It is not commercially practicable to produce a welded tube which shall uniformly have the same strength at the weld as in other parts of the metal. The temperature to which it is necessary to heat the metal for welding is such that the material may be burned to a greater or less extent, a condition which it is not always possible to detect.

For these reasons, boiler tubes and other tubes or pipes which must stand high pressures and which are subjected to great variations of temperature, are preferably made without welds or seams.

There are several methods for producing seamless tubes which are applied to various materials, including steels of practically all compositions, brass, copper, etc. The method of making seamless tubes in general use consists in piercing a hole axially through a billet of circular cross section, reducing the wall thickness of the tube so produced by rolling, and finishing, when the conditions require, by further reducing the wall thickness by cold drawing. Some compositions of brass will not stand piercing, hence tube billets of these compositions are cast hollow and reduced in size by drawing.