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Equipment and Tools
Before using any equipment, it should be inspected before use to ensure that it is in a serviceable condition. Any equipment that is discovered or thought to be defective should be isolated until it can be fixed by an approved maintainer.
Extra caution should be taken in cold weather with gas-fuelled equipment. Moisture trapped in the equipment may freeze and this may cause valves to malfunction. It is recommended that equipment is thawed out with hot water and cloths, never with naked flames, before use.
Electrical Equipment
In order to minimise personal harm from electric shock, electric welding power sources for shipboard use should have a direct current (DC) output not exceeding 70V, with a minimum ripple. When DC equipment is not available, then AC output power sources may be used providing they have an integral voltage limiting device to ensure that the idling voltage (the voltage between electrode and workpiece before an arc is struck between them) does not exceed 25 V RMS.
The device may be affected by dust or humidity and therefore, a function test should be completed each time a welding set is used. Some voltage limiting devices are affected by their angle of tilt from the vertical, so it is important that they are mounted and used in the position specified by the manufacturers. This requirement can be affected by adverse sea conditions.
A ‘go-and-return’ system utilising two cables from the welding set should be adopted; the welding return cable should be firmly clamped to the workpiece.
The direct current output from power sources should not exceed 70 volts open circuit. The ripple on the output from the power source should not exceed the values in the table within the equipment instruction manuals.
The ripple magnitudes are expressed as percentages of the DC, and the ripple peak is that with the same polarity as the DC. The conditions in the table to the right are normally met by DC generators incorporating commutators and by rectifier power sources having a 3-phase bridge rectifier operating from a 3-phase 50/60 Hz supply. Rectifier power sources should not be operated from a power supply of less than 50 Hz.
Should it be necessary to use a power source with a DC output having a ripple magnitude in excess of those stated in the equipment manual, then a voltage limiting device should be incorporated into the power source to ensure that the idling voltage does not exceed 42 V. This could be necessary when using a single phase rectifier power source.
Earthing of the workpiece is used to protect against internal insulation failure by keeping the workpiece at or near earth potential until the protective device (e.g. a fuse) operates to cut off the mains supply. Where the welding circuit is not adequately insulated from the earthed referenced mains supply, the workpiece should be earthed.
The ‘return’ cable of the welding set and each workpiece should be separately earthed to the ship’s structure. The use of a single cable with hull return is not recommended.
The workpiece earthing conductor should be robust enough to withstand possible mechanical damage. It should also be connected to the workpiece and a suitable earth terminal by bolted lugs or secure screw clamps. Some manufacturers recommend earthing as one of their measures to reduce electrical interference. This is not a safety-related measure, but the manufacturer’s advice should be followed.
If an alternative method of protecting against welding transformer insulation failure is used, the hazards caused by stray welding currents can be avoided by not earthing the workpiece or the welding output circuit. Self-contained engine-driven welding sets and welding power sources do not need the workpiece to be earthed. It should be noted, however, that other equipment connected to the workpiece may require earthing for safe operation.
Electrode holders should be fully insulated so that no live part of the holder is exposed to touch. Also, where practicable, they should be fitted with guards to prevent accidental contact with live electrodes and as protection from sparks and splashes of weld metal. A local switching arrangement or other suitable means should be provided for rapidly cutting off current from the electrode if the operator should get into difficulties, but also for isolating the holder when electrodes are changed.
To avoid voltage drop in transmission, the lead and return cables should be of the minimum length practicable for the job and of an appropriate cross-section. Cables should be inspected before use; if the insulation is impaired or conductivity reduced, they should not be used. Cable connectors should be fully insulated when connected and installed so that current carrying parts are adequately recessed when disconnected.
Precautions to Be Taken during Electric Arc Welding
In addition to the protective clothing earlier described, the welding operator should wear non-conducting safety footwear. Clothing should be kept as dry as possible as some protection against electric shock; it is particularly important that gloves should be dry as wet leather is a good conductor. An assistant should be in continuous attendance during welding operations. They need to be alert to the risk of accidental shock to the welder and ready to cut off power instantly, raise the alarm and provide artificial respiration without delay. It may be desirable to have a second assistant if the work is to be carried out in difficult conditions.
Where persons other than the operator are likely to be exposed to harmful radiation or sparks from electric arc welding, they should be protected by screens or other effective means.
A welding protective screen.
In confined spaces, where the operator may be in close contact with the ship’s structure or is likely to make contact in the course of ordinary movements, protection should be provided by dry insulating mats or boards.
There are increased risks of electric shock to the operator if welding is done in hot or humid conditions; body sweat and damp clothing greatly reduce body resistance. Under such conditions, the operation should be deferred until a time the adequate level of safety can be achieved.
In no circumstances should a welder work while standing in water or with any part of their body immersed. The electrode holder should be isolated from the current supply before a used electrode is removed and before a new electrode is inserted.
This precaution is necessary because some electrode coatings have extremely low resistance. Even a flux coating which usually is insulating can become damp from sweating hands and thus potentially dangerous. When the welding operation is completed or temporarily suspended, the electrode should be removed from the holder. Hot electrode ends should be ejected into a suitable container; they should not be handled with bare hands. Spare electrodes should be kept dry in their container until required for use.
