Subsea Robotic Friction-Welding-Repair System
Authors: Meyer A. , Roos A. , dos Santos J.F. , Gibson D. , Blakemore G. , Hammerin R. 
Published: October 2008

Within the scope of the European funded research project ROBHAZ (Affordable Underwater Robotic Welding Repair System) a subsea robotic repair system has been developed and tested. This system consists of a marinised TRICEPT robot and a multi-purpose friction welding head. It could be deployed to the worksite either by a work-class ROV or as a Remote Operated Tooling (ROT) depending on the type of the application and the location. The main emphasis of the development work was placed on the up grading of an existing mobile friction welding head designed for friction stud welding and the marinisation of an industrial robot with six degrees of freedom built on a frame structure to ensure maximum rigidity. In the present study, the development work leading to the subsea robotic friction welding repair system is presented and discussed. Possible applications of the developed system are also presented.

Introduction

The European funded research project ROBHAZ (Affordable Underwater Robotic Welding Repair System)1 has been conceived to address the need for a diverless welding repair system providing a metallic bond of the damaged region (instead of a mechanical connection) but avoiding the problems associated with wet and hyperbaric arc welding. To fulfil this vision a system has been devised based on an advanced friction welding process (i.e. Friction Hydro Pillar Processing - FHPP) coupled to a marinised high-end electric robot.

To perform the repair welds and machining operations a small and mobile friction welding head designed for friction stud welding, known as the HMS 30002, 3, was selected. The axial stroke of this machine was extended to allow repairs of sections up to 30mm. Parallel to the modification of the weld head, underwater repair procedures were developed. The modified welding head was integrated in a specially designed carrier to be mounted onto a subsea handling system.

To produce defect free FHPP repair welds, axial forces in the order of 15 kN to 20 kN are required. In combination with a high positioning accuracy this gives very challenging requirements for the handling system. The only system available on the market, which could fulfil these specification, is the TRICEPT robot. This is a six axes electric robot with parallel kinematics extensively used in the automotive, aircraft and space industries. After a conceptual study the robot was marinised for subsea applications, rated down to 400 m water depth.

After appropriate process parameters were established, the modified HMS 3000 was mounted onto the marinised TRICEPT robot forming the prototype subsea welding repair system. Machining sequences and parameter for the different tools (i.e. drilling, milling, grinding, etc.) were developed and integrated with a tool changing system. The whole system was then subjected to validation tests first in dry and later in wet environment. Figure 1 describes schematically the development activities carried out in this project. Possible applications of the developed system are also presented.