Ultrasound for Slow Speed Bearing Monitoring, Part 1

October 29th, 2015

Reliability centered maintenance plays a crucial role in plant efficiency, particularly among those facilities that rely on slow speed bearings. By proactively monitoring these moving parts, an industrial plant can cut back on failures, reduce downtime, optimize work hours and become a more productive organization altogether. Ron Tangen, CMRP, demonstrated just how beneficial a strong plant maintenance plan can be and how ultrasound technology can be an integral part of that. Tangen’s June 2015 presentation at Ultrasound World XI in Clearwater Beach, Florida, featured the Dakota Gasification Company’s efforts to improve reliability.

Part 1: Program Logistics

The Dakota Gasification Company is an industrial plant that converts coal to clean synthetic fuels. Founded in 1984, the plant’s capital cost is now over $2 billion with 725 employees. DGC spends around $90 million per year in maintenance costs alone. The organization produces a number of fuels that impact various industries, such as:

  • Synthetic natural gas
  • Ammonium sulfate – agricultural fertilizer
  • Carbon dioxide – for enhanced oil recovery
  • Cresylic acid – pesticides, resin
  • Krypton and xenon – gas-lasers, lighting, windows
  • Liquid nitrogen – refrigeration
  • Phenol – plywood resin

Clearly, dozens of industrial plants rely on DGC to deliver the necessary amounts of synthetic gases. Any downtime or inefficiency within DGC would go beyond their own factory – it could influence the production of numerous other organizations.

Conveyor belts make up a massive portion of the moving parts DGC relies on in its production process. Each belt is made up of a head, snub, bend, take-up and tail – DGC’s plant contains over 400 main pulley bearings in its conveyor belts. They suffered 2-4 catastrophic failures each year, which had a ripple effect in terms of cost: There’s the bearing itself, but also manpower, production lost, collateral damage to the belt and the gearbox, along with potential fire and safety risks.

DGC realized it needed to reduce the amount of catastrophic bearing failures it suffered. To do so, it needed to upgrade its bearing maintenance plan. Initially, DGC only relied on a weekly visual inspection along with a spot infrared radiometer check. Reducing failure would require a more comprehensive plan that incorporated more technologies.

Gas manufacturing plants must used PdM to improve reliability.Gas manufacturing plants must use PdM to improve reliability.

Mitigate catastrophic failures
A plant as large as DGC must accept the operational reality that all bearings will fail – there is no getting around that. However, a plant can exercise some control over when they fail – that is, do bearings break down and malfunction early and unexpectedly, or can the maintenance technicians predict a failure and replace or repair the bearing before early failure? At the highest level, it’s a two-step process:

  1. Verify bearing reliability
  2. Monitor bearing health

To accomplish the second step, plant maintenance professionals must optimize the bearing’s life by using the correct bearing, the correct operations and the correct maintenance strategy. Then they can reduce catastrophic failure through the right predictive maintenance technologies used at the proper intervals.

“Using the P-F Curve, maintenance professionals can better plan and accommodate a bearing failure.”

Using the P-F Curve, maintenance professionals can better plan and accommodate a bearing failure. Their job begins before the point of failure – using proper lubrication practices and tools can lengthen a bearing’s operational life. But once the failure begins, it’s important that maintenance technicians recognize it early. Ultrasound can provide the earliest failure detection technique, while vibration, oil analysis and infrared can also be of use.

Bearing monitoring information
DGC began their revamped predictive maintenance program in 2010, complete with ultrasound, infrared, vibration analysis, oil analysis and several other technologies. The organization used seven different routes on 5-week intervals to inspect their 400-plus bearings. Once the new program was in place, their failures declined significantly:

  • 2011: One failure
  • 2012: No failures
  • 2013: No failures
  • 2014: Two failures
  • 2015: No failures as of June

They showed major strides, but still had room for improvement. That’s because reliability centered maintenance is about continuous improvements – there is no end goal because each year comes with new challenges that must be faced with renewed focus.

However, by continuing to gather specific data to create more detailed trend analyses, DGC expects to register steady gains. The best ultrasound programs allow for trending, sound file analysis, failure classification, documentation, test result information and user comments. Then the software will generate a summary report and a 12-month projection – valuable tools for tracking progress or demonstrating the program’s value to upper management.

In one specific case, DGC was able to analyze a sound file of a bearing and found it to be demonstrating the tell-tale signs of failure. The team removed the bearing for visual inspection and found it to be clearly worn, with significant cracks, chips and breaks. Rather than allowing the bearing to run to complete failure, disrupt production and potentially become a safety hazard, DGC’s technicians replaced it then and there and their productivity suffered no setbacks.

In Part 2 of this 2 part series, we take a closer look at the exact methods behind slow speed bearing analysis, including tools, strategies and what to look out for.

Recommended instruments:  Ultraprobe 15,000, Ultraprobe 10,000

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