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How to use gaskets? How to install the gasket

1 Check before installation

(1) Inspection of gasket

1) Whether the material, form and size of the gasket meet the requirements;

2) The surface of the gasket is not allowed to have any defects such as mechanical damage, radial nicks, severe corrosion, damage to the inner and outer edges;

3) The selected gasket should be compatible with the flange sealing surface form.

(2) Inspection of bolts and nuts

1) Whether the material, form and size of bolts and nuts meet the requirements;

2) The nut should rotate flexibly on the bolt, but should not shake;

3) Bolts and nuts are not allowed to have scars or burrs;

4) The thread is not allowed to be broken;

5) The bolts should not be bent.

(3) Inspection of flange

Check whether the form of the flange meets the requirements, whether the sealing surface is smooth, whether there is mechanical damage, car markings, radial nicks, severe corrosion, welding scars, oil coke residues and other defects. If it cannot be repaired, the specific treatment methods should be studied.

(4) Inspection of pipeline and flange installation quality

1) Partial mouth——The pipeline is not vertical, not concentric, and the flange is not parallel.

The allowable deflection value between two flanges: when using non-metallic gaskets, it should be less than 2mm; when using metal composite gaskets, oval gaskets, octagonal gaskets, and flanges connected to the equipment, it should be less than 1mm.

2) Wrong port-the pipeline is perpendicular to the flange. But the two flanges are different.

When the bolt hole diameter and bolt diameter meet the standard, the bolt can be passed into the bolt hole freely without other tools.

3) Opening the mouth — the flange gap is too large.

Allowable opening value between two flanges (outcoming pipeline pre-tensioning value and gasket or blind plate thickness): the opening of the pipe flange should be less than 3mm, and the flange connected to the equipment should be less than 2mm.

4) Wrong hole --- the pipeline flange is concentric, but the two flanges correspond to the screw

The chord distance between the bolt holes (or the diameter of the bolt hole center circle, etc.) has a large deviation.


(1) The two flanges must be on the same centerline and parallel. It is not allowed to use bolts or pointed steel brazing to be inserted in the bolt holes to correct the flange, so as to prevent the bolts from bearing greater stress. The flange sealing surface and water line (sealing line) should be cleaned carefully before installation. Spiral wound gaskets* are used for flanges that do not have a dense seal line.

(2) Only one gasket can be added between the two flanges, and the method of adding more gaskets is not allowed to eliminate the defect of excessive gap between the two flanges. The gasket must be installed upright, not skewed, to ensure uniform pressure, and to prevent the gasket from extending into the pipeline and being eroded by the medium and causing eddy currents.

(3) When tightening the nut, when the nut is below M22, use a torque wrench to tighten, and when the nut is above M27, use a pneumatic wrench.

When using a torque wrench, in order to ensure that the gasket is evenly compressed, the bolts should be tightened symmetrically and evenly in 2-3 times

(4) In order to avoid bending of the bolts when tightening the nuts and jamming when loosening, the two ends of the bolts should be coated with scaly graphite and lubricant. For the rough back of the flange, a smooth washer should be added under the nut. The end of the bolt with a steel seal should be exposed at the end that is convenient for inspection.

(5) Since the bolts are tightened in a cold state, they will loosen when the temperature rises. Where the temperature of the medium is above 300℃, the bolts should be heat-flanged when the temperature of 250~280℃, when the temperature of the medium rises to tight. In order to prevent the bolts from being unable to be removed during maintenance, when the temperature of the medium drops to 200-250°C, first loosen the bolts with bolt loosener at the bolt-nut joints, and then loosen the nuts by 30°-60°.