Understanding the Basics

Corrosion of steel is a process by which the metal deteriorates over time due to exposure to various environmental factors. This can include moisture, chemicals, and oxygen. It is a common problem for many steel structures and components and can lead to loss of strength, structural integrity, and, ultimately, failure.

Steel corrosion occurs when the metal reacts with its environment to form rust, an iron oxide. The presence of salts, acids, or other aggressive substances in the environment can accelerate this reaction. Over time, the rust can continue to spread and cause further damage to the steel, reducing its overall strength and stability.

Preventing and mitigating steel corrosion is vital to ensure the longevity and safety of steel structures and components. Various methods can be employed to slow down or stop corrosion, such as applying coatings, using corrosion-resistant alloys, or controlling the environment.

Basic Process of Corrosion of Steel


The first stage of corrosion is initiation. This is when the surface of the steel is exposed to corrosive agents, such as water or oxygen. This exposure can cause small cracks, pits, or other defects to form on the steel surface.


Once initiated, corrosion can then spread, or propagate, throughout the metal. As the deterioration continues, the cracks or pits grow more prominent, and the metal begins to dissolve and degrade. This can lead to the formation of corrosion products, such as rust.


In some cases, the corrosion process can slow or even stop when a protective layer of corrosion products forms on the steel surface. This protective layer is called a “passive film,” It can limit further corrosion by preventing the steel from being exposed to the corrosive agents.


The passive protective film can become unstable under certain conditions, such as changes in pH, temperature, or exposure to aggressive environments. When this happens, the passive film can break down, and the corrosion process can restart and propagate.

Factors Influencing Corrosion

There are several key factors that influence the rate and extent of corrosion in steel:

Environmental Conditions

This encompasses the presence of chlorides, sulfates, moisture, and oxygen which can accelerate the corrosion process. For example, steel structures in coastal areas often bear the brunt of corrosion due to the salt-laden sea breeze.


Generally, an increase in temperature can speed up the corrosion reaction. This is because, at higher temperatures, the molecules in metals and corrosive substances move more quickly, increasing the rate of reaction.

pH Levels

The acidity or alkalinity of a substance, measured by its pH, can influence corrosion. A low pH (acidic conditions) can accelerate corrosion, whereas a higher pH (alkaline conditions) can help to protect the metal.

Material Properties

The properties of the steel itself, such as its composition, microstructure, and mechanical properties also play a role in its susceptibility to corrosion. Certain alloys resist corrosion better than others due to their composition.

Presence of Protective Coatings

The use of protective coatings, like paints or special anti-corrosion treatments, can greatly reduce the rate of corrosion. These coatings act as a physical barrier, protecting the metal from the corrosive environment.

Galvanic Corrosion

Galvanic corrosion occurs when two dissimilar metals come in contact with each other in the presence of an electrolyte, leading to corrosion of the less noble metal. Thus, the choice of materials used together in a structure can significantly influence the corrosion rate.

Physical Stresses

Corrosion can also be facilitated by physical stresses on the metal such as tension, bending, or repeated loading and unloading. These stresses can cause microscopic cracks in the metal surface where corrosion can initiate.

Exposure Time

The length of time the steel has been exposed to a corrosive environment directly affects the rate of corrosion. The more prolonged the exposure, the more severe the damage.

Pollution Level

The level of pollution in the environment, particularly sulfur compounds from industrial processes or vehicle exhaust, can significantly escalate corrosion rates. These compounds can interact with moisture in the air to form acids, which are particularly corrosive.

By understanding these factors, we can better predict, prevent, and manage corrosion in steel structures and components.

Benefits of Pipeline Corrosion Inspection

Pipeline corrosion inspection is a crucial preventive measure that has numerous benefits, which include:

Ensuring Safety

Regular pipeline corrosion inspections can help prevent catastrophic failures that can lead to accidents or environmental disasters. By identifying areas of corrosion early, any necessary repairs or replacements can be made to maintain structural integrity and safety.

Prolonging Lifespan

Through early detection and mitigation of corrosion, the lifespan of the pipeline can be significantly extended. This means that the return on investment for the pipeline infrastructure is improved as it can function effectively for a longer period.

