Infrared and thermal testing
Encyclopedia
Infrared
and thermal testing is one of many Nondestructive testing
techniques designated by the American Society for Nondestructive Testing
(ASNT). Infrared Thermography is the science
of measuring and mapping surface temperatures.
All objects emit electromagnetic radiation
of a wavelength
dependent on the object’s temperature. The frequency of the radiation is inversely proportional to the temperature. In infrared thermography, the radiation is detected and measured with infrared imagers (radiometers). The imagers contain an infrared detector that converts the emitting radiation into electrical signals that are displayed on a color or black & white computer display monitor.
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 °C to 150 °C (70 to 270 °F) above ambient temperatures. But, when engineers use its patented proprietary systems to locate subsurface targets such as Underground Storage Tanks (USTs), pipelines
, pipeline leaks and their plumes, and in this project, hidden tunnels, we are looking for temperature patterns typically in the range of 0.01 °C to 1 °C above or below ambient temperatures.
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.
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
An infrared thermographic scanning system measures surface temperatures only. But the surface temperatures that are measured on the surface of the ground, above a buried pipeline, are, to a great extent, dependent upon the subsurface conditions.
The subsurface configuration effects are based upon the theory that energy cannot be stopped from flowing from warmer to cooler areas, it can only be slowed down by the insulating effects of the material through which it is flowing. Various types of construction materials have different insulating abilities. In addition, differing types of pipeline defects have different insulating values.
; 2) convection
; and 3) radiation
. Good solid backfill should have the least resistance to conduction of energy and the convection gas radiation effects should be negligible. The various types of problems associated with soil erosion and poor backfill surrounding buried pipelines increase the insulating ability of the soil, by reducing the energy conduction properties, without substantially increasing the convection effects. This is because dead air spaces do not allow the formation of convection currents.
In order to have an energy flow, there must be an energy source. Since buried pipeline testing can involve large areas, the heat source has to be low cost and able to give the ground surface above the pipeline an even distribution of heat. The sun fulfills both of these requirements. The ground surface reacts, storing or transmitting the energy received.
carrying fluids at temperatures above or below the ambient ground temperatures (i.e., steam, oil, liquefied gases, or chemicals), an alternative is to use the heat sinking ability of the earth to draw heat from the pipeline under test. The crucial point to remember is that the energy must be flowing through the ground and fluids.
Ground cover must be evaluated for temperature differentials (i.e., anomalies such as high grass or surface debris), as to how it may effect the surface condition of the test area. Of the three methods of energy transfer, radiation is the method that has the most profound effect upon the ability of the surface to transfer energy. The ability of a material to radiate energy is measured by the emissivity of the material. This is defined as the ability of the material to release energy as compared to a perfect blackbody radiator. This is strictly a surface property. It normally exhibits itself in higher values for rough surfaces and lower values for smooth surfaces. For example, rough concrete may have an emissivity of 0.95 while a shiny piece of tinfoil may have an emissivity of only 0.05. In practical terms, this means that when looking at large areas of ground cover, the engineer in charge of testing must be aware of differing surface textures caused by such things as broom roughed spots, tire rubber tracks, oil spots, loose sand and dirt on the surface and the height of grassy areas.
(ISO)
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
and thermal testing is one of many Nondestructive testing
Nondestructive testing
Nondestructive testing or Non-destructive testing is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage....
techniques designated by the American Society for Nondestructive Testing
American Society for Nondestructive Testing
The American Society for Nondestructive Testing, Inc. or ASNT is a technical society for nondestructive testing professionals. ASNT evolved from The American Industrial Radium and X-Ray Society which was founded in 1941. Its headquarters is located in Columbus, OH, and there are 70 local sections...
(ASNT). Infrared Thermography is the science
Science
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...
of measuring and mapping surface temperatures.
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.
"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 bridgeBridgeA bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle...
decks, highwayHighwayA highway is any public road. In American English, the term is common and almost always designates major roads. In British English, the term designates any road open to the public. Any interconnected set of highways can be variously referred to as a "highway system", a "highway network", or a...
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."
