Oxy-Acetylene vs. Arc Welding: Cost, Safety, and Usage
When you ask anyone about welding, those who have any idea of what it is or how it works are likely to talk about arc welding. The image of the dark-tinted welding mask, the bright sparking welding torch, and the ability to fuse two things together have saturated popular media.
Those a little more “in the know” will recognize that arc welding is just one category of welding and that anything that joins two pieces of material together can rightly be called a “weld,” even if there’s no electricity involved. In fact, popular types of glue are even branded as welding.
Two of the most common types of welding when metal is involved are arc welding and oxy-acetylene welding. What are the differences between these, the pros and cons, and which one should you learn? It’s all relatively straightforward, but it’s still worth learning about the differences in a direct comparison.
How Does Oxy-Acetylene Welding Work?
Oxy-acetylene welding is also known as “gas welding” because of the way the process functions. It’s also referred to as oxyfuel welding because acetylene is just one of a handful of different fuel gasses that can be used for the process. The most common is propane, but natural gas, propylene, and MAPP can all be used as well.
The way it works is fairly simple. You have two sources of gas; one is oxygen, which is the purest oxidizer and enhancer for flames, and the other is a combustible fuel. Pumping both through a torch, mixing them, and blasting them out of the nozzle creates a jet of combustible gas. That gas is ignited and produces a hot flame, which can be controlled through the position of the torch and the flow rate of the gasses.
The flame generated by the ignited gasses is hot enough to melt steel, albeit at a relatively slow rate. The heat is thus applied to a joint, and a filler material is also melted into the weld pool, where it can mix and create a solid connection between the two work pieces.
How Does Arc Welding Work?
Arc welding is a somewhat newer process than gas welding, though “new” is relative here, as both have been around for well over a century.
Arc welding uses the power of an electrical arc to rapidly melt conductive metals. A current is circulated through a circuit, with one end of the circuit on the welding torch and the other on the workpiece. When the two come close together, the circuit completes in a high-energy arc, which melts the metal in the immediate area. This, along with a filler material, creates a weld pool that solidifies into a single solid joint.
Thus, in concept, the two kinds of welding are similar; they both use a source of high heat to melt metal along with a filler material, so that the resulting pool of molten metal mixes and flows together, solidifying into a single piece.
While gas welding is called gas welding because of the use of a fuel gas, that doesn’t mean arc welding doesn’t use a gas. In fact, arc welding processes generally use a shielding gas to protect the weld pool from outside contaminants. Certain kinds of arc welding, like MIG (Metal Inert Gas) and TIG (Tungsten Inert Gas), even use gas as a defining part of their names. That said, anyone referring to “gas welding” is talking about oxy-acetylene welding, not arc welding.
Note: There are other kinds of welding beyond these two processes. Stir welding, laser welding, and others are all available. For a complete rundown of different welding processes, see this guide.
Comparing Gas Welding and Arc Welding
So, how do the two processes compare? Since the two are used for more or less the same purposes, it’s easy to do a direct comparison.
Temperature of the process.
Temperature is one of the biggest differences between oxyfuel and arc welding.
Oxyfuel welding uses fuel and air to generate a very hot flame. This flame can reach temperatures as high as 3,600 degrees C, which is around 6,500 degrees F. This is extremely hot! In fact, steel melts at around 2,800 degrees F, though different alloys will have dramatically different melting points. Oxyfuel torches generate more than enough heat to melt steel for a joint.
While this amount of heat is high (and may even sound excessive), it’s actually significantly lower than the heat generated by arc welding. Arc welding creates an electric arc that can reach temperatures of up to 10,000 degrees F.
This isn’t even as hot as it can potentially go.
While excessive heat might sound like a bad thing, the truth is there’s a lot of leeway. Lower heat is actually worse because of how thermally conductive metal is. The slower the work surface heats up, the larger the “heat-affected zone” will be. A larger heat-affected zone means more area of steel that can end up softened and warp, bend, or otherwise be compromised. Arc welding flash-melts the metal under the arc, leaving a drastically reduced heat-affected zone compared to gas welding.
Of course, at much higher temperatures, the electricity is no longer the star of the show. At a certain temperature, the gas pumped through the torch is no longer a shielding gas or a fuel; it’s a resource to be turned into superheated plasma. This plasma then blasts through the torch, melts and blows away the metal from an area. Plasma is used for cutting, not welding, but plasma cutting is essentially just “arc welding on steroids” when you look at it the right way.
