Anti-corrosion of buried pipelines
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I would like to ask everyone for advice. I am working on a project related to oil storage and transportation, and concerning pipeline anti-corrosion, pipelines buried near the sea are required to use an enhanced 5-oil-4-cloth coating. But later, through discussions between the owner and the construction contractor, it was reduced to two layers of fabric and three layers of paint. Whether this will work, and what specific harms there are
Firstly, the standard grade uses 2 layers of fabric and 4 layers of coating; the enhanced grade uses 3 layers of fabric and 5 layers of coating, while the ultra-enhanced grade uses 4 layers of fabric and 6 layers of coating. Since your location is near the sea, the soil has a high degree of corrosiveness. The main cause of corrosion is undoubtedly chloride ions. I believe your clients are considering cost factors.
With normal anti-corrosion construction, two layers of fabric and three coats are sufficient; the initial design of four layers of fabric and five coats was perhaps overly conservative. The difference between the two is their thickness, which primarily results in different strengths and different resin contents. Two layers of fabric and three coats can meet the requirements, provided that the fabric is thick enough; in other words, it must have sufficient weight. For use in pipes, a weight of 600 or 800 g/cm2 is generally required, as this ensures that there is enough resin for proper penetration. Additionally, if corrosion protection is needed, two additional surface coats are necessary, and these two coats are not included in the count of the two layers of fabric
Anticorrosion coating structure: a. Standard anticorrosion type (two bases and two top coats): one primer → one primer → one top coat → one top coat. The dry film thickness is about 100 μm. b. Enhanced anti-corrosion type (one fabric and three coats of paint): one coat of primer → one layer of glass fiber fabric → two coats of topcoat. The dry film thickness is about 200 μm. c. Highly enhanced anti-corrosion type (two fabrics, four coats of paint): one coat of primer → one layer of glass fiber fabric → one coat of primer → one layer of glass fiber fabric → two coats of topcoat. The dry film thickness is approximately 300 μm. Or one coat of primer → two layers of glass fiber cloth wrapped continuously → one coat of primer → two coats of topcoat. The dry film thickness is approximately 300 μm. d. Extra-strong anti-corrosion type (three layers of fabric and five layers of paint): One primer + two layers of glass fiber fabric wound continuously → one primer → one layer of glass fiber fabric → one primer → two layers of topcoat. The dry film thickness is approximately 450 μm. Or one coat of primer → one layer of glass fiber cloth → one coat of primer → one layer of glass fiber cloth → one coat of primer → one layer of glass fiber cloth → two coats of topcoat. The dry film thickness is approximately 450 μm. The external anti-corrosion protection for buried steel pipelines includes coatings based on petroleum asphalt as the anti-corrosion layer material (including: three-oil two-cloth, four-oil three-cloth, five-oil four-cloth), as well as coatings based on epoxy coal tar asphalt as the anti-corrosion layer material (including: two-oil, three-oil one-cloth, four-oil two-cloth).
First of all, it should be noted that both \"two coats and three layers of oil\" and \"four coats and five layers of oil\" do not meet the technical standards; according to SYT 0447-96 requirements, the extra-strength version with two coats should have seven layers of coating； According to the requirements of GJJ33-89, the reinforced grade with two layers of fabric should have five coats of paint; applying only three coats of oil to the two layers of fabric definitely does not meet the technical specifications. Is it possible to reduce it from four layers to two layers? I believe that as long as construction and inspection are carried out in strict accordance with the standard technical requirements, two layers will be sufficient to meet the usage requirements. As for the \"harm it may cause,\" it should not result in any harm; it merely reduces the thickness and grade of the anti-corrosion layer slightly.
3PE provides better corrosion protection, as it uses a polyethylene coating for protection
1. It is possible to determine the appropriate type based on the soil’s resistivity. The thicknesses of different types vary greatly; generally, for ordinary types: soil resistivity > 20. For enhanced types: soil resistivity 5–20. For ultra-enhanced types: soil resistivity
Owners who save so much money surely don’t want to invest in cathodic protection! Cathodic protection is advisable.
Long-distance pipelines generally employ external current cathodic protection technology; of course, the surface also requires a protective coating.
It is recommended to take into comprehensive consideration the physicochemical properties of the substance transported by the pipeline, temperature and pressure, as well as the acidity or alkalinity of the surrounding soil