Running From Failure

Lindsay Hall, Noria Corporation
Tags: oil analysis, Case Studies

How much money would be lost without the technology of oil analysis? Millions, billions? Would the term "cost-effective" even be a valuable motivator? It probably would, but likely under more negative connotations, such as lower quality products and services. The following four examples illustrate the powerful need for oil analysis in industry, and will help define the potential savings that can result from the proper use of oil analysis. With the appropriate tools and analytical instruments, it is possible to avoid failure, without it catching back up to you.

Loose Bolts
The first example involves a Cummins K200 series engine that was employed in a haul truck at an iron ore mine. The engine had been in production for 349 hours when an oil analysis was performed. Using an oil analysis spectrometer, results indicated increasing copper wear in the engine (Figure 1), which has a life expectancy of five years based on 25,000 hours.

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Figure 1. Spectrometric Wear Metal Trend for Copper

Because the engine remained in the break-in phase, diagnostic engineers recommended the replacement of the filter and oil. Based on wear particle readings, it was also recommended that the filter be cut open and visually examined for abnormalities.

Upon draining the oil, maintenance personnel noticed copper wear particles on the engine sump drain plugs. Once the engine pump was removed, it was obvious that the main oil pump drive gear-retaining bolt had come loose. After discussion, the engineers agreed that when the bolt went adrift, the gear-retaining bushing moved out of the housing, causing excessive wear on the main drive gear shaft inner bushing and thrust washers.

Maintenance and OEM personnel believed the pump drive-retaining bolt had likely come loose due to incorrect torqueing. Once the problem was solved, a new oil pump was installed and the haul truck was placed back into production. Based on a scale of 16 hours to repair the engine, the mine saved at least $8,000 in unscheduled downtime. If the failure had gone undetected, a complete overhaul or replacement may have been necessary, which would have cost up to an additional $184,000.

Cracked Hoses
The spectrometer saved the day again when it was used to analyze a Caterpillar series 3408 engine that had been in production for 7,672 hours. The engine was employed in a rubber wheel dozer at an iron ore mine. Oil analysis results indicated increasing trends in the iron, chromium, aluminum and silicon readings, as indicated in Figure 2. Diagnostic engineering suspected dust (silicon) intrusion was occurring, causing upper combustion area wear.

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Figure 2. Iron, Silicon, Chromium and Aluminum Wear Readings in the Caterpillar Series 3408 Engine

During a visual inspection of the air-intake system, the air-cleaner securing bolts were found to be loose and the first hump hose from the air cleaner cracked. Maintenance personnel replaced the cracked hose and secured new nuts and bolts on the air-cleaner. The loose securing bolts were believed to have caused the hump hose to fatigue and crack due to excessive movement.

If this failure had gone undetected, collateral damage could have required a complete replacement costing up to $111,000. Luckily, oil analysis detected a problem and the mine was able to save at least $21,200 in unscheduled downtime, based on a $530 per hour operating cost and 40 hours to inspect and repair the engine.

Increasing Iron
This next example, which also takes place at the iron ore mine, once again illustrates the usefulness of the spectrometer when performing proactive analysis. The component is a 24/36 reduction air-cooled gearbox in the primary conveyer that can be found in the mine's primary crusher. Rated at 145 kW at 1,200 rpm, the gearbox had been in production for approximately two years hauling at a maximum rate of 6,500 tons per hour. The life expectancy of the gearbox is five years based on 25,000 hours.

In addition to the spectrometer, a ferrogram maker was utilized as an analytical instrument. The oil analysis results indicated an increase in iron wear rates and wear particle inspection confirmed excessive iron particles. Therefore, maintenance was recommended to take regular vibration readings and to inspect the gearbox for all moving components to determine the cause of wear.

Upon examination, the increase in iron and fluctuations in the chromium and nickel readings indicated possible bearing and/or gear wear. Wear particle analysis also revealed an excessive amount of particles less than 10 microns in size while vibration analysis readings showed an increase in the output shaft bearing frequency. Based on this information, the condition monitoring and maintenance personnel decided to change the gearbox during the next scheduled plant shutdown.

After stripping down the gearbox, it was discovered that the self-aligning outboard bearing fitted to the output shaft was distressed. The inside and outside bearing race and the bearing rollers were damaged and in possible failure mode.

Following the correction of the problem, the savings to the mine were estimated to be at least $390,000 in unscheduled downtime based on a production rate of 6,500 tons per hour, an ore price of $6 per ton and 10 hours to change the gearbox (6,500 × 6 × 10 = 390,000). If undetected, the failure could have cost an additional $505,000 in replacement or overhaul costs.

Injector Head
The final example focuses on a series 777D water truck employing a Caterpillar HEUI series engine that has been in operation for 15,746 hours. Oil analysis results from an HSV viscometer indicated a sudden decrease in viscosity and flashpoint, while the fourier transform infrared (FTIR) spectrometer indicated simultaneous fuel dilution (Figures 3 and 4).

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Figure 3. 222 Engine Flash Point and Fuel Dilution

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Figure 4. 222 Engine Viscosity Readings

The diagnostic engineering department recommended the fuel system be pressure tested and inspected. The visual inspection revealed the injector in the No. 1 cylinder head had seized. The injector was changed and daily oil samples were analyzed to ensure the problem had been corrected. If the failure had gone undetected, it could have added up to $199,000 in replacement costs. As it was, the immediate reaction of the crew saved at least $5,830 in unscheduled downtime (based on $583 per hour operating cost and 10 hours to repair the engine).

Conclusion
Personnel at the iron ore mine have witnessed the cost savings and benefits of utilizing available oil analysis technology. Along with the oil analysis instruments used in these case studies - the Spectroil M/C oil analysis spectrometer, T2FM ferrogram maker, HSV viscometer and the Spectro FTIR spectrometer - the reaction times, appropriate diagnoses and successful corrections resulted in the absence of complete failures. The mine was able to avoid catastrophes while saving money in the process.

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