ERW Tubes for Internal High Pressure Forming Tubing Material Selection

ERW tubes are produced from hot or cold rolled flat coils according to astm a 513 specification; drawn mandrel (dom) tubes are produced from fully annealed erw tubes by cold drawing process.

I. Internal high pressure molding erw pipe selection:

ERW tubes are produced from hot or cold rolled flat coils according to astm a 513 specification; in order to achieve the quality of the hydroformed surface, the coils should be free of dirt, pickled and oiled.

In the tube mill, the coils are cut to size, then the sheets are fed into a number of forming rolls, welding stations, final sizes, and then cut to length in a continuous high-speed process

To facilitate uninterrupted production and to achieve consistent quality, many coil ends are welded together; ERW tube mills typically operate at speeds between 150 and 500 ft/min (46 and 152 m/min).

There are a variety of layouts for the tube roll forming stage, with some older mills using fewer roll sets, which are usually more aggressive in hardening the material.

However, most modern mills are designed to better control strain hardening during the forming stage by using gentler forming methods.

Tensile tests of specimens cut from various locations in and around the longitudinal direction of the tube usually show varying degrees of strain hardening.

Note that the yield stress of the tube is high and varies considerably around the tube, and also note the W-shape of the tube curve. For ideal internal high-pressure forming of the tube, the height of the w should be minimized so that it is positioned close to the sheet line. After the forming stage, the tube enters the welding station.

To obtain a high quality weld, the edges of the steel strip are heated by the resistance method and pressed together with a set of special rolls. This method of butt welding does not require any additional filler material. During the welding process, a certain amount of iron protrudes on the inside and outside of the pipe surface.

This is called weld flash and is usually removed immediately after the welding operation using the forming tool. For most hydroforming applications, flash is removed or "scarified" from both surfaces.

In some applications, where internal weld flash may be rolled or highly controlled to a specific size, laser welding can be used instead of resistance welding.

Laser welding is generally of higher quality than resistance welding, and for laser welded tube parts requiring very high expansion rates, the heat affected zone around the weld is significantly lower, and the use of laser welded tubes is often beneficial.

However, rolling speeds are limited to laser welding speeds in the range of 30 to 50 ft/min (10 to 15 m/min). After the welding stage, the tube is allowed to cool before entering the sizing station.

By far the tubes are usually slightly larger in diameter and the focus is on weld quality and high forming speeds. At the sizing station, the tubes have been sized, diameters and ovality to the required tolerances.

For tubes to be hydroformed, diameter reduction at this stage should be kept to a minimum to preserve the forming properties of the material.ERW tubes are typically available in diameters from 0.5 to 12.5 inches (12.7 to 317.5 mm), with wall thickness factors from 5 to 100.

Laser welded tubing is available up to 125 WF, and as the wall factor increases, it becomes increasingly difficult and costly to produce tubing using this technique.