How condition monitoring enhances a PdM program

Tags: condition monitoring, predictive maintenance, maintenance and reliability

 

Equipment failure can be expensive, and potentially catastrophic. Unplanned production downtime, missed contract deadlines, costly machinery replacements, as well as safety problems, environmental concerns and regulatory violations are all potential consequences of a maintenance program that fails to predict and monitor equipment problems.

 

Instituting a full-featured predictive maintenance (PdM) program using condition monitoring (also known as CM) can help minimize unwelcome surprises, yielding an impressive return on investment. Logging live equipment condition data on a regular basis through a CM routine offers plants a more scientific approach to managing equipment performance. Plants go to great lengths to understand production processes. It makes sense to apply the same rigor to understanding equipment critical to those processes.

 

Typically, plants that have developed effective PdM programs using CM discover that monitored assets rarely cause unplanned problems or downtime. This freedom from emergencies allows maintenance departments to address back-burner issues that can improve the overall condition of the operating assets even further. Smooth operation also improves the morale of maintenance technicians.

 

The initial implementation of CM usually uncovers many small, hidden, subtle problems. Resources are needed to address these issues and, at first, the existing maintenance budget may appear inadequate for the task. But once initial problem stabilization occurs, a PdM program soon starts to recoup its initial costs. As the maintenance team gains a more thorough knowledge of the condition of its productive assets, the rate at which new problems appear declines even further, and the program starts paying dividends. The initial outlay required to purchase data collection equipment and train personnel will generally more than pay for itself after one or two key machinery “saves.”

 

Enter the OEMs

Collecting data on a routine basis enables technicians to identify trends and thus anticipate imminent machine failures. With advance notice comes sufficient time for planning corrective actions.

 

Although most organizations see the need for routine CM, many do not have the in-house resources to operate a monitoring program cost-effectively and efficiently. Often, the staff members who collect and analyze the machinery information are also responsible for the day-to-day operations and spend much of their time handling emergencies. Running data collection routes to gather information for long-term trending inevitably is a lower priority than repairing a failed part that’s holding up production.

 

In some plants, there is only one person trained in vibration analysis, which clearly becomes a problem when that person retires or transfers to another position. Even when experts stay on board, it is increasingly difficult for them to stay abreast of the skills needed to accurately interpret the reams of collected data.

To address these issues, major OEMs are filling the maintenance gap, offering their end-user customers enhanced product service and operation expertise through CM programs. OEMs have developed their expertise through monitoring and evaluating their own equipment, understanding processes and competitor systems, and partnering with condition monitoring hardware and software vendors.

 

With monitoring programs, OEMs provide plant maintenance groups with crucial information about the health of their machinery – from performing vibration and temperature analysis to fully instrumenting equipment during manufacture, to oil sampling, thermography and monthly route collection using ultrasonic flow measurement.

 

All rotating equipment can benefit from routine monitoring. Decisions about how often and to what degree monitoring should occur depend largely on criticality, cost and accessibility. Critical, high-dollar, un-spared equipment would likely call for full instrumentation to allow continuous monitoring and protection. Most other plant equipment can be covered adequately with a monthly data collection monitoring program.

 

End-to-end monitoring

Flowserve Corp. is among the OEMs offering PdM and CM programs that help maintenance departments achieve their desired performance levels. With these full-featured, proactive programs, Flowserve brings its expertise inside the plant gates, focusing on pumps, compressors, fans, valves, gearboxes and other equipment critical to operational excellence. Flowserve’s CM offering – Condition Data Point Monitoring (CDPM) – and its PdM programs are part of its larger equipment management program, called LifeCycle Advantage.

 

Flowserve’s technicians start by collecting and analyzing data about equipment conditions, typically providing the plant’s maintenance department with complete, comprehensive reports within three business days of testing. The reports identify critical problems, recommend corrective actions and track the status of recommendations. The report documents include a summary report that maintenance departments can use as a basis for reducing the overall cost of asset ownership.

 

A companion Flowserve offering, Flowstar.net equipment management software, enables plant personnel to manage and update equipment data in real time via the Internet. The data available includes detailed cause of failure and maintenance recommendations for specific equipment, which can be sorted and filtered to provide further insight into ways to improve plant performance. The software also allows users to calculate equipment reliability parameters, such as suction-specific speed, and facilitates can share resources and knowledge to maximize efficiency and minimize the plant maintenance burden.

 

Applying CM

To meet a plant’s specific needs, facility managers can apply the Flowserve Condition Data Point Monitoring program in a stepwise procedure. This approach gives users access to the specific level of technology that’s appropriate for their particular purposes.

 

For example, Flowserve’s Vibration Collection and Analysis module monitors how a piece of hardware responds to external forces. With this technology, bearing problems, cavitation, recirculation, misalignment, resonance and imbalance can be identified. While Flowserve on-site technicians use handheld devices to gather vibration data from the designated equipment, off-site analysts look for vibration signatures that exceed preset alarm limits, and then make recommendations for reducing or eliminating the causes.

 

This type of vibration analysis was used to predict and prevent unexpected failure at a chemical plant in the northeastern United States, starting with a routine vibration check of the machine train of a double-suction cooling tower pump. Unusual vibration of the pump motor was discovered. The motor outboard-bearing vibration spectrum indicated a high-frequency spike at 56x running speed, as well as excessive play. At the time of the check, the internal condition of the motor was unknown, but the spectrum pointed to the possibility of loose or cracked rotor bars.

