Nace CP 1, Course Manual

Page: 423 / 535

RP0193-2001
16 NACE International
Figure 11: Perforated Pipe Installed for Reference Electrode
NOTE: Special consideration must be given during
the design and installation of access pipes to assure
that any tank-containment system is not breached.
CAUTION: Extreme caution must be exercised
when boring or water jetting under tanks.
9.4.2.1 A constant distance should be
maintained from the tank bottom to the reference
electrode.
Increasing space between tank
bottom and reference electrode increases the
voltage drop.
9.5 Test Stations and Junction Boxes
9.5.1 Test stations or junction boxes for potential and
current measurements should be provided at sufficient
locations to facilitate cathodic protection testing.
9.5.2 The test station or junction box should be
mounted on or near the side of the tank in an area that
is protected from vehicular traffic.
9.5.3 The test station or junction box should allow for
disconnection of the anodes to facilitate current
measurements and potential measurements for voltage
drop as required to evaluate the protection level.
If
desired, test leads from buried reference electrodes
can be terminated in the same test station as tank
bottom test wires.
9.5.4 Junction boxes can be used to connect
continuity bonds or protective devices.
9.5.5 The test station or junction box in a galvanic
system may be equipped with calibrated resistors
(shunts) in connections between the anodes and the
tank to measure the anode current output and thus the
estimated anode life.
Shunts are typically rated
between 0.001 and 0.1 ohm.
9.5.6 The test station or junction box should be clearly
marked and accessible for future monitoring of the tank
bottom and, if possible, should be attached to the tank.
9.5.7 All lead wires to the test station or junction box
should be protected from damage by a minimum 46-
cm (18-in.) burial and/or placement within a conduit.
Warning tape may be installed over direct-buried
cables to prevent the possibility of damage during
future excavation.
9.6 Safety Considerations
9.6.1 All personnel to be involved in the installation of
the cathodic protection system should participate in a
thorough safety-training program.
9.6.2 All underground facilities, including buried
electric cables and pipelines in the affected areas,
should be located and marked prior to digging.
9.6.3 All utility companies and other companies with
facilities crossing the work areas should be notified and
their affected structures located and marked prior to
digging.
9.6.4 All areas with low overhead wires, pipelines, and
other structures should be located and noted prior to
any construction.
9.6.5 Operations and maintenance personnel should
be notified of pending construction to coordinate
necessary shutdowns or emergency considerations.
Reference Electrode