Cost Savings

If left unchecked, corrosion can lead to significant repair and replacement costs. Regular inspections allow for the maintenance of pipelines before the corrosion becomes too severe, thereby avoiding hefty costs in the long term.


Corroded pipelines can compromise the efficiency of the flow of materials. Regular inspections ensure that pipelines remain in optimal condition for the transportation of oil, gas, or other substances, which optimizes productivity and profitability.

Regulatory Compliance

Regular inspections help to ensure compliance with safety and environmental regulations. Any issues can be addressed promptly to prevent potential fines or penalties associated with non-compliance.

Minimizing Downtime

Pipeline failures due to corrosion can lead to significant downtime which can negatively impact operations and profitability. Regular inspections and proactive maintenance can significantly reduce the risk of unexpected downtime.

Establishing Maintenance Priorities

Through regular inspections, pipeline operators can gather valuable data about the rate and location of corrosion. This information can be used to prioritize maintenance activities and manage resources more effectively.

Enhancing Reputation

Conducting regular inspections and maintaining the integrity of the pipeline can enhance a company’s reputation. It signals to stakeholders that the company is committed to safety, environmental responsibility, and operational excellence.

Predicting Future Corrosion

By keeping track of corrosion patterns and rates, inspections can also aid in predicting future corrosion areas. This foresight allows for effective planning and prevention strategies, further extending the service life of the pipeline.

Each of these benefits contributes to the overall operational efficiency, cost-effectiveness, and safety of pipeline infrastructure. By proactively managing and preventing corrosion, operators can protect their investments and ensure the longevity and safety of their infrastructure.

Importance of Pipeline Corrosion Inspections

Pipeline corrosion inspections are paramount for a number of reasons that extend beyond the aforementioned benefits.

Asset Protection

Pipelines are significant investments and their longevity is directly tied to the financial health of the entity that owns them. Regular inspections help to preserve these assets and protect them from premature failure due to corrosion.

Environmental Responsibility

Leaking pipelines due to corrosion can lead to the harmful release of substances into the environment. Inspections help identify potential weak points and thereby prevent such environmental hazards.

Public Health

Corrosion in pipelines, especially those carrying water or gas to residential areas, can impact public health. Regular inspection ensures the quality and safety of these essential services.

Industry Reputation

Regular inspections and subsequent maintenance demonstrate a company’s commitment to safety and environmental stewardship, thereby enhancing its reputation in the industry.

Operational Continuity

Pipeline failures can cause severe disruptions to operations, leading to downtime and lost revenue. Regular inspections allow for planned maintenance activities, thus ensuring operational continuity.

Liability Mitigation

Regular inspection and maintenance of pipelines can help to mitigate potential legal liabilities. Any harm caused due to pipeline failure can lead to lawsuits and fines. Proactive inspections demonstrate due diligence in maintaining safe operations, thereby reducing the likelihood of legal complications.

Risk Mitigation

Inspections also play an integral role in risk mitigation. They aid in identifying potential risks and help in the implementation of appropriate measures to counter these risks. This can include anything from minor repairs to complete replacements, depending on the severity of the corrosion detected.

Customer Satisfaction

Ensuring the smooth and uninterrupted supply of oil, gas, or water, contributes significantly to customer satisfaction. Regular inspections help to maintain the quality of these services, leading to happier, more loyal customers.

Sustainability Goals

By focusing on preventive measures such as regular inspections, companies can contribute to sustainability goals. Less frequent pipeline replacements mean reduced consumption of resources and lower environmental impact, aligning with global conservation efforts.

Insurance Premiums

Regular pipeline inspections can potentially lead to lower insurance premiums. Companies that can demonstrate a consistent record of preventive maintenance may be viewed as lower risk by insurers, reflecting in lower premium costs.

Workforce Morale

A well-maintained infrastructure can also boost workforce morale. Employees are likely to take pride in working for a company that prioritizes safety and environmental responsibility. This can also lead to improved productivity at work.

The importance of pipeline corrosion inspections cannot be understated. It’s a proactive measure that ensures the smooth operation and longevity of the infrastructure, while also serving to protect the environment, public health, and the reputation of the organization.