Gas Equipment
Gas Welding and Cutting
While this section deals almost exclusively with oxygen and acetylene, other fuel gases may be used and similar precautions should be taken. The pressure of oxygen used for welding should always be high enough to prevent acetylene from flowing back into the oxygen line. Acetylene should not be used for welding at a pressure exceeding 1-atmosphere gauge as it is liable to explode, even in the absence of air, when under excessive pressure. Non-return valves should be fitted adjacent to the torch in the oxygen and acetylene supply lines.
Flame arrestors should be provided in the oxygen and acetylene supply lines. They will usually be fitted at the low-pressure side of regulators although they may be duplicated at the torch.
Should a backfire occur (i.e. the flame returns into the blowpipe and continues burning in the neck or mixing chamber) the recommended first action is to close the oxygen valve on the blowpipe to prevent internal burning. Then immediately followed by shutting off the fuel gas at the blowpipe valve. When the cause of the backfire has been discovered, the fault rectified and the blowpipe cooled down, the blowpipe may be re-lit.
If there is a flashback into the hose and equipment, a hose fire or explosion, a fire at the regulator connections or gas supply outlet points, the first action should be to isolate the oxygen and fuel gas supplies at the cylinder valves or gas supply outlet points. But you should only do this if it can be done safely. Further action should follow in accordance with the vessel’s fire drill requirements.
Only acetylene cylinders of approximately equal pressures should be coupled. In fixed installations, manifolds should be clearly marked with the gas they contain. Manifold hose connections including inlet and outlet connections should be such that the hose cannot be interchanged between fuel gases and oxygen manifolds and headers.
Only those hoses specially designed for welding and cutting operations should be used to connect any oxy-acetylene blowpipe to gas outlets. Any length of hose in which a flashback has occurred should be discarded. The connections between hose and blowpipe, and between hoses should be securely fixed with fittings which comply with Standard EN 1256.
Blowpipes should be lit with a special friction igniter, stationary pilot flame or other safe means. Should a blowpipe-tip opening become clogged, it should be cleaned only with the tools specially designed for that purpose. When a blowpipe is to be changed the gases should be shut off at the pressure-reducing regulators.
To prevent a build-up of dangerous concentrations of gas or fumes during a temporary stoppage of after completion of the work, supply valves on gas cylinders and gas mains should be securely closed, and blowpipes, hoses, and movable pipes should be removed to lockers that open onto the open deck. Oxygen should never be used to ventilate, cool or blow the dust off clothing.
Compressed Gas Cylinders
Compressed gas cylinders should always be handled with care, whether full or empty. They should be properly secured and stored in a location appropriate to their intended use and the risks which accidental release of gas may present. The cylinders should be secured in a way that they are still quick and easy to release, for example in the case of fire. Where appropriate, cylinder trolleys should be used to transport cylinders from one place to another.
If the cylinder design permits protective caps over the valve, such caps should be screwed in place when the cylinders are not in use or are being moved. Where the cylinder design does not permit protective caps over the valve, the valve system should be protected from accidental damage from for instance impact. Valves should be closed when the cylinder is empty.
Where the International Maritime Dangerous Goods (IMDG) Code requires cylinders of different gases to be segregated, such gases should be stored in separate, well-ventilated compartments that are not subject to extremes of temperature. If gas is flammable, the compartment in which the cylinders are stored should have no electrical fittings or other sources of ignition and have prominent, permanent ‘NO SMOKING’ signs displayed at the entrance and within the space. Empty cylinders should be segregated from the full ones and so marked. All gas cylinder stores should be appropriately marked with safety signs. If you are handling compressed gas cylinders you also need to take the following precautions:
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Controls should not be operated with oily hands. Keep cylinder valves, controls, and associated fittings free from oil, grease, and paint.
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Gas should not be taken from compressed gas cylinders unless the correct pressure-reducing regulator has been attached to the cylinder outlet valve.
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Cylinders with leaks that cannot be stopped by closing the outlet valve should be taken to the open deck and away from any sources of heat or ignition. Then slowly discharge the gas into the atmosphere.
Excessive force should never be used on cylinder valve spindles or hexagon nuts of regulator connections in an attempt to stop a leak. Neither are sealing tape nor other jointing materials recommended for use in an attempt to prevent leaks between metal-metal surfaces that are designed to be gas tight. Trying to prevent a leak on an oxygen cylinder, could result in an initiation of a metal oxygen fire.
Increased Temperature in Gas Cylinder
A watch should be kept on acetylene cylinders to ensure they are not becoming hot. If they are, this could be a sign of acetylene decomposition and there is an increased risk of explosion.
The cylinder stop valve should be closed immediately, which may limit or reduce the decomposition but is unlikely to stop it. An emergency action, such as evacuating the area and prolonged cooling by immersion or with copious amounts of water will still be required. Consideration should be given to dumping the cylinder overboard although the movement of the cylinder can promote rapid decomposition and cooling should continue while it is being moved.