Some steel pipelines buried underground, originally designed to last for decades, develop perforations and leaks within just a few years. This “short lifespan” not only causes enormous economic losses but can also lead to serious safety and environmental incidents.
The rapid corrosion of underground pipelines is by no means caused by a single factor; rather, it is the result of the combined effects of the environment, construction practices, and materials.
I. Causes of Rapid Pipeline Corrosion
1. Stray Current Interference
- If there are subways, electrified railways, or high-voltage power lines near a pipeline, “stray currents” can be generated in the soil. When these currents flow along the pipeline and exit the pipeline at a certain point to return to the soil, electrochemical corrosion occurs on the steel at the discharge point. In such cases, metal loss can occur at a rate measured in years or even months.
2. Microbial Corrosion
- In oxygen-deprived, moist underground environments (such as swamps or dense clay), microorganisms such as sulfate-reducing bacteria proliferate. The substances produced by their metabolism are highly corrosive and form localized deep pits on the pipeline surface, commonly known as “pitting corrosion.” Although this type of corrosion affects a small area, it penetrates the metal rapidly.
3. Substandard Anti-Corrosion Coating Quality or Damage During Installation
- The anti-corrosion coating serves as the first line of defense against soil corrosion. If manufacturing processes at the factory are substandard, or if the surface is bumped or scratched during transportation or on-site hoisting, the coating may develop pinholes or cracks that are difficult to detect with the naked eye. Once moisture penetrates, corrosion will silently spread in hidden areas.
II. The Mainstay of Modern Underground Pipeline Protection
To overcome the complex corrosive environments encountered underground, the pipeline industry has developed corrosion-resistant coatings with enhanced performance. Currently, the two mainstream solutions on the market are:
1. FBE-coated steel pipes
FBE is a corrosion-resistant coating formed by high-pressure spraying of epoxy powder onto the surface of preheated steel pipes, causing it to melt, cure, and solidify. It bonds extremely strongly to the steel pipe surface and offers excellent resistance to chemical corrosion and cathodic delamination. This type of pipe is particularly well-suited for standard pipeline networks in relatively flat terrain with low soil aggressiveness, or as the base layer of a composite corrosion-resistant coating.
2. 3PE-Coated Steel Pipes
These are currently recognized as one of the pipe types with the best overall protective performance. It combines the advantages of three materials: an FBE base layer, a copolymer adhesive middle layer, and a high-density polyethylene outer layer. 3PE-coated steel pipes are like a thick suit of armor for the steel pipe, effectively withstanding impacts from earth and rock during construction and backfilling. They are suitable for complex projects involving harsh geological conditions, areas with abundant gravel, or those requiring directional drilling.
III. Engineering Recommendations for Extending the Service Life of Underground Pipelines
To prevent pipelines from being corroded and perforated within just a few years, purchasing high-quality pipes alone is not sufficient. It is necessary to adopt a three-pronged approach:
1. Scientific Material Selection and Environmental Investigation
Before construction begins, the soil resistivity, pH value, and the presence of stray currents must be carefully measured and evaluated. Based on the actual geological conditions, appropriate anti-corrosion materials should be selected.
For normal sections, FBE-coated steel pipes can be used. However, for areas with complex geological conditions or rocky sections, 3PE-coated steel pipes should be given priority due to their higher mechanical strength and better resistance to external damage.
2. Strict Control of Construction and Backfilling Quality
After the pipeline trench is excavated, it is strictly prohibited to directly backfill the trench with soil or sand containing sharp stones. Before backfilling, the entire pipeline must be inspected using a holiday detector (spark testing equipment) to check for any damage to the anti-corrosion coating.
If any coating defects are found, they must be repaired immediately according to the relevant standards.
3. Mandatory Installation of Cathodic Protection Systems
No matter how good the anti-corrosion coating is, small defects or leakage points may still occur. Therefore, underground pipelines must be equipped with a cathodic protection system (such as sacrificial anode protection or impressed current cathodic protection).
Through electrochemical methods, cathodic protection ensures that the pipeline becomes the cathode under protection, thereby reducing corrosion.
The combination of anti-corrosion coating and cathodic protection is currently one of the most effective and economical methods for extending the service life of pipelines.