Investigators determined that the pipeline ruptured due to stress corrosion cracks on the outside surface, and the polyethylene tape coating applied to the pipe’s exterior surface as an anticorrosion technique had deteriorated over time.
Polymers are complex molecules formed by chains of duplicated groups of atoms (monomers); these groups are typically linked by covalent bonds along a “backbone” of carbon or silicon atoms. Important polymeric materials related to corrosion include plastics and synthetic rubbers (elastomers).
Case histories are presented where polyethylene
encasement and cathodic protection have been used
together to effectively control external corrosion of
ductile iron pipelines in corrosive soils. The four case
histories evaluated include impressed current and
galvanic anode protection.
Two of the most fundamental and informative field measurements are soil resistivity surveys and pipe-to-soil potential surveys.
The principle of a close-interval potential survey (CIPS or CIS) is to record the pipe-to-soil (P/S) potential profile of a pipeline over its entire length by measuring potentials at intervals that do not significantly exceed the depth of the pipe (often ~1 m).
Most pipeline cathodic protection (CP) applications involve either galvanic anode or impressed current CP (ICCP) systems installed in earth for protection of external surfaces. Of the galvanic anode installations in neutral soils, magnesium is the most commonly used anode material. Rectifiers are the most common source of direct current power for impressed current systems.
Wireless monitoring technologies provide the ability to
acquire impressed current cathodic protection (ICCP)
system performance data from remote locations using
modem-equipped personal computers. The technology
can monitor the remote ICCP system’s amperage,
“instant-on” and “instant-off” potentials in a central
location, and provide personnel with immediate
warnings of system problems. Case studies are presented for one Air Force and three Army installations, each with a different approach for the monitoring.
The need for real-time data is affecting the ability
to provide cathodic protection (CP) to pipelines.
The connection of electronic equipment required for
remote pressure monitoring, metering information, valve operators, and other functions creates a direct short from the CP on the pipeline to the electric power company alternating current grounding system. In essence, the CP system now must protect not only the pipeline, but also a sizeable bare copper grounding grid. This problem creates pipe-to-soil potentials that may not meet the desired criterion. This article covers the use of decoupling devices to remedy this problem.
Several types of anode installations for tank bottoms are possible, but the methods selected do not always produce the desired results. This two-part article discusses a case history in which existing cathodic protection (CP) was ineffective and testing methods did not identify system deficiencies. This led to the premature failure of the tank bottom. Part 1 covered the findings of an investigation conducted to identify the cause of the corrosion. Part 2 describes the remedial approach taken to enhance CP for effective corrosion control.
There are several types of anode installations that
distribute protective current to a tank bottom. In
some cases, however, the methods selected do not always produce the desired results. This two-part article discusses a case history in which existing cathodic protection (CP) was ineffective and the methods used to verify the performance of CP did not identify system deficiencies. This led to the premature failure of a tank bottom. Part 1 covers the findings of an investigation conducted to identify the cause of the corrosion. Part 2 discusses the
remedial approach taken to enhance the CP for effective corrosion control.
“Stop, Look, and Listen.” These words from railroad crossing signs are good ones to keep in mind when troubleshooting cathodic protection (CP). Some trouble shooting efforts are pretty straightforward, involving depleted anodes, broken wires, burned out rectifier stacks, and the like. But there are occasions when nothing seems to make sense, and then it’s time to “stop, look, and listen” and figure it out. Here are a few experiences from nearly 45 years of CP work.
After being in operation for some time, cathodic protection (CP) systems at compressor stations, refineries, and other industrial plants can experience problems. For example, the CP potential distribution can change for various reasons, because of isolating flange failures, alterations in pipeline systems, grounding systems, or reinforced concrete foundations. Some areas become underprotected and others overprotected. The extent of CP current required may exceed the capacity of rectifiers, and may also increase interference on foreign pipelines. This article describes the results of corrective measures for these problems.
Designing cathodic protection (CP) systems for
buried piping in power plants and other similar
industrial facilities offers several unique challenges. This
article discusses these challenges and provides case
histories to illustrate the impact they have on CP system
design and operation.
Mixed metal oxide (MMO) anodes find extensive
use in impressed current cathodic protection
installations. Part 1 of this article covered the electrochemistry, manufacture, and operation of these anodes. Part 2 presents three case
histories showing application of MMO anodes.
After experiencing severe telluric current activity on
a pipeline, the author researched the subject. The
causes and effects of telluric currents are explained
and precautions for obtaining data on forecast
telluric activity are given.