considered to be the same as bare pipe and is not to
be confused with pipe coated with an underground
type dielectric coating.
The type of electrical isolating pipe joint to be
used requires engineering design consideration. In
general, the dielectric parts of an isolating joint
will not withstand structural or environmental
stresses as well as an all-metal type of joint. If
the pipe on the cathodic protected side of the
underground electrically isolating pipe joint,
including the joint, is not effectively coated,
interference type corrosion may occur unless other
measures are taken. Factors to be considered
include:
a.
Deflection stresses
b.
Pull-out stresses
c.
Expansion-contraction due to temperature changes
d.
Is function as a union necessary?
e.
Is field assembly of critical parts practical?
f.
Hazardous locations to be avoided
g.
Accessibility if above ground
h.
Location of test box if below ground
i. Importance of coating the adjacent pipe if below
ground
j.
Vulnerability to short circuiting
Factor of safety on pull-out strength required has
to be engineered for the specific conditions
involved since no blanket provisions are fully
applicable to all cases. The requirement for
isolating flanges or couplings should be based on a
study of the conditions. If the new piping is a
short extension to an existing old piping system not
under cathodic protection, an isolating fitting
should be installed at the point of connection,
since the new piping will be anodic to the older
system. If the older system is under cathodic
protection, no isolating fitting should be used.
**************************************************************************
3.4.1
Rectifier Installation
Mounting shall be as shown. [Pole or wall mounting shall be equipped with
a channel bracket, lifting eyes, and a keyhole at the top.] [Cross-arm
brackets shall accommodate a 102 by 102 mm 4 by 4 inch cross-arm.]
SECTION 13112A
Page 32
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