The present study discusses the main aspects involved in the selection of welding consumables as well as shielding gas flow and compositions used to produce weldments at 600m and llOOm water depth The application of these concepts has been illustrated with results from tests carried out at the above mentioned depth range. Also described are the components and mode of operation of a fully automatic system providing an adaptive loop control of welding operations performed under hyperbaric conditions.
For much of the world, especially in the Gulf of Mexico and Brazil, the best potential for major new oil and gas reserves lies beneath the deep water of the continental slopes, or in other words, at depths below 450msw The difficulties involved vary from place to place with environmental conditions, but 450msw to 500msw is d significant depth level since it is about the present limit for ambient pressure diving
On the other hand, the fall in oil prices has substantially reduced the income of the offshore industry which has been particularly reflected in a decline of the R&D activities This situation is particular evident in the case of underwater welding technology The substantial costs and manpower required for the development of mechanized and fully automated welding technology cannot apparently, at present, be afforded by the majority of those companies either requiring or providing such technology
Hence, in order to adress the problems posed by repair and maintenance at water depths below the limits of manned intervention, GKSS Research Centre Geesthacht GmbH has set up a R&D Programme to develop sensor aided, fully automated robot based underwater welding systems The present study has been divided in three main parts. Initially, a brief discussion has been conducted on high deposition welding processes and consumables for hyperbaric welding. In the second part, the most relevant investigations concerning the control of weld metal chemistry of flux cored wires deposited under hyperbaric conditions have been introduced and discussed. The application of these concepts to deep waters is then illustrated with results from mechanical tests, carried out on fully welded joints, produced in the pressure range of 600msw to llOOmsw. Finally, a description of the components and mode of operation of a fully automatic system providing an adaptive close loop control of welding operations performed under hyperbaric conditions is presented
A general overview of the historical development of hyperbaric welding indicates that as the working depth increased and the code requirements became more and more stringent, GTAW was established as the most adequate process for root and eventually hot passes. However, the slow rate of welding and the restricted deposition rate, characteristics of the GTAW process, seemed to be a severe handicap, particularly in the case of filler and cap passes Among the higher deposition rate welding processes which could be considered for hyperbaric use, the solid wire gas metal arc welding (GMAW) and flux cored arc welding (FCAW) seemed to be the obvious choices.