JANUARY 31 2003
New or supplemental CP must be compatible with existing CP systems.
New Piping Systems. Corrosion control by coating supplemented with
cathodic protection, or by some other proven method, should be provided in the initial
design and maintained during the service life of the piping system, unless investigations
indicates that corrosion control is not required. Consideration should be given to the
construction of pipelines in a manner that facilitates the use of in-line inspection tools.
Whenever non-metallic or plastic pipes, joints, valves or other components
are used in a metallic distribution system, an insulated No. 8 AWG copper wire, must be
thermite-welded to the existing steel section and run the length of the new non-metallic
section. This wire can be used as a locator tracer wire and to maintain continuity to any
future steel gas main extension.
Existing Piping Systems
Coated. Cathodic protection should be provided and maintained, unless
investigations indicate that cathodic protection is not required.
Bare. Studies should be made to determine the extent and rate of corrosion
on existing bare piping systems. When these studies indicate that corrosion will affect
the safe or economic operation of the system, adequate corrosion control measures
should be taken.
SYSTEMS NOT REQUIRING CATHODIC PROTECTION (EXISTING).
Aboveground tanks in contact with the earth built to present criteria (on an oil-filled sand
pad with plastic liner underneath) do not require CP. All other ferrous tanks in contact
with earth must be cathodically protected. All steel water distribution storage tanks
must be cathodically protected on the interior.
FIELD TESTS. CP system design must be based upon specific field tests
made at the proposed construction site. Tests include (but are not limited to) soil
corrosivity (resistivity) and water chemistry/corrosivity (pH).
DEVIATIONS. Special conditions sometimes exist where cathodic protection
is ineffective or only partially effective. Such conditions may include elevated
temperatures, disbonded coatings, thermal insulating coatings, shielding, bacterial
attack, and unusual contaminants in the electrolyte. Deviations may be acceptable in
specific situations provided that responsible corrosion control personnel can
demonstrate the criteria within this publication and MIL-HDBK-1004 are satisfied.