d. Where both sides of an insulating joint are not accessible above
ground for testing purposes.
3.2.8
Underground Pipe Joint Bonds
Underground pipe having other than welded or threaded coupling joints shall
be made electrically continuous by means of a bonding connection installed
across the joint.
3.3
ELECTRICAL ISOLATION OF STRUCTURES
**************************************************************************
NOTE: The cathodic protection system will fail
unless full engineering considerations are applied
to selection, location and installation of
electrically conductive joints and electrically
isolating joints including the use of underground
type dielectric coatings (not paint).
Adequate electrical conductivity of a pipe joint
made by means other than welding should be
determined by a "corrosion expert." The "corrosion
expert" must be accredited or certified by the
National Association of Corrosion Engineers (NACE)
as a NACE Accredited Corrosion Specialist or a NACE
certified Cathodic Protection (CP) Specialist or be
a registered professional engineer who has
certification or licensing that includes education
and experience in corrosion control. Allowable
electrical resistance depends on the cross sectional
area of the pipe metal, the resistivity of the pipe
metal, and the effectiveness of the coating on the
pipe. Effectively coated pipe underground requires
only a fraction of the electrical conductivity at
joints needed for bare pipe. Shop painted pipe is
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?
SECTION 13110A
Page 25
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