Which material is typically used for long-distance transmission mains?

• A. Plastic pipe
• B. Ductile iron pipe
• C. Steel pipe
• D. Copper tubing

Answer: (C)

When selecting material for a long transmission main, the key requirement is to carry high internal pressures over large distances with strong, reliable joints. Steel pipe meets this need best because of its high strength, which allows the pipe to handle high pressures without becoming prohibitively thick. It’s also easily fabricated into large diameters and welded to form long, continuous runs with few weak points, reducing the number of joints where leaks could occur. Steel’s stiffness helps resist deflection and sag over long distances, and there is a long history of successful use in transmission mains, with established methods for corrosion protection such as coatings and cathodic protection.

Other materials have their places, but they don’t align as well with the demands of long, high-pressure transmission lines. Plastic pipes offer corrosion resistance and easier installation but can be limited by long-term pressure ratings, temperature sensitivity, and joint performance at very large diameters. Copper tubing is suitable only for small, domestic-scale systems due to cost and inadequate size. Ductile iron pipe is common in distribution mains, where pressures and service life demands differ, but for the longest, highest-pressure transmission mains, steel remains the typical choice because of its strength, weldability, and proven performance.