million CM per 1000 amperes of welding current and be secured by metal-to-metal contact to an integral part of the
vessel on which the welding is done.
. Figure 1, steps
1, 2 and
3 illustrate correct methods for installing welding generators.
of these cases
should be noted that the only ground in the circuit is to the ship where welding is being done so there is no possibility of
current flowing from the ship's hull into the water. It is entirely safe to place the welding generator on the pier, or have it
installed permanently on a repair ship, provided both positive and negative welding cables to the ship are well insulated
from ground and all other grounded structures, and that no welding cables are returned from the vessel to shore or
adjacent vessels for welding in either location. Figure 2, steps 1, 2, 3, and 4 illustrate incorrect methods for installing
welding generators. Steps 1 and 2 (fig. 2) illustrate the condition when a welding generator, placed on a vessel and with
the negative cable grounded to that vessel, is used to weld on another vessel. This situation often occurs when a
welding generator on a tender or repair ship is used to weld on another ship. Obviously, the way to correct this situation
is to insulate the negative cable of the generator from ship A and run both positive and negative leads to the ship where
the welding is being done as illustrated in figure 1. Step 3 (fig. 2) illustrates the condition when the negative side of the
generator is grounded at the pier. This might occur if the negative leads are connected to crane tracks, pipe lines, or
submerged or buried structures, or if the negative cables are immersed in water at some points. If the positive side of
the generator becomes grounded to the vessel, of course, the situation would be considerably worse since the entire
generator voltage would cause a continuous short circuit current to flow from the positive cable to the ship's hull. Step 4
(fig. 2) illustrates conditions when one generator
on two ships. There seems
to be a general impression
that if two ships are connected together with a cable of reasonable size--say 1,000,000 CM, and 100 feet long, that all of
the current used on ship B will return to the generator through this cable. The resistance of the cable is of the same order
as the resistance through the water, so part of the current will flow from ship B through the water to ship A, corroding the
hull of ship B. Measurements show that the resistance of the water path between two vessels alongside each other is
about .01 ohms. The resistance of the cable would be about .001 oh ms, hence about one-tenth of the welding current
used on ship B would flow through the water.
d. In view of the foregoing, steps shall be taken to correct all unsatisfactory welding installations that are causing
electrolytic corrosion resulting from welding.