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Underwater Welding Techniques Esam F. Alajmi. Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 3, (Part - 6) March 2016, pp.86-88 RESEARCH ARTICLE OPEN ACCESS Underwater Welding techniques Esam F. Alajmi The Public Authority For Applied Education And Training ABSTRACT Welding demand in offshore and marine applications is increased with the increasing in oil and gas activities as well as increasing in the marine transportation and industrial applications. In this paper, a brief description of the different commercial underwater techniques will be presented taking into account showing detailed description of a few advanced welding techniques . I. INTRODUCTION And cause rapid deterioration of any The increasing demand for oil and gas has metallic components in the electrode holder. Fig. 1, led to increase the offshore oil and gas activities shows and to move the exploration into the deep water. the overall wet welding process diagram. For wet The desire to build, maintain and repair offshore welding AC is not used because of electrical safety structures has brought the need for underwater and difficulty in maintaining an arc underwater. welding. Underwater welding is the process of welding at elevated pressures, normally underwater. Underwater welding can either take place wet in the water itself or dry inside a specially constructed positive pressure enclosure and hence a dry environment. It is predominantly referred to as "hyperbaric welding" when used in a dry environment, and "underwater welding" when in a wet environment.Principle of Operation The welding circuit must include usually a knife switch operated on the surface and commanded by Figure 1: Schematic Diagram of Underwater Wet the welder and is used for safety reasons. When DC Welding Technique is used with (+ve) polarity, electrolysis will take place and cause rapid deterioration of any metallic Equipment for underwater wet welding components in the electrode holder. For wet The underwater wet welding equipment welding AC is not used because of electrical safety has to meet all the safetyaspects. Due to the limited and difficulty in maintaining an arc underwater. time spent under water,the diver-welder has to be provided with satisfactory operating conditions. Classification of Underwater Welding Equipment has to beregularly maintained according Underwater welding can be divided into to stipulated regulations in order insure itsproper two main types: functioning. Main equipment needed for wet 1- Wet Welding underwater welding can be summarized in the 2- Dry Welding following: Diving equipment 1- Wet Welding The diving equipment includes dry diving Wet welding process is carried out suit, dry suit full-face mask, surface supply atambient water pressure in which, the weld is umbilical cord, air tank on the surface exposed to the water. This is carried out by a withregulation manometer and compressor for special water-proof stick electrode, with no filling the air tank. physical barrier between water and welding arc. The increased freedom of movement makes wet Welding power sources welding the most effective, efficient and Intensive dynamic behavior ofthe power economical method. Welding power supply is source is necessary to obtain a stable electric arc in located on the surface with connection to the greater depths. Welding power sourcemust be diver/welder via cables and hoses. When DC is adjusted for underwater wet welding, not only in used with +ve polarity, electrolysis will take place the matter of good arc behavior but also in theaspect of diver-welder safety. Safety switch www.ijera.com 86|P a g e Esam F. Alajmi. Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 3, (Part - 6) March 2016, pp.86-88 For safety reasons, the electrical circuit is fitted with a safety switch, which interrupts or 2- Dry Underwater Welding establishes theflow of current necessary for Underwaterwet welding is primarily used underwater welding or cutting as diver request or in at shallow depths when need for largerdepths case of accident. emerge underwater dry welding procedures is first choice. Moreover, usage of underwater drywelding Communication system methods offers completion of full penetration For constant connection and coordination welds with mechanical properties adequate of works between the surface and the diver, two- towelding in normal conditions. Additionally, it is waytelephone communication system has to be possible to perform preheating or post weld applied in order to facilitate the realization and heattreatment in order to decrease hydrogen content organizationof underwater activities. and improve weld properties. Underwater welding in a dry environment Welding cables, and welding and cutting is carried out in chamber sealed around the holders structure to be welded. The chamber is filled with a Special cables with special insulation class gas (commonly helium containing 0.5 bar of have to be used for underwater welding and cutting oxygen) at the prevailing pressure. The habitat is in orderto prevent breakthrough of electric current sealed onto the pipeline and filled with a breathable into the water or to the platform structure, which mixture of helium and oxygen, at or slightly above may causesafety problems and difficulties in the ambient pressure at which the welding is to take welding. place. This method produces high-quality weld joints that Mechanical tools system meet X-ray and code requirements. The gas Mechanical tools for underwater works tungsten arc welding process is employed for this may be driven electrically, hydraulically and process. The area under the floor of the Habitat is pneumatically.Electric drive is avoided because of open to water. Thus the welding is done in the dry safety problems, and mostly hydraulic and but at the hydrostatic pressure of the sea water pneumatic tools are used. surrounding the Habitat made possible by encompassing the area to be welded with a physical The advantages and disadvantages of wet barrier (weld chamber) that excludes water. The underwater welding techniqueare indicated in weld chamber is designed and custom built to accommodate braces and other structural members Table 1. whose centerlines may intersect at or near the area Advantages that is tobe welded. The chamber is usually built of - The versatility and low cost of wet welding makes steel, but plywood, rubberized canvas, or any other this method highly desirable. suitable material can be used. Size and - Fast method. configuration of the chamber are determined by - It is less costly compared to dry welding. - The welder can reach portions of offshore structures dimensions and geometry of the area that must be that could not be welded using other methods. encompassed and the number of welders that will No enclosures are needed and no time is lost be working in the chamber at the same time. - building. There are different dry underwater welding Minimalequipment needed for mobilization. - methods, it can be achieved by: Disadvantages - There is rapid quenching of the weld metal by the 2-1 Dry Habitat Welding: surrounding water. Although quenching increases Using a chamber in ambient pressure (at the tensile strength of the weld, it decreases the ductility and impact strength of the weldment and ambient water pressure) in a large chamber from increases porosity and hardness. which water has been displaced, in an atmosphere Hydrogen Embrittlement– Large amount of such that the welder/diver does not work in diving - hydrogen is present in the weld region, resulting gear. This technique may be addressed as dry from the dissociation of the water vapour in the arc region. The H dissolves in the Heat Affected Zone habitat welding. As shown in fig. 2, welders are 2 completely in dry environment and weld properties (HAZ) and the weld metal, which causes Embrittlement, cracks and microscopic fissures. are equivalentto one welded in normal conditions. Cracks can grow and may result in catastrophic However, much more fit-up time is necessary to fix failure of the structure. the habitat andprepare it for welding. Another disadvantage is poor visibility. The welder some times is not able to weld properly. - Table 1: Advantages and Disadvantages of Wet Underwater Welding Process www.ijera.com 87|P a g e Esam F. Alajmi. Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 3, (Part - 6) March 2016, pp.86-88 The important applications of underwater welding are: Offshore construction for tapping sea resources Temporary repair work caused by ships collisions or unexpected accidents Salvaging vessels sunk in the sea Repair and maintenance of ships Construction of large ships beyond the capacity of existing docks Repair and maintenance of underwater pipelines Figure 2: Specially designed habitat 4- Future Scope for Underwater Welding Considerable industrial effort has been 2-2 Dry Chamber Welding: made to improve process performance and control Welding at ambient water pressure in a strategies for thevarious underwater welding simple open-bottom dry chamber that processes. For future scope in underwater welding, accommodates the head and shoulders of the the major efforts on research and development welder/diver in full diving gear as shown in Fig.3. should be focused on the following topics: Automation of the underwater joining and inspection of the welded structures Mechanized underwater welding for actual usage of a very large floating structures
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