Betsy Ullrich
Sr. Health Physicist
Region I
During
construction of pipelines and fabrication of large metal structures,
welding is used to join the parts. It is very important to know the
welds are structurally sound and the whole piece will be strong enough
for its job. For example, the pipes used to transport natural gas must
be properly welded together so that the gas does not leak from the
pipes.
And
metal I-beams used in constructing a parking garage must be properly
welded so that the structure can hold the weight of the vehicles in the
garage. How can this be done? Often, workers perform “radiography” using
sealed sources to inspect the weld to see if it is correct.
What
is radiography? It is term used to describe using gamma rays or x-rays
to inspect the structure of some large dense material. Although x-ray
machines may be used for this, they are limited by their need for an
electrical source, and because x-rays can only penetrate certain
materials. A radiography device (sometimes referred to as a radiography
camera) uses sealed sources that emit gamma radiation that can penetrate
very dense materials such as metal. Radiography devices can be used
without electricity and are portable, making them handy to use at work
sites.
Because
a radiography source, while small in size, emits gamma radiation that
can penetrate several inches of metal, it must be stored in its shielded
container. When a weld needs to be inspected, a long guide tube is
connected to the device that allows the source to travel to the location
that needs to be inspected. A long drive cable also is attached to the
other end of the device. This allows the radiographer performing the
inspection to stand far away from the radiation source during the
inspection. Typically, the source is in the guide tube only a few
seconds to a few minutes, depending on what is being inspected.
Radiography
is used to inspect welds on pipes for oil rigs; large tanks that hold
gasoline; airplane engines; and other large metal structures. So the
next time you use natural gas, or park your car in a multi-story garage,
you might remember the important role a radioactive source plays in
keeping you safe.
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