Nace CP 1, Course Manual

Page: 143 / 535

Safety 4:6
CP 1–Cathodic Protection Technician Course Manual
©
NACE International, 2000
12/01/04
situation, an electrical bond must be temporarily installed around the
location where a pipe section is to be cut or a flange is to be disconnected.
Another situation where a high-energy spark may be generated is when a
cathodically protected structure is inadvertently or purposefully electrically
connected to another metallic structure. At the moment the connection is
made, a spark may occur. For example when a ship or barge containing a
combustible material docks at a cathodically protected dock, the barge and
the dock will usually make electrical contact through metallic hawsers or
other components. To avoid a potentially disastrous situation, standard
practice involves bonding the dock and the barge using two bonding wires
prior to opening any hatch on the barge. Using this technique, if a spark
occurs, it occurs at the location where the bond is attached and prior to
release of any potentially explosive vapors. Another precaution is to turn
off the cathodic protection rectifier(s) until the vessel is securely bonded to
the dock.
Finally, any cathodic protection component that might generate an ignition
spark should not be allowed within specific areas where explosive
atmospheres may exist. Examples are within dikes around tanks containing
combustible materials, facilities housing or encompassing propane, natural
gas or combustible product pipeline components, gas or oil production
platforms, etc.
Standard rectifiers and many types of lightning arresters are potential
ignition sources. In special situations where a rectifier must be installed in
an area where explosive atmospheres could exist, an oil-immersed rectifier
with explosion-proof fittings, switches, and components must be employed.
Care should be exercised to ensure that the explosion-proof design of the
equipment meets the classification of the area and that the design is not
defeated by improper installation.
Cathodic Protection Surveys
There is always a possibility of encountering hazardous potentials while
conducting cathodic protection measurements. A number of precautions are
suggested:
•
Assume that the potential to be measured may be hazardous. Do not
contact a measurement circuit until the potential is determined to be
safe.
•
If AC may be present, measure AC voltage first.