Some Special Acetylene Considerations

Acetylene is, in some ways, the centerpiece of the oxyacetylene cutting or welding process, and although its use is generally fairly straightforward, several special considerations need to be observed while making use of acetylene.

One of the most important acetylene facts of which you should be aware is that due to the highly volatile nature of the compound, you cannot drain the cylinder too quickly of its acetylene contents. The withdrawing rate for acetylene is a maximum of 1/7 of the total contents of the bottle in one hour. Thus, if you have a 40 cubic foot acetylene tank – generally the smallest size available – then you should withdraw 5.7 cubic feet or less per hour. If you have a 125 cubic foot cylinder, then up to 17.8 cubic feet can be withdrawn in a 60-minute period.

Exceeding this amount makes the acetylene “unstable” – which is a euphemism best translated as “increasingly likely to spontaneously explode.” Refilling the cylinder can only be done at the same maximum rate, so when you return the bottle to the gas supplier for a refill, expect the refilling process to take 7 hours. You should also find out how many cubic feet per hour your cutting torch uses with different torch tips, and plan your acetylene tank size accordingly.

The acetylene is the actual source of the oxyacetylene flame, with the oxygen only serving to stabilize, shape, and intensify it. If there is a problem with ignition, the fault likely lies with insufficient acetylene rather than not enough oxygen. For example, if the torch makes loud popping or snapping sounds during striking but no flame appears, then the amount of acetylene should be slightly increased until striking becomes successful.

Acetylene gas may explode if it comes into contact with copper, so copper should be scrupulously avoided when cutting or welding with an oxyacetylene torch. This rule applies to copper alloys, as well, assuming that the copper makes up two thirds or more of the alloy. Lesser amounts are usually not problematic, though the very safety-conscious may want to avoid them also.