As the price of raw materials fluctuates, industries must minimize costs and maximize profit margins. One way to control costs is to become leaner and more efficient. Every time companies remove waste in their processes, they save money. That includes maintenance and efficiency of pumps that move materials through a facility.
Ensuring that the operating conditions, temperatures and pressures are right for each pump application requires fine-tuning of instrumentation. Also understanding the condition of motors, bearings and couplings that drive pumps requires attention for efficient operations.
Process manufacturing plants require proper operation of hundreds or thousands of sophisticated devices to perform critical operations accurately and reliably. These include instruments, pumps, valves, pipes and tubes. These devices perform best when they undergo regular inspection, testing, calibration and repair. Calibrating measurement equipment enables optimization and can improve quality—whether in the food, chemical, power, pulp and paper, or oil industry.
Centuries of industrial experience have established the value of carefully recording the details of those inspections, tests, calibrations and repairs. Businesses and governments often require specific record keeping to ensure that full value is delivered to customers and that the health and safety of the public is protected.
However, traditional testing, calibration and documentation practices are also labor-intensive. With senior operators in scarce supply, downsized teams sometimes choose to defer regular calibration and testing. The latest industry findings suggest that smaller teams can feasibly conduct and document device calibrations at a lower overall cost than the larger teams they replaced, with additional productivity and operational reliability benefits.
Many maintenance activities were often performed in an instrument shop. But for pumps, motors, control valves and the instruments measuring process flows—because they have many related connections—testing is more cost effective when performed in-situ.
To verify proper operation of a pump system, personnel must be able to collect data about the material moving through the pump. This usually involves a field instrument that has two parts: a primary element and a transmitter.
- Primary elements include flow tubes, orifice plates, pressure sensors, wet chemistry sensors—such as pH, oxidation reduction potential (ORP) and conductivity probes—level gauges and temperature probes. Primary elements typically produce a signal—usually voltage, current or resistance—that is proportional to the variable they are designed to measure, such as level, flow, temperature, pressure or chemistry. Primary elements are connected to the input of field transmitters.
- Field transmitters include pressure, temperature, analytical and flow devices. They process the signal generated by the primary element, first characterizing it in linear format and applying engineering unit coefficients to it. Then they transmit the signal in analog (usually 4-20 milliamp [mA] direct current) or digital format (usually some variety of fieldbus).
When a field instrument is manufactured, both the primary element and the transmitter (or the actuator if it is a control valve) are calibrated at the factory. The calibration data is supplied with the unit and is often lost. Entering this information into centralized calibration records when the device is put into service should be a standard practice—and not just for efficiency's sake. Centralizing calibration information ensures that knowledge stays with the facility even as teams change.
Analog devices—often called 4 to 20 mA loop devices—transmit a signal that is an electrical analog representation of a measured physical quantity. They transmit an electric current that is proportional (analogous) to the magnitude of a measured physical quantity, with 4 mA of current representing the minimum scaled value and 20 mA representing the maximum scaled value. Although many systems that include pumps are now digital, analog devices are still in active use.
Digital devices convert a measured physical value into a digital signal. Many digital encoding methods are used in the process industry, including Foundation Fieldbus, Profibus and Highway Addressable Remote Transducer (HART). Many in the industry believe that fieldbus (digital) field devices do not require calibration. This is not true. Although a fieldbus signal—whether Foundation Fieldbus, Profibus or connected HART—provides diagnostic information, it does not provide information about the accuracy of the device. It also does not verify that the device is reporting the process accurately.
Control valves have actuators that also require calibration to adjust for wear, valve repacking for leakage remediation and the effects of sticking or "stiction." These valves must be given a full or partial stroke test if they have not been actuated regularly to ensure dependable operation.
Pumps & Vibration
Industrial rotary pumps are designed for smooth operation. In their ideal state, they would operate with almost zero vibration. The flexible couplings often used to connect pumps to motor drive shafts are prone to misalignment. Many argue that flexible couplings are able to accept some misalignment. However, the problem is that the forces are still present and can still be transferred to the seals and bearings, causing them to wear more rapidly and fail much sooner. In addition, the forces from misalignment generate vibration and heat, which can lead to premature bearing wear in both the pump and the motor. Ultimately, this can cause equipment failure. Other troublesome issues in motors include soft foot—where the motor foot is off kilter—as well as electrical issues such as harmonic distortion coming from a motor or variable frequency drive.
Best practices in motor maintenance affecting pumps include vibration testing to diagnose problems and laser shaft alignment to ensure proper operation. Additionally, power analyzers can help diagnose problems related to harmonics and other variants that can damage rotating equipment.
Permitting & Paperwork
Administrative tasks, from obtaining permits to documenting and filing results, can add to the cost and time required to perform even an in-situ calibration. In many cases getting all the necessary paperwork (permits, isolation, etc.) in order often takes longer than the work itself.
