The Role of Electron Beam and Friction Welding in The Fabrication of Offshore Technology Structure

Abstract

ABSTRACT This paper briefly outlines the limitations of welding processes currently in use in offshore technology and considers the main areas which could benefit most from the introduction of new joining techniques. Electron beam and friction welding are discussed mainly in the context of welding fairly thick section, tubular components and their advantages and limitations are reviewed particularly with reference to the manufacture of piles. No insurmountable technical problems are foreseen, but development effort is required to determine joint fit-up and alignment tolerance for both processes which although basically different have similar problems in the context of thick section welding. The main advantages seen for these two processes are improved production rate reduced requirement for skilled labour and lower unit weld costs. The possibility of applying friction welding to underwater welding repair and installation is also discussed. INTRODUCTION The welding processes currently used in offshore technology structures basically involve the deposition of weld metal by arc processes which may be manual, semi or fully mechanised. All of these processes involve the preparation of the joint edges and multi pass techniques in order to achieve full penetration for the thicker sections. The limitations of these techniques are associated-with low joining rates, requirement for skilled labour, use of expensive filler materials, possible use of pre-heat, restrictions on welding position, (e.g. submerged arc welding is limited to downhand) and there are many problems of a metallurgical nature concerned with weld defects and joint properties, particularly toughness. With the worldwide increasing demand for offshore structures and distribution lines, the welding requirements are likely to stretch the capability of existing processes and skilled man-power availability. There are of course limitations other than welding, associated with the production of offshore structures. However, the availability of a mechanised process capable of a high joining rate would be a considerable breakthrough. It is considered that both friction and electron beam welding offer great potential in this area. This paper outlines some of the process characteristics and problems which need to be considered in the context of their introduction into the offshore technology industry. CURRENT STATE OF THE PROCESS Historically speaking, friction welding is an old process but serious developments began in Russia and the United States in the 1950's and later in Great Britain .in 1960 when the Welding Institute built its first experimental machine which was used to demonstrate the potential of the process for welding bars up to 1 in. diameter. Historically speaking, friction welding is an old process but serious developments began in Russia and the United States in the 1950's and later in Great Britain in 1960 when the Welding Institute built its first experimental machine which was used to demonstrate the potential of the process for welding bars up to 1 in. diameter.