On March 21, 2011, an explosion at the Carbide Industries, LLC calcium carbide manufacturing plant in Louisville, Ky., took offline the largest calcium carbide furnace in the Americas. Carbide Industries produced 75 percent of the material used to generate acetylene gas, the primary fuel for precision cutting in welding applications. Calcium carbide is being imported from other countries, but the acetylene shortage is expected to last well into next year, accompanied by rising prices and delivery delays up to nine months.
The workaround is switching to alternative fuels such as propane, propylene and HGX propane. Alternative fuels have some limitations, but the difference in cost compared to current acetylene prices may justify the adjustments the operator will need to make to achieve satisfactory results, depending on application.
Propane, for example, does not burn hot enough for welding tasks but can (with the right torch and tip) produce clean cuts comparable to acetylene. Propylene’s flame temperature is 600 degrees higher than that of propane and offers good cutting properties, but its flow rate is too strong for welding. HGX propane is standard propane combined with a cutting additive, HGX-3, at a ratio of one part per thousand and increases the flame temperature of propane by 15 percent, according to Energy Additives in Michigan, making it suitable for aluminum and cast iron welding.
Switching to an alternative fuel requires these equipment modifications:
• Replace all R-grade fuel hoses with T-grade hoses. Propane and other alternative fuels will disintegrate R-grade hoses and become a safety hazard.
• Replace the acetylene regulator with one designed for alternative fuels. The new fuel regulator shows readings in levels specific to the fuel type and can deliver alternative fuel at a higher psi than the 15-psi max draw limit for acetylene.
• Propane and propane-based gases are half again heavier than acetylene and work best with a low-pressure injector-style torch for proper flow.
• Replace acetylene-cutting tips with tips designed for alternative fuels.
Operators using alternative fuel will also need to adjust their torch lighting techniques. Here are three to start with:
• Technique 1. Turn the fuel valve a quarter turn and light. Then turn the oxygen preheat valve a quarter to a half turn and ’walk up’ the flame.
• Technique 2. Turn the fuel valve a quarter to a half turn and light. Place the tip on the workpiece at about a 45-degree angle, open the oxygen preheat valve a quarter to a half turn until the flame snaps into place, then walk up the flame as normal. Use this technique on a windy day, if the shop fan is blowing on the work area, or if the flame goes out when using Technique 1.
• Technique 3. Turn both the fuel and oxygen valves a quarter to a half turn, light the flame as soon as possible, and walk up the flame.
Alternate fuels require a different technique to achieve a neutral flame. The flame needs to be ‘walked up’ or forced to prevent starving or extinguishing the flame. Here’s how:
After lighting the torch and adding the initial preheat oxygen, alternately add more fuel and more preheat oxygen by turning the respective valves a quarter to a half turn at a time until the fuel gas valve is completely (or almost completely) open. Then add oxygen until the flame creates a loud whistling sound and the primary cones reach their shortest point. Depress the cutting oxygen lever and readjust the preheat oxygen if necessary. Note that with propylene, adding a small additional amount of preheat oxygen will produce a more concentrated flame with a heat pattern similar to acetylene.