Editor-in-Chief Elisabeth Lisican showcases a handful of features to read in the April 2017 issue of Water & Wastes Digest.
With rapidly increasing customer demand and shrinking system redundancy, the Tarrant Regional Water District had to improve pumping station reliability to maintain system efficiency and prevent service outages
As the population of the Fort Worth, Texas, area grows from about 1.5 million in 2000 to about 2.25 million by 2050, the demand for water will place an increasing load on the supply system in the years to come.
The increase from 50–80% of system capacity will require almost all equipment to be online, resulting in less system redundancy available for backup in case of a mechanical failure. Compounding matters, operations and maintenance staffing has decreased by 30% over the past 10 years. Increasing power costs will create the need for improved pumping system efficiency.
Recognizing that a severe failure at one of six unmanned pumping stations (eight stations by January 2008) transporting water from four reservoirs could cause at least a partial loss of service, Tarrant Regional Water District (TRWD) has taken long-range steps to increase the system’s capacity and pumping infrastructure.
More immediate help was secured in 2001 with the installation of an integrated online pump station vibration monitoring system that automatically provides both operations and maintenance personnel with continuous performance and condition data.
“We currently monitor vibration levels on a continuous real-time basis to make sure they remain within the upper and lower control limits,” said Boyd Miller, pipeline operations manager for TRWD. “We also analyze the data monthly to make sure there is no change that might indicate the onset of a problem or a potential failure. We don’t just sit and wait on an alarm or for something to go wrong. We get a great deal of information by looking at the trend charts and analysis reports.”
Since this system was implemented, TRWD has seen an increase in overall system reliability; 20% reduction in emergency costs; lower maintenance costs; 100% increase in the accuracy of factory acceptance testing; 50% reduction in staffing requirements for remote stations; and fewer unplanned outages due to unexpected failure of critical equipment.
Factoring in all improvement costs, the district’s annual savings are in line with the original cost-justification estimates that projected a 10-year economic benefit of $306,000.
“We’re on target to achieve the 10-year savings projected in the original cost justification,” Miller said. “The savings will actually increase with the new pumping stations because many of our costs are fixed while the avoidance of repair costs will be greater. In effect, the payback period will be shorter.”
In the past, bearing failures, broken motor rotor bars, or other failures occasionally occurred across the 34-pump system, along with flow problems such as cavitation or re-circulation. To detect existing or developing threats, maintenance workers conducted daily visual inspections and monthly predictive maintenance evaluations, which were both time consuming and expensive as personnel had to travel a 150-mile circuit to reach all the stations.
Vibration analysis using portable equipment was only partially successful because of the lack of data necessary to build performance trends.
As a result, evolving pump and process problems could go undetected for long periods, resulting in unexpected failures or accelerated equipment wear and component damage. High emergency maintenance costs were all too common.
A new approach
Since 2001, the 34 pump/motor sets ranging in size from 1,000 to 5,500 hp have been equipped with CSI 4500 Machinery Health Monitor systems, which continuously monitor vibration, perform advanced processing, and calculate specific analysis parameters. Status and alarms are displayed in the pump stations via Emerson’s AMS Suite: Machinery Health Manager, which stores all trend data to be used for advanced predictive diagnostics. The multiple stations are tied to a central host via a frame relay network, and the host connects with the plant network.
“We’re building two new pump stations with 10 new 5,000 hp motor/pump units, and our online vibration monitoring system is expanding right along with it,” Miller said. “With the network already in place, it is just a matter of adding points being monitored.”
The condition of all pumping station critical equipment can be observed from the host. This workstation has full diagnostic, analytical and reporting capabilities, allowing maintenance decisions and planning to be made from that central location. Because the online monitor of the central host sits beside the SCADA host at the TRWD Control Center, SCADA operators who control the pumps can monitor the status of equipment, as well. When a potential problem appears, maintenance personnel can further evaluate and confirm alarms using the central host to perform advanced diagnostics. Maintenance supervisors can initiate work orders that feed into the utility’s computerized maintenance management system (CMMS).
