Development of Automatic Underwater Welding With Local Cavity Formation Method

Abstract

ABSTRACT This paper describes the development of automatic underwater welding system based on an unique localized dry environment by a fluid curtain. With only the welding machine submerged, the system is operated by remote control in the ocean in connection with materials supply and supervision of works, thus considerably reducing its reliance on diving and underwater operations. In this process, a stabilized gaseous zone can be created only around the welding spot just underneath the welding torch by inclined water jet stream from the outer circumference of the double nozzle. Then various gas shielded arc welding methods such as TIG, MIG and C02 arc welding are performed in the dry environment. (Fig. 1, 6, 11, 12) As the initial plan, a submersible automatic welding machine has been produced, and the trial test of this system has been successfully performed on objects submerged in a large cistern while supervising and controlling-their welding conditions by TV monitoring from outside the cistern. (Fig. 15, 16, 17) Welding results have proved excellent, being not much different from those undertaken in an ordinary environment on land. (Fig. 13, 14, 18) INTRODUCTION From the viewpoint of natural resources development and utilization of space, recognition and concern have been rapidly elevated with regards to the importance of ocean development and thus the conception of super giant ocean projects such as various offshore plants, sub-sea production systems, etc. are being mapped out actively. For the construction of these gigantic structures, full-scale underwater fabrication techniques are indispensable. Among these the underwater welding technique is expected to play the most vital role. Thus early development is earnestly desired by various fields concerned. Up to the present, the two currently available underwater welding are the dry and wet methods. For the sake of obtaining reliable weld, it is unquestionably desirable to be welded in a dried environment. Dry method; however, requires a special chamber that entirely covers the work, which brings limited use in the shape of object as well as extremely high cost. Wet method on the other hand, has depended much upon submarine work by divers. And because of many points which are still at issue with respect to reliability, efficiency and workability, underwater welding has not yet been put in full-scale practical use. Recent developed local cavity methods are noted because of their better handiness than that in the dry technique and also the much better reliability than in the wet processes. The authors have developed a unique local cavity formation process by a fluid curtain and its application to welding, cutting and painting underwater. This method utilizes the effects of shutting off the water invasion by the momentum of fluid jet and smooth exhausting of cavity gases by flow entrainment. This paper describes the principle of cavity formation, cavity formation conditions and its application to welding.