engineering

Infrared and thermal testing

Infrared and thermal testing is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Infrared and thermal testing rather than just read about it. In short: Infrared and thermal testing refer to passive thermographic inspection techniques, a class of nondestructive testing designated by the American Society for Nondestructive Testing (ASNT). Infrared thermography is the science of measuring and mapping surface temperatures. "Infrared thermography, a nondestructive, remote sensing technique, has proved to be an effective, convenient, and economical method of testing conc…

Key takeaways

Infrared and thermal testing belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Infrared and thermal testing to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Infrared and thermal testing from memory before moving on to harder problems.

Reference excerpt

Infrared and thermal testing refer to passive thermographic inspection techniques, a class of nondestructive testing designated by the American Society for Nondestructive Testing (ASNT). Infrared thermography is the science of measuring and mapping surface temperatures.

"Infrared thermography, a nondestructive, remote sensing technique, has proved to be an effective, convenient, and economical method of testing concrete. It can detect internal voids, delaminations, and cracks in concrete structures such as bridge decks, highway pavements, garage floors, parking lot pavements, and building walls. As a testing technique, some of its most important qualities are that (1) it is accurate; (2) it is repeatable; (3) it need not inconvenience the public; and (4) it is economical."

Principles There are three ways of transferring thermal energy:

conduction convection radiation All objects emit electromagnetic radiation of a wavelength dependent on the object's temperature. The wavelength of the radiation is inversely proportional to the temperature. According to thermodynamics, emitted energy will flow from warmer to cooler areas, and the rate of energy transfer will vary according to the efficiency of the heat transfer processes and the insulating effects of the material through which energy is flowing. In principle, a targeted object or feature will have different thermal properties than its surroundings; for instance, a buried metallic pipe conducts heat more readily than the surrounding soil, so if the fluid it is carrying is at a different temperature than the ambient conditions, the pipe will be visible to a thermal imaging sensor without having to perform an excavation to locate the pipe. Various types of construction materials have different insulating abilities. In addition, differing types of pipeline defects have different insulating values and/or vary in the magnitude of energy supplied. Because of the potential heterogeneities in the surrounding pipe (i.e., different types of soils), it can be difficult to distinguish targeted objects from background noise.

Sensitivity An infrared thermographic scanning system can measure and view temperature patterns based upon temperature differences as small as a few hundredths of a degree Celsius. Infrared thermographic testing may be performed during day or night, depending on environmental conditions and the desired results.

In practice

In infrared thermography, thermal radiation is detected and measured with infrared imagers, also known as thermographic cameras or radiometers. The imagers contain an infrared detector that converts the emitted radiation into electrical signals that are displayed on a color or black and white computer display monitor. After the thermal data is processed, it can be displayed on a monitor in multiple shades of gray scale or color. The colors displayed on the thermogram are arbitrarily set by the Thermographer to best illustrate the infrared data being analyzed.

Sample applications

A typical application for regularly available IR Thermographic equipment is looking for "hot spots" in electrical equipment, which illustrates high resistance areas in electrical circuits. These "hot spots" are usually measured in the range of 40 to 150 °C (104 to 302 °F) above ambient temperatures. When engineers use proprietary systems to locate subsurface targets such as underground storage tanks (USTs), pipelines, pipeline leaks and their plumes, and hidden tunnels, their locations are identified by temperature patterns typically in the range of 0.01 °C to 1 °C above or below ambient temperatures.

Roofing In this roofing investigation application, infrared thermographic data was collected during daytime hours, on both sunny and rainy days. This data collection time allowed for solar heating of the roof, and any entrapped water within the roofing system, during the daylight hours. IR data was observed until the roof had sufficiently warmed to allow detection of the entrapped wet areas because of their ability to collect and store more heat than the dry insulated areas. The wet areas would also transfer the heat at a faster rate than the dry insulated roof areas. At this point in time, the wet areas showed up as warmer roof surface temperatures than the surrounding dry background areas of the roof. During the rainy day, with minimum solar loading, any entrapped leak plumes would become evident because of their cooler temperature as compared to the dry roof areas

… excerpt ends here. Continue reading the full article.

Illustrations

Infrared and thermal testing: Inset shows false color infrared thermograph of a roof on a sunny day; the white surfaces (colored blue in the thermograph) have been coated with an elastomer to reduce solar loading and have a surface temperature of approximately 60 °F (16 °C); the gray surfaces (colored red/white in the thermogram) are a standard asphalt (bitumen) coating and have a surface temperature of approximately 160 °F (71 °C). — Inset shows false color infrared thermograph of a roof on a sunny day; the white surfaces (colored blue in the thermograph) have been coated with an elastomer to reduce solar loading and have a surface temperature of approximately 60 °F (16 °C); the gray surfaces (colored red/white in the thermogram) are a standard asphalt (bitumen) coating and have a surface temperature of approximately 160 °F (71 °C).

Worked examples

Example 1 — a first encounter with Infrared and thermal testing

Start with the simplest possible case. Write down what Infrared and thermal testing claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Infrared and thermal testing before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Infrared and thermal testing ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Infrared and thermal testing

In research: Infrared and thermal testing appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Infrared and thermal testing in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Infrared and thermal testing is common in secondary-school and first-year university syllabi. It links to neighbouring topics Infrared imaging, Nondestructive testing, so understanding it makes those chapters shorter.
In everyday life: Look for Infrared and thermal testing outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Infrared and thermal testing in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Infrared and thermal testing means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Infrared and thermal testing out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Infrared and thermal testing in simple terms?

Why does Infrared and thermal testing matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Infrared and thermal testing?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Infrared and thermal testing.