Surprise BSE Change

Thermal Growth – No Problem

Recently a power plant was installing a new coupling after an extended outage. A new pump shaft and element were installed during the outage, and significant work was performed on the turbine. The original distance between shaft ends (DBSE or BSE) was 14.0 inches, and the FLEXXOR Coupling spacer was designed for this dimension. However, the correct amount of thermal growth and equipment thrust was unknown at that time.

Thermal Growth Determination

Before the installation could continue, a discussion about thermal growth and thrust position ensued. The team realized that the net result of the shaft movement would amount to a different BSE than was expected. The difference in shaft position was about 0.100 inches. Since the allowable axial movement of the coupling was +/- 0.090 inches, it was crucial to set the hubs and shafts properly so that the running BSE would not be in a position to overly stretch or compress the coupling.  


Correcting the Axial Position of the Coupling Hub

Once the correct shaft spacing was determined, the hubs needed repositioning. Since the pump side hub was already fixed in its position by the shaft taper, the adjustment needed to happen on the turbine side where the shaft was straight. Luckily CouplingCorp had designed the hubs to have some adjustability in the axial position of up to 0.250 inches. So, within minutes, the Anderson Clamp Hub was loosened, repositioned, and re-tightened in the new position. 

Thanks to the ease of use of the Anderson Clamp Hub, the mechanics overcame a last-minute hurdle with no sweat. No heat or hydraulics were needed, and one mechanic could make the adjustment very quickly.

How CCA Saved a Customer Millions

A CouplingCorp customer came with a problem that can be common. The original shaft attachment device they were using had a set screw to hold it in place on the shaft. Over time the vibrations of the hub on the shaft caused micro fretting between the set screw and the shaft. This small movement created a weak spot on the shaft which eventually caused shaft failure.

Stress Risers in Shafts

In any shafts that carry high torsional load, a stress riser can be catastrophic.  In this particular case, the shaft was also carrying a cantilevered load which added to the stress on the outer surface of the shaft.  The micro-cracking that happened at the set screw contact point was enough of a stress riser to cause a full crack even on a shaft running at relatively low speeds.

This is a cautionary tale for any shafts that have surface irritations like this or other intentional features.  For example, keyways in shafts are often problematic if the inside corners do not have an appropriate fillet.  It’s always good to inspect shaft to avoid surprises.

The customer wanted to find a mechanical device without a set screw which would be easy to install, simple to uninstall, and, most importantly, it had to be customized to fit a unique geometry which supported a bearing. Luckily CouplingCorp was able to create the perfect solution. The Anderson Clamp Hub™ is a mechanical clamping device that has a fully customizable flange which was able to handle a tight tolerance bearing surface.

Design Flexibility

One distinct advantage of the Anderson Clamp Hub is the ability to access the loading screws from either end as chosen by the user.  Sometimes it can be very helpful to access the loading screws from the shaft end side because there is more wrench clearance.  With some other keyless devices, loading screws are typically found on the back end of the hub where they can be very close to the bearing housing which leaves very little room for access.  In other cases, it can be more helpful to have the loading screws on the other end, which is achievable with the Anderson Clamp Hub.  This design freedom gives the user a much more user-friendly device.

By working with CouplingCorp on this application, the customer was able to solve the shaft failure problem.  In the process of making that change, they were able to save millions of dollars in warranty parts on their entire installed base.

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Does This Look Familiar? It Doesn’t Have To.

After many years of struggling with maintenance and vibration issues, a pipeline company decided to upgrade their couplings. The pipeline was powered by 4500 HP motor-driven pumps running at 1800 RPM. They came to Coupling Corporation of America for several reasons. First, the FLEXXOR coupling would allow them to have a high-performance coupling with low spring rates that could handle the rigors of remote locations, including unpredictable misalignments. Second, they really wanted the convenience of the Anderson Clamp Hub so that their mechanics could easily remove and install the hubs when it was time for maintenance.

After designing and manufacturing the couplings and hubs for the fleet of pumps, CouplingCorp was on site for the first installation to ensure a good fit and provide training for the staff that would install the remaining couplings and perform maintenance in the future.

Before the new FLEXXOR couplings could be installed, the original gear couplings had to be removed from the motor and pump shafts. In many cases, we don’t have the pleasure of watching the original hub being removed from the shaft, but in this case, we were privy to seeing an all-too-common sight in the world of heated hubs. The motor hub was not cooperating when it was heated, and it was not pulling off the shaft using a hydraulic piston. After several head-scratching sessions, more men, more torches and more hydraulic pistons were applied to the hub, the hub still would not move. In addition, the site engineers were even worried that the bearing might have to be compromised due to the enormous amounts of heat being applied to the shaft.

After several hours of hard work in the hot sun, the hub started to move with the help of several sledgehammers (joining the torches and hydraulic pistons). To make things more exciting, the leftover grease from the gear coupling came running out in a blaze of glory, giving the hub removal the feel of a bonfire!

The following video shows the excitement of the moment.


Several hours after the fire was extinguished and the hub was fully removed, the motor shaft temperature had finally dropped to a workable range. The mechanics pulled out the new Anderson Clamp Hub and received the on-site training covering how to properly install and remove the hub. Once ready, the new Anderson Clamp Hub was installed on the shaft in about 30 minutes – without the need for a bonfire!

This type of success story is common here at Coupling Corporation of America. The Anderson Clamp Hub has been in the field for over 20 years, providing customers with a simple way to connect their couplings to their shafts – whether straight, tapered, or keyed.  Before your mechanics embark on their next fiery adventure, let Coupling Corporation help you upgrade to a safer, faster coupling.