Seamless, Straight or Spiral Weld Steel Pipe

The three main styles of steel pipe are seamless, straight weld or spiral weld, named for the way in which they are manufactured. Though these three types of pipe can often be used interchangeably, some styles of pipe are better suited for certain projects.

What All Steel Pipe Has in Common

The main raw material used in all steel pipe production is steel, which is made up primarily of iron. However, steel pipe commonly includes other elements such as aluminum, manganese, titanium, tungsten, vanadium and zirconium. No matter whether the pipe is seamless or welded, steel pipe is durable, rust proof, easy to install and highly customizable, making it a top choice in a wide range of industries.

How Straight Weld Steel Pipe Is Made

Straight weld steel pipe is made by taking a long, coiled ribbon of steel called a skelp and cutting it into a flat rectangular sheet. From there, the steel is fed through a rolling machine that forces the edges of the rectangle together to create a cylinder. Finally, the cylinder is sealed with a weld. Once completed, straight weld steel pipe will have a single, straight seam down its length.

How Spiral Weld Pipe Is Made

Just as with straight weld pipe, spiral weld pipe is created by casting raw steel and then forcing the edges together, finishing the pipe by sealing it with a weld. The difference is that the coil is wound at an angle, so the weld runs around the outside of the pipe in the shape of a helix, rather than in a straight line. This allows for more variation in the pipe’s diameter and thickness.

How Seamless Steel Pipe Is Made

Seamless steel pipe is made by stretching steel out into a seamless tube. The pipe begins as a solid cylindrical block of steel called a billet. The billet is heated and pierced through the center with a mandrel, after which the steel is rolled and stretched until it meets the required length, diameter and wall thickness. Unlike straight and spiral weld steel pipe, seamless steel pipe has no seam.

Best Applications for Straight and Spiral Weld Steel Pipe

Generally, welded pipe is considered weaker because of its seam. Though improvements have been made in the manufacturing process and quality assurance regimens have enhanced the performance of welded steel pipe, it is typically used for lighter weight applications such as transporting gas, electrical conduit and plumbing. Welded steel pipe is cheaper than seamless steel pipe.

As mentioned above, the spiral weld on spiral weld steel pipe allows for more variation in the pipe’s diameter and thickness, and it is commonly favored when making custom pipes. Spiral weld is most often used for pipe diameters between 24 inches and 120 inches, and for thicknesses of 1 inch or less.

Best Applications for Seamless Steel Pipe

Seamless pipes lack a weld and are generally considered safer, making it a top choice high-pressure, high-temperature applications, such as those in oil and gas, power generation and the pharmaceutical industry. Seamless steel pipe is also more lightweight and has thinner walls, which makes it excellent for things like bicycles and to transport liquids. The downside of seamless steel pipe is that the rolling and stretching manufacturing process produces an inconsistent wall thickness compared to welded pipe, and it’s also more expensive to purchase.

If you would like to learn more about steel pipe, more information can be found in our blog post, "All About Steel Pipe."


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