The process of manufacturing tubes, which can be basically divided into two: the process of sewn pipes (welded) and that of seamless pipes. In this post we will delve into the first ones, which are widely used for their versatility, their efficiency for mass production, low costs and material savings.

As with most sectors whose standards are recognized internationally, seam pipes are also known by their English name: welded tubing, or more specifically by some of the subgroups of seam pipes, such as ERW tubing (Electric Resistance Welded, that is, welded by electrical resistance), CDW tubing (Cold Drawn Welded, that is, cold drawn soldiers) or DOM (Drawn Over Mandrel, that is, stretched on a winch shaft).

In any of the types of seam tube manufacturing, the starting point is the same: a sheet coming from a steel coil cut in the length of the circumference of the tube and in the length of the tube which, by means of a process Rolled, it is folded with rollers more or less separated according to the diameter of the desired tube until the sheet is joined longitudinally and forms the tube. It is welding that differs according to the process.

Welded pipes welded by electrical resistance (ERW)
ERW tubes, welded by electrical resistance, have become in recent years an efficient alternative to seamless pipes, both in terms of price and performance, since the technologies for welding tubes used by manufacturers are every more advanced In this sense, the technical superiority of the seamless pipes that we mentioned in the post about tube manufacturing processes has an increasing equivalence with the ERW seam pipes, especially in some applications with low-medium pressure and temperature requirements.

These types of seam tubes undergo a specific type of process that involves spot welding and seam welding. It is commonly used in the manufacture of round, square and rectangular steel tubes.

The steel sheet is unwound from the coil and cut sideways according to the desired tube width and to condition the edges to be welded. Next, this sheet passes through a series of separate contoured rollers according to the desired diameter or side of the tube and is cold formed, snapping the longitudinal ends together. These ends are welded by electric shock.

The welding generates a relief that must be equal to the outside diameter of the tube, after testing its resistance, with a series of rollers that achieve the precise finish, before straightening the tube and cutting it to size.

The material used in the manufacturing process of sewn pipes is usually SAE 1010 steel, normally available in cold rolled steel coils (CREW) for pipes with a thickness of 0.1524 cm or less, and in hot rolled steel coils (HREW) for pipes with a thickness of 0.21082 cm or more.

Cold-stretched seam tubes (CDW)
The cold-stretched CDW tubes are ERW stitched tubes, welded by electrical resistance, which are then subjected to an additional process, in which the tube is stretched through a matrix with a penetrator, similar to the tubes manufactured seamlessly, so that the size (wall thickness, inner and outer diameter), as well as the integrity of the weld and the surface finish are precisely controlled to produce tubes of the desired size and properties.

These tubes can undergo further processes of cutting, machining, deburring, galvanizing, etc.

These tubes are the most versatile and sold within welded tubes, since they comply with EN-10305-2 (DIN 2393) and ISO 9001.

Applications of CDW seam pipes
As we saw in the post that collected the different types of tubes according to the manufacturing process (with seam and seamless), one of the advantages of sewn pipes with respect to seamless extrudates is that they allow a lower tolerance range. The CDW tube, which is an improved version of welded or welded pipes, is especially characterized by its close tolerances and high mechanical properties, so it is used in applications such as automobile components (shock absorbers, hydraulic cylinders, sleeves, bushings, axes, etc.)

Stretched pipes on a shaft (DOM)
Like the CDW tubes, the DOM (Drawn Over Mandrel, in English) tubes also start from an ERW manufacturing process, with seam welded by high or low frequency electrical resistance), but differ in the finish, which in the case of The tubes eliminate all instantaneous welding and the tube is cold extracted on an axis, to the point that it is sometimes included between the seamless or seamless tubes, since it is almost invisible.

Applications of DOM seam pipes
DOM tubes are widely used in the automotive industry and the construction sector, in machined parts, rollers, shafts, sleeves, steering columns, etc.