Developments in Manual Wet SMA-Welding
Authors: Szelagowski P. , Stühff H. , Schafstall H.G , Blight J. , Pachniuk I. 
Published: October 2008

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.