IR Thermography in Maintenance

Infrared thermography is a tool that has become more and more widely used for preventative maintenance on mechanical and electrical systems over time. It takes advantage of the infrared radiation properties to extract useful conclusions for the condition of the equipment under test. It is neither non-destructive, nor an interrupting procedure and has no solid substitute.

George Scroubelos

George Scroubelos

Executive VP, Dr.

ACRM A.E.

Chairman H&S

Committee HMS

gs-rms@otenet.gr

Avgoustis Tatakis

Avgoustis Tatakis

Electrical Engineer MSc.

Level 1 Certified

Thermographer

Greece

Studies prove that a planned repair job takes only a fraction of the time needed for an unplanned job, thus planned or even better preventive maintenance is a must in the leaders of all industries. Being proactive as a “firefighter” the following advantages can be gained:

  • Maintenance costs – down by 50 percent
  • Unexpected failures – reduced by 55 percent
  • Repair and overhaul time – down by 60 percent
  • Spare parts inventory – reduced by 30 percent
  • 30 percent increase in machinery mean time between failures (MTBF)
  • 30 percent increase in uptime.

Infrared vision and thermography has various implementations in a wide variety of sectors such as medical, military, process monitoring, electrical or mechanical engineering, energy evaluations, R&D etc. Infrared scanning is recommended as a regular maintenance procedure throughout all industries since no other tool can extract such solid results as quickly and without interrupting the process flow, a benefit essential for the industry regardless of the life “era” of equipment (bathtub model).

  • Initially, base line data of the equipment needs to be established; this information that could also possibly be useful at a later date in case of warranty claims.
  • In the middle, data to prevent malfunctions is needed before such malfunctions occur by periodic scans that are performed as part of a routine preventive maintenance programme, and over time, trends can be evaluated to identify potential problems. It is a great tool to elevate to predictive maintenance.
  • At the end of the life cycle, data to find the exact time line where the non-repairable or uneconomical break down happens is required.

Advantages & Disadvantages of IR Thermography

Advantages:

  • It is a non-contact type technique
  • Fast, reliable & accurate output
  • A large surface area can be scanned in a very short time
  • Presented in visual & digital form
  • Data can be stored for later image processing and analysis
  • Requires very little skill for monitoring (but not for evaluation, see disadvantages)
  • Due to the mobility of modern IR cameras they can be made available at any time and at any place
  • No production interruptions, on the other hand all equipment should work at nominal load
  • Complies with legislation or insurance requirements
  • Easily prioritize emergencies.

Disadvantages:

  • Cost of instrument is relatively high (though you must take into account the time, labour costs and early warning savings)
  • It is unable to detect the inside temperature if the test subject is separated by a non-transparent for IR radiation medium such as glass or other covers
  • Following the above it is a surface method and expertise and knowledge to evaluate the results is needed
Figure 1

Figure 1. Uneven load (15A diff.) found by IR thermography. Source: Tatakis A.

Table 1. N.E.T.A. Maintenance Testing Specifications, 1 for electrical equipment.

Table-1

Table 2. Military Standard, 2 for electrical equipment.

Table-2

Table 3. Experience-Based, 3 for electrical and/or mechanical equipment.

Table-3

Maintenance of Electrical Equipment

IR thermography is becoming the most reliable diagnostic tool in electrical equipment maintenance. Indoor and outdoor equipment such as panels, switches, relays, transformers, cables, power grids etc. can be examined easily. Temperature variations unseen by the human eye can be detected instantly before any major events:

  • Breakdown and stoppage of production
  • Serious accident on workforce
  • Short circuits and fires.

In case of loose connections, imagine the amount of connections in a plant and the time needed to regularly fasten them all, not to mention the extended time of exposure of the technician to the risk of electrocution.

Table 4. Voltage Flash Protection Boundary (NFPA 70E).

Table-4

A loose connection can dramatically influence neighbour components, raise temperature and reduce the life span of components and insulations, destroy the connector or switch due to arcs, raise power consumption and reduce voltage.

