Guide to Welding Gas
Table of Contents
There are several types of welding gas available including acetylene, MAPP, Natural Gas and Propane. The combination of oxyacetylene gas used along with oxygen is the most popular for welding steel. Oxygen helps any burning process by increasing the temperature and rate of combustion, which is why it is used along with the gasses described on this page in a separate cylinder. Oxyacetylene provides a high temperature flame. An alternative is Oxymapp (liquefied petroleum), although it burns at a lower temperature than oxyacetylene. The implications are that it is a longer process to preheat and then weld steel. Another choice for welding with gas are propane, which is used for oxyfuel cutting, soldering and brazing. The issue with propane welding is that the gas does not contain carbon, which causes the welded metal to become brittle. There are also applications for butane and natural gas.
Hydrocarbon welding gases, such as propane, butane, city gas, and natural gas, are not suitable for welding ferrous materials due to their oxidizing characteristics. In some instances, many nonferrous and ferrous metals can be braze welded with care taken in the adjustment of flare and the use of flux. It is important to use tips designed for the fuel gas being employed. These gases are extensively used for brazing and soldering operations, utilizing both mechanized and manual methods.
These fuel gases have relatively low flame propagation rates, with the exception of some manufactured city gases containing considerable amounts of hydrogen. When standard welding tips are used, the maximum flame velocity is so 1ow that it interferes seriously with heat transfer from the flame to the work. The highest flame temperatures of the gases are obtained at high oxygen-to-fuel gas ratios. These ratios produce highly oxidizing flames, which prevent the satisfactory welding of most metals.
Tips should be used having flame-holding devices, such as skirts, counterbores, and holder flames, to permit higher gas velocities before they leave the tip. This makes it possible to use these fuel gases for many heating applications with excellent heat transfer efficiency.
Air contains approximately 80 percent nitrogen by volume. This does not support combustion. Fuel gases burned with air, therefore, produce lower flame temperatures than those burned with oxygen. The total heat content is also lower. The air-fuel gas flame is suitable only for welding light sections of lead and for light brazing and soldering operations.
Acetylene Gas Generator
Acetylene is created when calcium carbide, which is a man made substance, reacts to water. It can keep indefinitely, and is used in welding with separate cylinders of oxygen and acetylene gas, which is kept at high pressure. Cylinders are stored upright in order to keep the stored gas stable.
It is a colorless gas with a strong garlic odor. It burns at 5,600 degrees Fahrenheit with a neutral flame and is used for hard facing, heating, brazing, cutting and welding. Note that acetylene should not be compressed above the level that causes instability which is 15 PSI.
MAPP gas is part of the acetylene family. It contains the gasses propylene, propadiene and methylacetylene. I is used for cutting and heating, although a special welding rod is needed to avoid the oxidizing characteristics associated with the MAPP flame. At neutral the flame temperature is 5,300 Fahrenheit.
Natural gas is widely available. Specialized cutting and welding equipment is required. The gas burns at 5,025 Fahrenheit with a neutral flame.
Propane and Oxygen Welding Demonstration
Demonstration of how to set up propane and oxygen welding equipment.
Like natural gas, propane is also widely available. It is sold in a liquid state in cylinders that are available in sizes between 20 pounds and 100 pounds. The flame temperature is 5,200 Fahrenheit with a neutral flame. It is used for heating and cutting.
Standard oxyacetylene equipment, with the exception of torch tips and regulators, can be used to distribute and bum these gases. Special regulators may be obtained, and heating and cutting tips are available. City gas and natural gas are supplied by pipelines; propane and butane are stored in cylinders or delivered in liquid form to storage tanks on the user's property.
The torches for use with air-fuel gas generally are designed to aspirate the proper quantity of air from the atmosphere to provide combustion. The fuel gas flows through the torch at a supply pressure of 2 to 40 psig and serves to aspirate the air. For light work, fuel gas usually is supplied from a small cylinder that is easily transportable.
The plumbing, refrigeration, and electrical trades use propane in small cylinders for many heating and soldering applications. The propane flows through the torch at a supply pressure from 3 to 60 psig and serves to aspirate the air. The torches are used for soldering electrical connections, the joints in copper pipelines, and light brazing jobs.
Standard Cylinder Sizes
Gas welding cylinders are commonly purchased in these standard sizes:
- 80 cubic feet
- 122 cubic feet
- 244 cubic feet
Common Acetylene Cylinder Sizes
- 60 cubic feet
- 100 cubic feet
- 300 cubic feet
Air-fuel gas is used for welding lead up to approximately 1/4 in. (6.4 mm) in thickness. The greatest field of application in the plumbing and electrical industry. The process is used extensively for soldering copper tubing.
Working Pressures for Welding Operations
The required working pressure increases as the tip orifice increases. The relation between the tip number and the diameter of the orifice may vary with different manufacturers. However, the smaller number always indicates the smaller diameter. For the approximate relation between the tip number and the required oxygen and welding gas pressures, follow the manufacturers instructions. Note sample tables below for acetylene.
Welding Gas References
Page Author: Jeff Grill