Surpassing the Challenges of a Robotic Traction System for Movement inside Long Flexible Obstructed Pipes

Abstract

Abstract The obstruction inside flexible lines with hydrates or paraffins is quite common in offshore production systems. In these cases, in order to perform the clearance of the pipes, many different techniques, usually time consuming and expensive, are currently used. This article presents the development of a new self-propelled robot that is under design to become an alternative solution for this problem, which has been a research challenge by decades. The use of robots with umbilical cables inside long obstructed pipes with several curves and bends is currently an important challenge in the robotic field, especially due to the increased traction forces that may occur. The main challenge is the force in the umbilical cable caused by the friction between the cable and the inner pipe surface. This force can be theoretically outlined by the capstan Euler-Etelwein equation (usually applied to the case of rounding a capstan with a rope). In an early study, a theoretical model for cable traction was developed and experimentally validated. This model was used to calculate a typical friction force in a standard pipeline. Several in-pipe movement strategies were analyzed and a suitable mechanism was defined as the main element for the robot traction mechanism. Therefore, we show in this study that the traction challenge can be surpassed by a properly cable materials selection composed with a suitable traction system design. A mechanism base in an inchworm-like movement was selected due to its high traction capacity and, based in an extensive study, a hybrid (electric-hydraulic) system was developed. The electric power transmission is provided through the umbilical, and electric motors drive pumps which supply hydraulic power to linear pistons that execute the movement of the mechanical elements, moving the entire system. Previous analysis and tests indicate that the designed system will be suitable to perform the necessary missions.