### Corrosion, Cathodic Protection & Pipelines: Topic 3 – Internal Corrosion & Microbiologically Influenced Corrosion (MIC) of Pipelines

Pipelines are the arteries of the oil, gas, and water industries, providing a safe, reliable, and efficient means of transporting vital resources. However, internal corrosion and Microbiologically Influenced Corrosion (MIC) pose significant threats to pipeline integrity, leading to potential safety hazards, environmental damage, and substantial financial losses. Understanding and controlling these forms of corrosion are crucial for maintaining the safety, reliability, and longevity of pipelines.

In this third article of our series, we delve into the mechanisms, prevention, control, and monitoring of internal corrosion and MIC in pipelines, providing detailed insights for professionals tasked with ensuring pipeline integrity.

#### Understanding Internal Corrosion and MIC in Pipelines

Internal Corrosion: This type of corrosion occurs within the pipeline and is primarily caused by the interaction of the pipeline's internal environment with the transported fluids. Pipelines transporting wet gas, liquid hydrocarbons, water, and well fluids are particularly susceptible to internal corrosion.

Mechanisms of Corrosion:

- Hydrogen Sulfide (H?S) and Carbon Dioxide (CO?) Corrosion: These gases are common in oil and gas production and can lead to the formation of acidic environments that corrode steel pipelines.

- Flow-Induced Corrosion: High-velocity fluids can cause erosion-corrosion, where mechanical wear exacerbates chemical corrosion.

- Multi-Phase Flow: In pipelines carrying a mixture of gas, liquid, and solids, the different phases can cause localized corrosion and wear.

- Corrosion Rate Calculations: Accurate calculations are essential for predicting pipeline longevity and scheduling maintenance.

- Microbiologically Influenced Corrosion (MIC): MIC is caused by the activity of microorganisms, such as sulfate-reducing bacteria, which can create aggressive environments leading to pitting and localized corrosion.

- Corrosion Under Deposits: Accumulation of solids in pipelines can create differential aeration cells, leading to localized corrosion.

- Neutral Aqueous Solutions: Corrosion can also occur in the presence of neutral water, especially in pipelines that are not properly dehydrated.

#### Corrosion Prevention and Control Methods

Effective corrosion control requires a multi-faceted approach, including:

- Internal Coated Pipelines: Coatings provide a physical barrier between the pipeline material and the corrosive environment, significantly reducing corrosion rates.

- Corrosion Inhibitors: Chemical inhibitors can be injected into the pipeline to form a protective film on the metal surface, preventing corrosive agents from reaching the metal.

- Bactericides: These chemicals are used to control the population of corrosive bacteria, particularly those responsible for MIC.

- Dehydration: Removing water from the pipeline can prevent many forms of internal corrosion, especially in gas pipelines.

- Cleaning Pigging: Regular pigging operations remove deposits and scale that can harbor bacteria or create conditions for under-deposit corrosion.

#### Corrosion Monitoring Systems and Techniques

Monitoring is a critical component of pipeline integrity management, enabling early detection of corrosion and timely intervention. Key techniques include:

- Types of Corrosion Monitoring Systems (CMS): These systems can include electrical resistance probes, linear polarization resistance probes, and hydrogen probes to monitor corrosion rates in real-time.

- Location and Use of Coupons: Coupons are small metal samples placed inside the pipeline to measure corrosion over time.

- Iron Count and Bacteria Count: Analyzing the concentration of dissolved iron and bacteria in pipeline fluids can indicate the presence of corrosion.

- Residue and Fluid Analysis: Chemical analysis of pipeline residues and transported fluids provides insight into the corrosive potential of the environment.

- Temperature and Flow Monitoring: Fluctuations in temperature and flow rates can exacerbate corrosion, making it essential to monitor these parameters closely.

#### Pipeline Inspections and Corrosion Assessment

Regular inspections are necessary to assess the condition of the pipeline and the effectiveness of corrosion control measures:

- In-Line Inspections (ILI): Tools like smart pigs are used to detect and quantify corrosion, wall thickness, and metal loss along the length of the pipeline.

- Non-Piggable Pipeline Inspections: Manual ultrasonic thickness measurements and other NDT methods are employed where ILI tools cannot be used.

- Corrosion Rate and Assessment: Data from CMS and inspections are analyzed to determine the corrosion rate and identify the underlying mechanisms.

- Identification of Corrosion Mechanisms: Understanding the specific causes of corrosion, whether chemical, mechanical, or biological, is key to developing targeted mitigation strategies.

#### Fitness for Purpose and Remaining Life Assessment

As pipelines age, it's crucial to assess whether they remain fit for service:

- Remaining Life Assessment: This involves estimating the remaining safe operating life of a pipeline based on current corrosion rates and damage.

- Fitness for Purpose: Engineers evaluate whether the pipeline can continue to operate safely under its current conditions or if repairs or replacements are necessary.

#### Conclusion

The control and management of internal corrosion and MIC in pipelines are critical to ensuring the safety, reliability, and efficiency of oil, gas, and water transportation systems. A comprehensive Pipeline Integrity Management (PIM) program that includes corrosion control, inspection, assessment, and communication is essential for maintaining pipeline integrity. By understanding the mechanisms of corrosion, applying effective prevention and control methods, and utilizing advanced monitoring and inspection techniques, operators can extend the life of their pipelines while safeguarding human life and the environment.

Further Let us explore the challenges and solutions related to external corrosion and cathodic protection of pipelines, providing a holistic view of corrosion management in pipeline systems.

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