Due to intensive and concentrated research activities during the last 10 to 15 yr, the quality of wet-welded joints has been improved to an extent that this process is currently regarded as a potential alternative to the more costly dry hyperbaric welding processes in comparable water depths. The wet welding process has matured to an interesting alternative repair process due to its high flexibility and versatility and its low investment costs with respect to achieving comparable weldment quality. However, due to the previous bad reputation of the poor weldment quality in former times, related to extremely high hardness, high porosity, high hydrogen contamination, and, in combination with this, high cracking susceptibility, the wet welding process still requires concentrated activities to improve its reputation and credibility, especially in European oil field application. New acceptance creiteria, more detailed information on the achievable weldment quality, and especially the development of life-predicting data for wet-welded components on the one hand, and new design criteria especially related to the process application in wet environment as well as excellent training of diver welders on the other hand, have been required. Advanced testing methods had to be applied, additional design criteria had to be developed, and achievable weldment quality data had to be included in acknowledged and approved standards and recommendations in training and certification standards for diver welders. All these data are now available. These results have been achieved with the financial support of the European Community through the THERMIE PROJECT FUNDING.
The increasing interest taken by the international diving industry in wet welding plays an important part in determining research activities to improve the process and consumables for offshore applications, particularly for higher strength steels at greater water depths. On the basis of an investigation comparing the properties of existing electrodes for underwater applications, specially modified electrodes have been tested by the authors. One of the objectives achieved was an improvement in the mechanical properties and a reduction of porosity for welding with ferritic electrodes at great water depths (100 m sea water, msw) and, in addition, a comparison was made of hydrogen pick-up by selected electrodes. The work presented is part of a joint programme carried out by GKSS Research Centre, Geesthacht, and Comex Services, Marseilles, sponsored by the European Economic Community, to develop a wet welding procedure for structural applications.
This report presents the results from manual and robotic dry hyperbaric FCAW down to 450 msw. The influences of welding parameters, technique and consumables on overall weldment quality have been investigated. Based on the obtained results, which comply with BS 4515-84 and API 1104-83, a preliminary definition of welding procedures using the studied consumables, can be made.
The increasing interest of the international diving industry in wet welding enforces research activities worldwide, to improve process and consumables for its offshore application, particulary on higher strength steels in greater water depths. On the basis of an investigation comparing the achievable properties amongst existing electrodes for wet underwater application, further developments to improve weldment quality have been carried out by the authors. Special emphasis has been put on the improvement of the mechanical properties and the reduction of porosity especially considering the application of ferritic electrodes in greater water depths (100 msw). INTRODUCTION Szelagowski et al.[l] have reported about achievable weldment qualities in wet welding down to 100 msw. In these tests commercially available electrodes have been tested, compared and evaluated. These results have been obtained in different test series carried out in close collaboration between GKSS Research Center and coMEX Services. A comparison between these results and those published [2,3] demonstrate already the high standard of the achieved values. Nevertheless flUther developments were found necessary to achieve better weld metal properties and overall quality allowing therefore the application of the process to offshore structures and pipelines. The sucessful use of wet welding techniques in the Gulf of Mexico has been attribute to the relative low carbon equivalent steels used and the thinner wall thicknesses required. Wet welding of high carbon equivalent steel with ferritic electrodes can lead among others to cracking in the heat affected zone (HAZ). A solution for the problem of welding higher strength steels is suggested in the application of stainless steel electrodes or nickel base electrodes [2,3]. The deposited weld metals are said to be able to retain hydrogen in solid solution and decrease the tendency of hydrogen cracking in the HAZ. This investigation[ 2j reported a high depth sensitivity of the nickel based electrodes and it has been shown, that these electrodes present excessive defects in depths exceeding more than 10m. These defects can be probably attributed to reduced heat input, which decreases with increasing depth. Therefore, the use of such electrodes is currently restricted to shallow waters. Presently, the depth limit for ferritic electrodes is reported to be 100 msw [4], which coincides with those observed by [1]. New developments in the field of wet welding have recently been presented by the Paton Institute, Kiev. This Institute has concentrated efforts in the development of the flux cored arc welding process for wet application. Preliminary results have been reported in [5,6]. Research actitivities from Paton Institute were focused on process parameters such as droplet transfer and arc stabilities in water depths down to 50 msw. [5]: The new developments are concentrating on the application of self shielded flux cored arc welding. The welds have been performed by a mechanical welding system in a fresh water filled hyperbaric chamber. By the application of an "Unsteady Process Analyser" electric and short circuit time parameters could be established.
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