MRO Today - Is the gee whiz in the technology, or the cost?

Is the 'gee whiz' in the technology, or in the cost?
The upsides, downsides and costs of the latest predictive maintenance technologies

by Dan Anderson

The use of sound, smell, vision and touch to detect symptoms of a bad bearing or misalignment foreshadowed the development of sophisticated gadgets that now can sense problems long before they become obvious to human senses. Modern predictive maintenance equipment use the following approaches to monitor plant machinery performance. Here’s what you can expect
from them.

Vibration sensors
How they work: Vibration sensors use a transducer to measure the vibrations associated with rotating or reciprocating machinery. By comparing vibration levels against baseline readings of “normal” vibration in equipment, technicians can detect changes in vibration that indicate potential problems.

Capabilities and caveats: Sensors must be calibrated for accurate readings and operators must be properly trained to get useful readings. Readings must be taken under similar conditions. A pump used to move solutions of different specific gravities should be compared to baselines established while pumping each product under normal operating conditions.

While vibration analysis can detect changes in pump vibration, it won’t catch other telltale problems such as restricted fluid flow or electrical surges that can also greatly affect equipment health.

Cost: Simple hand-held vibration sensors vary widely in cost, ranging from bare-bones, low-end $200 units up to highest-tech $4,000 models. Portable vibration analyzers, depending on software associated with them, cost from $6,000 to $25,000.

Oil analysis
How it works: Oil analysis looks for the presence of minute amounts of certain metals and other contaminants in oil samples from engines, gearboxes and hydraulic systems. Based on these contaminants, you can get a good idea what’s wearing or leaking in a power transmission system.

Capabilities and caveats: “Oil analysis can detect very small changes in a machine’s operation, “says Chuck Hamilton, field engineer with Farmland Industries Inc., which completes oil analysis for thousands of clients in the Midwest.

“The analysis is so sensitive we can even tell if an engine has had a valve cover gasket replaced from the increased parts per million of silicone we see in the oil samples. We can spot excess wear of gears and bearings long before they fail, just by the amount of chromium or other metals in a sample.”

Sloppy sampling can give false readings, so good sampling technique is important. Equipment should be brought to operating temperature before drawing samples. Sampling devices should be clean of contamination and drain or sampling holes should be flushed with a neutral solution and wiped clean to prevent false contamination.

The history of each machine should be included with every sample. The number of hours since overhaul or repair and number of hours since last oil change can influence the amount of contaminants in a sample and the way the lab analyzes test results.

Cost: Oil samples, when conducted on a contractual basis with a laboratory, cost from $5 to $20 per sample.

Infrared thermography
How it works: Infrared thermography uses infrared-sensitive equipment to measure the amount of heat radiating from a piece of equipment. Simple point-and-shoot spot radiometers/thermometers are hand-held and can measure temperatures at specific points on gearboxes, transformers, steam traps and other heat-producing machinery.

Sophisticated infrared imaging equipment takes “pictures” of equipment in operation and produces images that show temperature differences on the surface of the equipment. Infrared imaging equipment is expensive, but allows you to compare the temperatures of various parts of equipment at one time.

Capabilities and caveats: Infrared sensing equipment can’t look “inside” equipment. It can detect excess heat from a damaged bearing if it transfers to the surface of a piece of equipment, but it may not pinpoint the bearing as the source of the heat. Heavily shielded or cooled equipment may give false, “normal” readings.

Cost: Infrared spot testers range in price from $200 to $3,000, depending on their sophistication. Infrared imaging cameras range can cost from $35,000 to $80,000.

Ultrasound sensing equipment
How it works: Ultrasound sensing equipment detects high frequency sounds associated with many machinery problems. Because high frequency signals are extremely directional, they can be used to pinpoint leaks in fluid systems as well as noise-related problems in mechanical systems, even in noisy operating environments. Operators hear signals through headsets while observing gauges that monitor the volume and location of high-frequency sources.

Capabilities and caveats: “In a laboratory, we can use ultrasound to detect a .05 inch leak in a pipe operating under only 5 psi from a distance of 50 feet,” says Alan Bandes of UE Systems Inc. “As with any of the predictive maintenance technologies, calibration is important, and the operator must be properly trained, but ultrasound systems can be very sensitive and reliable methods for detecting everything from fluid leaks and bad bearings to corona discharges in sealed electrical switchgear.”

While ultrasound testing equipment is sensitive to any condition that creates noise or sound, it can’t detect “silent” conditions such as increased resistance and heat build-up in electrical equipment. Operators must have baseline information on equipment being tested to guarantee accurate analysis of conditions.

Cost: Ultrasound sensing equipment ranges in price from $1,000 to $4,000.

This article appeared in the June/July 1998 issue of MRO Today magazine. Copyright, 1998.