practice for common pipe connection methods1

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1. Threaded connection

➤ Thread processing

Divide 2-3 cuts, the thread should be clear, complete, and smooth, without burrs and messy threads. If there is a broken wire or missing wire, it shall not exceed 10% of the total number of threads. The thread should also meet the requirements of the assembly tolerance, with a 1/16 taper to prevent the thread from being too loose or too tight.

➤ Threaded assembly

After tightening, reveals 2-3 threaded screw tails, remove the excess filler, and apply red lead to rust-proof the exposed threads. Red lead has the same brushing width, uniform coating, no flow or leakage.

common problem

Hemp is not cleaned

Length of exposed thread

Irregular painting

Paint freely

Anti-rust treatment of exposed thread


2. Flange connection

➤ Pipe flange

1) The matching flange specifications and models are the same; when connecting with the equipment flange, they should be matched according to their specifications;

2) The flange connection is coaxial and parallel, and the flange surface is perpendicular to the center of the pipe;

3) The tightening bolts have the same specifications, the same direction, and the exposed length of the bolts is 1/2 of the bolt diameter or flush with the nut;

4) When connecting the valve, the nut is placed on the valve side;

5) Keep the top two screw holes of the horizontal pipe flange horizontal, and the two screw holes of the vertical pipe flange against the wall are parallel to the wall.

The common problems are:

The flange inner ring is not welded

The bolts on both sides are not aligned

Flange mismatch

➤ Duct angle steel flange

1) Flange production should be flat flange surface, equal diagonal length, and full weld seam;

2) The flange bolt holes and rivets are evenly spaced and meet the requirements of the specification, and the four corners of the flange are provided with screw holes;

3) When connecting flanges, the bolt direction should be uniform and the length should be the same, and the bolt material should correspond to the air duct;

4) After the flange is tightened, it should be tight and leak-free, the flange surface gap should be even, and the gasket should not protrude into the pipe or protrude outside the flange;

5) No corrosion of the bolts after flange connection.

The hole spacing of bolts and rivet holes of the air pipe flange of the medium and low-pressure system shall not be greater than 150mm, and the air pipe of the high-pressure system shall not be greater than 100mm. The four corners of the rectangular duct flange shall be provided with screw holes.

➤ Duct sheet steel flange

1) The flange should be perpendicular to the duct and fit closely;

2) Apply sealant to the inside and outside of the four corners of the duct flange to seal;

3) The four corners of the flange are fixed by bolts, with spring clips or top wire clamps in the middle, with a spacing of ≯150mm, and the outer end is ≯100mm from the edge of the duct.




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