During operation the metal of pipelines losses necessary properties and different kinds of defects are appearing. Areas that have exhausted their resources have to be repaired or replaced completely. However, for underwater pipelines process of replacement is very costly. One of the cheap way is the drawing through the existing pipe the smaller diameter one. In addition to general economic effect we obtain additional protection pipe outer pipe (casing).

  A numerical model to calculate drawing forces and determine the contact forces of interaction of the inner pipeline with the pipe of a larger diameter has been developed. The module takes into account the complicated geometric profile of the outside pipe, the possibility of loss of contact by support rings, the mass of the inner pipeline and the action of buoyancy force, longitudinal and transversal (due to sag) force from the pulling rope, the compliance of the pipe-ring system, etc. The results of calculation were used in determining the interval of the rings disposition and the choice of their dimensions (height). Described is the effect of a tensed string when the increased coefficient of friction entails a nonlinear growing increase of drawing force.

  Scheme of drawing process: the small pipe is fixed support-directive rings (SDR), located at specified intervals (not necessarily equal), small pipe is drawn by a rope, which is attached to the winch.