Regularly scheduled inspections, preventative maintenance and condition monitoring can assist in the early identification of potential problems, preventing damage to the coupling and connected equipment. There are a number of maintenance strategies that can be used to identify and prevent coupling failures and each methodology comes with pros and cons. The best strategy for an auxiliary pump will differ significantly from that of a 50,000 HP steam turbine compressor train.
Unplanned outages due to mechanical failures can cost millions of dollars of lost production time to Oil and Gas companies. While it’s difficult to quantify the cost of unplanned downtime, an outage of a single day may exceed ~$6.5M, for the average U.S. refinery. The shift from Reactive Maintenance (RM) to data driven Proactive Maintenance (PAM) strategies can not only reduce lost revenue from unplanned outages but reduce the overall costs associated with operating and maintaining plant equipment by 60%.
The Modified Goodman Diagram or similar fatigue diagram, is used to determine if the coupling can achieve infinite life when selecting a coupling for an application. The theoretical constant (torque, centrifugal, and axial misalignment) and alternating (angular misalignment and torsional oscillations) stresses, are quantified and plotted against each other. If the coupling is operated below the safe working stress line after the required Factor of Safety has been applied, the coupling can theoretically achieve infinite life.
While still used in many applications, the primary choice for turbo machinery applications used to be a gear coupling. With the advances in turbo machinery technology, increased power and speed led to problems meeting balance requirements and ensuring extended service life with these designs. Today, new applications will almost always use a non-lubricated disc or diaphragm coupling which is a non-wearing mechanically flexible design and offers improved dynamic stability.