Critical Spares and Recertification for Turbomachinery Couplings

Turbomachinery is Critical Equipment

In the oil and gas, petrochemical, and power generation industries, turbomachinery is considered ‘critical equipment.’ These high-performance machines generally operate at 1,000 horsepower and rotate 3,000 rpm or greater and include all rotating machines whose reliability is essential to plant operations and whose failure or shut down for maintenance results in production loss.

In most facilities, critical plant equipment has a robust maintenance plan in place, precisely because of high out-of-service costs. Maintenance staff will keep track of this maintenance using asset management software, ensuring all necessary equipment records are maintained. If not properly maintained, many of the components that connect to and support critical turbomachinery equipment, such as high-performance couplings, can cause unscheduled downtime.. All the care and attention given to critical items counts for nothing if there is a potential failure to one of these “wear items.”

Turbomachinery Couplings: The Canary in the Coal Mine

Turbomachinery couplings are generally designed for infinite life when they are operated within their rated capacities. However, engineers and operations managers realize that “infinite life” is theoretical and is often different from real life. Changes in operating conditions can impact the life of couplings, reducing their service life. These changes can result in expensive downtime or potentially equipment damage or failure. If a failure is severe or worst case, catastrophic, it can also damage equipment beyond the application in which the coupling is running.

Modern turbomachinery is a highly complex engineering system and at times there are outages, both planned and unplanned. In today’s competitive landscape, there is sometimes a tendency towards getting processes up and running as quickly as possible, and spares are not always top of mind. This is a potential blind spot which, unsurprisingly, can leave operators and end-users without critical spares when they need them most.

Because couplings may be considered a ‘minor’ part of the overall system, they are often overlooked. In reality, they are crucial components and are typically designed to be the weakest link in the train so as to prevent damage to the connected, critical equipment. Because of this, the coupling is often the first item in the train to show signs of damage or distress during an event. Damage to a 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, while cracks in the outer disc may signal that the coupling is operating under excessive misalignment. 

The coupling can therefore be thought of as the ‘canary in the coal mine.’

Causes Of Coupling Wear

There are many factors that contribute to coupling damage. These include:

• Operating outside of design parameters
• Assembly/disassembly and handling damage
• Corrosion
• Contamination
• High temperatures
• Harsh environments

The Importance Of Spare Couplings

With lead times for new couplings typically ranging from 12-16 weeks – or more for larger units – it is recommended to stock spares for all critical equipment in a facility. Not only will this avoid extended downtime after an event, it will also eliminate logistics issues, such as delays clearing customs and ongoing shipping complications as a result of pandemic restrictions. In addition, it will eliminate the temptation to use third party couplings which, while they may be more easily available, do not comply with the original Regal Rexnord design standards and specifications and should be avoided at all costs.

The Consequences Of Not Having Spare Couplings

Recently, a major Louisiana-based LNG facility experienced a coupling failure that resulted in an unplanned shutdown. This occurred because the couplings were running beyond their rated capacity. 

It then transpired that the site in question only had a small number of spare couplings, but not the full complement of different sizes for all critical machinery in the train. Crucially, it did not stock a direct drop-in replacement for the damaged coupling. The end user therefore had to reach out globally to the major equipment OEM and Regal Rexnord’s engineering team to find a workable solution.

In the end it was decided to use a similar, but not identical, coupling to get the train back up and running. “Mixing and matching” of coupling components is not recommended, however, and should never be done without consulting Regal Rexnord. Luckily for the end user, the Regal Rexnord engineering and field service teams found a workable solution within a few days to get the site operational and running at full power.

If a direct drop-in replacement had been available, it would have taken a single shift to complete the changeover with no involvement from major equipment OEMs or coupling manufacturers. Luckily in this case, fitting the alternate spare – and working on an expedited basis - only took a few days resolve. If there had been no spare couplings at all, the start-up delays could have taken up to 16 weeks.

Coupling Recertification