How to torque a flange properly?
In this post we emphasize the importance of knowing how to properly torque a flange and we will show some tightening sequence patterns.
The tightening sequence allows us to control the tension variation without damaging the joint.
The flange tightening sequence
Flanges are one of the most commonly used joint connections between pipes or valves, (usually when 50 DN is exceeded). The flanges are joined by force or torque applied to the bolts, which will exert a pressure determined towards a insulating medium such as a gasket .
One of the factors that determine the success of the joint tightness when tightening a flange is, without a doubt, the tightening sequence of the bolts , which ensures a balanced tension throughout the joint.
Why is the tightening sequence important?
The tightening sequence is essential as it allows us to control the tension variation in the flange gasket components. In the case of the gasket, it must be compressed evenly along the face of the flange.
For example, if we tighten the adjacent screws instead of the opposite ones, the compression of the gasket would be uneven, compromising its tightness and probably damaging it.
The flanges must be parallel, the most optimal method is to use a tightening pattern of the correct partial load bolts and then add more load.
Charlie Chaplin in an iconic scene from “Modern times” from 1936.
What tools can I use?
Successful bolt tightening requires both experience and tools appropriate to the size of the application:
- Hand wrenches
- Impact wrenches
- Hydraulic torque wrenches
- Beam and Gear Assisted Hand Wrenches
- Hydraulic Bolt Tensioners
What patterns do I use to tighten the flange?
In the following figure we see a sequence of 12 bolts we see that the pattern consists of always tightening the opposite, for example, the sequence would be:
1-7-4-10…
In this figure, balancing is performed by combining opposite bolts with a slight variation:
1-2-3-4 …
In this case, a flange with 48 bolts, the tightening sequence is different, the bolts would be grouped into 12 groups of 4 bolts, so the groups should be tightened as defined in the first sequence:
1-7-4-10-2-8-5-11-3-9-6-12