Pipeline Integrity Management: Pipeline Corrosion Detection and Prevention

Pipeline integrity management is absolutely crucial in all aspects of pipeline operations.  Assurance of pipeline integrity is indeed a true minimum requirement, or a license to operate, of a pipeline operator today. The most prevalent cause of pipeline leaks (by far) remains 3^rd party excavations near pipelines. Pipeline operators in the U.S., though, have done a good job raising pipeline awareness within local communities, with excavation contractors, and with local responders.  When an unfortunate event does occur due to 3^rd party excavations near a pipeline today, it is generally because the excavator was unaware of the pipeline’s existence and had not placed the proper one-call to the local authorities.  The next most significant pipeline integrity issue is with corrosion.  Over the years and with integrity monitoring technical advancements, U.S. pipeline operators and service providers have done much to reduce leaks due to corrosion.  However, data analysis shows that from 1998 to 2017, approximately 12% of all reported pipeline incidents in the United States were caused by corrosion. This fact highlights that there remains a need for continuous improvement in corrosion monitoring and mitigation as part of a comprehensive pipeline integrity management program.

As pipelines age and operational stresses take their toll, a range of corrosion mechanisms may impact pipeline integrity. From external corrosion caused by interactions with the environment to internal corrosion triggered by fluid chemistry, unmonitored and unmitigated corrosion-related deterioration may lead to leaks, ruptures, and other problems.

Fortunately, advanced technologies and methodologies for detecting and preventing corrosion have the potential to eliminate these impacts. Inline inspection tools, non-destructive testing techniques, protective coatings, and cathodic protection systems have seen rapid innovations to enhance performance, cost-effectiveness, and reliability.

This article will provide an overview of the latest technologies and best practices related to pipeline corrosion monitoring and prevention.

The Science of Corrosion

Corrosion is a naturally occurring phenomenon that may severely impact pipelines over time if not monitored and not mitigated. It occurs due to electrochemical reactions between a metal surface, fluids, and the environment. If allowed to occur, this could lead to a gradual deterioration of the pipeline.

How Corrosion Occurs in Pipelines

The most common driver of corrosion in pipelines is interaction with water or aqueous solutions, which act as electrolytes. When a pipeline metal is exposed to an electrolyte, small electric currents flow through tiny corrosion cells. Positively charged metal ions move from the anode to the cathode, causing the pipeline metal to slowly dissolve.

In addition, characteristics of the internal fluids, including oxygen content, temperature, acidity, velocity, and debris content, can accelerate corrosion mechanisms. External soil environments and microbial organisms can also drive corrosion.

Types of Corrosion Affecting Pipelines

The most prevalent types of unmitigated corrosion found in pipelines include:

• Uniform or General Corrosion: Evenly distributed corrosion leading to thinning over large areas. Caused by chemical or electrochemical reactions.
• Pitting Corrosion: Localized holes or “pits” in the pipe wall due to chemical or electrochemical reactions at discrete sites.
• Crevice Corrosion: Localized corrosion occurs inside tight crevices and gaps where fluid flow is limited.
• Microbiologically Influenced Corrosion: Caused by microbial organisms like bacteria that grow on the pipe surface.
• Stress Corrosion Cracking: Growth of cracks under tensile stress and specific corrosive environments.

Understanding the science behind common pipeline corrosion mechanisms is crucial for selecting effective monitoring and prevention methods tailored to industry needs.

Current Methods in Corrosion Detection

A range of testing and inspection methods are currently used in the industry to detect and measure corrosion in pipelines.  These include non-destructive testing methods, visual inspection techniques, manual inspections, and corrosion coupons.

Visual Inspection Techniques

A basic visual inspection of pipeline externals and internals can identify obvious signs of corrosion and related damage. Techniques like direct assessment are commonly used. However, external coatings and lack of access to pipeline internals limit thorough visual inspection.

Manual Inspections

Manual inspections, the most fundamental of corrosion detection methods, involve visual assessments conducted by trained personnel. Inspectors look for signs of corrosion, such as discoloration, pitting, and material loss. While manual inspections are straightforward and require minimal equipment, their efficacy is limited by human error, accessibility to the pipeline, and the inability to detect subsurface corrosion.

Corrosion Coupons

Corrosion coupons are small, standardized metal strips that are exposed to pipeline conditions and later analyzed for corrosion rate. This direct measurement method provides valuable data on the corrosive environment within the pipeline. However, corrosion coupons offer only localized information and require periodic retrieval and analysis, making them less effective for real-time corrosion monitoring.

Limitations and Challenges

While manual inspection and monitoring methods play an important role in corrosion detection, they can miss localized damage. In addition, access constraints, limited data points, and the inability to inspect full pipeline lengths reduce effectiveness.  For these reasons, it is critical to introduce non-destructive testing inspection methods of monitoring.

