ABSTRACT A literature review on the factors affecting weld metal chemistry on hyperbaric flux cored arc welds has been carried out. The following aspects have been considered: shielding gas flow, shielding gas activity and oxidation/ deoxidation reactions. It has been shown that the available knowledge allows an adequate selection of conditions leading to acceptable weld metal chemistry in hyperbaric FCAW. 1. INTRODUCTION 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. This choice seemed apparently evident since the independent control over heat source and rate of filler metal feeding make this process ideal for varying root gaps and less sensitive to eventual instabilities, assuring therefore satisfactory penetration and fusion. Moreover, the fact that the GTAW weld metal is not affected by the idiosynchrasies of pressure dependent oxidation/ deoxidation reactions, implied that? the resulting mechanical properties were comparable to those obtained under atmospheric conditions. However, the slow rateof welding and the restricted deposition rate, characterisitcs of the GTAW process, seemed to be a severe handicap. Although the literature generally restricts itself to the loose association between the low deposition rate of the GTAW process and increasing operational prices, experience indicates that this might not always be the case. In general, it is difficult to precise the role played by the actual hyperbaric welding time on the final price of an offshore operation. Current market forces, existing contracts between service companies and contractors and the extent of pre-welding activities and requirements usually determine the bigger share of the total price. On the other hand, longer bottom times, with the associated operational risks, as well as the psychological and physical implications to the divers can be as important as the financial aspects involved. At any rate, by the mid-seventies, the search for an alternative high deposition rate process was underway. The obvious choices were the shielded metal arc process (SMAW), already extensively used at comparatively shallower depths, solid wire gas metal arc welding (GMAW) and flux cored arc welding (FCAW). However, a series of fundamental works on SMAW and solid wire GMAW showed that for both processes a considerable amount of ingenuity would be required to overcome some of the reported problems. In the case of GMAW (solid wire), the observed problems were related to the effects of pressure on the physics of consumable arc systems, particularly those affecting bead formation and arc stability. On the other hand, for the SMAW process, the general pressure dependence of gas absorption and gas/metal reactions limits the maximum permissible working depth and requires strict consumables handling procedures as well as extensive use of pre and post-weld heat treatments.