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1:04 am
May 2, 1999
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Infrared Thermography for PPM

With increasing demand to cut costs and remain competitive, many companies are expanding their maintenance programs to include predictive and proactive technologies such as infrared thermography

Recent years have seen an increase in the acceptance and use of infrared thermography for preventive and predictive maintenance. While early applications were confined primarily to electrical and structural situations, today’s industrial environment has found new and diverse applications for thermal imaging and noncontact temperature measurement.

The introduction of focal plane array (FPA) imagers during the early 1990s revolutionized infrared imaging by providing high-resolution imaging systems while greatly reducing size and weight. Thermal imaging systems have evolved from cumbersome systems often weighing more than 20 kg (44 lbs.) to systems resembling a video camera that fit in the palm of the user’s hand.

These high-resolution infrared imaging systems allow thermography to be applied to more applications than ever before, such as with mechanical systems, intricate process equipment, and printed circuit boards. Infrared thermography can detect unseen problems such as loose or deteriorated electrical connections. Timely repair of these incipient failures can provide tremendous cost savings by avoiding unscheduled downtime.

Infrared thermography also can provide substantial savings by helping to detect problems in products or processes. Permanent improvements in such systems often offer the greatest cost benefit because the repairs are permanent and savings are realized every day that the process operates. Even greater savings are realized when the process or product output is increased.

infrared-2

Infrared thermography can be used in a wide range of applications. Thermograms show (1) a deteriorated connection within an air switch jaw, (2) wet insulation within a flat roofing system, (3) a hot spot on a steel ladle caused by deteriorated refractory, and (4) the heat pattern caused by an improperly aligned motor.

Theory
The theory of thermal imaging is simple. All objects above absolute zero (0 Kelvin) emit infrared radiation. While infrared energy is invisible to the human eye, infrared imagers detect and convert these invisible wavelengths into visible light images that are displayed on a screen. Images can be either monochrome or multicolored where the shades of gray or color represent temperature patterns across the surface of the object. These thermal images can be viewed in real time or stored on videotape, computer disk, or PC card. Thermal images then can be recorded onto photographic film or paper; the images are called thermographs or thermograms.

Thermal imaging is both noncontact and nondestructive. Since it is noncontact, it is useful for inspecting energized electrical systems as well as mechanical systems and rotating equipment. Since the infrared energy emitted from a surface is proportional to its temperature, imaging radiometers are capable of providing surface temperatures as well as images.

Equipment technology
Early sensor technology typically used a mechanical scanning system to focus infrared energy onto a single element detector. As a result, displayed thermal images often had poor resolution. Visible light photographs were often required in order to help identify the object of interest in a thermogram.

Early infrared sensors also required liquid nitrogen or compressed gas in order to cool the sensor. The introduction of Stirling cycle and thermoelectric coolers in the 1980s eliminated the need for user-installed cryogenic fluids and gases.

Many infrared imagers now use FPA detectors. These multi-element, solid-state detectors are arrayed together to provide a high-resolution image and eliminate the need for a mechanical scanning system within the optical path.

Detector size is often expressed in terms of the number of horizontal and vertical elements. Typically, FPA detectors have more than 70,000 elements or pixels. As a result of the large number of pixels, thermograms taken with an FPA imager often do not require a corresponding visible light control photograph to help identify the object.

There are currently two types of FPA imagers being offered: cooled and uncooled. Cooled FPAs have been commercially available since the early 1990s. These systems operate in the 3-5 micron range and generally provide excellent sensitivity.

The newest FPA imaging systems use uncooled detectors. Unlike previous infrared systems that sensed photons, these systems operate by sensing changes in electrical resistance across the detector. The microbolometers produce high-resolution images but do not require cryogenic cooling systems. Currently all microbolometers operate in the 8-12 micron range. The increased resolution found on FPA and microbolometer systems enables users to discern minute temperature variations and provides highly accurate temperature readings.

Originally designed for military and aerospace applications, early microbolometers did not provide temperature measurement. Since 1998, many manufacturers have begun to offer microbolometers that can measure temperature. Although they represent the newest detector technology, it is expected that microbolometers will gain in popularity within the next few years.

