THREADED PIPES FOR USE WITH TANK SKINS

  

The plant recently started up, for making threaded pipes for use with tank skins, is one of the Company’s strong points as regards the manufacture of underground fuel tanks.
The basic idea is that of directly transforming the coil into a threaded connection for tanks. The threaded connections are made from a helical pipe by unwinding a coil, automatic flattening, helical roller levelling, automatic welding from the inside using procedure 135 (EN 288) and from the outside using procedure 121 (EN 288) and subsequent plasma cutting to the predefined length.
The result of this production process is a pipe having geometrical and resistance properties that are clearly superior to those that can be obtained with the classic roller levelling methods.
Indeed, as we had predicted, the result is a threaded connection that even without convex end plates, notwithstanding its considerable diameter compared to its thickness, is basically self-supporting and so, in total unloading conditions, the distortion due to its own weight proves to be considerably less than what can be encountered in metal sheets roller levelled using the traditional method.
The concept of this structural stiffness is easy to understand if account is taken of the progress of the welding which, in fact, stiffens the pipe by following the helical cross-section of the metal sheet and contributes to the stability of the structure with its transverse component.