Force-fit flange connection:
8 steps to a professionally installed flange

The following equipment is recommended:

1. Inspection and Cleaning

All components must be checked for any damage. The flange connection, in particular the sealing surfaces of the flanges, the seal and the groove for O-rings must be clean before installation. Furthermore, the contact surfaces of the loose flange/backing ring and plastic flange must be free of foreign particles.

2. Joining the parts

When welding the flange connection to the pipeline using the heated tool butt welding process (butt fusion process), a welding machine with a collar holder should be used if possible when using short legged flanges. It is also important to pay attention to the position of the loose flange/backing ring during welding, as it may not be possible to push it over the welding bead afterwards, depending on the flange used. It is important to pay attention to the arrangement of the bolt holes when using fixed flanges. As a rule, these must be aligned symmetrically to the main axes of the pipeline.

3. Aligning the parts

The flange connection, consisting of the plastic flange, gasket and loose flange/backing ring, must be aligned centrally to the pipe axis. When aligning the gasket, check that the gasket dimensions match the outer and inner diameter of the flange sealing surface. Before tightening the bolts, the sealing surfaces of the flanges must be parallel to each other and in close contact with the gasket. Tightening the sealing surfaces, e.g. by tightening the bolts, is not permitted. The connection must be installed without tension. Failure to observe this will result in overloading, which will cause the flange connection to fail.

For horizontally laid pipelines, the hole position of the top or bottom two bolts should be horizontal.

4. Bolts

The length of the connecting bolts must be selected so that the bolt thread does not protrude more than 2 to 3 threads on the nut. Washers must be placed on both the bolt head and the nut.

5. Lubrication

In order to achieve the required bolt preload force at the specified tightening torque and to facilitate loosening after a longer period of operation, all sliding surfaces of the bolted joint, such as the thread, the bearing surface of the nut and, if necessary, the head bearing surface with a moving bolt head, must be provided with a lubricant (e.g. molybdenum sulficate).

6. Gasket

The gasket used must meet the requirements of the application, such as resistance to media, pressure and temperature. The sealing properties must be agreed with the supplier. We generally recommend the use of G-ST profile gaskets and integrated O-rings, which are characterized by sealing at low surface pressure

Important: the gasket needs to be clean, dry and undamaged. The use of assembly pastes for the gasket is not permitted. Used gaskets must not be reused.

7. Tightening the bolts

The connecting bolts must be tightened diagonally and evenly in several steps using a torque wrench. The required torque depends on the shape and material of the selected gasket as well as on the friction in the bolt thread and on the nut contact surface.

Installation note: With the profile loose flange, it is important that the bolts are inserted at the full surface side.

• If the gasket manufacturer specifies lower bolt torques than those in Table 1, these should not be exceeded.
• Upper limit values for bolt torques when using elastomeric gaskets and new, lubricated bolts (friction coecient μR = 0,15) are shown in the table.
• It is recommended to use a torque wrench that complies with the ISO 6789 series.
• For diameters of more than 180 mm, it is recommended that two people working simultaneously tighten the opposite bolts.

8. Retightening

Retightening with the recommended torque should be carried out a few hours later and also the next day. The selected tightening method and the friction coecient of the bolt connection can lead to considerable deviations in the actual sealing force achieved due to their scattering. For this reason, it is important to adhere to the specifications mentioned under points 6 and 7.

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