Correctly tightened bolts make use of their elastic properties and should behave like springs to work effectively. Their spring analogy is attributed to when load is applied as the bolt stretches and tries to return to its original length, creating compressive force across the joint members.
The elongation applied within the elastic range is relieved when the load is removed and the amount of elongation increases when more load is applied. It is the further application of load which takes the bolt to a point where it begins to fail, this is termed its ultimate tensile strength (UTS). At the UTS-point, if additional force is applied to the bolt, it will continue to elongate until it finally breaks. To prevent bolt failure, attention should be paid to:
Advantages of controlled bolting techniques
Known, controlled and accurate bolt loads
Controlled bolting techniques incorporate tooling which have controllable outputs. The correct calculations are determined to provide the operator with the required tool settings ensuring ease of use.
Consistency of bolt loading
This is crucially important on joints which have gaskets, as an even and consistent compression is required to prevent damage and for the gasket to work effectively.
The safe operation of controlled bolting equipment eliminates the unsafe actions of manual uncontrolled tightening as controlled bolting equipment requires skilled operators to follow specific procedures.
Reduced operational time
Replacing manual effort with the use of controlled bolting tooling increases productivity by reducing the tightening time and operator fatigue.
Reliable and repeatable results
Using calibrated, tested equipment and skilled operators who follow specific procedures achieves known results consistently.
The right results first time
Ensures the correct assembly and tightening of the joint are carried out the first time, saving time and resource.
How many tensioners are required?
Most applications can be tensioned with one hydraulic tensioner. However, on applications where there are multiple bolts to be tensioned, it is advised the operator uses one hydraulic tensioner for every other or for every fourth bolt.
On circular flanges, to increase work productivity, it is recommended that at least four hydraulic tensioners should be used. This method of bolt tensioning ensures that the flange is closed evenly, safely and quicker than if only a single tensioner was used.
Uneven bolt tensioning can result in:
Not all applications allow for simultaneous tensioning devices on bolts, in such cases at least two tensioning pressures can be applied. This is to account for a load loss in those bolts already tensioned as the next sets are tightened.
Every tightening procedure should be started by lubricating the nuts and bolts followed by hand tightening until they are flush against the flange. Please note, when tightening the bolts, always ensure use of the correct sequential bolt order for the flange.
Controlled bolting techniques
4 and 8 Bolt flanges
12 + Bolt flanges
Start preventing failures today by ensuring 100% accuracy every time with HTL’s extensive range of solutions:
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