In addition to devices that impact quality, devices that are part of safety shutdown systems and those regulated by government oversight require documented records. Documenting calibration has traditionally meant writing the date and time, the pre-calibration readings, the post-calibration readings and any other observations the technicians made in a log book. Surprisingly, many plants continue to document calibration work by hand. But pencil-and-paper documentation has many shortcomings.
First, it both produces and perpetuates errors. The data in hand-written records are often illegible or insufficient. Facilities that use a computerized maintenance management system (CMMS) must then account for the additional time required to manually enter hand-written data, with additional possibilities for error.
Recording the condition of critical motors and pumps was once something that required a vibration expert with a high-end vibration analyzer, which many companies could not afford. Recent technology has introduced easy-to-use vibration testers and machine health screening tools that allow a maintenance technician to determine machine condition on their pumps without the need for an in-house expert or hiring a consultant.
Another challenge to maintaining a calibration and testing program is changes to the workforce. The 1980s brought budget cuts and layoffs. Engineering, maintenance and operations staffs were cut substantially. A new "lean manufacturing" philosophy took root that continues today.
Smaller teams have less time for mentoring and on-the-job-training. This prevents equipment- and system-specific knowledge from being successfully transferred from individuals to institutions. As older operators and engineers retire, they take their equipment and system knowledge with them. "Every day at 4 p.m., the plant's institutional knowledge walks out the front gate," says the chief instrumentation and controls engineer of a large Midwestern refinery, "and sometimes it doesn't come back."
Many facilities still need two technicians for each in-situ calibration—one at the transmitter and one at the control system. The Fieldbus Foundation estimates that commissioning requires two techs for a minimum of two hours. But calibration and documentation can be done more efficiently.
A new generation of smarter field calibration tools is increasing worker productivity by consolidating multiple tools into one unit and performing functions beyond basic test and measurement, such as assisting with analysis and documentation. Multifunction documenting process calibrators are handheld, electronic test tools that measure pressure, temperature and a wide variety of electrical and electronic signals. Benefits include:
- Fewer tools that technicians need to keep with them in the field and be trained to use
- Similar calibration processes and data output across multiple devices, compared with a different process to collect a different set of data from each tool and device
- Automated procedures that replace many manual calibration steps
- No second technician required to record the as-found and as-left state of the field device
- Faster calibration time
- Error calculation of a single tool rather than having to add the errors of several tools
- Giving maintenance staff the time needed to schedule repairs and acquire parts
- Taking faulty equipment offline before a hazardous condition occurs
- Fewer unexpected failures
- Extending the life of maintenance that reduces costly repairs
The biggest savings from using a documenting calibrator comes from the route management tool built into the device. Using a single set of permits and paperwork for an entire set of calibrations reduces costs considerably. Calibrating multiple instruments in the course of a route reduces the cost per calibration, compared with individually calibrating single instruments.
Testing rotating equipment such as pumps and motors has been proven to deliver many benefits, including:
The Cost Misalignment
One of the most ignored efficiency wasters is motor misalignment. Most maintenance personnel choose to ignore the misalignment in their machines and live with the increased need to replace bearings and seals. In addition to increased repairs, the energy wasted from misaligned machines can quickly add up and cut into the company's operating expenses. With today's laser alignment tools that are easy to use and do not require re-training every time they are used, a maintenance technician can quickly align any coupled motor pump to expand cost savings to all pumps in the plant.
Implement a CMMS
Computerized maintenance management systems (CMMS) can help a plant keep close tabs on maintenance costs. These systems often have many different modules including those that track both costs and maintenance data. Calibration data and the performance of rotating equipment are likely candidates for tracking data with CMMS.
Tracking Calibration Data
Unlike paper documentation, calibrator data is never illegible, cryptic or partial. Documenting calibrator data can be downloaded into many CMMS systems with no transcription or filing.
Because documenting process calibrators automatically record the as-found and as-left state of each field device in-situ and can be operated by a single technician, route-based practices using documenting calibrators can save as much as 50 percent of the time and cost of traditional manual, single-device calibration methods. So the same lean team can accomplish twice as many calibrations in a given period of time.
Instead of ignoring looming threats, investigate how existing practices can be made more efficient. Implement route-based calibration, paperless documentation and CMMS data management. More calibrations will occur more consistently, knowledge will be transferred from the individual to the team and institution, and both productivity and quality will increase. Besides saving maintenance costs, the savings on legal costs and lost revenue from accidents can be in the millions. In the event that disaster strikes, good calibration records can be a part of a facility's defense during legal action.
Tracking Equipment Data
Tracking baseline vibration performance data of a new pump system enables maintenance personnel checking motor and pump performance to track the ongoing health of rotating equipment against a baseline of similar machines. This enables the maintenance technician to screen machines with problems, diagnose the most common faults, correct the problem themselves and return the machine back to service as quickly as possible.