The possibility of replacing acetylene and ethylene as welding gas must be determined by combustion ability, economy, and safety. Oxy-acetylene cutting, for example, has the flame temperature at 3,100°C (2,900°C for ethylene and 2,800°C for propane), and steel plates of 300 mm thickness are cut, (0.5 m/min), whereas the cutting speed in oxy-ethylene mixture (ratio 1:1.5) is raised by 20% (0.6 m/min). However, the width of the heat affected zone (HAZ) increased from 1.3 mm to 1.8 mm (12% higher risk of material deformation). The American Welding Society (AWS) refers that acetylene covers 65% of heavy welds such as Marine steel plates and ethylene 30% of motor vehicle sheet (<5mm thick) welds (15% more economical than propane).
From supply chain and cost, the unit cost of acetylene is 5.2 US dollars per cubic meter (special cylinder storage, 0.15MPa pressure), and the unit cost of ethylene is 3.8 US dollars per cubic meter (liquid storage tank, 1.5MPa pressure). The mixture (acetylene ethylene ratio 1:1) reduces the cost of gas by 22% (from $9 / hr to $7 / hr). But acetylene production is supported by the calcium carbide technology (14,000kWh/ton consumption of energy and 5.2 tons/ton of CO2 emissions), while ethylene from naphtha cracking consumes 3,500kWh/ton energy and emits 2.1 tons/ton of CO2, stricter ecological protection (carbon tax of $60 /ton), and thereby a clandestine 31% cost increase of acetylene.
Safety risks limit the substitution process with a lower explosive limit (LEL) of 2.5% for acetylene (2.7% for ethylene), but the explosion range of acetylene ethylene is extended to 2.5-36% (2.7% for pure ethylene). When static electricity (energy ≥0.02mJ) or pipeline leakage (probability 0.01%/year) occurs, the explosion probability increases by 15%. The BASF German facility substituted propane (LEL 2.1%, safer) for acetylene when an explosion was triggered by a leak of an acetylene – ethylene mixture in 2021, with repair costs of €4.8 million.
Process flexibility determines the application context, ethylene in auto welding robots due to flame stability (fluctuation ±1.5% vs. Acetylene ±3%) is used more extensively, and the welding pass rate is improved from 92% to 97% (auto body weld strength ≥350MPa). Though acetylene remains the preferred first option for engine block-type casting repair owing to its temperature (3,100°C), acetylene ethylene has also proved useful in welding titanium alloy by improving pool fluidity by 18% (under argon shielding) and reducing porosity from 5% to 1.2% (X-ray inspection).
Environmental protection and regulation trigger substitution, acetylene combustion gases 1.8kg/m³ CO₂ (ethylene 1.2kg/m³), the EU Industrial Emissions Directive requires a 30% reduction in welding gas carbon emissions by 2025, forcing companies to switch to low-carbon substitutes (e.g., hydrogen-ethylene blend, CO₂ emissions 0.9kg/m³). But then the acetylene ethylene mixture can be controlled if combined with carbon capture technology, which adds 25 percent to the cost, and is used currently by only 12 percent of European welder producers.
Local substitution of gas mixture is supported by case studies:
CRRC Group used ethylene (40%) to weld high-speed rail car body, and cut US $1.2 million per annum in gas costs (8% of welding cost savings).
Newport News Shipyard in the US stores acetylene for cutting heavy plates above 50mm (significant efficiency gains), and uses propane for the rest of the process (safety focus).
In short, acetylene ethylene cannot completely substitute for conventional welding gases, but can be used as an additive in some situations (e.g., thin sheets for high-precision, titanium alloy), balancing performance, cost and risk (market share of mixture gases will increase 3.5 percent annually to 18 percent in 2030).