Non-Destructive Testing Methods

Advanced non-destructive testing (NDT) methods complement and enhance manual inspection techniques:

• Ultrasonic Testing: Precise ultrasonic thickness measurements identify local wall loss from pitting, crevice, and microbiologically influenced corrosion.
• Magnetic Flux Leakage: Detects corrosion damage and pitting in ferrous pipelines by identifying leakage flux path distortions.
• Radiographic Testing: X-rays or gamma rays produce images that identify internal and external corrosion damage.

Smart Pigging Technology

‘Smart pigs’ are sophisticated inline inspection tools that provide detailed data on pipe conditions as they travel through the length of the pipeline. Inline inspection data enables the identification of corrosion, such as metal loss defects, pitting, cracking, and mechanical damage.

Data Analysis and Reporting

Advanced data integration, analysis, and reporting software has also enhanced pipeline corrosion detection capabilities. Predictive intelligence software can even estimate corrosion growth rates and future failures.

A combination of manual and high-tech inspection methods is essential for accurate, repeatable, and comprehensive corrosion detection.

Corrosion Prevention Techniques

A multifaceted approach using a combination of prevention methods is the most effective corrosion mitigation strategy for pipelines. Commonly used techniques include:

Cathodic Protection Systems

Cathodic protection is an electrochemical process to prevent corrosion on pipeline surfaces. It works by making the pipeline cathode the least corrosive area to drive current toward carefully placed anodes. This inhibits the metal loss process. The two main types are:

• Sacrificial Anodes: Made from materials with more negative electrochemical potential than the pipe. Commonly made from magnesium, zinc, or aluminum alloys. They are “sacrificed” by slowly corroding instead of the pipeline.
• Impressed Current Cathodic Protection: Uses inert anodes and an external DC power source to drive current and inhibit pipe corrosion. This method offers more control and is capable of protecting large pipeline systems in a variety of soil or water conditions. Regular monitoring and adjustments by specialized technicians are essential to ensure its effectiveness.

Coating and Lining Solutions

Anti-corrosion protective coatings provide a physical barrier between the pipe surface and corrosive environments. Common external pipeline coatings include fusion-bonded epoxy and abrasion-resistant overcoats. Internal linings such as liquid or powder epoxy also protect against internal corrosion.

Regular inspection and scheduled maintenance are crucial to ensure coating integrity over pipelines’ service lifetimes. Any failures or damage must be repaired.

Material Selection and Design

Pipelines made using corrosion-resistant alloys, fiberglass pipes, or thermoplastic materials can enhance lifespan and integrity. However, their higher costs often limit widespread use. Careful design also reduces risks of crevice, pitting, and microbiologically-influenced corrosion.

By combining compatible prevention methods, pipeline corrosion can be effectively mitigated to reduce safety risks, environmental impacts, and costs across oil and gas infrastructure.

Overall, harnessing modern technologies and solutions for fighting pipeline corrosion promises a continued future for the industry. Staying abreast of the latest innovations in this domain should be a key priority for all stakeholders.

Frequently Asked Questions (FAQs) about Pipeline Corrosion Monitoring

1. What causes corrosion in pipelines?

Corrosion in pipelines is primarily caused by the interaction between the pipeline material and its surrounding environment. This process is accelerated by the presence of water, oxygen, and other corrosive agents, leading to the deterioration of the metal. Factors such as the material of the pipeline, environmental conditions, and the presence of protective coatings also play a crucial role in the rate and type of corrosion that occurs.

2. Why is corrosion detection important for pipeline integrity?

Corrosion detection is vital for maintaining pipeline integrity because it helps identify potential weaknesses before they result in leaks, ruptures, or failures. Early detection of corrosion allows for timely maintenance and repairs, thus preventing environmental pollution, ensuring the safety of communities near pipelines, and minimizing the economic impact associated with pipeline failures.

3. What are some common methods used for detecting corrosion in pipelines?

Common methods for detecting corrosion include visual and manual inspections, the use of corrosion coupons, ultrasonic testing, magnetic flux leakage, radiographic testing, and smart pigging technology. Each method has its advantages and limitations, and often, a combination of these techniques is employed for comprehensive corrosion monitoring.

4. Can corrosion be completely prevented in pipelines?

While it is challenging to completely prevent corrosion, its impact can be significantly mitigated through proper design, the use of corrosion-resistant materials, and protective coatings. Additionally, implementing regular maintenance schedules, corrosion monitoring programs, and employing cathodic protection can drastically reduce the rate of corrosion and extend the lifespan of pipeline systems.

5. How does smart pigging technology differ from other corrosion detection methods?

Smart pigging technology involves the use of intelligent devices (smart pigs) that travel inside the pipeline, collecting data on its condition as they go. Unlike external inspection methods, smart pigs provide detailed information about the internal state of the pipeline, including the presence of corrosion, cracks, and other anomalies. This technology allows for comprehensive and accurate assessment without interrupting the flow of contents through the pipeline, making it a highly efficient tool for corrosion detection.