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U.S. Department
of Transportation

Pipeline Safety Stakeholder Communications

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Fact Sheet: Corrosion

Quick Facts:

  • Corrosion is the natural process where materials made from metal deteriorate through an electrochemical reaction known as oxidation (rusting).
  • Corrosion on pipeline systems can be prevented through material selection, protective coatings, cathodic protection systems, corrosion inhibitor additives, and line cleaning to remove water & other contaminants.
  • Data show that from 1998-2017 approximately 18% of pipeline incidents on average were caused by corrosion.
  • Improved technologies continue to lead to better prevention, monitoring, detection, and mitigation of pipeline corrosion, for both newly installed and existing pipelines.
  • Federal pipeline integrity management regulations promote early identification of corrosion issues on pipe or pipeline equipment by requiring periodic inspections, testing, and assessments, and timely repair or replacement where necessary.
  • Corrosion is considered a time-dependent threat which means it grows or worsens with time if left unmitigated. As a result, early detection and mitigation are necessary to minimize the impact of corrosion.
  • Refer to other fact sheets on PHMSA’s Stakeholder Communications website for specific discussions of internal corrosion, external corrosion, selective seam corrosion, and stress corrosion cracking, microbiologically-influenced corrosion, and AC & interference corrosion.

What is corrosion and why does it occur?

Corrosion is the deterioration of a steel pipeline that results from an electrochemical reaction with its immediate surroundings. This reaction causes the iron in the steel pipe or other pipeline appurtenances to oxidize (rust). Corrosion results in metal loss in the pipe. Over time and if left unmitigated, corrosion can cause the steel to lose its strength and possibly render it unable to contain the fluid in the pipeline at its operating pressure. Because pipelines are extremely long-serving and critical infrastructure, it is paramount for pipeline operators to maintain the physical integrity of pipelines. Fortunately, there are effective methods for preventing and mitigating corrosion damage to pipelines, including many that are very technologically advanced that deal with various types of corrosion. When these protective measures are effective, or when sufficient mitigative efforts are sustained, steel pipelines can last indefinitely.

Corrosion can be characterized by where and/or how it occurs. For example:

  • External corrosion occurs due to environmental conditions on the exterior surface of the steel pipe that can cause an electrochemical interaction between the exterior of the pipeline and the soil, air, or water surrounding it. Galvanic and atmospheric corrosion are common types of external corrosion.
  • Internal corrosion occurs due to a chemical attack on the interior surface of a steel pipe from the products transported in the pipe. This can be from either the commodity transported, or from other materials carried along with the commodity, such as water, hydrogen sulfide, and carbon dioxide.
  • Other types of corrosion can occur due to specific material defects or environments. These include stress corrosion cracking (SCC), microbiologically-influenced corrosion (MIC), stray current interference corrosion, and selective seam corrosion. These types of corrosion problems can be exacerbated by environmental conditions, manufacturing processes, pipe wall erosion from the transported commodity, physical location with respect to other structures, and applied stresses resulting from routine and normal pipeline operations.

What are the risks from corrosion?

Corrosion can result in gradual and usually localized metal loss resulting in reduction of the wall thickness of the pipe. If not prevented or mitigated effectively, the result can be through-wall pinholes in the pipe material or a loss of pipe strength at that location that can causes a crack or split in the pipe wall. The result is either leakage from the pipe (typical) or an open break failure (rupture) of the pipe (much less typical) unless the corrosion is repaired, the affected pipe section is replaced, or the operating pressure of the pipeline is reduced.

Where corrosion involves a longitudinal seam of a pipe or cracks in the pipe, the likelihood of a break or rupture increases. Stress corrosion cracking and selective seam corrosion are in this category. Hydrogen cracking or embrittlement can also weaken a pipeline when isolated points of elevated steel hardness exist - this is a rare material defect present in some older types of pipe.

Left untreated, corrosion can weaken the pipe where the corrosion occurs, and make the pipe more susceptible to overpressure events, earth movement, and other external stresses. Thus, corrosion can sometimes also increase the risk of other types of pipeline failures.

Pipeline failure rates from corrosion

Transmission and gathering pipelines. Historically, corrosion is one of the two most prevalent causes of pipeline failures, most often manifesting as leaks or seeps. For the 5-year period of 2013-2017, approximately 17% of reported incidents on gas transmission, gas gathering, and hazardous liquid pipelines were caused by corrosion.

Natural gas distribution pipelines. Over the same 5-year period (2013-2017) approximately 1% of incidents on natural gas distribution pipelines were caused by corrosion. Natural gas distribution system mains and service lines operate at much lower pressures and are typically made of non-corrosive materials (like plastic). Even if a gas distribution line is made of steel, the likelihood of a pipe rupture is low because of the lower operating pressures, and most corrosion failures would result in leaks.

What is being done to prevent/mitigate pipeline corrosion?

  • Modern manufacturing processes for steel pipe and protective pipe coatings are subject to rigorous fabrication, inspection, and quality control standards to reduce the occurrence of defects that can lead to corrosion-related failures.
  • Operators use coatings, cathodic protection systems, pipe cleaning techniques, product quality controls, and other approaches to prevent corrosion.
  • Federal pipeline safety regulations require pipeline operators to develop and implement integrity management programs and continually inspect and assess the integrity of pipelines that could affect areas of high consequence, such as populated areas or environmentally sensitive areas. Operators are required to periodically inspect and assess their pipelines for corrosion and other integrity issues, and repair or replace affected pipe. Inspections are typically performed using one or more types of specialty inline inspection (ILI) tools, hydrostatic pressure testing, or a process called “direct assessment”).

Corrosion: What more can be done

  • Public: Be aware of pipelines located near you. Always respect the pipeline right-of-way and be observant for signs of pipeline damage, leakage, or security concerns. Remember that your and your community’s safety may be involved. Know the phone numbers and call the pipeline operator and local public safety officials immediately to report any pipeline safety concerns.
    • Be observant of changes to soils and vegetation around pipelines. These could be signs of a leak. Report these and possible earth movement or other conditions that could impact the pipeline to the pipeline operator immediately.
    • Note any suspicious activity, especially at aboveground pipeline facilities such as valve or pumping stations; report such activity to local public safety officials and the pipeline operator immediately.
    • Do not dig or build on a pipeline right-of-way. Always call to have underground facilities located and marked before you dig (dial 811).

  • Industry: Pipeline operators should follow current regulations, guidelines, and standards to ensure the integrity and security of their pipeline facilities. This includes evaluating all potential threats that may impact the integrity of their pipelines.
  • Regulators: PHMSA must continue to work closely and in cooperation with other organizations to ensure pipeline integrity management requirements address evolving concerns. Federal and state pipeline safety regulators must continue to inspect operators’ integrity management programs to ensure they are effectively identifying and assessing potential threats, including corrosion, and are implementing appropriate activities in a timely manner.

Corrosion: Where can I learn more?

Date of Revision: 09242018