Cathodic protection for USTs: protecting underground storage tank (UST) systems from corrosion

              Cathodic Protection
for USTs
WHAT IS IT?
􀁘􅡃 Cathodic protection shields steel UST systems
from corrosion that causes deterioration and
potential failure of the UST.
􀁘􅡔 There are two types of cathodic protection systems:
1. Galvanic Systems (Sacrificial Anodes)
2. Impressed (Induced) Current Systems
WILL YOU BE IN COMPLIANCE?
􀁘􅡁 Adding cathodic protection along with spill and
overfill protection meets the EPA 1998 upgrade
requirements (hyperlink) for existing USTs provided
the UST system already has leak detection
installed.
􀁘􅡃 Cathodic protection can only be added on tanks
which are structurally sound as determined by an
integrity assessment test. Contact the UST section
for integrity assessment methodologies.
􀁘􅡃 Cathodic protection can also protect metal piping
associated with the UST system.
REGULATORY REQUIREMENTS &
DOCUMENTATION
􀁘􅡓 State law requires that field-installed cathodic pro-tection
systems at UST sites be designed by a cor-rosion
expert. Visit the NACE website:
www.nace.org or contact NACE’s customer service
at (281) 228-6200 for a list of corrosion experts.
TESTING & RECORD KEEPING
􀁘􅡃 Cathodic Protection systems must be tested by a
cathodic protection tester certified by ADEQ with-in
six months of UST installation or repair, and at
least every three years thereafter. Call 602-771-
4316, or 1-800-234-5677, extension 771-4316 for
a copy of the ADEQ-certified list of cathodic pro-tection
testers.
􀁘􅡋 Keep the results of the last two tests to document
that the cathodic protection is working.
􀁘􅡁 Additional requirements for an Impressed Current
system:
1. Inspect an impressed current system every 60
days to verify that the system is operating.
2. Keep the results of your last three (3) 60-day
inspections to document that the impressed
current system is operating properly.
HOW DOES CATHODIC PROTECTION WORK?
A. Galvanic Systems (Sacrificial Anodes)
1. Sacrificial anodes are pieces of metal attached to
the UST system that are more electrically active
than the steel UST system. Because these
anodes are more active, the corrosive current
will exit from them rather than the UST system.
Thus, the UST system is protected while the
attached anode is “sacrificed.”
2. Sacrificial anodes can be attached to existing
bare steel USTs or to new coated steel new
USTs for a pre-engineered cathodic protection
system.
3. If the sacrificial anodes are attached to a coated-steel
UST, the coating must be of a suitable
dielectric material. In other words, the coating
will electrically isolate the UST from its environ-ment
and meet applicable industry codes. An
asphalt coating is not considered a suitable
dielectric coating.
4. For all galvanic system, depleted anodes must be
replaced for continued cathodic protection of
the UST system.
HOW DOES CATHODIC PROTECTION WORK?
(continued)
B. Impressed (induced) Current Systems
1. An impressed current cathodic protection system
consists of anodes, cathodes, a rectifier and the
soil.
2. The rectifier converts the alternating current to
direct current. The direct current is then sent
through an insulated copper wire to anodes that
are buried in the soil near the UST system.
3. Typical anode materials are ceramic, high silicon
cast iron, or graphite. Ceramic anodes are not
consumed, whereas high silicon cast iron and
graphite anodes partially dissolve each year and
must be replaced over time.
4. The direct current then flows from the anode
through the soil to the UST system, which acts
as the cathode, and back to the rectifier through
another insulated copper wire.
5. As a result of the electrochemical properties of
the impressed current cathodic protection system,
corrosion takes place only at the anodes and not
at the UST system.
6. Depleted anodes must be replaced for continued
cathodic protection of the UST system.
FOR MORE INFORMATION CONTACT:
Arizona Department of Environmental Quality
UST & Division Support Section
1110 West Washington Street
Phoenix, Arizona 85007
(602) 771-4255
toll free number: (800) 234-5677 Ext:771-4255
Website: www.azdeq.gov
􀂆􈙉 Impressed Current CP system checked every
60 days?
􀂆􈙇 Galvanic system tested within six month of
installation?
􀂆􈙇 Galvanic system tested every three years?
􀂆􈙃 CP system repaired by a corrosion protection
expert?
􀂆􈙄 Depleted anodes in galvanic system replaced?
􀂆􈙄 Documentation of CP system designer credentials
maintained?
C H E C K L I S T
In the event of any discrepancy between this infor-mation
and the Arizona Revised Statutes or Arizona
Administrative Code, the statutes or rules shall take
precedence.
Publication Number: C05-02