The Massachusetts Water Resources Authority (MWRA) is a large, unionized public utility serving 2.6 million people in the Boston metropolitan area. In 2000, the MWRA embarked on a comprehensive, multi-phased asset management initiative. Its program includes dedicated staff along with a diverse senior management steering committee who organized early, communicated often, and conducted research and cross-industry benchmarking that allowed for a timely implementation of best practices, resultant efficiencies, and cost- saving benefits.
As part of this initiative, MWRA’s Deer Island water treatment plant has purchased condition monitoring equipment and providing training to more than 50 maintenance technicians over the past 2 years. The maintenance staff has been performing vibration monitoring and spectral analysis, lubricating oil sampling, acoustic ultrasonic detection, ultrasonic thickness testing, laser alignment, and infrared thermography tasks.
Ultrasonic detection recommended
Reliability centered maintenance (RCM) analysis of the plant’s primary scum pumps resulted in the recommendation of a preventive maintenance task using acoustic ultrasonic detection to monitor the motor and pump bearings to provide advance warning of potential failures.
Using an ultrasonic detector from SDT North America, Cobourg, ON, condition monitoring engineer Dan Parry found unacceptable noises and noise levels in 10 of 14 primary scum pumps, indicating potential bearing problems. The next step maintenance planner Michael Costa took, however, was to collect lubricating oil samples from six of the pumps’ gearboxes and send them off to National Tribology Services, Peabody, MA, for testing.
Results showed viscosities that were much too high, indicating that the wrong lubricating oil had been used. Oil in all the pumps was changed to the correct oil and ultrasonic monitoring was repeated.
This time, only two pumps were found with unacceptable noise levels. Costa scheduled an alignment check before considering replacement of the bearings.
Bad coupling found
While checking one machine with laser alignment equipment from Ludeca, Miami, FL, mechanics Bob Greatorex and Peter McGee immediately saw that the coupling was in bad shape and noted that the machine was badly out of alignment. A new coupling was installed and the machine was laser aligned. Repeated ultrasonic detection confirmed that the problems had been solved. No further maintenance was required.
Preventive maintenance expenditures of about $280 for ultrasound testing, oil sampling, coupling replacement, and alignment resulted in cost savings that can be estimated in two ways:
1. If one machine had been allowed to run to failure, it would have cost about $5600 in parts and labor to completely rebuild it.
2. If more intrusive maintenance (replacement of bearings) had been performed after the first round of ultrasonic monitoring, the total maintenance cost for one machine would have been about $3400.
Avoided costs for this maintenance event range from $5320 for scenario 1 to $3120 for scenario 2 for each machine. When applied to all 14 primary scum pumps, expending $3920 for preventive maintenance provided cost savings of $43,680 to $74,480, while increasing equipment availability and reliability. s
Nancy Ettele is program manager, condition monitoring, at MWRA’s Deer Island Treatment Plant, 190 Tafts Ave., Winthrop, MA 02152; (617) 660-7725