 

The results of an additional reading focused on the lower-frequency portion of the spectrum, which showed pole pass frequency side bands around the running speed harmonics. This provided further evidence of a rotor bar issue. The plant decided to switch over to the spare pump and was able to bring the equipment down in an orderly fashion. Subsequently, a teardown of the motor revealed two broken rotor bars. If the equipment had not been properly monitored and correctly analyzed, the motor could have failed catastrophically – destroying not only itself, but also potentially damaging much of the equipment surrounding it.

 

Temperature trending and analysis

With Flowserve’s Critical Temperature Trending and Analysis module, analysts can detect abnormal operating conditions at predetermined locations throughout the plant. Technicians, equipped with handheld data collectors, can track temperatures at bearings on motors and pumps, at process equipment and on mechanical seal hardware including seal flush, quench and heat exchanger reservoirs. Collected data is downloaded to the asset management software and analyzed for nonconformities or notable changes in operating conditions.

 

A new modality in the early detection of equipment failures is temperature trending of bearings and mechanical seal flush plans. This method helped save machinery at a refinery in the Midwest. An API Plan 11 seal flush plan directs flow from the pump discharge nozzle to the seal cavity through a flow-restricting orifice. The flush line temperature downstream of the orifice and the discharge temperature were routinely measured on a monthly basis. When operating normally, the temperature on both sides of the orifice should be similar, indicating regular flow.

 

After months of normal readings, there was an increase in the temperature differential across the orifice on an overhung chemical duty pump, indicating a plugged orifice. If the operation had been allowed to continue under these conditions, it would have caused seal failure and ultimately would have required teardown of the equipment. However, due to Flowserve’s CDPM program, maintenance personnel were able to clear this condition with a low-dollar work order that involved breaking the line, clearing the restriction and reassembling.

 

Compare that fix to the cost of pulling out the pump and replacing the seal and bearings. Predictive maintenance resulted in enormous savings for the operator, both in direct repair cost and equipment downtime. Knowing what to trend, together with consistent data collection monitoring, enables the detection and correction of abnormal performance.

 

Thorough inspection via trigger point monitoring

Flowserve’s Trigger Point Monitoring module identifies specific conditions that have been proven to lead to premature component failure. Flowserve technicians thoroughly examine the plant, inspecting pumps and documenting items such as critical pressures, process and seal fluid flow rates, reservoir levels and pump speed. The collected data are downloaded to the asset management software and analyzed for nonconformities or notable changes in operating conditions.

 

Another significant machinery “save” occurred at a power plant in the northwestern United States. Each year, the boiler feedwater pumps at the plant receive a comprehensive inspection by a pump performance specialist. To obtain readings on the total flow through each pump, technicians used a dual channel ultrasonic flowmeter on the suction line. They then took pressure and temperature readings, and compared equipment performance to the original test curve performance.

Results indicated that over the life of the pump, performance degraded 13 percent from the original factory performance curve. Vibration readings taken at the bearing locations showed excessive vibration both in the pump and at the inboard end of the turbine. The probable cause of this high vibration was imbalance, determined from the vibration spectrum and the time waveform. Through this analysis, the plant was able to plan for maintenance before performance degraded further, resulting in emergency shutdown and lost revenue.

 

Acting as an adjunct to the Trigger Point Monitoring Module, further insights into machinery performance can be gained through Flowserve’s Lube Oil Analysis module. Maintenance managers can utilize Flowserve’s Lube Oil Analysis module to discover abnormal lubrication and machine conditions that may exist at a plant. Lubricant samples are subjected to a battery of tests including spectroscopic analysis, wear particle counts, Fourier transform infrared spectroscopy, viscosity measurements, the Karl Fischer water test and, if the particle count is out of spec, analytical ferrography.

 

The return on investment

How can plants best measure the success of a routine condition monitoring program? One of the easiest methods is to track the average cost per work order on the rotating equipment. CM programs are designed to detect potential failures before they become catastrophic. Clearly, using predictive maintenance to prevent failure will cost less than maintaining the equipment after it has been seriously damaged or compromises safety or regulation standards. With CM, there should be fewer emergency work orders and maintenance activities can be better-planned.

 

Each machine “save” that was a direct result of the CM program can be logged by a plant reliability engineer who assigns a monetary or other value. The value is generally determined by estimating the maintenance cost (had the equipment run to catastrophic failure) and subtracting the cost of the repair. If the “save” prevented losses due to downtime or lowered production output or avoided a safety or environmental issue, those additional and significant savings must also be calculated.

 

Using industry averages to compare maintenance savings with the cost of a monitoring program, plants can expect payback in as little as one month. These quick returns can be used as supporting evidence when approaching upper management about incorporating CM and a predictive maintenance program into the budget. OEMs or industry partners can provide this type of supporting data.

 

Applying the rigor of condition monitoring in a predictive maintenance program offers a wide range of benefits, and plants employing such a program can achieve excellent long-term results. Combining CM and predictive maintenance with the use of asset management, other equipment management, and procurement applications and services can provide an extremely positive ROI.

 

For more information, contact Flowserve at 972-443-6500 or visit www.flowserve.com.