If the frame relay network is interrupted, monitoring and data storage continue independently at the stations. Memory built into each monitor can actually store data while the Ethernet network is down. When the frame relay network is restored, the central host is updated and normal operation resumes.
Achieving system reliability
Online vibration monitoring now identifies equipment issues before reliability is threatened and capital expense is incurred. Progress over the last three years can be grouped into four areas:
Pumping system reliability
Since implementing the system, no unexpected pump failures have occurred. Now, both maintenance and operations personnel watch for developing problems and process changes. Problems such as misalignment, loose mounting, cracked rotor bars and irregular flow have been identified, monitored and strategically corrected. Real-time data collection and alarming provide the opportunity for real-time decision making with time to plan and act before a service interruption occurs.
In addition, the collected data is trended and analyzed to develop parameters for normal and abnormal operation. Online monitoring has given operations and maintenance personnel the ability to “diffuse the ticking time bomb.”
Process operational tuning
A number of booster stations exist between the reservoirs and the central treatment facility. Optimum system efficiency is obtained with minimal booster tank levels while providing adequate net positive suction head for the pumps. These levels are not constant because of varying reservoir levels. Operators can now use vibration as a process variable to balance the system. If a tank level falls below minimum, flow noise at the pump is noticed and quantified by the online monitoring system and presented to the operators.
“Having the online vibration monitoring capability will be a big advantage in dealing with warranty issues at these new locations,” Miller said. “We’ve already performed preliminary testing at the factory to establish operational vibration levels, and that criteria will be applied for final acceptance in the field. The manufacturer of the motor/pump units will have to meet vibration and noise requirements in addition to meeting pump performance standards. We’ll have actual documented baseline performance measurements and levels if there is any substantial change in vibration levels during the warranty period. That will be a valuable assurance during the early operation of the new pumping stations.”
In addition, the online system alerts operators to such resonance and flow problems such as cavitation and recirculation. Integrated online monitoring assists the operator in running the system cooler and smoother for greater output and longer equipment life.
Equipment acceptance testing
All rebuilt and new equipment must meet performance specifications before being put into service. Integrated online monitoring is being used to effectively identify and correct problems before component damage occurs. If problems develop during the warranty period, operational performance and trend documents can be used to verify non-conformance. TRWD personnel practicing predictive maintenance based on the online monitoring system have detected pump and/or motor defects on at least four different occasions. These problems, all of which were identified before the equipment was put into service, had to be corrected by the manufacturer.
With a smaller maintenance staff, it is important to prioritize work and eliminate unnecessary tasks. The online monitoring system provides efficient collection, analysis, and reporting of pump condition data, which automatically comes to the operator or analyst in a format appropriate to his or her skill level. This frees up resources for higher priority activities.
In addition, maintenance work can be based on actual condition rather than recommended time intervals. Prior to online monitoring, pumps and motors were rebuilt on a fixed schedule, regardless of condition. By establishing ranges for operational parameters, current and forecast mechanical condition can be calculated with greater accuracy, often allowing for maintenance to be delayed. Efficiency and mechanical condition are now carefully considered during annual planning. This has resulted in a shift from a reactive to proactive maintenance culture, which affects planning, scheduling and purchasing.
Predictive diagnostics have prevented failures and the embarrassment of having to deal with equipment failures after the warranty period has expired.
As the SCADA system is upgraded, direct integration of online alarm information to the SCADA will occur. All critical information can be accessed via one system, and vibration analysis parameters will become process control parameters.
Currently, no automated emergency shutdown exists, but certain sudden failure parameters can be detected with the online system and will be integrated into the SCADA system for controlled emergency stops.
Additionally, it is TRWD’s intention to directly link the online system to the CMMS, enabling the automatic generation of work orders. When assigned tasks are completed, equipment histories within the online monitoring system will be updated automatically.