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BP Chemicals has set itself the target of implementing a 'best industry policy' and reducing fugitive emissions to air by 50%, over a 7 year period from 1990 levels, at its main sites in the UK, Europe and the USA. The plant at Hull processes a specialist chemical used in agro-chemical applications. This is produced at the elevated temperature of 250°C and pressures of 550 psi. In the past, if production was affected, for instance, by lack of steam due to boiler problems, the plant would shut down giving rise to thermal cycling, which sometimes resulted in pipe flange leaks.
Previously, the standard practice was to torque tighten the valve flange bolts on installation to create good leak proof joints. However, during 1994/95, the plant spent £15,000 on sealing leaks, highlighting the limitations of the torque tightening method. In line with its environmental policy and the joint aims of improving safety and reducing maintenance cost, BP Chemicals decided to use RotaBolts to ensure that flanges and gaskets were correctly and uniformly loaded.
A total of 900 RotaBolt load monitored fasteners were fitted to all flanges in September 1995 and since this time there has been a dramatic reduction in leaks, despite the plant being shut down on more than one occasion.
"The success of the Rotabolt work carried out during our 1995 plant shut-down has been recognised across the site and there are other applications where engineers are considering the technique as a means to improving flange integrity", said Tim Kaye, plant manager.
"Our application was an ideal situation in that we needed a method which was time efficient in its implementation whilst also producing an extremely accurate method of bolt tensioning", he added.
One of the advantages of using RotaBolts is that tension can be guaranteed to an accuracy of +5% and checked instantly using a simple thumb and finger test. When the rotor cap is 'locked' at the prescribed limit, the engineer knows that the correct tension is being maintained. Conversely, if the cap revolves, there is an immediate indication of a loss of tension. At Hull this feature has enabled simple tension checks to be made on initial start-up, and where necessary allowed joints to be re-tightened prior to full production.
RotaBolts are widely used to overcome the problems inherent in conventional tightening methods. The major limitation of the torque wrench is that it only registers the condition of the mating surfaces at the joint, not the axial load on the fastener. On tightening, this leads to inaccuracies in design load tension of +/- 30% and higher depending on the lubrication, cleanliness and condition of the threads. With hydraulic tensioners, the consequences of load transfer relaxation during the tightening cycle means that the residual bolt load is unpredictable and uncontrollable.
The accuracy, ease and reliability of RotaBolt fasteners have been well proven in the international offshore oil and petrochemical industries. Today, they are widely adopted throughout the spectrum of general engineering industries.
For more information on RotaBolt, click here
