An Inside Look at the Oxyfuel Process

February 2025

Many metalworkers use oxyfuel processes to fabricate, cut, dismantle, maintain, repair, preheat, temper, anneal, bend, and shape products that are part of our daily lives. Despite this, some school administrations are considering removing oxyfuel processes from their curricula because they believe it is an archaic process. However, instructors and industry professionals understand that oxyfuel processes have been essential to the domestic fabrication industry since 1907 when the Brooklyn Navy Yard used oxyacetylene torches to cut portholes in 3-in. armor plates (Ref. 1). 

For those advocating for the removal of oxyfuel processes, it’s important to note that many welding codes require minimum preheat and interpass temperatures as well as postweld heat treatment — all of which students practice with oxyfuel processes. Additionally, oxyfuel remains widely used because of its convenience, cost-effectiveness, portability, and versatility in performing a range of tasks, from cutting and heating to gouging, scarfing, washing, welding, and brazing.

From a financial perspective, equipping a school or training facility with a professional-grade oxyfuel outfit costs a few hundred dollars and can last for decades. Factoring in the educational discounts (often 30–40% below the manufacturer’s suggested retail price), schools can acquire ten booths with cutting, heating, and welding/brazing outfits and required personal protective equipment (PPE) for $5000–$10,000, depending on the outfit.

 

Building Core Competencies

Teaching oxyfuel processes equips students with essential knowledge for a successful career in metalworking. Key topics include the following:

  • Identifying hazards of metalworking (heat, sparks, molten metal, and UV light) and understanding the importance of PPE.
  • Understanding the triangle of combustion or “fire triangle” (fuel, oxygen, and heat) and learning how to control each element.
  • Practicing good housekeeping by maintaining a work area free of combustible materials that could fuel a fire.
  • Properly identifying, handling, and securing cylinders in use and storage.
  • Safely installing, operating, and shutting down gas flow and pressure regulation devices — Fig. 1.
  • Inspecting and maintaining equipment for safety and performance.
  • Recognizing oxyfuel-specific hazards like reverse flow, flashback, backfire, and sustained backfire.
  • Understanding basic metallurgy and chemistry principles (rapid oxidation, tempering, quenching, work hardening, and microstructure).
  • Using measuring and math skills to compensate for kerf, ensure proper fit-up, and apply good workholding techniques.
  • Preparing materials for welding by following proper weld prep procedures.
  • Reading the weld pool, developing a cadence for adding filler metal, and mastering weld pool manipulation.

 

WJ Dec 24 - Feature 04-Henderson-ESAB - Fig 2.tif
Fig. 1 — Students learn the fundamentals of regulator operation and gas safety by using oxyfuel processes.

 

Practical Advice for Oxyfuel Processes

The remainder of this article presents fundamental advice and a few more advanced tips for oxyfuel processes. For clarity, they are divided into gas choices, lighting the torch, cutting advice, and shutdown.

 

Gas Choices

  • Use acetylene for a more focused heat-affected zone — Fig. 2.
  • Use alternate fuels (e.g., not acetylene) to heat larger areas because they release more heat in the secondary flame. For example, when heating a large area to cherry red with acetylene, the starting point cools before the torch reaches the end of the plate.
  • Use acetylene for gas welding because it gives off CO2 during combustion, shielding the weld pool from atmospheric contamination.
  • Recognize that most people won’t notice the cutting speed difference between acetylene and propane. The former burns about 10% hotter (5720° vs. 5112°F), but propane has a greater total heat of combustion, making it equally as fast at cutting. Also, remember that the cutting oxygen does the real work. Any speed difference is usually related to technique.
  • Choose torches with a spiral mixer for fuel gas flexibility. These torches are calibrated to work with both high-pressure fuels, like acetylene, and low-pressure fuels, such as propane.
  • Use regulators and cutting/heating tips only with their intended gases. These components are fuel gas specific because of the density and pressure differences between gases.

 

WJ Dec 24 - Feature 04-Henderson-ESAB - Fig 1.tif
Fig. 2 — Choose acetylene to create a focused heat zone, as shown here. Propane will heat a larger area (e.g., big beams, larger-diameter pipe, buckets, etc.) and cost less.

 

Lighting the Torch

  • Open the oxygen valve on the handle when using a standard combination torch and adjust the flame from the oxygen valve on the cutting attachment. This ensures maximum oxygen flow to the cutting lever.
  • Set a neutral flame by observing how the length of the secondary flame shortens as preheat oxygen is added. In a proper neutral flame, the inner and outer cones are nearly equal in length, indicating the correct oxygen-to-fuel ratio.
  • Recognize a carburizing flame by its excess acetylene. As acetylene is added, the inner cone becomes much smaller than the outer cone, which appears rough and feathery.
  • Identify an oxidizing flame by its excess oxygen. When too much oxygen is added, a loud hissing sound occurs, and the inner cone remains sharp.
  • Use different lighting techniques for alternate fuels. If wind extinguishes the flame, place the tip at a 45-deg angle on the work surface to create back pressure on the flame and reduce its burn velocity. Light the torch, then, while keeping the torch in place, open the cutting oxygen valve until the flame audibly snaps into place.
  • Check for a neutral flame with alternate fuels by placing the torch near the workpiece. The preheat flames create a star pattern with clearly defined legs about 2–3 in. long. An oxidizing flame will have shorter, sharper legs, while a carburizing flame will have longer, more feathery legs.

 

Tips for Cutting

  • Support the torch with your off-hand, brace your elbows, and hold the torch tip about ¼ in. from the workpiece for a steady cut. Practice movements before lighting the torch, and learn to slide your elbows. Oxyfuel makes a precise cut, but any hand movement will be reflected in the cut.
  • Preheat the starting point of the metal to a bright cherry red, indicating “kindling temperature,” at which oxygen can react with the ferrite in the steel to start the cutting process. Only then should you depress the cutting oxygen lever.
  • Follow through for a good drop cut by continuing to depress the cutting oxygen lever and moving the cutting oxygen stream past the edge of the metal.
  • Don’t focus on the leading edge of the cut. Instead, look where you want to go, and your hands will follow.
  • Use your ears. A consistent sizzling sound is the best indicator of proper travel speed.

 

Shutdown

Regardless of fuel gas, always follow the same shut-off procedure: oxygen first, fuel gas last. Shutting off the oxygen first removes the most critical leg of the fire triangle and lets the operator check for a fuel gas valve leak after shutting off the fuel valve. If a small flame remains attached to the torch, it might be time to repair the fuel valve.

 

Closing Thoughts

While anyone can learn to use a torch safely, mastering fast and precise cuts takes practice and skill. The effort is well worth it, as these skills are essential for a successful career in metalworking.

In 2023, North America’s acetylene market reached $3.2 billion, with approximately 40% of use coming from metal fabrication applications (Ref. 2). Natural gas, propane, and propylene are also used across the industry. Those gases do not burn themselves; welders are expected to be proficient with a torch and familiar with various gases. As a result, many welding trade and technical schools teach oxyfuel processes to meet the needs of the skilled trades. 

 

References

  1. Henderson, J., and Hussary, N. 2013. A history of the oxyacetylene and plasma cutting processes. Welding Journal 92(10): 44–49.
  2. Industry Arc. Acetylene Market Research Report- Market size, Industry Outlook, Market Forecast, Demand Analysis, Market Share, Market Report 2024-2030. Retrieved from industryarc.com/Research/Acetylene-Market-Research-509334.
     

 

This article was written by John Henderson (sales director, gas equipment, at ESAB) for the American Welding Society. This article was also presented at FABTECH 2024.