Coupling Recertification Saves Plants Time and Money
Unplanned downtime can be incredibly costly when you consider lost production and the stress of having to scramble for replacement parts and staff emergency labor (oftentimes at overtime rates).
In many facilities, the most critical plant equipment likely has a robust proactive maintenance plan already in place, due to high out-of-service costs. Often, the maintenance staff keeps track of this maintenance in asset management software and thus, necessary equipment records are well kept and clear. However, the components that connect to and support critical equipment can cause unscheduled downtime if not properly maintained. The care and attention given to the critical items can be all for naught if there is a potential failure to one of these “wear items.”
For example, seals in a turbine compressor are usually replaced on a time-based maintenance schedule. Other items, such as high-performance couplings, may be designed for infinite life if they are operated within their rated capacities. Engineers and operations managers know “infinite life” is theoretical and oftentimes different than real life. Changes in operating conditions impact the theoretical life, thus altering coupling service life. These changes could result in expensive equipment failure and unplanned downtime. If the failure is severe (or worst case, catastrophic), it can damage auxiliary equipment beyond the application in which the coupling is running.
Coupling recertification can be one way to ensure the components which power equipment stay in peak operating condition.
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What is Coupling Recertification, and Why Should I Do It?
“The process of recertifying a coupling is like a 50-point inspection on a car,” explained Jeff Wiles, turbomachinery service manager for Regal. “Used couplings are returned to the factory and reconditioned to ‘like new’ condition for about half the cost of buying a replacement.”
High-performance couplings are designed for infinite life and can outlast the equipment to which they are connected when operated within their design limits. However, many facilities have increased intervals between when plants are taken offline for scheduled turnarounds. This is often to reduce the number of turnarounds and thereby maximize runtime and lower total costs. With this approach, equipment runs longer, increasing the chance for couplings to sustain the damage that can cause unplanned downtime. The last thing an operations team wants to hear is that one of their lines is down.
“Couplings are often overlooked, as they can be a less expensive part of a multimillion-dollar piece of equipment,” said Matt McGinnity, couplings business leader for Regal.
To extend the performance life of coupling and equipment, coupling recertification should be incorporated into proactive maintenance plans and scheduled turnaround times. Depending on the size and design, a typical new coupling can have a lead time of up to 16 weeks, which includes time to design the coupling, material procurement, and manufacturing. A recertification lead time can be a fraction of new coupling lead time. A typical lead time for recertification is about four weeks from the time the service provider receives the coupling to the completion of the recertification process.
The cost of a recertified coupling can be half the cost of new one, depending on its condition and the required operations to recertify. An advantage of recertified couplings is that they are returned as good as new with the original factory warranty.
Many plant operators appreciate obtaining a certified coupling for a lower price, instead of paying the full price of a new coupling — not to mention getting it in four weeks instead of 16 weeks.
Causes of Coupling Wear
In general, the factors that may contribute to coupling wear and tear include:
- Operating in high temperatures
- Operating in harsh environments
- Damage from coupling handling
- Irregular operating schedule
“The most common issue found during recertification is corrosion damage,” said Wiles. “Damaged disc packs are also very common. Fortunately, less than 10% of couplings returned to Regal for recertification are beyond repair and need replacing.”
The recertification process reverses any damage that has occurred to the coupling while in operation; this includes all the things that may not be visible with the naked eye.
Damage to the coupling may also be an early indicator of more significant problems in other equipment. For example, disc pack fretting could result from resonant torsional frequency. Cracks in the outer disc may signal that the coupling is operating under excessive misalignment. If these are found during the recertification process, this could result in modifications to the coupling design to help mitigate future risks and improve the operation of the equipment. Changes can also be made during installation to make corrections or adjustments to how the equipment is run.
To assess the extent of the wear damage and spot any potential cracks in the disc packs during recertification, the coupling is disassembled. A complete mechanical and metallurgical evaluation then takes place and is documented in the analysis report. All hardware — shims, bolts, nuts and washers — and the disc packs are replaced. A glass bead blast cleaning process is used to remove any rust or stains on the coupling. The coupling is then rebalanced for optimum performance.
Additionally, if anything is found during the inspection or plans exist to modify the equipment, the coupling can have updates or modification made to it. New parts can be fabricated and replaced within the coupling assembly to not just recertify, but upgrade.
Though recertification can support planned turnarounds, McGinnity also suggests having a spare coupling on hand. “It acts as further protection against any unplanned downtime,” he said. “With over 90% of returned couplings being candidates for recertification, even if you decide to purchase new, we always recommend that the replaced coupling be recertified for future use.”
A coupling taken out of service during unplanned downtime can affect how fast a plant is able to get back up and running. Though coupling recertification lead times are about half the lead times of buying new, recertifying couplings during planned downtime means that your coupling service provider can recertify your coupling and keep you on schedule.
Which Couplings can be Recertified?
Recertification is done for high-performance couplings, or those rotating at 1,800 rpm or higher. Couplings sent for recertification typically come from plants in the oil and gas industries, such as ethylene plants, petrochemical plants and refineries.
Since these are high-performance couplings that must be calibrated with precision, recertification is a factory-provided service. McGinnity and Wiles both warn against customers taking apart their own couplings.
“High-performance couplings are precision balanced for high-speed running. If you do it yourself, you should not expect the coupling to run as it did before,” said McGinnity.
Regal Beloit declines selling disc packs alone for certain applications to ensure couplings are not disassembled and damaged in the process.
McGinnity said those who recertify couplings know the value in it.
By incorporating coupling recertification into maintenance plans, operations with high-performance couplings can ensure peace of mind while taking a proactive approach to protect their business.
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