By: Reggie Fett, Motor Circuit Analyst

Synopsis

Summary of Action

Supporting Data

Conclusion

By: T.J. Garten, IR/MCA Specialist

Bean Conditioner – Horizontal Rotary Vessel

Synopsis

Fault

Summary of Action

Supporting Data

Figure 1: Pre-repair Demodulation Spectrum

Figure 2: Pre-repair Historical Data

Figure 3: Pinion Wear

Figure 4: Broken Welds on Pinion Gear Pillow Block Pedestal

Figure 5: Post-repair Demodulation Data

Conclusion

The corrective action taken during the repair of the failed trunnion bearing resulted in an altered elevation of the rotary vessel. The attempts to adjust for this were inadequate and resulted in a changed mating pattern between the pinion gear and bull gear assemblies. Over time, the increased impacting caused the pinion shaft to deflect, breaking the welds on the pedestals. This deflection also caused an angular misalignment between the pinion shaft and the gearbox output shaft. The level of misalignment may also have been affected by utilizing dial indicators for precision shaft alignment rather than the on-site laser alignment equipment. As the trunnion rollers wear, the clearance between the pinion gear and bull gear’s high spot decreases, resulting in increased shaft deflection. The increased shaft deflection results in transmitted vibration to the feed screw platform and torsional stress on the gearbox output coupling.Future corrections need to take into account all clearances and their effect on correlating components. Monitoring of adjusted components should be within days of adjustments and load changes. Installation of remote accelerometers on the pinion gear shaft pillow blocks would allow for quicker analysis of shaft misalignment, bearing condition, and pinion gear mesh frequencies.

By: Aubrey Green, Lead Analyst, Allied Reliability

Case Study Information:

While working as a Predictive Maintenance Technician in a paper mill, an analyst received a telephone call from the Pulping area. Their samples of white liquor were showing particles (turbidity). These particles were affecting the quality of pulp that was being produced. When these sand-like particles were processed in the paper machine, they produced a large mark. This mark lowered the quality of the paper. The department wanted to know if the analyst had any information on the process that could be causing the problem. They were particularly interested in pump vibration that would show the origins of the particles.

A quick look through the vibration data showed no issues that could be noted. The analyst asked for a simple piping diagram of the route of the white liquor from the clarifier to the digester. Armed with this information, the analyst decided to start at the beginning of the system and work to the end.

The system began with white liquor clarifiers started the system. Samples of liquor at the clarifier stage showed a few expected particles in the system. There was not enough turbidity to cause the problem the Pulping Department was experiencing. The analyst continued to study the diagram, looking for potential problem areas.

A holding tank was located before the digester. Between the clarifier and the tank there were only pipes and pumps, and the analyst decided to focus his attention on the tank. He knew he needed to find an accurate way to see what was in the tank. White liquor is extremely caustic, so dropping a weight into the tank would be dangerous. In addition, there were only one or two places to access the tank from the top.

Based on past experience, the analyst knew that the tank level could be determined with an Infrared (IR) camera. The temperature differential between the tank contents and the gas above the contents can be enough to show the tank level. The analyst had used this procedure many times in the past to confirm actual tank levels versus instrument readings. In this situation, he thought that if there was material in the bottom of the tank, it may have a temperature differential also.

Since the tank was not insulated, the image was not difficult to acquire. Using a thermal imager, the analyst took an image of the tank (Figure 1). The level of the tank was quickly noticeable. In addition, there was a wedge of material in the bottom of the tank, which was evident because the tank was known to have a flat bottom. This deposit was the result of years of particles from the clarifier settling in this tank. The inlet piping shown on the left of the image was actually acting as an agitator, mixing the particles with the white liquor before sending it to the digester.

Figure 1: Image of White Liquor Tank Showing Deposit

The analyst showed the image to the operator, who remarked, “Now we have an x-ray machine to see inside our tanks.” In this case, his comment was true.

An immediate resolution to the problem was needed, but the tank could not be taken out of service. The concentration of particles increased as the tank level lowered. Therefore, the tactical plan was to keep the tank level high enough to keep the concentration of particles at an acceptable level. The strategic plan was to clean the tank when it could be taken out of service.

Conclusion:

The deposits were removed from the White Liquor Tank during the next mill outage. Following that, the issues with turbidity were determined to be eliminated.

Dealing with hazardous chemicals in tanks and discovering problems within a containment may seem to be a daunting issue. Using the right technology in the right manner can give you insight to internal conditions and help you solve the problems in an efficient and effective manner.

Don’t Let the title fool you, this is a great and very short case study!  Allied Reliability SME Aubrey Green examines a dilemma at a salt evaporation plant in upper NY.  Read it for yourself here:

Radio Frequency Interference on Commtest VBx Series Data Collectors from Improperly Grounded Equipment

Allied Reliability Analyst Keith Smith shares this case study conducted on a vertically mounted belt driven grinding mill with faulty bearings.  The bearings have failed several times over a period of two (2) years. Before this time, the mill had no recorded bearing failures (as confirmed by the CMMS).   Read on to see how Keith solves this mystery two years in the making.

Grinding Mill Bearing Study

Allied Reliability Analyst Tim Greismer offers this case study on the motor of a Coal Pulverizer which was failing and creating operational problems for the coal plant.  Vibration analysis failed to isolate the problem, Tim and his team use Motor Circut Analysis to identify the root cause of the issue.  In this study he walks you through his process.  Read it for yourself here:

MCA Detects Where Vibration Analysis Could Not

As published in SMRP Solutions Magazine August 2011, GPAllied SME Darrin Wikoff addresses the Increasing Pace of Change in today’s dynamic business climate.  Read it for yourself here:

The Increasing Pace of Change

GPAllied SMEs Shon Isenhour and Brandon Weil take a fresh look at how best to manage your partnerships and build a recipe for success.  As published in SMRP Buyers guide 2011.

Read it for yourself here.

Ricky Smith SME for GPAllied examines the common roadblocks and excuses surrounding maintenance planning.  Ricky will walk you through steps that can take you from where you are to ‘World Class’.  Article as printed in the July issue of Asset Management and Maintenance Journal.  Read it for yourself here:

Maintenance Planning is Too Hard in my Workplace

GPAllied Subject Matter Experts Chris Colson and Doug Plucknette dive into how equipment reliability delivers low-cost, energy-efficient assets at plants around the world.  As published in the July edition of Uptime Magazine.  Read it for yourself here:

Clean, Green & Reliable