Shielded Metal Arc Welding for Underwater Welding


Underwater Welding Processes Problems in Underwater Welding Types of Underwater Welding Wet Welding Dry Welding Hyperbaric Welding Cavity Welding Conditions of a Good Underwater Welding Process Shielded Metal Arc Welding for Underwater Welding TIG Welding for Underwater Welding MIG Welding for Underwater Welding Applications of Underwater Welding

Shielded Metal Arc Welding for Underwater Welding

Shielded Metal Arc Welding for Underwater Welding - Manual shielded metal arc welding is an economical process for underwater welding. This process can be carried out in all positions with the same success as welding in air. The D.C. welding equipment used for underwater welding must have a capacity of at least 300 Amp for each welder. All electrical leads, lighting gear, electrode holder, gloves, etc., must be fully insulated and in good condition. Ferritic electrodes with a coating based on iron oxide should be used as they resist hydrogen cracking. Positive polarity of the work is preferred. This means that 65-75% of the heat is in the metal being welded.
The weld pool is easier to handle and has enough fluidity to fill in undercut to a large extent. Electrode having positive polarity may have to be used for overhead butt welding or welding cracks in the vertical and overhead positions. Current settings for underwater welding are normally higher* than for welding in air, and the control of these settings must be accurate to ensure consistent work. Generally, the greater the depth of the water, the higher must be the machine settings. While preparing tile job before welding, where possible, all edges to be welded should be rough ground to fit and all paint and loose scale should be removed.
	For striking tile arc, the electrode is held at an angle of about 35-400 to the surface of the plate and its end is struck against the plate. After the arc has started, the electrode is held on the plate and pressure is exerted to keep it there. he electrode coating crumbles from the electrode tip and the welder maintains proper arc length. The arc length should be about the same as that for surface welding. The speed of welding, even in clear water, will be slower than the speed when welding is carried out at the surface (in air). Underwater welding, like surface welding will require butts and fillets in various positions.
However, the most common preparation for underwater welding is the fillet, which is, unfortunately, the more difficult of the two joints to weld. Underwater fillet welds invariably require an oscillation, whereas underwater butt welds are very seldom performed in this way. This is because a fillet weld requires more control and a higher current setting. When butt welding flat position the welder should position himself in such a way that the work is at a level with his chin and should attempt to weld towards himself. Thus he can see the groove he is welding in. In horizontal-vertical fillet welding the welder should be behind the arc and weld away from himself. This will give him his best view of the arc in operation and will allow observation of the build up of the bead as welding proceeds.
Slight oscillation of the electrode in this case gives more control over the weld pool and greatly assists the welder in producing a well shaped fillet. The electrode angle in relation to the line of the weld should be about 10° off the vertical, pointing forward in the direction of travel. The electrode angle across the line of the weld should be about 15° up from the lower leg of the fillet.When welding in vertical position, the welder has a maximum range of vision as well as freedom of movement. The metal flows readily, due to the welding heat being carried upwards with the rising gas. The welding electrode is held at about 35° angle from the plate, pointing upwards. The angle across the weld should be 900. A major problem which the welder will face when welding in vertical position is the tendency for the weld pool to become too fluid.

In such position, it is therefore advisable to use DCRP which tends to keep most of the welding heat in the electrode rather than in the workpiece. To sum up, an underwater welder must learn by sight, feel and hearing to recognise the characteristic conditions of a satisfactory welding technique.

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