The corrosion rate can depend on many factors, including the type and concentration of corrosive agents, the presence of impurities in the steel, the surface conditions of the steel, and environmental factors such as temperature, humidity, and mechanical stress.

Corrosion is a primary concern for oil and gas pipelines as it can cause significant damage to the pipeline, leading to leaks, reduced flow capacity, and in severe cases, pipeline failure. 

Reasons for Controlling Corrosion in Oil and Gas Pipelines


Pipeline corrosion can result in leaks and spills, posing a significant risk to public safety, the environment, and wildlife.

Economic Loss

Corrosion can lead to reduced flow capacity, which results in a loss of revenue for the pipeline operator and a decrease in the supply of oil and gas to customers. Additionally, the cost of repairing or replacing damaged pipelines can be high.

Environmental Impact

Leaks and spills from pipelines can have serious ecological consequences, including contamination of soil and groundwater, damage to wildlife and habitats, and harm to public health.

Regulatory Compliance

The oil and gas industry is subject to strict pipeline safety and environmental protection regulations. Pipeline operators are required to implement measures to prevent and control corrosion.

Operational Efficiency

Corrosion can lead to a decrease in the efficiency of a pipeline’s operation. It can cause blockages and reduce the flow rate, thus demanding more energy to pump oil and gas through the pipeline. By controlling corrosion, pipeline operators can maintain optimal operational efficiency.

Asset Longevity

Controlling corrosion also contributes to the longevity of the pipeline infrastructure. Corrosion is a significant factor in the degradation of metal, which can lead to a shortening of the pipeline’s lifespan. Proper monitoring and control of corrosion can help pipelines last longer, reducing the need for costly replacements.

Investor Confidence

Investors are more inclined to invest in operations that are safe, reliable, and efficient. Pipeline corrosion can raise concerns about the possibility of leaks, failures, and subsequent regulatory penalties, which can affect investor confidence. Managing corrosion effectively can reassure investors of the integrity of the operation.

Company Reputation

Pipeline failures due to corrosion can negatively impact a company’s reputation, leading to a loss of trust among stakeholders, including customers, investors, and regulatory bodies. Effective corrosion control can help maintain a positive reputation for responsibility and reliability in the industry.

Future Readiness

As the industry moves towards stricter environmental and safety standards, having corrosion control measures in place ensures readiness for future regulatory changes. It signals a proactive approach to safety and environmental protection, making it easier to adapt to new regulations when they come into effect.

Therefore, it is crucial for oil and gas pipeline operators to implement effective corrosion control and management strategies to minimize the risk of pipeline failure and ensure their pipelines’ safety, reliability, and efficiency. This typically involves regular monitoring and maintenance of the pipeline, including applying protective coatings, cathodic protection, and other corrosion mitigation measures.

The Federal Energy Regulatory Commission (FERC) regulates the safety of natural gas pipelines under 45 CFR Part 192, which establishes standards for the design, construction, operation, and maintenance of pipelines. Along with 45 CFR Part 195, “Transportation of Hazardous Liquids by Pipeline,” is a regulation from the Pipeline and Hazardous Materials Safety Administration (PHMSA). According to these regulations, pipeline operators are required to perform various corrosion control and inspection activities to ensure the integrity and safety of their pipelines.

Corrosion Inspections That Must Be Performed

External Corrosion Control

External corrosion is a significant concern for pipelines, and operators must implement measures to prevent it. This can include applying protective coatings, cathodic protection, and monitoring for corrosion.

Internal Corrosion Control

Internal corrosion can occur when the pipeline is exposed to corrosive substances such as water, acids, or salts. Operators must implement measures to control internal corrosion, including monitoring the chemical composition of the pipeline’s contents, controlling the flow rate and velocity, and using corrosion inhibitors.

Corrosion Monitoring

Operators must regularly monitor their pipelines for signs of corrosion, using tools such as corrosion coupons, electrical resistance probes, and ultrasonic thickness measurements.

In-Line Inspection

Operators must use in-line inspection tools to assess the pipeline’s condition and detect corrosion, cracks, and other anomalies. This may include devices such as smart pigs, which use sensors to gather data on the pipeline’s condition.