General Recommended Spectral Responses For Preventive Maintenance Applications

Application
Indoor electrical systems
Outdoor electrical systems
High-temperature targets
Highly reflective targets
Boiler/heater tubes – gas fired
Boiler/heater tubes – coal fired
Long-distance imaging
Smooth-surfaced roofs
Gravel-surfaced roofs
Glass
Plastics
2×5 microns
X

X
X
X

X
X
X

8×14 microns
X
X

 

X
X

X

Traditional, new applications
Infrared thermography can be applied anywhere the knowledge of heat patterns and associated temperatures will provide meaningful data about a process, system, or structure. Infrared thermography is useful for condition assessment, forensic investigations, and quality assurance inspections.

Using infrared thermography to detect incipient failures within electrical systems is well documented. Over the past 20 years, the inspection and subsequent repairs of electrical distribution systems have saved companies millions of dollars in avoided downtime.

Infrared thermography continues to be used successfully to inspect building envelopes and flat roofs, boilers and steam systems, underground piping systems, refractory systems, and rotating and process equipment. Results and opinions regarding thermography’s effectiveness for rotating equipment inspections have been mixed. However, recent research has found that infrared thermography can be used to accurately detect problems in belted and mechanically coupled rotating equipment.

In 1997, a cross-technologies study was conducted at Eli Lilly in Indianapolis, IN. The study results found that infrared thermography detected misalignment, over/under lubrication of bearings, and improper tension in belted systems more readily than vibration analysis. The study also found that temperature readings taken on the drive-end bell housing within 1 in. of the drive shaft closely approximate the internal winding and bearing temperatures.

For optimum results, a baseline inspection must be made upon installation or retrofit of mechanical equipment. Equipment then must be inspected periodically and results trended. Further investigation or corrective action can be undertaken when an alarm limit is reached.

From the results of the cross-technologies study, predictive maintenance procedures at Eli Lilly were modified to increase infrared thermographic inspections of rotating equipment. This change has allowed more equipment to be inspected while reducing the unit cost for each item inspected and increasing the overall effectiveness of the maintenance program.

Equipment selection
Thermal imaging systems vary greatly in their performance and capabilities. The spectral response of a system is dependent upon the type of detector and lens materials used in the construction of the system. While it is possible to buy filters and accessories, some imagers may not be suited for certain applications due to their spectral response.

Spectral response for commercial imagers generally falls into two categories: 2-5 microns (near infrared) and 8-14 microns (far infrared). Commercial infrared imagers and radiometers are not manufactured in the 5-8 micron range due to atmospheric absorption of infrared energy at these wavelengths. The accompanying table shows recommended spectral responses for general PM applications.

It is important to note that there is currently no single imager that will perform every type of infrared inspection. The selection of the imaging system is dependent upon the object being inspected. For some applications such as plastics, it may be necessary to consult with the manufacturer to determine if a particular system can achieve the desired results.

Training
Infrared imaging systems have become more sophisticated; however, they are often easier to use than older systems. Because of this, many people mistakenly believe that infrared thermography can be performed with little or no training. While infrared thermography is a science, it is also an art.

Since the greatest limiting factor in an infrared inspection is often the thermographer, proper training is critical to success. This includes knowledge of infrared theory, heat transfer principles, weather influences, and radiometer operation and limitations as well as a thorough understanding of the system being inspected.

Because of the many variables involved in procuring an accurate radiometric reading, the thermographer will have to address all variables that affect the object being inspected. Some of these variables include target emissivity, background radiation, target size, weather and atmospheric influences, spectral response of the imaging system, and specialty filters. While advances in technology continue to improve the performance and capabilities of thermal imaging systems, proper use of infrared imaging equipment requires formal training.

In-house or contract service
Whether starting or expanding an infrared predictive maintenance program, a company must decide whether to use in-house personnel or outside consultants. If frequent infrared inspections are planned and corporate management is committed to investing in proper equipment and training of personnel, using on-site employees may be appropriate.

