s2906 Arc Welding on Waterborne Vessels.pdf

June 1982 (6/95)

NOAA Standard Specification S2906

ARC WELDING ON WATERBORNE VESSELS

1. PURPOSE

The purpose of this directive is to set out rules that shall be followed in regard to the proper use of arc welding equipment when welding on waterborne vessels in order to reduce damage to the underwater body, shafting and propeller by pitting and deterioration.

2. SCOPE

The continued occurrence of serious pitting of underwater hulls of various vessels makes necessary the strict adherence to the requirements contained herein. The procedures in grounding welding leading leads should be closely followed to avoid damage to underwater hulls and appurtenances.

3. INSTRUCTIONS

A. Welding motor-generator sets or rectifiers shall be so installed that the welding and ground leads from shore to ship or from ship to ship shall be connected only to the vessel on which welding is to be done. The welding lead as well as the ground lead shall be thoroughly insulated and at no time shall be allowed to become submerged in the intervening water. Welding shall be done on but one ship from one source of welding current.

The ground lead shall not be electrically connected to any object ashore or to any other vessel except the one which welding is being done. The ground cables should have an area of at least one 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.

B. Figures 1, 2 and 3 (See Enclosure 1) illustrate CORRECT methods for installing welding generators. In all of these cases, it 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. Figures 4, 5, 6 and 7 illustrate INCORRECT methods for installing welding generators. Figures 4 and 5 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 repair ship is used to weld another ship. Obviously the way to correct this situation is to insulate the negative cable of the generator from

Arc Welding on Waterborne Vessels S2906

Ship A and run both positive and negative leads to the ship where the welding is being done, as illustrated in Figure 1. Figure 6 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 to flow from the positive cable to the ship's hull. Figure 7 illustrates conditions when one generator is used to weld on two ships. There seems to be a general impression that if two ships are connected with a cable of reasonable size, say 1,000,000 CM and 100' long, all of the current used on Ship B will return to the generator through the cable. The resistance of the cable is of the same order as the resistance through the water so part of the current 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 0.01 ohms. The resistance of the cable would be about 0.001 ohms, hence about one-tenth of the welding current used on Ship B would flow through the water.

4. ACTION REQUIREMENTS

No welding shall be done on a water-borne ship until the hook-up of welding equipment has been examined and approved by the Contracting Officer.

5. SAFETY

No welding or burning shall be undertaken without the presence of a fire watch. All equipment in way of welding or burning shall be covered with a fire proof covering supplied by the Contractor.

Adequate precautions shall be taken by the Contractor before welding or burning to insure that contiguous compartments and tanks are gas-free. No hot work in tanks shall be started before consulting with the Contracting Officer and supplying a gas-free certificate as required by local authorities. No employee shall enter any tank void, cofferdam or closed area without first consulting and obtaining permission of the Officer of the Deck.