How can the service life of spiral welded steel pipes be extended?

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2021-03-16

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Spiral steel pipes are primarily used for water supply, heating, pile foundation projects, and more. Since long-distance pipeline transportation typically involves a long-term investment, project owners seek to extend the service life of these pipelines and ensure they remain in perfect condition throughout the contract period. So, how can the service life of spiral steel pipes be improved? The following sections provide a detailed analysis.

　　 Spiral steel pipe It is primarily used in water supply, heating, and pile‑foundation projects. Long‑distance pipeline transportation typically involves a long‑term investment, and project owners seek to extend the service life of such systems to ensure they remain intact throughout the contract period. So, how can the service life of spiral‑welded steel pipes be improved? The following aspects provide a detailed analysis.

　　Prior to installation, spiral-welded steel pipes must undergo enhanced-grade internal and external corrosion protection. After field jointing is completed, the joint‑repair areas must be thoroughly protected against corrosion, particularly on the interior. Corrosion typically initiates internally, and years of experience with in‑service pipeline retrofits have shown that the most severe corrosion occurs at the pipe joints.

　　During on‑site construction, mechanical lifting often damages the external anti‑corrosion coating of spiral steel pipes. Such damage should be promptly repaired with PE heat‑shrink tape to prevent widespread corrosion. The collapse of the Wanli Dam was due to a similar principle: a small flaw can lead to catastrophic failure. After pipeline operation begins, it is essential to strengthen post‑commissioning maintenance, particularly for exposed spiral steel pipes.

　　The theoretical hydrostatic pressure of a spiral-welded steel pipe is the value used in its static‑pressure calculations and differs from the pipe’s operating pressure. During operation, the internal fluid is in motion, so the operating pressure is not the same as the theoretical pressure. The theoretical static‑pressure value for a spiral‑welded steel pipe is determined based on its outer diameter and wall thickness; typically, it is calculated as follows: for non‑standard specifications, the theoretical value is 282 times the wall thickness divided by the outer diameter, while for national standards, it is 352.5 times the wall thickness divided by the outer diameter.

　　When designing the pressure rating of spiral-welded steel pipes, it is not sufficient to rely solely on theoretical calculations. For spiral-welded steel pipes with wall thicknesses less than 6 mm, this formula cannot be used to determine the theoretical hydrostatic pressure. Moreover, according to relevant standards, spiral-welded steel pipes with wall thicknesses below 6 mm are prohibited from being used for conveying process fluids.

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