Another issue is the uneven loading of the phase’s resulting malfunctions or interference to the grid. There is no faster and easier way to detect those problems than infrared scanning of the power cables. The other alternative, using the clamp meter to measure every one, seems at least irrational.

Delta-T Criteria

There are various acceptance criteria dependant on the standard they refer to, you should always keep to at least one when evaluating your findings; the first two are the most widely recognized (Tables 1–3).

Safety Issues

As mentioned before, due to the way that infrared thermography works, some safety covers or panels must be removed to perform the test, which raises the risk to the technician by exposing him to moving or live parts. The National Fire Protection Association (NFPA) has issued several documents that make up the 70 series, including NFPA 70E, Standard for Electrical Safety Requirements for Employee Workplaces, 1995. For thermographers, conducting electrical inspections is one of the greatest changes in work habits and will relate to protection from an electrical arc flash, which can be extremely harmful or deathly even in low voltages of 400 V. Also, thermographers who could not be qualified electricians may not be aware with the level of risk being near live components. NFPA 70E specifies boundaries and recommended PPE required in an effort to reduce the extent of injuries. The boundary distances for flash protection have been established in NFPA 70E (Table 4). If you are working within the following approach distances, flash protection is required.

Another approach is the use of an Infrared Inspection Window, which is by definition a window used to separate environments of differing pressures or temperatures, while allowing energy at a specified electromagnetic wavelength (IR) to pass between the two environments.

Other IR Uses

Infrared thermography can be used not only for electrical equipment but also to detect mechanical, structural or other problems. Therefore, IR scanning is recommended as a regularly scheduled maintenance procedure for:

  • Structural or energy losses:
    • Rooftop A/C units or HVAC malfunctions,
    • Exhaust fans,
    • Steam valves or traps verification of open or close condition,
    • Find leakages of heat, water, or air (note: must have higher or lower temperature than ambient to be detected).
  • Electric Motors:
    • Create motor baseline pattern for future comparisons.
    • Examine if the motor is working within the nominal temperature range.
    • Detect bearing, coupling or connection problems.
    • Air flow / cooling problem detection.
  • Belts, Pulleys and Bearings in conveyor lines.
Figure 2a
Figure 2b

Figure 2. Blocked vs. normal radiators or HVAC units. Source Tatakis A.

Conclusion

The infrared camera is an important component to help maintain a viable and safe manufacturing operation. Infrared thermography can be a maintenance tool in many ways and there is no substitute to its accuracy, safety or reliability. This technique is helping the plant engineer to predict any potential failure, thereby planning well before it becomes urgent. This saves precious production loss and ensures equipment safety.

 »»Bibliography ››ACRM brochure volume 7a, IR thermography applications in photovoltaic systems ››Aivaliotis P., Theofrastou D., Thermography applications in electricity production plants ›› Fairfield D., Predictive Maintenance and Use of Infrared Thermography ›› FLIR, Thermal imaging guidebook for industrial applications ›› FLUK E Infrared thermography: part of an effective preventive maintenance strategy at Weyerhaeuser ›› FLUK E, The Basics Of Predictive / Preventive Maintenance White Paper: Thermography ››Garnaik S.P. Infrared Thermography: A versatile Technology for Condition Monitoring and Energy Conservation ›› Infraspection Institute, Guideline for infrared inspection of electrical and mechanical systems. ›› IRISS, 10 Things you need to know about IR windows ›› ITC, Thermography course manual ››Montgomery M, Using IR Thermography as a Predictive Maintenance Tool in an Electronics Manufacturing Facility ››Robinson M., NFPA and its Implications on Thermographic Inspections ››Tatakis A., Thermography, an integral tool of preventive maintenance, 8th maintenance forum, Athens. ››Tsoukalis F., IR Thermography as a diagnostic tool in preventive maintenance of electrical equipment

Applications | 7.10.2013

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