Why metal manufacturers should consider alternate fuels in heating and cutting torch applications

As shops look for production improvements and cost savings, a shift away from acetylene to alternate fuels for oxyfuel cutting and heating may be the answer. Images: The Harris Products Group

Oxyfuel—a combination of oxygen and fuel gas—has been used for flame cutting, brazing, welding, heating, and a variety of other applications for more than 100 years. The most commonly used fuel gas for this process is acetylene.

As shops look for production improvements and cost savings, it's important to optimize these processes by combining proper fuel gases with the right equipment. One of the best ways to do that is to replace acetylene with alternate fuels for heating and cutting.

Using an alternate fuel like propane, propylene, natural gas, or proprietary gas blends can provide numerous cost and performance benefits. Here are four reasons to consider switching to alternate fuels.

Compared to acetylene, the overall cost of using alternate fuels for cutting and heating applications is considerably lower.

Alternate fuels have higher BTU numbers per cubic foot than acetylene, which means higher BTU per cylinder. A No. 5 acetylene cylinder has roughly 320 cu. ft. of gas, which equates to 470,400 BTU. A similar sized 100-lb. propane cylinder (propane has 8.66 cu. ft./lbs. and 2,563 BTU/cu. ft.) contains 2,219,558 BTU. It will take five acetylene cylinders to do the same amount of work as one alternate-fuel cylinder. Fewer gas cylinders also mean lower handling costs, lower rental charges, and less storage space.

In short, alternate fuels provide more BTUs per dollar spent. This can make a significant difference over the course of just one day on the shop floor. Compound this over a week, a month, or a year and the savings multiply.

There are many restrictions and safety concerns when using acetylene for heating and cutting applications.

For example, acetylene cannot be used at pressures higher than 15 PSIG; the gas becomes unstable and can decompose explosively. Obviously, this is a safety concern.

A common heating problem concerns flashbacks and sustained backfires, or flames coming back into the torch. This typically is caused by improper pressure settings or flow restrictions. With acetylene, there is a limit to the amount of gas that can be withdrawn from a cylinder for safety reasons. Only one-seventh of the cylinder's volume can be withdrawn per hour. Most acetylene heating tips exceed the withdrawal capacity of acetylene cylinders. To heat with acetylene safely and properly, you have to use the smallest heating tips and typically pigtail multiple cylinders together to allow for the needed withdrawal rates.

Alternate fuels, however, are more stable and do not have acetylene's strict withdrawal limits. They can be used safely at higher pressures, and flow rates and are not sensitive to shock. They also produce less carbon soot, which pollutes the work area and can cause respiratory issues.

Cost, safety, efficiency, and performance are the four reasons why shops should consider a move toward alternate fuels for heating, cutting, and brazing.

Alternate fuels have higher BTU per cubic foot—2,300 to 2,600 depending on the gas—than acetylene's 1,470 BTU/cu. ft. This allows for better heating efficiency. By using alternate fuels in the oxyfuel heating process instead of acetylene, the targeted heating temperature is reached faster.

Alternate fuels also can outperform acetylene when cutting. Some benefits and advantages of alternate fuels include decreased preheat times; increased travel speeds; clean, narrow kerfs; less top-edge rollover; less hardening of the cut face; and less slag. All of these factors result in a high-quality cut with less chipping, grinding, and cleanup time.

Once the decision is made to switch to alternate fuels, it's important to realize that simply changing the torch tip will not allow the user to realize all the advantages discussed. It is also recommended to convert to a low-pressure injector torch to get the full benefits of the gas. That is because alternate fuels mix at a different oxyfuel ratio (around 4.5-1) as compared to acetylene (1-1-1). If you only change the tip, you are not changing how the gases mix. Injector mixers designed for alternate fuels mix the oxygen and fuel gas thoroughly and at the correct ratios for increased BTU output and maximum flame performance. Check with your gas equipment supplier to determine which type of injector mixer you need.

In summary, the key to performance and efficiency while heating, cutting, and brazing is having the proper fuel gas and equipment. When switching to an alternate fuel, it's important to understand what equipment is needed to obtain the full benefits of the gas and achieve the cost savings, convenience, and safety advantages that alternate fuels can bring.

A heavy machinery company wanted to reduce costs in its maintenance/repair facility. It reviewed the potential savings of using alternate fuels, not just for heating but also for cutting. It also considered the proper heating and cutting torches and equipment that should be used with alternate fuels.

After making the switch to propylene, the company's overall gas use decreased; in addition, cylinder costs went down since fewer cylinders were needed. It also saved on production time, spending less time heating the parts. This resulted in drastic reductions in preheat time as well.

Six months later, the company made the switch at its second maintenance location.

A steel fabricator faced a significant safety issue: Its heating tips were melting. Unfortunately for one operator, that led to a flashback that injured his hand. The employees used acetylene with too large of a tip. The flow required for the large tip exceeded the withdrawal limits of the acetylene cylinders. The insufficient flow caused the flame to burn back into the tip. This melted the end of the tip and caused the orifices to close, only compounding the flow problem. Eventually, a sustained backfire occurred all the way into the handle, burning the operator's hand.

The company switched to an alternate fuel and installed properly sized tips, hoses, and high-flow flashback arresters for the regulators. It saved money by using alternate fuels instead of acetylene, eliminating the safety issue as well.