IEC 60974-8 pdf – Arc welding equipment – Part 8: Gas consoles for welding and plasma cutting systems
9.3Gas line purging
The GAs cONsOLE shall have a means to purge gas lines when changing to a different type of gas (for example，oxidizing or oxygen containing to combustible) to reduce the risk of fire orexplosion. In some cases, a small amount of combustible gas or oxygen may accumulate in the
torch.This volume shall be small enough so that no risk can result.
The purging shall occur after each change in gas routing or when the previous gas routingisunknown.
NOTE 1 A means of accomplishing this can be by purging the lines with a sufficient volume of an inert gas.
NOTE 2When a fisk of fire or explosion exists in the gas lines due to changing gas，the purging can be perfomedwith the fallowingpressure cycle:
a)reduce the pressure of the GAs CONSOLE circuit to atmosphare pre5sUure;bypurga the GAs CONSoLE circuit with the purging gas;
increase the pressure to the maximum pressure of purging gas;
dreduce the pressure of the cAs CONSOLE circuitto atmosphere pressure.Conformity shall be checked by risk analysis and the following test.
The gas lines，when installed with all devices (valves，fittings,etc.) shall be filled with acombustible gas and measured with a gas detector. Immediately after，the gas lines shall bepurged according to the instruction manual.Once purging has been completed, the contents of
the gas lines shall be measured with the gas detector to ensure that the lines have been purgedto a level below the lower flammability level (LFL) of the gas. If more than one combustible gasis used , the test shall be repeated for each combustible gas.
9.4.1 Design requirements
The GAs CONSOLE (external or internal) shall be designed to withstand or prevent an explosion.This shall be accomplished by complying with the requirements in 9.4.2,9.4.3，9.4.4, or 9.4.5.
All tests described below are dangerous，and shall be performed by a person with sufficienttechnical knowledge.
Purging means typically include positive pressure of an inert gas and forced ventilation (e.g.use of a non-arcing fan). Any automatic means to purge the cAs cONSOLE enclosure ofcombustible gases shall be activated before other electrical devices are energized.
Where a fan or other device is used for purging, a malfunction shall be indicated and the systemshall be prevented from continuing to operate.
After purging, the level of combustible gas shall not exceed the lower explosion level (LEL).
Conforrmity sha be checked in a draught-free environment by a) or b) below.
a) Simulate a continuous gas leak inside the enclosure equal to the maximum flow rate and
pressure as specified by the manufacturer. Monitor and adjust the gas in the enclosure until
saturation or stabilizationoccurs.Activate the purging device(s) and monitor the gas toensure it reaches the LEL before any electrical devices are energized. Repeat for each type
of combustible gas used.
b) Place a simulated arcing device inside the purged enclosure.Monitor and adjust the gas inthe enclosure until saturation or stabilization occurs. Operate all purging means and initiate
start-up sequence. Energize the arcing device to simulate the electrical devices start-up,and operate continuouslyensuring that no ignition occurs. Repeat for each type ofcombustible gas used.
NOTE A safe level of gas is 50 % of the LEL.9.4.3Safe design ofGAs cONSOLE126.96.36.199Prevention of ignition
The GAs cONSOLE shall be designed to prevent an ignition caused by a gas leak in the enclosure.Conformity shall be checked by completing the following test.
a) Place the energized equipment,i.e. the EXTERNAL GAs CONSoLE or the power source withINTERNAL GAs CoNSOLE , in a bag (or similar).
b) Simulate a gas leak inside the equipment to create an internal explosive atmosphere.c) Monitor the mixture until it is halfway between the LEL and the UEL of the gas.
d)Operate the GAs coNsoLE for a period of at least 1 h, during which all components capableof causing ignition are cycled at least 100 times.
e) Verify that no ignition occurred during the operating period.188.8.131.52Integrity of the enclosure
The enclosure, i.e the EXTERNAL GAS CONSOLE or the power source with INTERNAL GAS CONSOLE,shall withstand an explosion without degradation of the protective continuity circuit.
Conformity shall be checked by completing the following test.
a) Place the non-energized equipment,i.e. the EXTERNAL GAs CONSoLE or the power sourcewith INTERNAL GAs CoNSOLE , in a bag (or similar).
b) Simulate a gas leak inside the equipment to create an internal explosive atmosphere.c)Monitor the mixture until it is halfway between the LEL and the UEL of the gas.
d)lgnite the flammable mixture using an arcing device installed in the equipment to create anexplosion.
e) Verify that there was no flying debris.
f)Verify there is no contact with hazardous parts using the jointed test finger specified inlEC 60529.
g)Verify the continuity of the protective circuit by visual inspection and measurement.