Gas Welding & Heating Nozzles FAQs
Straight answers to the questions people ask most when choosing and using gas welding and heating nozzles.
How do I choose a welding nozzle size?
Welding nozzles are numbered by size. The number relates to how much gas flows, and so to how much heat you get and the thickness of metal you can weld. A small number suits thin sheet and a large one suits thick material. The numbering systems differ between makers, so do not assume a number from one maker matches another's.
Use the maker's chart for your nozzle, which gives the metal thickness and the pressures to use. A nozzle that is too small will not fuse the joint properly, and one that is too large can burn through thin metal or leave a messy weld.
What are heating nozzles used for?
Heating nozzles put a large amount of heat into a wide area. They are used to preheat thick steel before welding or cutting, to bend or straighten bars, pipe and plate, to free seized nuts, bolts and bearings, and to warm or dry parts before work. Multi-flame heads spread the heat evenly instead of focusing it on a point.
Heat the metal slowly and evenly to avoid distortion and cracking, and remember that heated metal stays hot long after it stops glowing. Keep flammable materials away, and never heat a sealed or pressurised container or part.
Can I use acetylene and propane heating nozzles interchangeably?
No. Nozzles are designed for a specific fuel gas, because the gases burn differently and need different amounts of oxygen and different port layouts. Propane and natural gas flames are cooler at the tip than acetylene but spread a lot of heat over a wide area, which is why propane is popular for heating.
Using a nozzle with the wrong fuel gas can give a poor or unstable flame, wastes gas and may be unsafe. Match the nozzle, torch and regulators to your gas, and use the maker's recommended pressures.
How do I fit a nozzle and check it is sealing?
Check that the nozzle seat and the thread are clean and undamaged, then fit the nozzle and tighten it snugly, by hand or with the correct spanner as the maker instructs. Do not overtighten, and never use sealing compound, tape or grease to stop a leak.
With the torch unlit, turn on the gases and check around the nozzle and the torch connections with a leak detection fluid made for the purpose. A leaking seat can lead to popping and backfires, so fix any leak before you light the torch.