Flying sparks and incorrect welding practices can cause premature failure of explosion protected equipment.
Flying sparks due to welding and cutting are the main causes of fires and explosions in hazardous locations. The welding arc creates extreme temperatures, and may pose a significant fire and explosion hazard if safe practices are not followed (see Fig. 1).
For the purposes of this article, “portable generator” is defined as any portable or mobile generator, or an auxiliary generator of a welding machine that is used for supplying energy to portable electrical equipment.” “Hot work” is defined as any operation presenting an ignition source such as, but not limited to, use of open flame or spark-producing equipment, welding, torch cutting, brazing, chipping, grinding, and abrasive blasting.
Fig. 1: Arcs and sparks during welding and cutting.
Damage caused by welding
Electric arc in MCCs and electric motors, actuators and drives is caused by welding on equipment, one of the failure modes for rolling element and non-rolling bearings. Remember, welders are not reliability experts but professionals who know how to weld and to construct and repair using all types of welding processes.
Maintenance supervisors should train their maintenance technicians, welders and contractors.
Fig. 2: Damage caused by welding.
So why do we accept this failure mode when it can be eliminated?
Note: Failure to accomplish this one task properly will cause bearing failure by electric arcing, which is a failure mode of bearings. In addition, it will cause failure of many different electrical components. Remember, electric current from welding will always follow the path of least resistance.
Fig. 3: Ex certified extension lead with Ex certified crocodile clamp.
Damage causes by welding
Electrical current passage through bearings can happen when the earth of the welding machine is connected to the equipment earth during the welding process. For example, a contractor does some welding at your plant and decides to attach his ground via your nearby electric motor. This would be a high amperage discharge, and might “weld” bearing parts together internally or pit them. This will cause a premature failure of the bearings that can cause production losses (see Fig. 2).
Electric shock is one of the most serious and immediate risks facing a welder. Electric shock can lead to severe injury or death, either from the shock itself or from a fall caused by the reaction to a shock.
Fig. 4: Electric motor with earth connection.
The end-user must test the earth leakage unit and record the reading to ensure the safe work environment. When using a mobile generator to supply power to welding machines or any other electrical equipment, it shall be ensured that:
- A Certificate of Compliance (CoC) was issued for the entire electrical installation. The user or the lessor, as the case may be, shall be in position of the CoC.
- Earth circuits with a resistance not exceeding 0,2 Ohm shall be complete between the generator and the installation (safety earth) and must be tested and recorded before any work commences.
- The generator is equipped with an earth-leakage protection device.
- The person responsible for bringing the mobile generator onto the plant is responsible to test the earth leakage and to record it daily, or every time it is moved. The test must be recorded and kept with the machine to be inspected by the safety officer at any time.
Note: An Ex certified extension lead for earthing purpose in hazardous locations must be used if suitable earth is not near the area where welding must take place. This is to prevent any arcs or sparks in an uncontrolled area in hazardous locations (see Fig. 3).
Fig. 5: Earth connection on hand station.
Note: Normal crocodile clamps can slip off and cause arcs or sparks in hazardous locations. This can be a source of ignition.
Bonding and earthing
Equipotential bonding must be established between any equipment used in hazardous locations to prevent electrical shock as well as arcs and sparks. The earth of a welding machine must never be connected to an earth of plant machinery as it will cause premature equipment failure.
Never use the external earth of equipment such as:
- Junction boxes
- Hand stations
- Distribution boards (see Figs. 4, 5 and 6)
Fig. 6: Distribution board with earth connection.
The earth of welding machines and generators may be connected to safety earth points such as:
- Main earth points
- Earth connection on vessels or structures
- Earth electrodes
Note: The use of equipment earth is strictly prohibited to prevent premature failures.
Safety is a critical consideration for any welding project. Arc welding is a safe occupation when proper precautions are taken but, if safety measures are ignored, welders face a range of hazards which can be potentially dangerous, including fires and explosions, electric shock, fumes and gas, and more. The employer must ensure a safe work environment according to Section 8 of the OHS Act 85 of 1993.
Main message here Ex safe operation is a must have. Any site related scope shall address hazardous area compliance. And well documented it has to be.
Keep up good work!