Quick Facts:
- Corrosion is the natural process that occurs when materials made from metal return to their original state through a chemical reaction known as oxidation.
- Corrosion of all types is one of the leading causes of pipeline leaks and ruptures.
- Improved technologies have led to better prevention, monitoring, detection, and mitigation of external pipeline corrosion – even for old pipelines.
- New pipeline Integrity Management regulations will promote early identification of potentially externally corroded sections and their repair.
- Refer to other Fact Sheets for specific discussion of issues related to corrosion in general, internal corrosion, selective seam corrosion, and stress corrosion cracking.
What is external corrosion and why does it occur?
Corrosion is the deterioration of metal that results from a reaction with the environment which changes the iron contained in pipe to iron oxide (rust). For example, if your car develops a rust spot, that is corrosion of metal. The same process can occur in various forms on pipelines . As is the case with your car, there are effective methods for preventing and arresting corrosion damage to pipelines.
External corrosion occurs due to environmental conditions on the outside of the pipe (e.g., from the natural chemical interaction between the exterior surface of the pipeline and the soil surrounding it). Typically, the exterior surface of a pipeline is coated in order to prevent the surrounding soil or other environmental condition from contacting the steel pipe, thus preventing the oxidation process. In addition, the oxidation process can be halted “electrically” on both bare pipelines as well as on pipelines that have been coated. When either or both of these protective measures break down, external corrosion can occur.
What are the risks from external corrosion?
External corrosion can result in the gradual reduction of the wall thickness of the pipe and a resulting loss of pipe strength. It can occur relatively evenly over an area of the pipe surface (sometimes referred to as “General Corrosion”) or in isolated spots on the pipe. This loss of pipe strength could result in leakage or rupture of the pipeline due to internal pressure stresses unless the corrosion is repaired, the affected pipeline section is replaced, or the operating pressure of the pipeline is reduced.
External pipeline corrosion creates weaknesses at points in the pipe, which in turn makes the pipe more susceptible to third party damage, overpressure events, etc. (i.e., corrosion doesn't necessarily need to cause the leak or rupture itself to increase risk).
Pipeline failure rates from Corrosion
While data specific to external corrosion alone is not available, corrosion in all its various forms is one of the most prevalent causes of pipeline spills or failures. For the period 2002 through 2003, incidents attributable to corrosion have represented 25% of the incidents reported to OPS for both Natural Gas Transmission Pipelines and Hazardous Liquid Transmission Pipelines.
Over this same period, approximately 1 percent of the incidents reported to OPS for Gas Distribution Pipelines were due to corrosion.
What is being done to prevent/mitigate external corrosion?
- The steel pipe in modern pipeline systems is coated to protect it from external environmental conditions that can lead to corrosion.
- Modern manufacturing processes for steel pipe and coatings are subject to rigorous fabrication and installation standards and quality control to reduce the occurrence of defects that can lead to corrosion-induced failures.
- Operators use cathodic protection systems to protect pipes from external corrosion. One type of this system imposes a very low-voltage, direct electric current on the pipeline to oppose the natural corrosion currents at locations where pipe coating is damaged or missing. Another type system is to connect the pipeline to an anode ground that attracts the corrosion-causing current. This sacrificial anode attracts the current away from the iron in the pipe.
- The Office of Pipeline Safety has implemented new Pipeline Integrity Management (“IM”) regulations that require all pipeline operators to inspect and assess all of their pipelines that could affect areas of high consequence such as populated areas or environmentally sensitive areas. The operators are required to inspect and assess their pipelines for integrity issues, such as corrosion, and repair or replace affected pipe.
- By implementing the requirements of the regulations and through responsible maintenance programs, pipeline operators continuously inspect their pipelines for external corrosion damage.
External Corrosion: What more can be done?
- Public : Be aware of pipelines located near you. Be observant for signs of pipeline damage, leakage, or security concerns. Report any concerns you have regarding pipeline safety to the pipeline operator immediately. Always respect the pipeline right-of-way. Do not dig or build on a pipeline right-of-way without first contacting the pipeline operator or your state one-call center.
- Industry : Pipeline operators and industry stakeholders can continue to develop and implement improved corrosion detection and prevention technologies. Operators must continue to implement corrosion protection effectively and strengthen pipeline integrity management programs. Operators must mitigate the effects of corrosion when it is detected.
- Regulators : OPS and state regulators must continue to inspect pipeline operators to ensure they effectively implement required integrity management and corrosion control programs to ensure that risks to pipelines are identified and mitigated at the earliest possible time. Better coordination is needed between local permitting agencies and pipeline operators to facilitate expeditious granting of permits when public safety is potentially threatened.
- Public : Be aware of pipelines located near you. Be observant for signs of pipeline damage, leakage, or security concerns. Report any concerns you have regarding pipeline safety to the pipeline operator immediately. Always respect the pipeline right-of-way. Do not dig or build on a pipeline right-of-way without first contacting the pipeline operator or your state one-call center.
- Industry : Pipeline operators and industry stakeholders can continue to develop and implement improved corrosion detection and prevention technologies. Operators must continue to implement corrosion protection effectively and strengthen pipeline integrity management programs. Operators must mitigate the effects of corrosion when it is detected.
- Regulators : OPS and state regulators must continue to inspect pipeline operators to ensure they effectively implement required integrity management and corrosion control programs to ensure that risks to pipelines are identified and mitigated at the earliest possible time. Better coordination is needed between local permitting agencies and pipeline operators to facilitate expeditious granting of permits when public safety is potentially threatened.
External Corrosion: Where can I learn more?
- http://nace.org/nace/index.asp
- http://corrosion-doctors.org/
- http://httd.njuct.edu.cn/MatWeb/corrosie/c_.htm
- http://www.windsun.com/CP_Stuff/Corrosion_Bas.htm
Date of Revision: 041306