Searching for the Hot Spot

In manufacturing, uniformity is essential. If failure occurs, hourly downtime costs can run into the millions. Hence, technicians rely on monitoring of all kinds, from fixed mount sensors to handheld thermal imagers to track thecondition of product and critical equipment.

Thermal imagers capture cmsimages created by the otherwise invisible infrared (IR) radiation emitted from objects. These cmsimages show a range of temperatures represented as color or tone variations and allow observers to pick out hot spots (or cold spots) that might signal electrical or mechanical, or process flow problems.

Temperature monitoring can detect overheating delivery system components, help solve irregularities in electrical power supplies, predict operational machinery failure, detect blockages in supply pipes, and identify product inconsistencies.

Given the number of process industries and associated equipment variations, the possibilities for thermal monitoring are endless. One approach is to monitor critical assets the most often, followed by equipment in harsh environments. For example, the sludge, solvents and particulates found in many processes puts extra stress on motors, affecting bearings, windings and insulation, and this stress shows up as heat detectable by a thermal imager.

What can be checked
Equipment that can be inspected based on thermalcharacteristics includes the following:

• Heat processes
Paper, glass, steel and food production all require the uniform application of heat. These processes often utilize thermocouples or infrared temperature sensors for thermal control. Frequently, spot measurements are not adequate due to process variations. Line scanners provide continuous thermal profiling in these cases, while portable thermal cameras can troubleshoot problems and determine the optimumspot to install the thermocouple or infrared sensor.

• Heat processes
Paper, glass, steel and food production all require the uniform application of heat. These processes often utilize thermocouples or infrared temperature sensors for thermal control. Frequently, spot measurements are not adequate due to process variations. Line scanners provide continuous thermal profiling in these cases, while portable thermal cameras can troubleshoot problems and determine the optimumspot to install the thermocouple or infrared sensor.

• Pipes
In processes, fluids need to be delivered to the right place at the right time and in the right amounts. If a pipe is obstructed it can cause a chain reaction that throws an entire process loop out of tune, creating oscillation. This will cause motors to cycle on and off too frequently, which in turn causes more frequent current surges that stress the electrical system and add harmonics that lower system efficiency and ultimately lead to equipment failure. Thermography can often pinpoint an obstruction, allowing correctiveaction before the whole loop goes down.

• Valves
Process control valves are also critical to delivering fluids to processes at the right time. A thermal imager can monitor for leakage, stiction (sticking) or excess friction. Also, a valve’s excitation coil may overheat from working too hard, pointing to a problem such as current leakage or valve size mismatch. When thermography indicates a problem, technicians can follow up by calibrating the valve or the valve’spositioner.

• Power distribution systems
With consistent, high quality power being essential for process manufacturing, thermal imagery can identify bad electrical connections, imbalances, overloads, harmonics, and other impending electrical equipment failures and prevent both uneven or inadequate power supply as wellas downtime.

• Motors, fans, pumps, conveyors
Thermal inspections of bearings, shafts, casings, belts, gearboxes and other components that emit heat before failure can prevent unexpected equipment breakdowns on moving equipment.

What to look for?

In specific processes, use thermal imaging to look at product uniformity. For example, a paper production process involves running the paper running through an oven to cure it. The coatings applied often require a combination of time and temperature to achieve the right cure point and finalmoisture level.

A handheld thermal imager can be used to examine the thermal uniformity of the product as it comes out of the oven. Thermal variations are often attributable to other process variables such as non-uniformity inmoisture or cure.

In general, use thermal imaging to look for hotspots, cool spots and other anomalies. Some suggestions about critical equipment to monitor and what thermography might detect:
• Motors – hot bearings and windings
• Motor control centers and switchgear– imbalance, overloads
• Steam systems – failed traps,obstructed piping
• Cooling systems – fouled cooling towers,blocked heat exchangers
• Furnaces and boilers – damagedrefractory, leaking ports
• Pumps – hot bearings, leaking seals
• Process piping – ineffective insulation,reduced flow
• Tanks and vessels – product or sludgelevels, leaks
• Conveyors – hot bearings and drives

Keeping track
Although the imminent failure of any piece of critical equipment constitutes a red alert, equipment conditions that pose a safety risk should take the highest repair priority. The same key operations, maintenance and safety personnel who determine which production assets are critical should play important roles in quantifying “warning” and “alarm” levels for those assets. Alarm levels for specific equipment can be set onFluke handheld thermal imagers.

