Keith B. Lawson
The success of Luminant’s non-destructive testing (NDT) program over the past 35 years is the result of our extremely talented employees and their trailblazing initiative to make it a successful program. Through new technologies in NDT, we’ve been able to prevent major equipment failures and future damages, while producing documented cost savings for the company.
At the heart of our success is our team, consisting of five full-time predictive maintenance (PdM) specialists, each a champion in his field, highly-skilled, motivated and taking tremendous pride in his work. Each specialist holds several certifications, including ultrasonic flaw detection, flaw sizing, vibration-ISO, thermography, ultrasound, magnetic particle and liquid penetrant, just to name a few.
Our PdM specialists are assigned dedicated routes and equipment inspections. The group currently inspects nearly 100,000 points yearly across Luminant’s nine mine sites, meaning the team’s work area spans 325 miles from northeast to central Texas. Needless to say, scheduling is critical to the team’s success, ensuring that PdM specialists are as productive as possible and the appropriate equipment is available when they are on-site.
The team is responsible for 15 draglines, 10 loading stations with 45 conveyors (one is 12-miles long and another is 5-miles long) and 600 pieces of mining rolling stock and railroad components. We also use our expertise to perform quality assurance inspections on components before installation and to evaluate both new and repaired components. Ultrasonic (pulse echo) techniques in large component testing take unique individuals who can think outside the box, evaluate many variables on the component at one time, and have the necessary knowledge base of each component’s geometry and design. Team members Robbie Cross, Jackie Merket, Tony Jumper and Michael Brinkman were chosen to work on the team because of these unique abilities in NDT and ultrasonic evaluation. Their field experiences, training and certifications are invaluable for the success of the program.
Our current maintenance philosophy includes components of reliability-centered maintenance (RCM), predictive maintenance, conditionbased maintenance and root cause analysis (RCA) - each has been part of Luminant’s culture for a long time. Implementation of a reliability strategy development methodology, like RCM, across our fleet has made a difference moving forward by utilizing a condition monitoring system on our 12-mile and 5-mile conveyors. RCM has helped our teams focus their efforts on the right proactive tasks while continuing to trend positively month by month.
Our predictive maintenance includes standardized inspections and inspection routes performed by trained maintenance employees and certified PdM specialists. This approach has kept our equipment safe for our employees, while at the same time, reduces costs to maintain the equipment. We deploy new technologies whenever possible to expand our evaluation and inspection abilities. For example, we are considering the purchase of alternating current field measurement equipment for detecting and sizing surface breaking flaws or cracks in gearing and other components that standard ultrasonic testing (UT) cannot inspect. Cracks in tooth valleys can be found with magnetic particle or liquid/dye penetrant, but the specialist needs to know how deep these cracks run into the band rim. Our goal is to deploy sustainable processes and procedures in proven technologies to ensure mining company success.
Over the past 30 years, the group has developed and improved its component testing procedures by building a library with thousands of inspection procedures, processes and scan charts. There are also hundreds of test components used for calibration and training. Failures are never acceptable, but when failures happen, the group uses the situation as a learning opportunity. PdM specialists focus on what could be done differently to identify the flaw and how it can be incorporated into the inspection and evaluation program going forward. Through our best practices, we improved safety and built up our asset reliability while ensuring the equipment is available.
We have had our successes and, perhaps more importantly, our failures along the journey to a worldclass program. It has been through these experiences that we have obtained a significant amount of data to help build and/or modify procedures and processes in NDT. We approach our work with a focus on being proactive instead of reactive. This helps us prevent major failures from occurring within our organization. We also share our experiences with others in the industry to help them prevent similar failures. By sharing knowledge, we have also gained knowledge.
Catastrophic failures on draglines can make or break a mining company. This is why we select motivated individuals who have a passion for NDT and PdM work. We continually measure results from our NDT program to ensure we are getting the desired results. Every component removed from service is evaluated by our specialists or sent to a lab to determine and document its general overall condition and to formulate a metallurgical test protocol. Occasionally, an immediate evaluation is necessary due to the component’s exposure to contaminants or the environment. For this reason, a field microscope can be operated from the specialist’s laptop, enabling him to take pictures and size the failed area for later evaluation.
