MGPS anode for Subsea Pipelines

Submarine pipelines, serving as the “underwater lifeline” for global energy and resource transportation, undertake the cross-oceanic transport of critical media such as oil, natural gas, seawater, and industrial wastewater. However, submarine pipelines, constantly immersed in the complex marine environment, always face the severe challenge of marine biofouling—barnacles, shellfish, algae, and other marine organisms continuously adhere to the outer and inner walls of the pipelines, forming a dense layer of biofouling.

Marine Growth Prevention System (MGPS) is a core technology for solving the problems of biofouling and corrosion in submarine pipelines. Through the scientific principle of electrolysis, it achieves dual protection of “antifouling + anticorrosion,” and has become an essential system for the construction and operation of modern submarine pipelines.

Types of MGPS Systems

Based on the transported medium (oil, natural gas, seawater, etc.), marine environment (water temperature, biological activity, salinity), and pipeline material (steel, titanium alloy, etc.), MGPS systems are mainly divided into three core types.

(I) Electrolytic Metal Ion Type MGPS

The electrolytic metal ion type is currently the most widely used MGPS type for subsea pipelines, accounting for over 70% of the subsea pipeline protection market share. Its core advantages lie in its simple structure, stable operation, wide protection range, and simultaneous antifouling and anti-corrosion functions, making it particularly suitable for pipeline protection in low-to-medium biological activity marine areas. This type of system uses copper, aluminum, and iron as core electrode materials, and drives an electrolytic reaction through a DC power supply to release metal ions and hydroxide flocculents, forming a double protective layer.

Core Components: Mainly includes copper anodes, aluminum/iron anodes, a DC control unit, a current monitoring module, and an underwater mounting bracket. Electrodes are typically installed at the pipeline inlet (inner wall protection) or key parts of the outer wall (outer wall protection), ensuring that metal ions can flow with the medium or diffuse into the entire protected area through seawater.

Key Features: The copper ions (Cu²⁺) released by the copper anode electrolysis, at a concentration of 2 μg/L, effectively inhibit cell division and growth of algae and shellfish larvae, preventing biofouling at its source. The aluminum/iron anode electrolysis generates aluminum hydroxide (Al(OH)₃) or iron hydroxide (Fe(OH)₃) flocculent substances, which are highly viscous and adhere to the pipe surface to form a dense protective film, isolating seawater from the metal substrate and achieving corrosion protection.

Applicable Scenarios: Submarine pipelines in temperate and subtropical waters with low to medium biological activity, such as offshore oil pipelines and seawater cooling pipelines in East and North China. It is also suitable for steel pipelines. If the pipeline is made of aluminum or copper, an iron anode must be used to avoid electrochemical reactions between the electrode and the substrate, which would exacerbate corrosion.

Advantages: Long electrode replacement cycle (3-5 years for copper anodes, 2-3 years for aluminum anodes), and remote monitoring of electrode wear, eliminating the need for frequent underwater operations, reducing maintenance costs and safety risks.

(II) Seawater Electrolysis Type MGPS

The seawater electrolysis type MGPS, also known as the “chlorine electrolysis type,” works by electrolyzing seawater to generate a strong oxidant that directly kills marine larvae and spores. It is suitable for protecting subsea pipelines in highly biologically active sea areas. This type of system has higher requirements for electrode materials, requiring them to possess strong corrosion resistance and high electrolysis efficiency, making it the preferred protection solution for subsea pipelines in tropical waters.

Core Components: It consists of a platinum-plated titanium electrode (or ruthenium-iridium coated titanium anode), an electrolysis reaction tank, a DC power supply, an oxidant concentration monitoring module, and an underwater sealing unit. The platinum-plated titanium electrode is the core component, capable of stable operation in high-salinity and highly corrosive environments, with an electrolysis efficiency exceeding 95%.

Key Features: This system generates strong oxidants such as chlorine (Cl₂) and hypochlorous acid (HClO) through the electrolysis of seawater (containing sodium chloride). These substances have strong bactericidal properties, killing algae and shellfish larvae within 10-20 seconds, achieving an antifouling efficiency of over 98%. Simultaneously, the oxidants inhibit bacterial growth within the pipeline, reducing the corrosive effects of biological metabolism, achieving a triple effect of “antifouling + antibacterial + anti-corrosion.”

Applicable Scenarios: Submarine pipelines in tropical, highly biologically active sea areas, such as deep-sea oil pipelines and seawater desalination pipelines in South China, Southeast Asia, and the Middle East; particularly suitable for submarine pipelines transporting clean water and industrial water injection, ensuring both water quality cleanliness and pipeline protection.

Precautions: Real-time monitoring of the oxidant concentration is necessary to prevent excessive concentrations from corroding the pipeline or polluting the marine environment after discharge. The International Maritime Organization (IMO) clearly stipulates that the oxidant concentration discharged from seawater electrolysis-type MGPS must be below 0.5 mg/L, and in some stricter regions, the standard has been lowered to below 0.3 mg/L.

(III) Composite MGPS

The composite MGPS is an upgraded product combining the advantages of the two types mentioned above. Through a dual mode of “electrolysis of metal ions + electrolysis of seawater,” it can both inhibit the growth of marine organisms and enhance the corrosion resistance of pipelines, making it suitable for large-scale subsea pipeline systems transporting complex media, such as deep-sea energy pipelines and multi-media transport pipelines in port industries.

Core Advantages: The operating mode can be adjusted according to seasonal changes and marine biological activity—switching to seawater electrolysis mode during the summer when biological growth is vigorous to improve sterilization efficiency; switching to metal ion electrolysis mode during the winter when biological growth is slow to reduce energy consumption and extend electrode life; simultaneously, the system has an automatic adaptation function, which can optimize electrolysis parameters in real time according to changes in pipeline medium flow and temperature to ensure stable protective effects.

