Everyone has experienced difficulty at some point with conventional “fitted” coupling bolts. The term “fitted” when applied to conventional coupling bolts is a misnomer. These bolts in reality are “clearance” bolts. When a conventional “fitted” bolt is tightened it shrinks in diameter, increasing any clearance that existed when the bolt was inserted into the hole. This is why couplings assembled with conventional bolts can often be a contributing cause of excessive vibration and extended outage durations due to the coupling slipping under operation.

 

During operation, the coupling can shift slightly and bind holes against the bolts. This causes the bolts to become tight in the coupling and difficult to remove. The mechanics may start using force to overcome them being tight in the holes. The use of this force may be enough for the bolt to pick up a gall and become stuck in the coupling during dis-assembly or reassembly leaving you with the only option of having to drill it out. This is both time consuming and costly.

 

In response to these common problems of bolt seizure and extended dis-assembly & reassembly times, conventional fitted coupling bolts are being replaced with Pilgrim Hydraulic Coupling Bolts on new and existing turbines

 

Hydraulic coupling bolts are truly “fitted”. As a hydraulic coupling bolt is tightened, the action of the tapered shank pulling into the matching taper of the sleeve causes elastic expansion of the sleeve until it contacts the bore ID. As a result, the sleeve always maintains a full fit with the bore and becomes a rigid, integral part of the entire coupling system that prevents any coupling movement.

The majority of the torque is transferred trough the sheer of the bolt body and not frictional clamping as clearance bolts do.

 

Working with our partner BFW: The World’s leading coupling experts, many of the world's leading OEMs as well as end users have relied on the BFW team to consistently provide them with the fastest coupling hole line boring services, the most effective hydraulic coupling bolt retrofits and, the assurance of trouble-free coupling disassembles and re-assemblies.

 

Line Boring will always be the best choice when preparing the coupling holes for hydraulic coupling bolts. Once the coupling concentricity's are set and the coupling is securely clamped the coupling is then machined with a coupling boring machine.  The boring bar is the key to guaranteeing a straight hole, the tool is fed along the bar completely passing through all the components. The hole is then honed to ensure parallelism, roundness and surface finish. The resulting hole is well within the manufacturer's tolerances ensuring the perfect sleeve fit and coupling repeatability after reassembly during future outages.

 

Hydraulic coupling bolts have been proven to be the answer for eliminating all coupling related bolting issues, but care has to be taken during installation to ensure you achieve the intended results.


The Importance of Coupling Bolting and Coupling Preparation.

Division / Sponsors: 
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Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

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Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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