Onshore pipelines are exposed to numerous corrosion threats throughout their operational life. Key contributors include aggressive soil chemistries, moisture and oxygen availability, transported fluid composition, stray current interference, and external mechanical stresses that compromise protective barriers, all of which accelerate pipeline degradation. This article examines the most prevalent forms of pipeline corrosion and outlines proven mitigation strategies, including cathodic protection (CP), coatings, and monitoring technologies.
1. External Corrosion Under Coatings
External corrosion is the most common integrity threat for onshore pipelines and is typically originates at coating defects. Small holidays, disbondment, or mechanical damage allow soil electrolytes to reach the steel surface, creating localised corrosion cells that can propagate rapidly. While high-quality coatings are the first line of defence, they inevitably degrade over time, increasing the demand on cathodic protection systems. An effectively designed and maintained CP system ensures that exposed steel remains polarised and protected, even at coating flaws where corrosion would otherwise advance unchecked. By combining robust coatings with optimised CP design, monitoring, and maintenance, pipeline operators can significantly extend asset life and reduce long-term integrity risks.
2. Stray Current Corrosion (DC Interference)
Pipelines can suffer accelerated localised corrosion when stray direct currents enter the metal and discharge at specific points. Common sources include foreign pipelines with their own CP systems, DC transit and rail networks, and solar farm earthing systems. The effects of stray currents can be predicted through computer-based interference modelling and verified in the field using, Close Interval Potential Surveys (CIPS) and corrosion monitoring coupons. Effective mitigation measures include installing interference bonds with resistors or diodes, coordinating rectifier outputs with neighbouring assets, monitoring current flow at test stations, and employing residual current devices (RCDs) on solar installations to limit earth currents and reduce the risk of interference, ensuring pipeline integrity is maintained.
3. AC Induced Corrosion and Personnel Safety
Pipelines running parallel to high-voltage AC transmission lines are susceptible to AC-induced corrosion and safety hazards. Mitigation strategies include using zinc ribbon or grounding rods paired with AC decouplers, installing gradient control mats at access points, and performing potential gradient assessments. To properly address these risks, an AC interference study together with modelling and design work is essential to define the mitigation requirements and determine the most effective protective measures.
4. Microbiologically Influenced Corrosion (MIC)
MIC can arise in soil environments, particularly in wet or anaerobic zones. Sulfate-reducing and iron-oxidising bacteria contribute to localised pitting and scaling.
Managing MIC involves maintaining coating integrity, ensuring strong CP polarisation, and monitoring for signs of microbial activity. In high-risk areas, soil treatment or CP upgrades may be considered.
5. Mechanical Damage and Ageing Coatings
Mechanical impacts from excavation or ground movement can lead to coating breaches and steel exposure. Older pipelines may also suffer from deteriorating coating systems.
To mitigate these risks, operators should monitor rights-of-way and carry out ECDA surveys such as CIPS and DCVG to assess coating condition and identify areas of concern. The survey results can then guide targeted maintenance actions and CP system adjustments to ensure continued protection of ageing infrastructure.
Integrated Corrosion Management Strategy
Pipeline integrity requires a layered defence:
- High-performance coatings to minimise exposure.
- Cathodic protection to shield exposed areas.
- Electrical mitigation for AC and DC interference.
- Internal corrosion control via chemistry and cleaning.
- Ongoing monitoring through ILI, CP surveys, and probes.
- Strategic remediation including recoating and CP upgrades.
Corrpro Europe supports clients across these domains, particularly in CP design, AC/DC interference solutions, and pipeline integrity assessments.
FAQs
Can CP prevent all pipeline corrosion?
No. CP is effective against external corrosion and electrical interference but does not address internal corrosion or mechanical damage. It should be part of a holistic corrosion control plan.
What standards govern corrosion protection?
Standards such as ISO 15589, EN 12954, and NACE SP0169-2013 provide guidance for the design, installation, and maintenance of external cathodic protection systems. AC mitigation for pipelines running near high-voltage transmission lines is addressed by specialized industry guidelines and best practices. Adhering to the relevant standards ensures compliance and effective protection against corrosion and AC-related risks.
How is buried corrosion detected without excavation?
Using smart pigs, CP surveys (CIS/DCVG), and corrosion probes. These techniques provide indirect evidence of corrosion and allow for timely intervention.
Is MIC common in pipelines?
MIC occurs in certain conditions like wet or anaerobic soils. It is not the most common threat but can lead to significant damage if undetected.
Can CP be applied to old pipelines with existing corrosion?
Yes. While it won’t repair damage, CP can reduce the corrosion speed and extend asset life. It’s especially useful when paired with condition assessments and repairs.
Worried about corrosion risks?
Corrpro Europe delivers complete corrosion management for pipelines, from CP system design and installation to AC interference mitigation and integrity surveys. Contact us to safeguard your assets and improve reliability.
