Steel-made precision tubes for drill rods by Steffen Zimmermann, Head of Technical Sales/Application Engineering; Sebastian Schulze, Application Engineer; Corentin Lorc’h, Quality Manager and Pierre-Jean Marchais, Process Engineer at Mannesmann Precision Tubes
Precision tubes made of steel are widely used for exploration or blasthole drilling. But to keep the drilling process running and the direction of drilling straight, tubes must behave elastically under service loads. This means no plastic deformation is allowed to take place to prevent drill rods from inelastic bending. Especially for long-distance drilling, tubes must withstand severe and harsh conditions. Besides the wear, mainly mechanical loads stress the precision steel tube by a combination of factors like tensile, torsion and bending loads at the same time.
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he engineering of drill strings needs to consider the static tensile properties, the tube dimensions and apparent ‘secondary factors’ like residual stresses and corresponding straightness. The manufacturing process of precision steel tubes must balance all these properties by adjusting the cold deformation during the cold drawing pa18
rameters, the heat treatment conditions and the tube straightness all along the production process. These production steps and their interactions will define the performance of drill rod characteristics. As soon as the level of tensile residual stresses exceeds a critical limit, the internal stresses will cause a premature local plastic
↑ New straightening machine at Mannesmann plant in Vitry-leFrançois; in the front: measurement to check straightness; in the back: straightening operations
deformation - the permanent distortion that occurs when a material is subjected to tensile, compressive, bending, or torsion stresses that exceed its yield strength and cause it to elongate, compress, buckle, bend, or twist. This local plastic deformation will lead to a fast and early deviation from the planned drilling direction and, in combination with increased Coring Magazine #18