If infrequent inspections are planned or the company cannot afford the initial investments in equipment and training, an outside consultant may be a better choice. While arguments can be made for either arrangement, properly trained and equipped personnel can help to increase the effectiveness of a PM program and a company’s bottom line. MT


Craig K. Kelch and R. James Seffrin are president and staff engineer, respectively, with the Infraspection Institute, 3240 Shelburne Rd., Suite C, Shelburne, VT 05482; (802) 985-2500; Internet www.infraspection.com Continue Reading →

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12:56 am
May 2, 1999
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Portable Infrared Imaging

An overview of cameras, the industry, technological improvements, where to use them, and suppliers.

infraredThe use of infrared thermography to evaluate the operating condition of electrical, mechanical, and process equipment for early warning signs of impending failure has increased dramatically over the past few years. The industry is forecast to continue growing at unprecedented rates, driven by:

  • Market awareness and acceptance. More information and articles are being published on this technology than every before.
  • Application diversity. Infrared thermography is used to inspect electrical and mechanical equipment, detect leaks in underground pipes, and check for subsurface metal corrosion, insulation deficiencies, building energy loss, and roof moisture intrusion. It also is used for monitoring and control of a wide range of processes. New applications are being developed continually.
  • Equipment. The equipment is compact, easy to use, provides high-quality imagery and fast analysis, and uses software that allows reports to be written easily. Prices continue to drop.
  • Standards. Standards for thermography are beginning to be developed (ASNT, ASTM, ISO), which means that it is gaining recognition and credibility. For example, in Canada, the United States, and Norway, most companies are requesting that thermographers have a Level I status to perform infrared thermography inspections.
  • Training. Training, educational programs, and seminars are now available at locations throughout the world.

The industry
Market evaluation companies such as Frost & Sullivan, Maxtech International, and Thomas Marketing Information Centre have prepared market studies and surveys that look at infrared thermography. The results are similar and show that infrared thermography is an emerging technology that is coming into its own. According to strategic research conducted by Frost & Sullivan, the total market is projected to experience a compound annual growth rate of 31 percent from 1996 to 2003.

Infrared equipment manufacturers are very aware of this growth potential and are positioning themselves to achieve greater market share. Raytheon purchased Texas Instrument IR Technology Divisions, Amber Infrared, and Santa Barbara Research Center. Last year FLIR Systems Inc. acquired Agema Infrared Systems. Most recently, FSI announced the purchase of Inframetrics, Inc., a privately owned infrared imaging company based in Billerica, MA.

Technology advances
Infrared camera technology has advanced significantly since the early 1960s when the Swedish company AGA introduced the first commercially available infrared imaging instrument. Early instruments were heavy and bulky, required liquid nitrogen to operate, provided black and white fuzzy images, and offered only relative temperature measurement that required the use of long and complex formulae. Infrared imagers fall into three categories. Electromechanically Scanned instruments collect and direct the incoming infrared radiation onto a single detector element, or linear array, by means of rotating or oscillating prisms or mirrors. The Pyroelectric Videcon imager uses a pyroelectric surface detector, which after being aimed at the target, develops a charge distribution that is proportional to the target’s radiant energy. The infrared focal plane array (FPA) camera makes use of a high-density mosaic of small detector elements, which are aimed at the target. Each element sees a single infrared pixel of the target, and no mechanically scanned optics are required. The size of the array ranges from a matrix of 128 horizontal elements x 128 vertical elements to one that contains 512 x 512 elements. These instruments are classified as staring systems in contrast to opto-mechanical scanning infrared devices.

The greatest single benefit of an FPA is its ability to generate high-quality images. In mechanically scanned single-element detectors, 14,000 to 26,000 picture elements make up the field of view. An FPA covering the same field of view will comprise 65,000 to 262,000 pixels. This means the FPA will have 3-10 times more image detail. An image with higher resolution allows problems to be identified without the camera operator having to change lenses, enhances analysis procedures, and provides an image that is easier to read and understand.

The FPA detector may be a significant breakthrough in technology but without advancements in the optics, electronics, and microprocessor technologies it would not have been possible to develop these cameras. The interaction between these components determines the diversity and quality of the instruments available today.