Hydrostatic Testing

Operators may be required to perform hydrostatic testing, where the pipeline is filled with water and pressurized to a certain level, to check for leaks and assess the pipeline’s ability to withstand pressure.

Risk-Based Inspection

Operators must use a risk-based inspection (RBI) program to prioritize examining high-risk pipeline segments and ensure that critical areas are thoroughly inspected regularly.

Direct Assessment

Direct assessment is another vital inspection method that involves evaluating the pipeline’s exterior condition from the surface. It typically includes methods like close-interval surveys, soil resistivity testing, or stray current interference.

Visual Inspection

Visual inspection is a straightforward technique that involves inspecting the pipeline for visible signs of corrosion. This can be conducted during routine maintenance or when the pipeline is exposed for other reasons.

Microbiological Testing

Microbiological-induced corrosion (MIC) is a significant cause of pipeline corrosion. Therefore, operators should perform regular microbiological testing to detect the presence of corrosion-inducing bacteria.

Coating Inspection and Evaluation

This inspection assesses the condition of the pipeline coating, which acts as the first line of defense against corrosion. Tools such as holiday detectors can be used to spot defects in the coating.

Ultrasonic Testing (UT)

Ultrasonic testing uses sound waves to detect and measure the wall thickness of a pipeline, which can help detect corrosion’s presence. It is particularly useful for detecting internal and external corrosion.

Radiographic Testing (RT)

Radiographic testing is a non-destructive testing method that uses X-rays or gamma rays to view the internal structure of a pipeline and detect corrosion or other defects.

These inspections are intended to ensure that operators are regularly monitoring their pipelines and taking necessary steps to control and prevent corrosion from maintaining the integrity and safety of their pipelines. Failure to comply with these regulations can result in fines, penalties, and other enforcement actions.

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Corrosion coupons are metal samples placed in pipelines to monitor the corrosion rate. The coupons are periodically retrieved from the channel and then inspected in a laboratory to determine the amount of metal loss and the corrosion rate.

Process of Examining Corrosion Coupons for Pipelines


Corrosion coupons are retrieved from the pipeline and cleaned to remove any debris or deposits that may interfere with the inspection process.

Weight Measurement

The weight of the coupon is measured before and after exposure to the pipeline environment to determine the amount of metal loss due to corrosion.

Visual Inspection

The coupons are visually inspected to determine the type and distribution of corrosion products on the surface, including rust, pits, and corrosion scales.

Thickness Measurement

The thickness of the coupon is measured using a micrometer or other precision instrument to determine the extent of metal loss due to corrosion.

Analysis of Corrosion Products

The corrosion products on the surface of the coupon may be analyzed to determine the type of corrosion and the factors contributing to it, such as the presence of certain chemicals or conditions in the pipeline environment.

Calculation of Corrosion Rate

The amount of metal loss and the exposure time are used to calculate the corrosion rate, expressed in terms of mils per year or other units.

Metallurgical Analysis

Once the initial visual inspection and measurements have been conducted, a more in-depth metallurgical analysis of the corrosion coupon may be performed. This could involve a microscopic examination of the coupon surface to identify the types of corrosion damage and their distribution. Techniques such as scanning electron microscopy (SEM) or energy-dispersive X-ray spectroscopy (EDX) may be used to provide detailed images of the surface topography and element composition.

Microbiological Testing

In instances where microbiologically influenced corrosion (MIC) is suspected, microbiological tests can be performed on the corrosion coupons. This typically involves culturing samples in a laboratory to detect and identify any bacteria present that could be contributing to the corrosion process.

Electrochemical Tests

For some corrosion mechanisms, electrochemical testing may be conducted. This process uses various techniques, such as potentiodynamic polarization or electrochemical impedance spectroscopy, to characterize the electrochemical behavior of corrosion on the coupon surface. This can help identify the type of corrosion, such as pitting or crevice corrosion, and provide insights into the corrosion mechanisms at play.

