The 4 Main Types of Oxy-Fuel Heating Cutting, & Welding Gases
A flame is a flame, right?
Well, not exactly.
While all industrial fuel gases are capable of generating a flame, their properties can be very different.
Here is a rundown of the four common types of oxy fuel heating, cutting, and welding gases.
Acetylene: The Old Standby
First, the nerdy stuff. Acetylene (a.k.a. ethyne) is an alkyne hydrocarbon consisting of two carbon atoms and two hydrogen atoms (C2H2). It was discovered in 1836 by Edmund Davy, who accidentally produced potassium carbide, which reacted with water to produce gas. The gas was given the name acetylene by French chemist Marcellin Berthelot in 1860.
Acetylene is intrinsically unstable, especially when pressurized. Because of this, industrial acetylene is dissolved in acetone and stored in porous cylinders which renders it safe for transport and use. This is why acetylene cylinders should always be stored upright. If acetylene cylinders are tilted, or if the operating pressure exceeds 15psi, liquid acetone can become introduced into the torch, which will cause the flame to drip from the orifice. This is also why acetylene has a withdrawal rate limit of 1/7 of the cylinder volume per hour.
From a performance perspective, acetylene has the hottest flame (around 5,720°F). It has a total calorific value of 1,470 BTU. The low hydrogen content of acetylene makes it an excellent choice for oxy fuel welding and cutting. When used as a cutting fuel, the inner cone of the flame will contain about 507BTU and the outer cone will contain about 963BTU. This allows for fast piercing with a minimal heat-affected zone. It also generates a fair amount of slag, requiring more post-cut cleanup. Acetylene is also highly prone to flashbacks. Flashback arrestors should always be used when cutting with acetylene.
Propane: Not Just for Grilling
Propane is an alkane consisting of three carbon atoms and eight hydrogen atoms (C3H8). It was discovered in 1857 by French chemist Marcellin Berthelot (the same man who gave acetylene its name). Propane is a liquefied petroleum (LP) gas and a by-product of natural gas processing and petroleum refining. Propane is heavier than air and has a tendency to sink when a leak occurs. This can pose a risk of explosion or fire, especially when propane is stored in basements near heat sources. Propane has a lower temperature flame than acetylene at around 5,122°F. Propane is not recommended for oxy/fuel welding.
The most notable potential benefit that propane offers is a significantly higher calorific value than acetylene at around 2,510 BTU. This makes it an excellent choice for heating. When used for cutting, the inner cone of the flame will contain about 255 BTU and the outer cone will contain a whopping 2,243 BTU! This allows a much faster preheat than acetylene but as a tradeoff for much longer piercing times and a larger heat-affected zone. Once the piercing is done, the cut speed is comparable to acetylene.
Propylene: The Other Prop-Gas
If propylene (C3H6) sounds similar to propane, that’s because it is. The prop- prefix that the two gases share means that they both have three carbon chains.
The molecular difference between propane and propylene is the number of hydrogen atoms (propane has eight, propylene has six). The similarities of the two gases don’t end there. Both gases have a comparable flame temperature and calorific value. The main difference between propane and propylene is the heat distribution when cutting. Propylene has a higher BTU value in the inner cone and lower BTU value in the outer cone than propane. The oxygen to fuel gas ratio is also slightly lower with propylene, making it somewhat more efficient than propane.
Methylacetylene-Propadiene: The gas you’ve never heard of (or have you?)
Methylacetylene-Propadiene (C6H8) is universally known as MAPP gas (a Linde trademark) or MPS.
There is some confusion surrounding the name. You might have heard that MAPP gas is no longer available. This is technically true. The last MAPP gas production plant in the US closed in 2008.
Gases available today are MAPP substitutes. MAPP gas does not offer many benefits over propane or propylene and is typically only used for small part heating and brazing. The one standout benefit of MAPP gas for cutting is its performance in high-pressure submerged cutting applications, but this is a rare application these days.
These four gases comprise the vast majority of fuels in use today for industrial heating, cutting, and welding. Many other gases exist, including branded gases which are usually one of the above-mentioned gases with a proprietary additive to enhance certain characteristics.
Knowing the capabilities and limitations of your fuel gas will make for a safer and more productive work environment. If you are unsure of the safety considerations of the gases you are using, please consult your gas supplier or OSHA standard 1910.253.
American Torch Tip is dedicated to providing the most up-to-date information surrounding the newest updates in the welding and cutting industry. Looking for more information about oxy fuel welding and cutting? Read our recent article about oxy fuel cutting and safety procedures.
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