How To Arc Weld

UNDERWATER WELDING TECHNIQUES



Welding in the wet (wet environment) is used primarily for emergency repairs or
salvage operations in shallow water. The poor quality of welds made in the wet is due to
heat transfer, welder visibility, and hydrogen presence in the arc atmosphere during
welding. When completely surrounded by water at the arc area, the high temperature
reducing weld metal quality is suppressed, and there is no base metal heat buildup at the
weld.


The arc area is composed of water vapor. The arc atmosphere of hydrogen and the
oxygen of the water vapor is absorbed in the molten weld metal. It contributes to porosity
and hydrogen cracking. In addition, welders working under water are restricted in
manipulating the arc the same as on the surface. They are also restricted by low visibility
because of their equipment and the water contaminants, plus those generated in the arc.
Under the most ideal conditions, welds produced in the wet with covered electrodes are
marginal. They may be used for short periods as needed but should be replaced with
quality welds as soon as possible.


The power source should be a direct current machine rated at 300 or 400 amperes.
Motor generator welding machines are most often used for underwater welding in-thewet.
The welding machine frame must be grounded to the ship. The welding circuit must
include a positive type of switch, usually a knife switch operated on the surface and
commanded by the welder-diver. The knife switch in the electrode circuit must be
capable of breaking the full welding current and is used for safety reasons. The welding
power should be connected to the electrode holder only during welding. Direct current
with electrode negative (straight polarity) is used. Special welding electrode holders with
extra insulation against the water are used. The underwater welding electrode holder
utilizes a twist type head for gripping the electrode. It accommodates two sizes of
electrodes.


The electrode size normally used is 3/16 in. (4.8 mm); however, 5/32-in. (4.0-
mm) electrodes can also be used. The electrode types used conform to AWS E6013
classification. The electrodes must be waterproofed prior to underwater welding, which is
done by wrapping them with waterproof tape or dipping them in special sodium silicate
mixes and allowing them to dry. Commercial electrodes are available. The welding and
work leads should be at least 2/0 size, and the insulation must be perfect. If the total
length of the leads exceeds 300 ft 991) m), they should be paralleled. With paralleled
leads to the electrode holder, the last 3 ft (0.9) should be a single cable. All connections
must be thoroughly insulated so that the water cannot come in contact with the metal
parts. If the insulation does leak, sea water will come in contact with the metal conductor
and part of the current will leak away and will not be available at the arc. In addition,
there will be rapid deterioration of the copper cable at the point of the leak The work lead
should be connected to the piece being welded within 3 ft (0.9m) of the point of welding.


(2) Welding in-the-dry (dry environment) produces high-quality weld joints that meet Xray
and code requirements. The gas tungsten arc welding process produces pipe weld
joints that meet quality requirements. It is used at depths of up to 200 ft (61 m) for
joining pipe. The resulting welds meet X-ray and weld requirements. Gas metal arc
welding is the best process for underwater welding in-the dry. It is an all-position process
and can be adopted for welding the metals involved in underwater work. It has been
applied successfully in depths as great as 180 ft (55 m).


There are two basic types of in the dry underwater welding. One involves a large welding chamber or habitat known ashyperbaric welding. It provides the welder-diver with all necessary welding equipment ina dry environment. The habitat is sealed around the welded part. The atmosphere pressure inside the chamber is equal to the water pressure at the operating depth.


b. Direct current must be used for underwater welding and a 400 amp welder will generally have ample capacity. To produce satisfactory welds underwater, the voltage must run about 10 volts and the current about 15 amps above the values used for ordinary welding.


c. The procedure recommended for underwater welding is simply a touch technique. The
electrode is held in light contact with the work so that the crucible formed by the coating at theend of the electrode acts as an arc spacer. To produce 1/2 in. (12.7 mm) of weld bead per 1.0 in. (25.4 mm) of electrode consumed in tee or lap joint welding, the electrode is held at approximately 45 degrees in the direction of travel and at an angle of about 45 degrees to thesurface being welded. To increase or decrease weld size, the lead angle may be decreased orincreased. The same procedure applies to welding in any position. No weaving or shipping is employed at any time. In vertical welding, working from the top down is recommended.


d. The touch technique has the following advantages:
(1) It makes travel speed easy to control.
(2) It produces uniform weld surfaces almost automatically.
(3) It provides good arc stability.
(4) It permits the diver to feel his way where visibility is bad or working position is
awkward.
(5) It reduces slag inclusions to a minimum.
(6) It assures good penetration.


e. In general, larger electrodes are used in underwater welding than are employed in normal welding. For example, when welding down on a vertical lap weld on 1/8 to 3/16 in. (3.2 to 4.8mm) material, a 1/8- or 5/32-in. (3.2- or 4.0-mm) electrode would usually be used in the open air. However, a 3/1- or 7/32-in. (4.8- or 5.6-mm) electrode is recommended for underwater work because the cooling action of the water freezes the deposit more quickly. Higher deposition rates are also possible for the same reason. Usually, tee and lap joints are used in salvage operations because they are easier to prepare and they provide a natural groove to guide the electrode. Thesefeatures are important under the difficult working conditions encountered underwater. Slag is light and has many nonadhering qualities.

This means the water turbulence is generally sufficient to remove it. The use of cleaning tools is not necessary. However, where highest quality multipass welds are required, each pass should be thoroughly cleaned before the next is
deposited.


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