Additional Cleaning

Following the metallurgical and microbiological analyses, additional cleaning may be required to remove any remaining corrosion products. This can involve mechanical cleaning methods or chemical cleaning processes, depending on the type and extent of the corrosion.

Final Inspection and Documentation

Once all tests and analyses have been completed, a final inspection is conducted. This includes a final weight and thickness measurement and a thorough visual examination to assess any changes following the additional cleaning. The results of all analyses, along with high-quality images of the coupon, are included in a comprehensive report that documents the findings and provides recommendations for corrosion management in the pipeline.

This information is used by pipeline operators to assess the effectiveness of their corrosion control measures and to make decisions about how to manage and mitigate corrosion in their pipelines. By regularly monitoring the corrosion rate, operators can ensure the integrity and safety of their pipelines and prevent the formation of leaks and other safety hazards.

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    Standards Used to Inspect Pipeline Corrosion Coupons

    NACE International

    NACE International, The Corrosion Society, is a professional organization that provides standards and guidelines for assessing and managing corrosion. NACE International publishes several standards related to the inspection of pipeline corrosion coupons, including NACE TM0177-2017 “Standard Test Method for Determining Corrosion Rates and Related Information from Electrochemical Measurements on Operating Plant and Laboratory-Exposed Coupons.”

    ASTM International

    ASTM International is a standards development organization that provides technical standards for various materials and processes, including the inspection of pipeline corrosion coupons. ASTM G1-03(2018) “Standard Practice for Preparing, Cleaning and Evaluating Corrosion Test Specimens” provides guidelines for preparing, cleaning, and evaluating corrosion coupons to obtain accurate and reliable results.

    API Standards

    The American Petroleum Institute (API) is a trade organization that represents the oil and natural gas industry and provides standards and guidelines for inspecting and managing corrosion in pipelines. API RP 11G2 “Recommended Practice for In-Service Inspection of Corrosion Coupons in Oil and Gas Production” provides guidelines for examining and interpreting corrosion coupons in the oil and gas production industry.

    ISO Standards

    The International Organization for Standardization (ISO) offers an array of standards related to corrosion control in the oil and gas industry. Among these, ISO 15156-3:2015 “Materials for use in H2S-containing environments in oil and gas production” provides guidelines for assessing and managing corrosion in sour service environments where hydrogen sulfide is present, which can be particularly corrosive to pipelines.

    SSPC Standards

    The Society for Protective Coatings (SSPC), now known as the Association for Materials Protection and Performance (AMPP), provides standards for the protection of industrial structures against corrosion. For instance, SSPC-SP 5/NACE No.1 “White Metal Blast Cleaning” is a standard that details a surface preparation method for removing all visible corrosion, mill scale, and foreign matter from steel surfaces.

    BS Standards

    British Standards (BS) also provide valuable guidelines for corrosion protection. BS EN ISO 3651-2:2004 “Determination of Resistance to Intergranular Corrosion of Stainless Steels” can be used to evaluate the performance of corrosion coupons made from stainless steel, a common material in pipelines.

    DIN Standards

    Germany’s Deutsches Institut für Normung (DIN) also offers relevant standards. DIN EN ISO 8044 “Corrosion of metals and alloys – Basic terms and definitions” provides a foundation for understanding and identifying different forms of corrosion, aiding in the effective assessment of corrosion coupons.

    These standards provide guidelines for the preparation, inspection, and analysis of pipeline corrosion coupons to ensure that the results are accurate and consistent. Using these standards helps to ensure that corrosion coupons are collected, handled, and analyzed in a standardized and consistent manner, providing valuable data for assessing and managing corrosion in pipelines.

    Let PMET Help

    Regular inspection and analysis of pipeline corrosion coupons are crucial for maintaining the integrity and safety of pipelines. By adhering to established standards by organizations such as NACE International, ASTM International, API, ISO, SSPC, BS, and DIN, you can ensure that your corrosion management strategies are effective and reliable. 

    At PMET, we’re committed to delivering accurate and highly reliable corrosion analysis services. Our team of dedicated professionals is ready to assist you in ensuring the longevity and safety of your pipelines. Feel free to reach out to us for any queries or assistance you may need in your corrosion management procedures. Contact us today for more details.