DG711 and DG511 Pipe Laser User Guide 67
CHAPTER
7
Refraction 7
1Refraction is the bending of
light at the interface of two
substances caused by a difference
in the speed of light. Shooting a
laser beam through a pipe having
gas and varying temperatures can
be compared to shining a flashlight
beam into a pool of water and
seeing the light bend.
2Refraction of the laser is
preceded by what appears to be a
flaming of the laser spot at the
edges. When this occurs, it is time
to mix the air within the pipe by
some external means such as a
blower. This occurs on sunny days
when a hot pipe is placed in a cool
ditch. The pipe bottom cools first
and the warmer air in the upper
half of the pipe causes the laser
beam to refract down towards the
cooler air.
3Solvent fumes can also cause
refraction from the glue used at
joints, or on very cold days when a
cold pipe is placed in a warm
trench.
4Refraction is a small diameter
pipe problem. When small
diameter pipe is set, it is
recommended to place the hot-sun-
baked side of the pipe down in the
trench so that it will cool faster
against the earth. This helps create
temperature stability in the pipe.
5Generally, refraction of the
laser beam occurs at the last four or
five joints of the pipe. This is
because the last few sun-baked