MIL-HDBK-1004/10
Section 10:
INSTALLATION AND CONSTRUCTION PRACTICES
Factors to Consider. Cathodic protection systems, and the
10.1
structure to be protected, must be properly installed in order for effective
protection to be achieved. NACE Standards RP-02-85 and RP-01-69 include
guidelines for installation of such systems.
Particular attention should be paid to maintaining the condition of
the coating on the structure and maintaining the structural continuity and
isolation required for proper cathodic protection system operation. If the
coating on a structure is damaged (or absent), cathodic protection
requirements will increase dramatically. A well-coated structure will often
require only 1 percent or less of the current required to protect the same
structure if bare. Sacrificial anode systems, which cannot be easily adjusted
to provide increased current output, are the most susceptible to poor
performance if the coating system does not meet original specifications. Open
bonds and shorts to other structures are common causes of inadequate
protection and the resulting interference can cause accelerated corrosion
damage. Careful inspection during the entire construction process, both of
the cathodic protection system and of the structures to be protected are vital
to the successful application of cathodic protection.
Planning of Construction. The most important factor in the
10.2
planning of construction of facilities that include cathodic protection is the
planning of inspections to insure that coatings are properly applied and not
damaged during construction, and that proper isolation and bonding are
achieved. For buried structures, these inspections must be performed before
backfilling. Once the structure or other system components are buried,
identification and correction of any discrepancies is difficult.
Pipeline Coating. Interference problems are severe for long
10.3
structures such as pipelines. It is highly desirable to reduce the amount of
current required to protect pipelines to the lowest levels possible. High
quality coatings, properly selected and applied, and installation of the line
without damaging the coating is vital to achieving protection at the low
current levels desired. Often, coating application and prevention of damage
during installation are more important than the materials used.
Over-the-Ditch Coating. Over-the-ditch coating systems have the
10.3.1
advantage of reducing handling of the coated pipe before installation. Over-
the-ditch coating is best used when long sections of pipeline are to be
installed in open areas under mild weather conditions. Depending on curing
time for the coating, the pipe may either be lowered directly into the ditch
after coating or may be held on skids until the coating is properly cured
before lowering it into the ditch. If the pipe is lowered into the ditch
directly after coating, the inspector should electrically inspect each section
using a holiday detector or "jeep" immediately before backfilling. If the
pipeline is held on skids, the skids should be padded to prevent coating
damage. Damage caused by skids must be patched before inspection of the
coating, lowering of pipeline into the ditch, and backfilling.
Yard Applied Coating. The use of yard or mill applied coatings is
10.3.2
preferred over field applied coatings since better surface preparation and
213
Previous Page
