Small teams can double the amount of calibrations they carry out with multifunction, documenting equipment.
10/19/2015
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.
Image 1. A laser shaft alignment tool is the most accurate way to precision-align motors to increase machine reliability and decrease operating costs. (Images courtesy of Fluke Corporation)
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.
Collecting Data
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).
Analog Devices
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
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
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.Documentation
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.Changing Workforce
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.Image 2. A multifunction process calibrator and a portable pressure pump are critical when calibrating pump sensors.
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.
Smart Calibration
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 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.
- 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