Cost of consumables.
Another one of the main differences between arc welding and gas welding is the list of consumables and their associated expenses.
Gas welding really only has two kinds of consumables: the filler rods used to melt into the weld pool to create a joint and the fuel gasses that are used to generate the flame in the first place. The gasses involved – oxygen and a fuel such as propane – need to be stored in pressurized cylinders and recharged or replaced periodically. These gasses need to be pure; otherwise, the combustion will be inconsistent or tainted, which can damage the resulting weld joint.
Arc welding, meanwhile, can have a variety of different consumables. Filler rods or wires are one thing; shielding gas is another. Together, those are comparable to gas welding. Then, you have additional consumption in the form of the electricity used to power the welding machine, as well as some parts of the torch itself, like electrodes, which can wear out over time.
Given that both use a filler rod and gas, you would think that the one using additional consumables is more expensive. However, that’s not always the case.
While you can see our full rundown on the cost comparison between oxyfuel and arc welding here, the one area of cost that many people overlook is operator time. The comparatively lower-quality welds produced by gas welding require more time to complete, more time to prep and finish, and more work throughout, all of which takes time, and time is money in any sort of fabrication process.
Safety in the process.
Safety can be another large concern when it comes to welding.
Both forms of welding use high heat to create molten metal, which is bright, gives off noxious fumes, and is a burn and fire hazard. These are the same regardless of the process used.
Gas welding has additional hazards in the form of fuel gasses. Since the fuel needs to be pressurized, those cylinders can be explosion hazards, especially if the open flame is mishandled. Leaks can also be devastating.
Arc welding, on the other hand, adds a variety of other kinds of hazards to the mix. Electric arcs can be extremely dangerous. In addition to the heat, they also give off intense light and UV radiation, which can be significant hazards to vision and even to skin; unprotected welders may get exposure burns similar to sunburn, and the risk of skin cancer, while small, is not zero.
While it may seem like gas and arc welding are just iterations of the same concept and are used for the same purposes, nothing could be further from the truth.
In actuality, each process has a defined role today. Arc welding took over some of the jobs that gas welding used to do – like fabrication in shipbuilding, pipeline building, and other large-scale creations – but there are some processes that arc welding simply cannot perform.
The reason for this is how arc welding works. You know that it relies on a circuit of electrical power between the torch and the workpiece. That implies something that many may overlook:
The workpiece must be conductive.
Arc welding cannot work on non-ferrous metals or non-metal components. It also struggles with metals that have extremely high melting points, though gas welding doesn’t perform any better in those scenarios.
Gas welding today is used for cases where metal needs to be joined, but that metal isn’t conductive, so arc welding is inappropriate. It’s usually used for thin sheets of metal as well and is common in the aerospace industry. Conversely, arc welding is used on conductive metals, thicker metals, and a variety of different industries.
Depth and quality of joints.
One of the greatest differences between arc and gas welding is how the process works to melt metal at depth. For thick pieces of steel, gas welding struggles. This is because it’s one defined heat source emanating from the torch, heating up the metal. Heat spreads evenly through the metal, so to get depth, you also need breadth; the weld pool and heat-affected zone will be large. This leads to a variety of issues, particularly in heat-treated or other materials where the heat should be minimized.
It also takes quite a bit longer the thicker or larger the metal is. Heat needs to be given time to work through the workpiece to achieve deep penetration.
Arc welding, conversely, is near-instantaneous. The arc generates such an immense amount of power that it can near-immediately melt the metal into a molten state, keeping the heat-affected zone to a minimum around the weld pool. This can more effectively create deeper, more thorough welds, which results in stronger joints. They also tend to be smaller and more pleasing to the eye, if that’s important, though it often isn’t.
Skill, Speed, and efficiency.
Gas welding is widely accepted as the more skill-intensive process. Having a steady hand, knowing when to melt the filler and when proper depth is achieved, how to adjust the torch, and how to minimize heat warping are all parts of the skills necessary to use gas welding effectively.
Arc welding can vary wildly depending on the process used. Often, MIG is considered a very easy and simple process to learn, while TIG is a lot harder to learn and use appropriately.
In modern fabrication, this isn’t always truly relevant since a lot of the work can be done by programming computers to do the work for you. Machines wielding a welding torch can be more precise, accurate, steady, and safe than human operators, so it’s no surprise that many fabricators are switching to machine welding wherever possible.
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