Clearly, uncooled infrared FPAs represent a revolution in infrared instrumentation. It is expected that the technology will continue to develop, particularly in the area of improved detector performance and reduced noise equivalent temperature difference and electronics.

As costs continue to decrease and production volumes rise, the price of solid state uncooled, lightweight systems should drop significantly. Expect to see larger arrays (640 x 480) and smaller, lightweight instruments using less power.

There is a movement now into a new semiconductor-based FPA detector technology, Quantum Well Infrared Photodetector. The interest in this technology is that it promises major advances for infrared focal plane arrays. It:

  • Provides excellent pixel uniformity, imaging, and sensitivity performance.
  • Offers large pixel format capability, up to 640 x 480.
  • Is tunable and can be made responsive from about 3 to 25 microns, for broad band and dual band applications.
  • Can be produced at relatively low cost and in large quantities.

The simplicity, flexibility, high performance, and low cost will guarantee the development of this technology.

Camera EvaluationOnce the plant’s requirements are understood, a plan established, applications identified, and a training course completed, then consider purchasing equipment. Do not purchase a camera and then try to work out what to do with it. That approach has caused many programs to fail. These points should be considered when choosing an instrument:

  • Portability
  • Rugged, compact design
  • Weight
  • Temperature range (both measurement and operating range)
  • Image resolution
  • Accurate, repeatable temperature measurements, under your specific conditions
  • Lenses (Will you require additional lenses for close-up or long-distance inspections?)
  • Viewer (Is the eyepiece adequate or is a viewer required for certain applications?)
  • Image storage and retrieval capabilities
  • Camera and peripheral accessories
  • Image analysis and report software (simple to use, exportable to other programs, etc.)
  • Warranty
  • Service, service, service (Get references, find out how long it takes to have equipment repairs, will a loaner instrument be provided?)
  • Technical support (Phone their technical support line with some questions and see how efficient, knowledgeable, and friendly they are.)
  • Training
  • Price (This is the last thing to consider. Do not buy on price; you will regret it. Purchase the instrument that works for your program.)

Establishing a program
In order to profit from the benefits of infrared thermography, regardless of the technology chosen, a company must give much consideration to establishing an infrared inspection program. One that is properly initiated is guaranteed to provide users with a quick return on investment. Typically this will occur within 3 months of purchasing and using the equipment, but many companies claim receiving a payback the very first day on which they performed an infrared inspection.

The first step in setting up a successful thermography program is education. Find out about the products and technology that are available and how they can be used:

  • Go to introductory seminars and conferences.
  • Request product data sheets and application literature from equipment vendors (see the accompanying chart).
  • Browse the Internet. This is a little time consuming, but there is a wealth of information on the Web.
  • Contact specialist groups and associations. They publish newsletters regularly and sponsor conferences and meetings each year.
  • Contract an independent consultant to assist in the assessment and education process.
  • Hire an experienced infrared service company and learn from their employees while they are performing an inspection in the field.
  • Take a training course before you purchase your instrument. This will provide you with an understanding of the infrared industry and technology, equipment, and application knowledge, and allow you to gain valuable experience from the instructors and other students. You will then be prepared to deal with and negotiate efficiently with the instrument sales representatives.

Selecting a camera
Although the methodology used to implement and purchase equipment, and the program requirements, vary from plant to plant or from person to person, the following observations should be helpful.

  • Select an instrument that will make inspections successful now and in the future. An infrared camera is a diverse tool. When deciding on a particular type, also take into account your future requirements.
  • Plan the implementation phase carefully. Decisions on how to collect and manage data should be made at the outset, and should focus on the desired output of the program. This planning will both simplify implementation and maximize the value of the program.
  • Provide good training for the personnel involved. Set aside sufficient time for the equipment operators to become proficient at their jobs. Strive for continual improvement and remember that each challenge that is successfully completed is followed by additional new and exciting opportunities. MT

Ron Newport is president of the Academy of Infrared Thermography, 177 Telegraph Rd., Suite 720, Bellingham, WA 98226; (360) 676-1915; e-mail airt@infraredtraining.net; Internet www.infraredtraining.net

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