Torsional strength comparison between two assembling techniques for aluminium drill pipe to steel tool joint connection

Two techniques for assembling an aluminium drill pipe to a steel tool joint were investigated: ‘hot’ assembling and ‘cold’ assembling. During hot assembling a difference of temperature between the two parts is exploited to impose contact interferences and then to obtain a friction bond that generates torsional strength. Hot assembling is ordinarily used. The cold assembling technique is introduced here as an alternative. During cold assembling connection make up, the contact interferences are obtained by imposing an external torque. This technique requires a proper lubricating compound between the mating surfaces, in order to reduce the torque required to make up the connection. After lubricating compound curing, the coefficient of static friction rises and a high torsional strength of the connection is obtained. Full scale experimental tests were performed both on hot assembled connections and on cold assembled connections. Cold assembling showed higher torsional strength than hot assembling; moreover cold assembling does not expose the aluminium alloy to high temperature, that can be a risk for the aluminium alloy microstructure. However, the use of the compound can be a reason of cold assembling torsional strength scatter.