Protective coverings. Pipe sections are coated at the factory or at the construction site with coal tar
enamel. Protective wrappings are put around the pipeline before it is buried. The enamel and
wrappings are waterproof. They act as a barrier between the pipeline and surrounding ground and
atmosphere, and they prevent current from leaving the pipeline. When a pipeline is repaired, it is
important that these protective coverings be restored to their original condition.
Sacrificial anodes. Another way to protect the pipeline is to use sacrificial anodes. One type of
sacrificial anode is magnesium. Bars of magnesium are buried in ground beds that are located away
from the pipeline. The anodes are connected to the pipeline with insulated copper wires. In this way, the
pipeline becomes the cathode, and the magnesium anode is sacrificed to protect the pipeline. Corrosion
is not stopped; it is only directed to a less important surface.
Mitigation bonds. Mitigation bonds are used to protect the pipeline from stray electrical current. These
bonds are insulated grounding cables that serve as paths of least resistance to stray electrical currents.
Stray current will tend to flow through these cables instead of the pipeline.
PART B - PIPELINE TESTING
A new coupled or welded pipeline should be tested before it is accepted for service by the using organization.
Testing is done to locate leaks, blockages in the line, and flaws in construction. Testing may be done with
water, fuel, or compressed air.
Water. Although testing with water is safer than testing with fuel, there are disadvantages to using water.
Water may be scarce in some area. It may not be practical or possible to pack the line with water. Water
expands as it freezes. It should not be used to test a line if there is any chance of the temperature falling low
enough to freeze the line. All water should be removed or displaced entirely from the line before it is packed
with fuel. In a combat situation, this process could use valuable time.
Fuel. Since there are problems testing with water, testing is usually done with fuel. Several conditions
should be met when fuel is used.
The test section should be outside of a city or heavily populated area.
Each building within 300 feet of the test section should be empty of people.
The test section should be watched by a patrol during the test.
The people running the test should be in constant contact with the patrol.
The fuel used should be a low-grade, noncritical fuel that does not vaporize quickly.
Compressed Air. If the test section is in an area with many people, the line should be tested with
compressed air. Compressed air should also be used to test a section of line that crosses a river.
NOTE: Compressed air can only be used on clean, vapor-free lines. Do not use compressed air testing for
high-pressure overland pipelines.
To test coupled and welded pipelines with compressed air:
Divide the pipeline into smaller sections than those used in testing with fuel or water. Consider the size
of the pipe and air compressor before deciding how long of a section should be tested. Do not try to test
more than 5 miles at a time. Use the gate valves placed 1 mile apart in the pipeline to break the test
section into 1-mile pieces. If the pipeline must be tested quickly, test the line mile by mile instead of by
5-mile sections. Break the line at each gate valve. Uncouple and move the air compressor forward for
each test. This method cuts down on the time it takes to empty a line of air.
Uncouple the beginning of the test section from the rest of the pipeline.
Cap off this section with a coupling made from a blank end. (To make this coupling, cut a hole in a blank
end and weld an air hose coupling to the blank end over the hole.)
Attach the air line from the air compressor to the blank end.
Close the gate valve at the end of the first mile of test section.
Pressurize the line at 90 pounds per square inch to the closed gate valve.
Patrol the line and swab the couplings with soapy water. Look for bubbles caused by air escaping at a
leak. Also, listen for the hissing sound of escaping air.
If a leak must be repaired: close the gate valve at the end of the next mile of the test section, open the
gate valve at the end of the first mile to relieve pressure, repair the leak, close the gate valve at the end
of the first mile, pressurize the first mile of pipeline, and patrol again to look and listen for leaks.
7-3
QM 5096
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