Underwater Welding Shielded Metal Arc Welding
There are two basic techniques used today in shielded metal arc wet welding: the self-consuming technique and the manipulative or weave technique. With the self-consuming technique, the electrode is dragged across the work and a significant amount of pressure must be applied by the diver. With the manipulative technique, the arc is held as it would be when welding on the surface and little or no pressure is applied to the electrode. The electrode can be maneuvered and manipulated by the diver. This method requires a great deal more skill and experience than does the self-consuming technique.
Underwater Welding Set Up Procedures.
The following steps should be followed to establish optimum welding current and voltages:
a. Before entering the water, set the amperage and run several beads on a plate.
b. Use the tong test ammeter to check the amperage.
c. After the diver enters the water, the first task is to clean a spot for the ground clamp. The spot should be in a position in front of the diver, as close as practical to the weld joint and should be scraped or wire brushed shiny clean. For diver safety, only C-type clamps should be used as grounding clamps for underwater cutting or welding operations. The clamp must be firmly secured to the work piece and the cable should have sufficient slack to prevent it from being pulled loose. The diver may elect to lightly tack weld the clamp in place when there is a possibility of it working loose. The ground should always be kept in the diver’s forward line of vision.
d. The diver should make a test weld to check the heat at working depth.
e. Via the communications system, the diver can instruct the tender to fine tune the welding machine, that is; increase or decrease the amperage as needed. The open circuit voltage may also require adjustment.
f. After the optimum settings are determined, welding can begin.
g. The diving tender should always maintain a written record of the following: 1) The welding amperage as read from the tong meter. 2) Both open and closed-circuit voltage as read from the volt meter. 3) Electrode diameter, type, manufacturer and waterproofing material. 4) Electrical polarity. 5) Length of welding cable. 6) Depth of work site. By accurately recording this type of information, lessons may be learned and applied to future dives, thereby decreasing the likelihood of mistakes being duplicated.
When using the self-consuming technique, the weld metal is deposited in a series of beads or strings by dragging the electrode against the work. The technique is suited to fillet welding and can be readily adapted to underwater work since it provides a natural groove to guide the electrode. Tests have shown that the beads, when in the form of a fillet, result in welds having approximately the same leg length (size) as the diameter of the electrode used; that is, a single pass with a 1/8-inch electrode produces a fillet weld having a 1/8-inch leg.
Fillet Welding in the Horizontal Position (Self-Consuming Technique).
In making fillet welds, pay particular attention to lead angles and work angles. The work angle is the angle between the electrode and the work in a plane at right angles to the long axis of the joint. The lead angle is the angle between the electrode and joint in the direction of travel. The following is the recommended procedure for fillet welding in the horizontal position:
a. Make sure the safety switch is open.
b. Thoroughly clean the surfaces to be welded.
c. Set the welding power source to deliver the proper current for the electrode being used
d. Hold the electrode against the plate at a work angle of 45° to the plate end surfaces. Tilt the electrode to a lead angle of 45° ± 15° in the line of intended weld. The angle variance, depends on the size of electrode used and the skill and technique of the diver.
e. Call for SWITCH ON. The arc should start when the tender (phone talker) closes the
safety switch. If the arc does not start, tap or rub the electrode tip against the work
until the arc is established. Be sure to keep the electrode at the point where the weld is
to begin. Once the arc is started, exert enough pressure against the work to allow the
electrode to consume itself. Maintain the original work and lead angles between the
electrode and line of weld by moving the hand perpendicularly toward the surface
being welded. Do not hold an arc as in topside welding, simply keep
the electrode in contact with the work. Run straight beads; do not weave. About 8
inches of weld metal will be deposited for every 10 inches of electrode consumed. It is
advantageous to use this method, especially when poor visibility makes it difficult to
hold an arc in the usual topside manner.