Red spells danger01 April 2006

For many businesses, getting started in thermal imaging has never been easier. The latest thermal imagers designed for industrial maintenance are both powerful and easy to use. Maintenance engineers can quickly learn how to use the imagers. Initial training, however, is advisable, as there are so many ways in which this technology can be put to use to predict potential problems. And, if used to their best advantage, thermal imagers will soon provide the return on investment by preventing downtime and avoiding catastrophic equipment failures.

After completing training, engineers will rapidly gain confidence, and see how and where it can best be used to advantage, enabling discussion of captured data with colleagues. This can eventually lead to the development of a full 'predictive maintenance thermal imaging plan' for the whole plant.

Written inspection procedures drive the quality of the data collected and ensure that inspections are done safely, bearing in mind the electrical, as well as mechanical, dangers that will be faced in some areas of the plant. Standard protective clothing should always be worn, where required. Key ingredients of inspection plans include safety issues and guidance for interpreting the data.

Unusually high temperatures may highlight potential problems, but will probably not determine the cause of a failing component. Inspection procedures should recognise this and identify the next stages in troubleshooting a particular problem - eg, the use of power quality tools, clamp meters and digital multimeters.

The next step in the process is to create inspection routes. Depending on the size and complexity of the plant, thermography may just become part of a larger predictive maintenance programme, possibly working from, and feeding into, a computerised maintenance management system (CMMS). This might well include data from a mix of other technologies, including analysis of vibrations, motor circuits, airborne ultrasound and lubrication, all used to monitor the condition of a plant. The CMMS may provide access to equipment lists and histories, and enable report generation and storage, and the management of work orders.

In fact, existing lists of equipment from a CMMS or other inventory system is a good starting point for determining an inspection route. Equipment whose failure would create production bottlenecks is obviously key to this, as are equipment failures that have occurred in the past.

The use of a database or spreadsheet is helpful to group the remaining equipment together, either by area or function, into inspection blocks. The first inspection cycle will take the most time, as equipment is located, the lists updated, access issues dealt with, and other key considerations. If the reporting software allows their storage, digital photos of each piece of equipment on the inspection route are a good idea, as this can help rapid and reliable identification of the correct piece of equipment each and every time.

Best cycle routes
The first few inspection cycles may yield a large number of finds. Then, after about three cycles, it is often beneficial to reorganise the routes, so that they are more efficient, and also to add new routes and equipment into the inspection cycle, as necessary. The optimum frequency of inspection will be determined by the needs of the equipment assets.

As equipment ages, is heavily loaded, or is poorly maintained, inspections may need to become more frequent. The frequency of thermal imaging inspections depends on a number of factors. The key drivers are safety, the criticality of the equipment, the expense of a failure, and the frequency with which problems impact production and/or maintenance. Plant records of past problems and failures can provide valuable guidance to inspection timings, once the equipment has gone through several cycles of inspection. The box on p24 shows some typical inspection frequencies, although these will, of course, vary from application to application.

When new equipment is installed, it can prove very useful to measure the initial thermal signature, not just as part of an acceptance process, but also to act as a future reference. Also, when repairs or modifications are made to equipment, it is very helpful if a CMMS is employed. That way, the thermographer is alerted to conduct a follow-up inspection, thus helping to ensure the repair has been carried out successfully.

Equipment awaiting repair may also need to be subject to increased monitoring to ensure that complete failure and downtime is avoided. So these visits need to be added into other weekly maintenance inspection routes.

In sizeable plants, routine inspections are conducted by more than one person, with the second person locating the exact equipment to be inspected, removing panel covers, taking load readings and watching out for the safety of the thermographer. On entering an inspection area, the engineer will take a moment to get orientated, to determine an emergency exit strategy and note any potential hazards. Many thermographers begin an electrical inspection by looking first at the panel covers while they are still closed. If any should appear abnormally warm, then the thermographers will take further safety precautions before accessing the equipment inside. Airborne ultrasound detection equipment provides a very useful supplementary signature and a level of assurance that things are safe.

When conducting a first-time baseline inspection, the standard routine is to capture thermal images of just problems or 'exceptions'. The equipment in question is viewed from several angles and any other data that might be useful is collected, including additional visual images of the component. Temperature measurements are taken of problem equipment. With the latest thermal imagers, allowances can be made for various emissivities and reflected temperature corrections. This can be effected either directly on the imager or via the accompanying software on the computer back in the office.

On later routine inspections, it may be possible to load an alarm temperature on to an image before it is uploaded into the camera. During the inspection, both that alarm setting and the previous image can be used to determine the extent of any changes that might have occurred. The new thermal image and data document the new condition. This can all be included in a report generated back in the office.

When the inspection has been completed, collected data can be downloaded to a computer in order to avoid the risk of accidental erasure. A reporting date can be fixed, findings discussed with colleagues and the date of the next inspection established.

The following suggested modifications to plant equipment are designed to make routine inspections easier, safer and more effective.
- High-emissivity 'targets' installed on such components as bus bars, tubular bus and any large metal electrical connectors near connection points can dramatically improve the reliability of radiometric temperature measurements.

- Infrared transparent 'windows' - either a crystalline material or a special plastic - installed in electrical panel covers, especially high-voltage, make it possible to inspect the components, without opening the enclosure.

- The clear plastic, 'touch-safe' covers that are increasingly prevalent inside electrical control cabinets are not transparent to infrared!

- Modification of equipment guards and covers on conveyance systems and motor couplings can enable bearings and couplings to be inspected. Also, the installation of a small, hinged door or metal mesh, instead of solid metal, can be helpful, as long as it does not compromise safety.
- Thermal mirrors - thick sheets of aluminum - can make it easier to 'see' a thermal signature.

The next step is to report the results. The software provided with the best thermal imagers supports simple, but useful, comparisons of asset condition over time. Fine-tuning of temperature measurements and adjustments to temperature level and span settings can usually be made with the software. Matching thermal and visual images is a very useful procedure, as is a second thermal image, either a comparison over time or a follow-up image. The equipment list can be updated with any changes, additions or deletions.

The report should clearly identify equipment inspected, related to the conditions found during the inspection - eg, equipment loading and environmental variables. Any emissivity and reflected background temperature corrections can also be stated. Where appropriate, the report can be tied into the CMMS system, so that findings can be tracked through their useful life.

Once the infrared data is correlated with data from other technologies, the actual operating condition of all assets will be known and can be reported in an integrated form.

Analysis of data over the long term is very important. First, trends become apparent that may not be obvious in a day-to-day analysis. Secondly, the success of the programme can be assessed. It will justify dedicating resources where problems are continuing to occur or reducing the frequency of inspection because few problems are being found. It can also help target maintenance investments and allocation of maintenance funds to get the best returns. Moreover, in addition to the imaging results, increased machine asset availability, production figures and production quality can also be recorded, alongside the distribution of maintenance expenditure over time.

Other opportunities include using thermography to look at manufacturing process applications. And facilities maintenance can use thermography, for example, for roof moisture inspections, locating building air leakage, analysing the distribution of conditioned air from HVAC, locating underground drains, pipes and lines, solving comfort-related problems in the office workspace and inspecting battery backup for computer systems.

Ken West is UK marketing manager for Fluke Industrial Test Tools www.fluke.co.uk

SOE

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