When I introduced my friend to welding we only used flux core wire and stick-welding. But recently he saw me welding with gas and oxygen cylinders attached to my welder and he asked about their purpose – which led to an interesting discussion around why welders use oxygen.
Welders mix oxygen with argon which increases the quality and durability of welds in certain types of metals. To provide oxygen safely and efficiently it’s contained at high pressure in specially designed cylinders that are able to evenly distribute internal pressure.
Oxygen causes oxidation which helps create better penetration in some cases but not others. It’s not useful when welding aluminum, magnesium, or other exotic metals. In this article, I cover the basics of oxygen use in welding.
Oxygen for welding
Oxygen is the most important gas for living beings, not flammable itself, but sustains combustion. However, it is highly oxidizing, reacts with combustible materials, and can cause fire or explosion.
Oxygen can be used in the most diverse methods of cutting and joining materials. For combustion, it is necessary to bring together the three elements that make up the triangle of fire, oxygen, heat, and fuel.
To produce a flame hot enough to join metal you need a special mixture of fuel gas and pure oxygen. There are various fuel gases welder use but the most common is acetylene. The second element, oxygen must be supplied by a pressurized cylinder.
To initiate combustion, an ignition source is required. When welding, a specific lighter must be used for this purpose. The oxygen cylinder for welding is indicated for cutting and welding processes when combined with acetylene gas, promoting a flame that can exceed 3000°C.
In an oxygen cylinder, for example, the internal pressure applied to each square centimeter of its surface is equivalent to a force exerted by a weight of 200 kg. Always follow welding safety guidelines when working with gas and oxygen.
How oxygen is produced for storage.
There are two methods used to process and store oxygen for commercial use: liquid air process and electrolytic process.
How liquid oxygen is made.
Liquid oxygen is produced through a series of processes. Atmospheric air is passed through an air separation unit and pure liquid oxygen is captured in containers. It’s then passed through a heat exchanger so it can be stored at cryogenic temperature in order to keep it from escaping.
Using an electrolyzer to make oxygen.
An electrolyzer is a mechanism that uses electricity to break down water into its molecular components, hydrogen, and oxygen, H2O. The oxygen gathers at the positive terminal and the hydrogen moves to the negative one.
Once the oxygen is separated it’s collected and compressed into cylinders. The three main types of electrolyzers are proton exchange membrane (PEM), alkaline and solid oxide.
Welding Oxygen Cylinder Sizes and Capacities
Oxygen cylinders come in different sizes and therefore have various capacities. The wall thickness varies between 5 and 8 mm., except at the base and on the shoulder, where the thickness increases to make handling safe and allow the data and values indicated by the standards to be stamped with letters at once.
The most commonly used oxygen cylinders for welding are 80, 122, and 244 cubic feet. These tanks are pressurized up to 2000 pounds per square inch and include a safety device that releases pressure when heated too high which could cause dangerous conditions like leaks.
You can rent or buy oxygen cylinders., most towns have a welding supply shop that will fill your tanks and rent out the bottles. I find this to be the best way for most beginners to start gas welding.
If you’re unsure what size oxygen tank you need, your welding supply shop should have some professionals on hand to help you out.
Information on the oxygen cylinder.
When you get an oxygen cylinder it should have a stamp, and it’s essential you understand what it indicates to help reduce the risks associated with their use. The primary risks are fire hazards and high-pressure releases.
The markings on oxygen cylinders provide critical information, such as the type of cylinder, maximum fill pressure, test date, and serial number. You can typically locate the stamp on the cylinder shoulder.
If you notice a plus (+) sign after the test date this designates that the cylinder can be filled 10% above the pressure stamped on the cylinder. Most oxygen cylinders must be hydrostatically tested for safety every five years, however, there are some that only need testing at ten-year intervals.
If you see a five-pointed star near the test date it designates that the hydrostatic test date has been extended an additional 5 years. The test ensures that tanks can hold up to the maximum fill pressure and won’t cause any harm or damage.
Can you use Industrial Oxygen for Breathing?
Basically, oxygen is a gas, and it is the same in both cases but there are a few critical differences of quality or grade and purity and of how it is kept and carried.
Industrial oxygen with some amount of impurities is still usable for breathing, but the oxygen that is used in medical facilities for breathing by human beings must not contain any impurity.
Though it is not recommended medically yet in a medical emergency, you can use industrial oxygen to breathe. Industrial oxygen comes from the same source as breathing oxygen. The difference between the two types is that, for industrial application, the degree of purity does not need to be so high.
Welding/Industrial Oxygen vs Medical Oxygen
Oxygen has both medicinal and industrial applications. The difference is found in the method of manufacture, packaging, and security controls that each one requires for its commercialization.
Medicinal Oxygen facilitates respiratory function, aid in lung and blood system exploration, and is an adjunct to anesthesia. It is also applied to establish diagnoses, in surgery, sterilization, and in the clinical laboratory for the calibration of some equipment and devices.
Industrial oxygen can be both organic and inorganic and is obtained from the air through a separation process or produced by chemical synthesis, complying with the requirements of the standard that governs the process.
Welding oxygen is the same oxygen that is inside a medical balloon. Industrial oxygen is 95% clean and medicinal oxygen is 98%, the oxygen concentration is what makes the difference.
We cannot put a patient who needs quality oxygen at risk by using the industrial one. What we recommend is that industrial oxygen should be transformed into medicinal oxygen.
Therefore, for medical applications, it is necessary to obtain oxygen with a very high degree of purity and to reach this level of purity and proceed with fractional distillation; it is necessary that, before liquefying the air, it goes through a filtering system to remove all the particulates (dust and particles in general), which must eliminate all the solid parts suspended in the air.