Core Components: It integrates a copper/aluminum anode module, a platinum-titanium plated electrode module, an intelligent control unit, multi-dimensional sensors (biological activity, salinity, temperature), and a cloud data platform to achieve intelligent control throughout the entire process.

Applicable Scenarios: Marine areas with high fluctuations in biological activity (such as subsea pipelines in estuary ports, where the mixing of seawater and freshwater leads to unstable biological activity), large-scale deep-sea energy pipelines (such as pipelines in deep-water oil and gas fields in the South China Sea), and composite pipeline systems for port-adjacent industries. Currently, the subsea pipeline networks of Singapore Port and Dubai Port have extensively adopted composite MGPS systems.

Application Value: Compared to single-type systems, composite MGPS improves protection efficiency by 20%, reduces energy consumption by 15%, and extends pipeline lifespan by 50%, making it particularly suitable for high-value, high-risk subsea pipeline projects.

Working Principle of MGPS Systems

The core working principle of MGPS systems is “electrolysis.” By applying a stable direct current to the electrodes, using seawater (or moisture in the pipeline medium) as the electrolyte, an oxidation-reduction reaction occurs at the electrodes, generating substances with antifouling and anti-corrosion functions.

(I) Working Principle of Electrolytic Metal Ion Type MGPS

This type of system achieves protection through a dual mechanism of “metal ion antifouling + hydroxide flocculent anti-corrosion.” It uses no chemical agents and meets green protection requirements:

Copper Anodic Oxidation Reaction (Core of Antifouling): Under the action of a direct current power supply, the copper anode undergoes an oxidation reaction. Copper atoms lose electrons and dissolve in the seawater or pipeline medium, generating copper ions (Cu²⁺), the reaction formula being: Cu → Cu²⁺ + 2e⁻. When the copper ion concentration reaches 2μg/L (2mg/m³), it can destroy the cell membrane and respiratory enzyme activity of marine larvae, inhibiting their growth and attachment. Copper ions exhibit targeted toxicity, effective only against marine larvae, with minimal impact on the marine ecosystem, thus meeting IMO environmental standards.

Aluminum/Iron Anodizing Reaction (Core of Corrosion Prevention): Simultaneously, the aluminum anode (or iron anode) undergoes an oxidation reaction, where aluminum atoms lose electrons to generate aluminum ions (Al³⁺), the reaction being: Al → Al³⁺ + 3e⁻. These aluminum ions combine with hydroxide ions (OH⁻) in seawater to form aluminum hydroxide (Al(OH)₃) flocculents. These flocculents are highly viscous and diffuse with the medium or seawater, adhering to the inner and outer walls of the pipe, forming a dense protective film approximately 0.1-0.3 mm thick. This film isolates corrosive media such as chloride ions and oxygen from contact with the metal substrate, significantly reducing the corrosion rate.

Cathodic reduction reaction (loop maintenance): A reduction reaction occurs at the iron cathode in the system (or the pipe itself acts as the cathode). Water molecules gain electrons at the cathode surface, generating hydrogen gas (H₂) and hydroxide ions (OH⁻). The reaction equation is: 3H₂O + 2e⁻ → H₂↑ + 2OH⁻. This reaction not only maintains the stable operation of the electrolysis loop but also, through the cathodic protection principle, reduces the potential of the pipe’s metallic substrate, further inhibiting seawater corrosion of the pipe.

(II) Working Principle of Seawater Electrolysis Type MGPS

The core of this type of system is “electrolysis of seawater to generate a strong oxidant, killing marine organisms.” The reaction process is concentrated within the electrolysis tank, offering greater controllability and making it suitable for high-intensity protection in highly biologically active marine areas:

Seawater Electrolysis Reaction: Driven by a DC power supply, a platinum-titanium plated electrode (anode) and cathode form an electrolysis circuit. Seawater (containing sodium chloride) undergoes an electrolysis reaction on the electrode surface. Chlorine gas (Cl₂) is generated at the anode, with the reaction formula: 2Cl⁻ – 2e⁻ → Cl₂↑; hydrogen gas (H₂) and hydroxide ions (OH⁻) are generated at the cathode, with the reaction formula: 2H₂O + 2e⁻ → H₂↑ + 2OH⁻. To ensure safety, the system maintains a flow rate of ≥1.5 m/s through a pressurized pipeline, allowing hydrogen gas to be discharged with the seawater, ensuring that the hydrogen concentration at the discharge port is below 25% of the lower explosive limit, complying with SOLAS safety standards.

Oxidant Generation: Chlorine gas generated at the anode reacts with seawater to further produce hypochlorous acid (HClO) and sodium hypochlorite (NaClO), with the following reaction equations: Cl₂ + H₂O → HClO + HCl, Cl₂ + 2NaOH → NaClO + NaCl + H₂O. Both hypochlorous acid and sodium hypochlorite are strong oxidants that can rapidly destroy the cellular structure of marine larvae, killing algae and shellfish larvae within 10-20 seconds, achieving an antifouling efficiency of over 98%.

The DC control unit automatically adjusts the electrolysis current based on seawater flow and biological activity data (collected in real-time by sensors) to ensure the oxidant concentration remains within a safe range of 0.2-0.5 mg/L. Too low a concentration will not achieve the desired antifouling effect, while too high a concentration will corrode the metal substrate of the pipe’s inner wall and may also pollute the marine environment after seawater discharge. In addition, the system also has an automatic acid washing function. When scale forms on the electrodes, the acid washing program can be started automatically to remove the scale and ensure stable electrolysis efficiency.