The main advantages of acetylene (C2H2) in metalworking include its high combustion temperature and versatility. It is stated by the American Welding Society (AWS) that the oxygen-acetylene flame possesses the highest temperature of 3100°C, with an increase of 3.3% compared to CO₂ arc welding (about 3000°C), and the heat affected zone (HAZ) width is 40% narrower (conventional value 1.5mm vs 2.5mm), which makes it especially suitable for high-precision cutting of 3-50mm thick steel. For example, in 2022, Shanghai Zhenhua Heavy Industry uses welding gas acetylene for port crane boom welding, with a cutting speed of up to 450mm/min (CO₂ laser cutting 380mm/min), and the construction time of a single equipment is shortened by 12 days. Fuel saving of 18% (acetylene consumption 0.8m³/h compared to CO₂ 1.2m³/h).
The reducing flame property of acetylene gives it unique technological benefits. In copper pipe brazing (wall thickness ≤2mm), acetylene neutral flame (oxygen fuel ratio 1.1:1) can control the copper oxidation rate at 0.3% (CO₂ protection welding is 1.2%), and increase the joint tensile strength to 220MPa (15% higher than the CO₂ program). German Rheinmetall 2023 test shows that the use of acetylene welding armor plate (hardness 500HB), the fatigue life of welds is 2.1×10⁶ cycles, 31% higher than CO₂ gas welding (1.6×10⁶ times), and the penetration depth is increased by 0.8mm (total penetration depth 5.2mm and 4.4mm). This role is particularly crucial in automotive repair business, American AAA Association statistics show that acetylene welding repair of the gearbox housing crack repair rate of only 2% (CO₂ program is 7%), a single repair savings of 35% on cost.
In terms of economics, the cost of acetylene overall is more competitive in some circumstances. Although acetylene’s unit cost ($6-8 /m³) is four times that of CO₂ ($1.5-2 /m³), its thermal efficiency (55-60%) is far greater than that of CO₂ arc welding (25-30%), so the cost of gas per meter of weld is only 12% greater. For the welding of shipyard thick plate (20mm), the man-hour cost of the acetylene process is $18 /m (CO₂ $22 /m), mainly due to the removal of auxiliary processes – no pre-heating (30 minutes /m saving) and no post-treatment (CO₂ slag removal costs account for 15% of the process). After China Jiangnan Shipbuilding Group rebuilt its production line in 2021, its acetylene consumption has increased by 25%, but the overall welding budget has decreased by 9%, with savings of more than 6 million yuan annually.
In terms of equipment flexibility and adaptability, acetylene is second to none. Oxy-acetylene torch (portable, weight ≤5kg) does not require power supply, while CO₂ welding requires a power supply of at least 15kVA (equipment weight ≥80kg). During the Wenchuan earthquake in 2023, the fire and rescue team used an acetylene cutter to cut an opening through the wreckage three times faster (35 seconds per steel bar) than hydraulic scissors, and successfully dealt with a 45° tilted H-shaped steel beam that CO₂ equipment couldn’t work on. In addition, the acetylene flame can be precisely controlled (heat input 500-3500W range), suitable for full spectrum processing from 0.5mm sheet to 300mm castings, while the CO₂ welded sheet below 10mm is up to 1.2mm/m deformation rate (0.3mm/m for acetylene).
Historical records confirm the long-term reliability of acetylene. Since the commercialization of oxygen-acetylene welding technology in 1903, the most important component welding qualification rate of the aerospace field (e.g., rocket engine nozzle) has been maintained at 99.98%, while the X-ray defect rate (porosity, non-fusion) of CO₂ welding in the same operational condition has been as high as 0.15%. According to a NASA report published in 2022, the SLS rocket fuel line acetylene brazed joint continues to retain 98% of its strength at -253°C liquid hydrogen (CO₂ welded joints drop to 82%). In spite of the onset of process competition, welding gas acetylene still holds sway over 38% of the global market for welding gases (CO₂ 29%), and its irreplaceability will persist for at least 20 years in heavy equipment manufacturing.