After the completion of a RCA of each failure or near failure, we establish a maintenance strategy and inspection procedures for identified failure modes. An example of this process can be seen in Figure 1 with a failure on a Marion 8750 series dragline main suspension line socket.
This failure was evaluated in the field with a DinoScope.
Figure 1: Beginning of the failure location verified with a field microscope.
One week later, another socket ear crack was discovered in a different location, but changes in the inspection process led to a better UT evaluation of the entire socket (see Figure 2). Maintenance and operations personnel had the opportunity to be proactive in their planning instead of reactive. Collateral damages were avoided by finding this near-failure early. Each dragline had to lower their booms to make these repairs.
Figure 2: Upper main suspension socket found crack using UT and magnetic particle testing (MT)
The NDT program for our mobile equipment fleet has also been invaluable. From our rebuilds and preventive maintenance programs, we have developed inspection processes and procedures. One of these is bore scoping the loader fleet differentials components, changing them from a time-based maintenance program to a condition-based maintenance program. Collateral damage was done to a tandem box after failure of a 14G or 16H/M final drive spindle. The challenge in this situation was to prevent a failure by inspecting the spindle with ultrasonics. The RCA data and the spindle evaluation revealed that the failure started at the bottom of the machine bolt hole and propagated outward in a torsional stress crack (see Figure 3).
Figure 3: Cracked motor grader axles found with UT and verified with MT after removal
It was also noted that the differential lock was on when turning. Working with OEM on component design and mine operation departments on operator training practices was the first step in isolating this failure. A scan chart was designed based on a new and broken spindle so a process for UT inspection could be implemented. The inspection was a success - in the first year, five cracked spindles were found and changed out before failure. Currently, 98 spindles are under UT inspection. When cracked spindles with the old design are found, they are being replaced with the new design spindles.
NDT is a large part of our overall reliability program, but condition monitoring is another tool we use with heavy and mobile equipment. Even though this technology has been a great help in preventing failures, it still requires a specialist to evaluate the data and recommend the best reliable course of action.
Over the past five years, we have expanded our ultrasound program. The program started with airborne processes on our pressurized booms and A-legs, but quickly moved into vibration and sound inspection routes. Before a condition-based monitoring system could be implemented on our longest beltline system, acoustic routes were started on all pillow block bearings. We are trending vibration, heat and the sound of the bearing while running (see Figure 4). This inspection process is currently covering 1,400 pillow block bearings. A sound library trains craft and technicians on how certain bearings sound when failing, including dry bearings, broken bearing cages, flat or damaged rollers, and damaged racing. Our experience with slow speed pillow block bearings using acoustics over standard vibration has actually been a huge success.
Figure 4: Acoustics routes on conveyor pillow block
We are also using acoustics with our infrared inspection routes for electrical components. Spot check acoustic routes on power line connections and substations can be done during the day with a more extensive infrared route at night if a problem is found (see Figure 5). Acoustics has enhanced our vibration and infrared programs, but each has its own place in reliability.
Figure 5: Cracked and leaking insulator - acoustics spot check audibly picked up the leakage in the day, infrared identified the heat at night and pinpointed the location
By mixing different NDT and reliability technologies together, we have developed many different recipes for success. One recipe that has proven itself time and again is the bringing together of a committed team and innovative tools and practices. We will continue to deploy sustainable technologies while measuring our results as well as our wins. We believe the best is yet to come on our journey towards world-class NDT and reliability.
Keith Lawson is a PdM specialist supervisor for Luminant. Luminant has nine mines located from Central Texas to Northeast Texas. Keith has 32 years of mining experience in maintenance, operations and railroad. He became a PdM specialist in 2006, and in 2007 became the PdM specialist supervisor.