WELDING ENGINEERING AND TECHNOLOGY - Underwater Welding - Ivica Garašić ©Encyclopedia of Life Support Systems (EOLSS) UNDERWATER WELDING Ivica Garašić Department of welded structures, University of Zagreb, Faculty of Mechanical Engineering and Naval Architecture, I. Lučića 1, HR 10000 Zagreb, Croatia Keywords: underwater dry welding, underwater wet welding, weldability, equipment. Contents 1. Introduction 2. Classification of underwater welding 3. Underwater wet welding 3.1. Physical Fundamentals, Weldability and Metallurgical Issues 3.2. Welding Process and Consumables 3.3. Equipment for Underwater Wet Welding 4. Underwater dry welding 4.1. Underwater Dry Welding Alternatives 5. Weld quality evaluation 5.1. Weld Classes 6. Conclusion Glossary Bibliography Biographical Sketch Summary Underwater technologies take special role in modern offshore facilities, pipelines, ships and floating objects repair and maintenance. Huge numbers of underwater structures which are used in oil and gas production, as well as increasing intensity of naval transport present the technological cornerstone of the economical development and strategic issues. On the other hand, almost daily we are witnessing various cases of environmental pollution that are caused by means of improper usage of these installations or inadequate maintenance. Maintenance of structures or eventual repairs under the water line demands application of sophisticated technologies such as underwater welding, in wet or dry environment. Underwater welding is unique process which integrates several, on the first sight, contradictory phenomena as water or gas at high hydrostatic pressure, electricity and electric arc as a heat source and metallurgical transformations during solidification of weld metal, everything constricted in a small space and short time. Interactions of mentioned physical phenomena in, what is considered normal conditions, presents not only the huge risk for the weld quality but life threatening safety risk for the welder. So, the question arises, how is it possible to weld underwater and achieve good and solid weld joint, able to perform all the tasks in harsh environment? Due to high safety risks, great importance and responsibility in performing of these activities is on the highly trained and educated human resources, including divers and organization team on the surface. Specially designed equipment is necessary for successful accomplishing of practical tasks. In global aspects