All objects emit electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
of a wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
dependent on the object’s temperature. The frequency of the radiation is inversely proportional to the temperature. In infrared thermography, the radiation is detected and measured with infrared imagers (radiometers). The imagers contain an infrared detector that converts the emitting radiation into electrical signals that are displayed on a color or black & white computer display monitor.
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 °C to 150 °C (70 to 270 °F) above ambient temperatures. But, when engineers use its patented proprietary systems to locate subsurface targets such as Underground Storage Tanks (USTs), pipelines
Pipeline transport
Pipeline transport is the transportation of goods through a pipe. Most commonly, liquids and gases are sent, but pneumatic tubes that transport solid capsules using compressed air are also used....
, pipeline leaks and their plumes, and in this project, hidden tunnels, we are looking for temperature patterns typically in the range of 0.01 °C to 1 °C above or below ambient temperatures.
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.
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
An infrared thermographic scanning system measures surface temperatures only. But the surface temperatures that are measured on the surface of the ground, above a buried pipeline, are, to a great extent, dependent upon the subsurface conditions.
The subsurface configuration effects are based upon the theory that energy cannot be stopped from flowing from warmer to cooler areas, it can only be slowed down by the insulating effects of the material through which it is flowing. Various types of construction materials have different insulating abilities. In addition, differing types of pipeline defects have different insulating values.
Background
There are three ways of transferring energy: 1) conductionHeat conduction
In heat transfer, conduction is a mode of transfer of energy within and between bodies of matter, due to a temperature gradient. Conduction means collisional and diffusive transfer of kinetic energy of particles of ponderable matter . Conduction takes place in all forms of ponderable matter, viz....
; 2) convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
; and 3) radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
. Good solid backfill should have the least resistance to conduction of energy and the convection gas radiation effects should be negligible. The various types of problems associated with soil erosion and poor backfill surrounding buried pipelines increase the insulating ability of the soil, by reducing the energy conduction properties, without substantially increasing the convection effects. This is because dead air spaces do not allow the formation of convection currents.
In order to have an energy flow, there must be an energy source. Since buried pipeline testing can involve large areas, the heat source has to be low cost and able to give the ground surface above the pipeline an even distribution of heat. The sun fulfills both of these requirements. The ground surface reacts, storing or transmitting the energy received.
Pipeline testing
For pipelinesPipeline transport
Pipeline transport is the transportation of goods through a pipe. Most commonly, liquids and gases are sent, but pneumatic tubes that transport solid capsules using compressed air are also used....
carrying fluids at temperatures above or below the ambient ground temperatures (i.e., steam, oil, liquefied gases, or chemicals), an alternative is to use the heat sinking ability of the earth to draw heat from the pipeline under test. The crucial point to remember is that the energy must be flowing through the ground and fluids.
Ground cover must be evaluated for temperature differentials (i.e., anomalies such as high grass or surface debris), as to how it may effect the surface condition of the test area. Of the three methods of energy transfer, radiation is the method that has the most profound effect upon the ability of the surface to transfer energy. The ability of a material to radiate energy is measured by the emissivity of the material. This is defined as the ability of the material to release energy as compared to a perfect blackbody radiator. This is strictly a surface property. It normally exhibits itself in higher values for rough surfaces and lower values for smooth surfaces. For example, rough concrete may have an emissivity of 0.95 while a shiny piece of tinfoil may have an emissivity of only 0.05. In practical terms, this means that when looking at large areas of ground cover, the engineer in charge of testing must be aware of differing surface textures caused by such things as broom roughed spots, tire rubber tracks, oil spots, loose sand and dirt on the surface and the height of grassy areas.
Standards
International Organization for StandardizationInternational Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...
(ISO)
- ISO 6781, Thermal insulation - Qualitative detection of thermal irregularities in building envelopes - Infrared method
- ISO 18434-1, Condition monitoring and diagnostics of machines - Thermography - Part 1: General procedures
- ISO 18436-7, Condition monitoring and diagnostics of machines - Requirements for qualification and assessment of personnel - Part 7: Thermography