Product Manual

DG711 and DG511 Pipe Laser User Guide 67
CHAPTER
7
Refraction 7
1 Refraction 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.
2 Refraction 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.
3 Solvent 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.
4 Refraction 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.
5 Generally, refraction of the
laser beam occurs at the last four or
five joints of the pipe. This is
because the last few sun-baked