[Skip to Content]
U.S. Department
of Transportation

Pipeline Safety Stakeholder Communications

Pipeline Safety Connects Us All

Fact Sheet: Internal Corrosion

Quick Facts:

  • Corrosion is the natural process where materials made from metal deteriorate through an electrochemical reaction known as oxidation (rusting). Corrosion on the interior surface of pipeline systems is referred to as internal corrosion.
  • Internal corrosion in pipeline systems can be prevented through proper material selection, product quality control, protective coatings, corrosion inhibitor additives, and line cleaning (to remove water & other contaminants).
  • Data show that from 1998-2017 approximately 12% of pipeline incidents were caused by internal corrosion.
  • Improved technologies continue to lead to better prevention, monitoring, detection, and mitigation of internal pipeline corrosion, for both newly installed and existing pipelines.
  • Federal pipeline integrity management regulations promote early identification of internal corrosion issues in pipe or pipeline equipment by requiring periodic inspections, testing, and assessments, and timely repair or replacement where necessary.
  • Internal 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 internal corrosion.
  • Refer to other fact sheets on PHMSA’s Stakeholder Communications website for specific discussions of corrosion, external corrosion, selective seam corrosion, and stress corrosion cracking, microbiologically-influenced corrosion, and stray current interference corrosion.

What is internal corrosion and why does it occur?

Corrosion is the deterioration of metal 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.

Internal corrosion occurs due to environmental conditions on the inside of the pipeline. In most cases, the corrosive materials are contaminants naturally contained within the transported commodity, such as hydrogen sulfide, carbon dioxide, other chemicals, or even water. 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 internal corrosion damage to pipelines, including many that are very technologically advanced.

Typically, either the transported commodity’s quality is controlled to remove or minimize contaminants, internal pipeline coatings are applied, corrosion inhibitors are injected, or some combination of these approaches are utilized to prevent internal corrosion. When these protective measures are effective, or when sufficient mitigative efforts are sustained, steel pipelines can last indefinitely.

What are the risks from internal corrosion?

Internal corrosion can result in gradual and usually localized metal loss on the interior surface of pipeline systems resulting in reduction of the wall thickness of the pipe or other equipment. This metal loss can occur relatively evenly over an area of the pipe’s interior surface (sometimes referred to as “general corrosion”) or in isolated spots on the interior surface (“localized corrosion” or “pitting”). The loss of material from corrosion can eventually result in “pinhole” leakage, or a crack, split, or rupture of the pipeline unless the corrosion is repaired, the affected pipe section is replaced, or the operating pressure of the pipeline is reduced.

Left untreated, some internal 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, internal corrosion can sometimes also increase the risk of other types of pipeline failures.

Pipeline failure rates from internal corrosion

Transmission and gathering pipelines. Historically, internal corrosion accounts for approximately 60% of all pipeline incidents caused by corrosion. For example, during the 5-year period of 2013-2017, approximately 12% of incidents on gas transmission, gas gathering, and hazardous liquid pipelines were caused by internal corrosion.

Natural gas distribution pipelines. Over the same 5-year period (2013-2017) less than 1/2 of 1% of reported incidents on natural gas distribution pipelines were caused by internal 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 internal corrosion failures would result in leaks.

What is being done to prevent/mitigate internal corrosion?

  • Modern manufacturing processes for steel pipe and protective internal coatings are subject to rigorous fabrication, installation, inspection, and quality control standards to reduce the occurrence of pipe and coating defects that can lead to internal corrosion.
  • Pipeline operators control the moisture and chemical content of the products transported through their pipelines (usually, but not always possible) to prevent internal corrosion.
  • Pipeline operators routinely run devices called “cleaning pigs” through their lines to remove accumulations of materials that can lead to internal corrosion.
  • Pipeline operators also sometimes introduce corrosion inhibitors into the pipeline to prevent internal corrosion.
  • These preventive measures are routinely monitored and tested to maintain their effectiveness.
  • 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 internal 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”.

Internal 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 own safety may be involved. Know the phone numbers in your area 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 internal corrosion, and are implementing appropriate activities in a timely manner.

Internal corrosion: Where can I learn more?

Date of Revision: 09242018