Each time a piece of equipment is inspected, saving a thermal image of it on computer enables tracking of its condition over time. Having a baseline data for comparisons will help determine whether a hotspot (or cool spot) is unusual or increasing over time and to verify when repairs are successful.

Whenever a thermal image detects a problem, the associated software can be used to document findings in a report that includes a digital photograph as well as a thermal image of the equipment. It’s the best way to communicate the problems you found and to suggest repairs. In general, if a catastrophic failure appears imminent, the equipment must be either removed from service or, if possible, repaired while operating.

In action

Until recently, the Jayhawk plant at the BP natural gas operation in Kansas had been using a contractor from six and a half hours away to conduct annual thermal imaging surveys of its key electrical equipment. This arrangement was problematic. When plant personnel needed a problem assessed, six and a half hours was too long to wait for a thermographer, especially in downtimesituations.

With newer thermal imagers on to the market being affordable, easier to use, but still powerful enough for facility maintenance, the plant’s main electrical contractor, Alltech, purchased a Fluke Ti30 Thermal Imager and began inspecting switchgear, junction boxes and other high voltage systems, conducting regular inspections of field equipment, and has found uses for the imager in vessel, pipe and valve inspections, and plans to use thermography to inspect low temperature cryogenic processes, as well.

The in-house move made sense. The thermography only contractors hadn’t been authorized to remove panel doors or make other electrical adjustments necessary to get clear thermal cmsimages. That meant the facility’s electricians had to be involved. As licensed electricians, Alltech now does all of that. They are also able to interpret the electrical significance of the thermal cmsimages, and in some cases, proceed immediately to repairs and then verify their success with additional thermal cmsimages.

Among other things, Alltech electricians use the imager to look for loose connections, because that’s where major problems such as meltdowns often occur. “We can find wire lugs that are loose but overheating only slightly. That means that we can detect potential problems long before they become serious problems,” says Barry Ungles, Alltech’s operation manager. “In some cases, we can tighten lugs on the spot if it’ssafe to do that.”

The right level

Then there is the sludge catcher, the big vessel that collects waste from the naturalgas. “At one point,” says Ungles, “plant personnel weren’t sure their level indicatorswere working correctly, which meant theyweren’t sure how much sludge was in thevessel.

“I made thermal cmsimages of this unit at the end of a hot day when the vessel had begun to cool. The image revealed the line between the heated sludge and the unrefined natural gas above it in the vessel, which cooled faster. Thermography proved to be a failsafe backup to the level indicators.”

A vessel entry to determine the sludge depth would have required a major plant shutdown and an extremely dangerous vessel entry. “With thermal imaging,” says Len Fisk, “we were able to determine this depth for a fraction of the cost of conventionalmethods.”

The imager also saved a $100,000 project at risk due to faulty pump seals, when the vendor engineers could not solve the problem. Thermal imaging revealed that the seal failure stemmed from overheating caused by insufficient flow and cooling – not from a faulty unit. If the pump seal had simply been replaced and the real problem left uncorrected, the failure would have leadto a spill.

In the gas fields, the Alltech electricians use the imager to monitor mechanical devices. Thermal cmsimages can detect alignment problems in rotating equipment– for example, between a motor and acompressor. With a thermal image, they canquickly discover when a bearing is heatingup because of misalignment.

High, medium, low

The software included with the imager helps set up inspection routes for the regularly scheduled inspections at the plant and in the field, and to adjust measurement parameters such as emissivity, RTC, temperature level, and gain for particular locations and piecesof equipment.

At Jayhawk, Ungles used the same software to report his inspection results.“It uploads all of the cmsimages I’ve takenand allows me to add side-by-side digitalphotographs, so that the technicians cantranslate the hot spots on thermal cmsimages tolocations on the digital photos.

“I add notes and analysis to each image and rate the inspected equipment, designating which should get attention first. For example, if a wire is rated for a maximum temperature of 150 °F and my scan shows that wire fastened into a terminal lug that is more than 200 °F, then I know I am looking at a meltdown fairly soon.

“In general, says Ungles “I use “high,”“medium” and “low” designations for scanned equipment with problems. “Low” means it can be addressed sometime.“Medium” means it needs to be to taken care of relatively quickly. “High” signifies do something right away. Each year, I put together a book of my findings, and the facility keeps that book on hand to guide its predictive maintenance activities.”

In additional to thermal imaging, the BP plant in Ulysses also uses oil sampling analysis and vibration analysis on its compressors, VOC packing leak detection on valves and pumps, hi-pot insulation resistance testing, and regular switchgear cleaning and electrical maintenance.

Based on information from Fluke Corporation
(www.fluke.com)