Message Board Thread - "Fly Over Steam Line Survey"

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Fly Over Steam Line Survey Ben 12/7/2005
Does ASNT (or any other industry recognized authority) have a written recommendation on how to perform an infra red study on a large steam distribution system using a fly over? Is there a standard that I can follow to quote as the normally accepted format? And if so what is it and where can I get a copy to use?
Re:Fly Over Steam Line Survey Greg at Stockton IR 12/31/2005

Here's a link to our Steam Leak FindIR product...

Also, below, an explaination that we send our clients with a report. Hope this helps you.

Greg S.

Understanding Aerial Infrared Steam System Imagery

Thermal infrared (IR) imagery is imagery that shows heat. It is often in the form of a grayscale picture whose shades of gray indicate the differences in temperature and emissivity of objects in the image. Typically, objects in the image that look lighter are warmer and those that look darker are cooler. Bright white objects are the warmest in the images. Black objects are the coolest. Any object with a temperature above absolute zero ( 0 Kelvin or –273 degrees Celsius) emits infrared radiation. An infrared picture only shows objects which emit infrared wavelengths in the 3000-5000 nanometer range. Objects in visible light wavelengths of 400 to 700 nanometers are detected, but only because they also emit heat. An example of this would be a warm street light that can be seen in the IR imagery. We record infrared imagery on digital media (hard drive) and may later copy it to a DVD-video and/or a JPEG digital image file. The image may be modified in a number of ways to enhance its value to the end user, such as creating a false-color image or adjusting the brightness and contrast of a grayscale image. The digital images are captured directly to JPEG format and placed on a CD-ROM.

Underground steam lines are almost always readily visible with infrared imaging, even when no notable problems exist. This is due to the fact that no matter how good the insulation, there is always heat loss from the lines which makes its way to the surface. Problem areas are generally quite evident, having brighter white IR signatures that exceed the norm. Steam line faults normally appear as an overheated line or as a large hotspot in the form of a bulge or balloon along the line. Overheated lines often occur when the steam line is located in a conduit or tunnel. If there is a leak in the line it will heat up the whole conduit with escaping steam. If a steam line is buried directly in the ground with an insulating jacket, a leak will usually saturate the insulation, rendering it largely ineffective and will begin to transfer heat into the ground around the leak, producing the classic bulge or balloon-like hot area straddling the line. Finally, some leaks may show up as an overheated manhole or vault cover. Manholes or vaults that contain steam system control apparatus which are leaking will often heat the covers to warmer than normal temperatures.

Steam line imagery can be a little misleading, unless one understands and interprets the relative brightness and temperature of a given line correctly. A steam line that is the same temperature from one end to the other that passes under different surfaces and materials can exhibit a variety of temperature variations. For example, five different apparent temperatures will result from the same temperature line that runs under a grass-covered field, an asphalt parking lot, a concrete loading dock, a gravel-covered area and bare earth pathway.

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