Tag Archive Guide for installation and use of gasket

1. Installation requirements
1, gasket and flange sealing surface should be cleaned, there must be no influence on the sealing performance of the scratch, spots and other defects.
2, the outer diameter of the gasket should be smaller than the flange sealing surface. The inner diameter of the gasket should be slightly larger than the inner diameter of the pipe, and the difference in the two inner diameter is generally 2 times that of the thickness of the gasket to ensure that the inner edge of the gasket is not extended into the container or pipe to prevent the flow of the fluid in the container or pipe.
3, the pre tightening force of the gasket should not exceed the design requirements, so as to avoid excessive compression of the gasket and lose resilience.
4. When the gasket is pressed, it is best to use the torque wrench. For large bolts and high strength bolts, it is better to use hydraulic tighten. The tightening torque should be calculated according to the given shim compaction, and the size of the hydraulic pressure of the hydraulic tightening device should also be determined by calculation.
5. When installing gaskets, tighten the nuts in turn in the right order. But it should not be screwed up once to achieve the design value.  Generally, it should be circulated at least 2~3 times, so that the stress distribution of the gasket is uniform.
6. For flammable and explosive medium pressure vessels and pipes, safety tools should be used when dressing gaskets, so as to avoid sparks caused by tools and flanges or bolts, resulting in fire or explosion accidents.
7, if there is any leakage, it is necessary to reduce pressure and replace or adjust the installation gasket.
Two. Special installation requirements
1. When installing a winding gasket with a flanged flange, attention should be paid to the concentricity of the seal and the pipe. In general, a strong ring is used to locate the inner circle of the bolt, and the eccentric installation is not allowed. When installing the basic type spiral wound gasket in the flange of the tenon groove surface, attention should be paid to keeping the gap with the groove wall surface.
2, when the metal covering gasket with a narrow width is installed, a certain thickness of the steel plate should be placed outside the pad, and then the flange is pressed so as to prevent the sealing of the covering filler in the gasket to be expanded and damaged.
3. When the working temperature of the flange is higher than 200 c, sealant should be coated between the flange seal surface and the gasket to prevent the sintering of the gasket and flange sealing surface at high temperature, which will increase the trouble for the repair and replacement of the gasket.
4, the sealing surface is not normal, the sealing surface can be coated with sealant and then install gaskets. The sealant is made up of manganese dioxide, lead, graphite powder and linseed oil. According to the sealing medium, working temperature and medium pressure and other conditions, choose the corresponding type and brand of liquid sealant.
5, for installing octagonal metal ring gaskets, when metal ring gaskets and flange sealing grooves are not well processed, they can be closely bonded through research. For large diameter metal ring gaskets, it is difficult to prepare and research. In order to fill the tiny uneven surface of the metal, sealant can be used.
Three. Inspection of bolts and flanges before installation
1. Inspection of bolts and nuts
1) the material, type and size of bolts and nuts should conform to the requirements of drawings.
2) the nut should be rotated on the bolt without being swaying.
3) the bolt should not be bending.
4) the bolt thread does not allow the disconnecting phenomenon.
2. Check flanges
Check whether the flange type meets the requirements, whether the sealing surface is clean, whether there is mechanical damage, radial scratches and rust.
3. Check the gasket
1, whether the gasket material, type and size meet the requirements;
2, whether the surface of the gasket has mechanical defects, radial marks, serious rust, internal and external edge damage and other defects.
3. For elliptical and octagonal metal gaskets before installation, check whether the size of the trapezoidal groove of the flange meets the requirements and whether the groove is clean. Red lead oil can be coated on the surface of the ring gasket to check whether the contact is good. If the contact is bad, it should be grinded.
Four. Requirements for the installation quality of pipes and flanges
1. partial mouth
The pipe and flange are not vertical and concentric, and the flange faces are not parallel. The allowable deviation between the two lanes is: when metal gaskets are used, they should be less than 2; when using metal non metal combined gaskets and metal gaskets, they should be less than 1.
2. wrong mouth
The pipe and flange are vertical, but the two flanges are not concentric.  When the diameter of bolt holes and the diameter of bolts meet the standards, it is acceptable to bolt freely into bolt holes without using other tools.
3. mouth opening
It means that the flange gap is too large. The opening value (excluding the pretension value of the pipe and the thickness of the gasket or blind plate) between the two French lanes is that the opening of the pipe flange shall be less than 3; the flange connected to the device shall be less than 2.
4. error hole
The pipe and flange are concentric, but the distance between the two bolts corresponding to the bolt hole is larger. The allowable deviation of the center circle radius of the bolt hole is as follows:
When the diameter of bolts is less than 30, the allowable deviation is + 0.5.
When the diameter of bolts is greater than 30, the allowable deviation is + 1.
The allowable deviation of the distance between two adjacent bolts is + 0.5.
The total deviation of the chord distance between any few holes is:
DN less than 500 flanges, the allowable deviation is 1
DN600 to 1200 flanges, the allowable deviation is 1.5
Flange deviation from DN1300 to 1800 is allowed to be + 2.
Five. The method of controlling the fastening force of the bolt
Before installation of bolted flanges, the tightening force should be estimated according to the new and old degree of bolts, lubrication status and material quality. If the fastening force is too small, the preload stress of the gasket is insufficient, and the connection can not be sealed. If the fastening force is too large, it often causes damage to gaskets or sealing surfaces. Therefore, the fastening force of the bolt must be controlled. The special tools such as the force wrench and the fixed torque wrench must be used to control the fastening force of the bolt, and the pretightening force is calculated and controlled.