Oxygen Cylinder (Bottle Oxygen) For Welding: The Basics

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Oxygen cylinders come mainly in three sizes (80, 122, and 244) and are measured in cubit feet. Each cylinder is pressurized to 2220 psi. The oxygen cylinders fittings are tightened clockwise or right-handed. Each cylinder has a safety device that releases pressure when temperature is high as a safeguard to expansion that can cause explosion.

Keep all combustibles away from oxygen including regulators, hose apparatus, cylinders and valves. Pure oxygen accelerates combustion of any material and is dangerous to use near grease and oil. Therefore, don’t handle oxygen cylinders with oily gloves or hands. Oil and grease will simultaneously ignite and explode or burn violently.

Welding-grade oxygen differs from a medical-grade oxygen. The medical-grade oxygen has a 99.5% purity and contains more impurities than welding oxygen, which is only 99.2% pure.


For starters, there are different purities of oxygen used in various applications. The two main oxygen options are the industrial oxygen and medical oxygen. The surrounding air only contains 20% oxygen and other gases such as nitrogen, carbon dioxide and inert gases make up the rest of the composition.

Oxygen is non-combustible by-itself. However, it speeds up combustion and can cause burning or explosions. This is a vital factor as the atmosphere is oxygen-enriched. The mixture of gases contains at least 23% of oxygen as determined by the compressed gas association or CGA.

Handle oxygen-enriched atmospheres carefully like you handle pure oxygen. Remember, the 23.5% oxygen can ignite other gases eight times faster than normal oxygen gas.

The United States Pharmacopoeia (USP), explains that before labeling a cylinder as oxygen, it must contain 99% oxygen.

How Are The Various Gases Separated? 

Oxygen is produced through two main processes for commercial use.

01. Air-Liquefaction Process 

Air-Liquefaction Process

This is a commercial oxygen production process commonly referred to as fractional distillation of air. During this process, gasses are first liquefied or turned to liquid through compression and cooling.

Repeated compression and cooling separate oxygen from nitrogen and other gasses based on their boiling points. After separating oxygen from other gasses, the purification process begins before it’s bottled for commercial use.

02. Electrolyte Process

Electrolyte Process

This process depends on water as the main source of oxygen instead of air. Electrolysis of water involves passing an electric current through the water to breakdown oxygen and hydrogen.

Hydrogen gas is collected at the negative terminal while oxygen is collected at the positive terminal. After collection, oxygen is compressed, then bottled in what you get as bottled oxygen. The difference between welding oxygen and medical oxygen has nothing to do with production but purification process. Most industrial oxygen is labeled by USP, and these compartments are not to medical or welding oxygen.

How Is Oxygen Isolated And Bottled For Welding?

The above oxygen production process is vital in isolation of oxygen for commercial or industrial application. The isolation process happens in two ways, by fractional distillation of liquid air and through electrolysis of water as explained above. Hen it comes to bottling, oxygen if first graded after being compressed, then bottled for welding or medical use.

01. Oxygen Grade For Welding

CGA has classified seven grades for oxygen which range from A to G. grade A is 99.0% oxygen and the highest grade which is grade G is 99.55% oxygen. Grading is a classification according to purity of oxygen and how much of other gasses are still present.

Grade A is the bare minimum labeled by USP and the grading is separated according to the industry the oxygen is used for. Oxygen is primarily graded for two industrial applications, welding and medical.

Welding oxygen has a purity of 99.2% which is slightly less pure than the one for medical grade or application. Welding oxygen is used to stabilize and produce heat for welding and metal joining for industrial applications. The source tank for oxygen for both applications is the same. What is different is the filling process which affects the price and grading?

02. Filing Welding Oxygen Cylinders

When taking your oxygen cylinder for filling or refilling, specify the use like welding. Welding oxygen cylinders are checked for acetylene. If acetylene is detected, the cylinder is cleaned before being refilled with oxygen, and if your cylinder has no acetylene; it gets refilled immediately.

Welding Oxygen Basics

All welding oxygen cylinders are transported using a cylinder truck that is specially fitted to keep them from getting knocked over, which is dangerous. Other basic things to know include:

  • A full welding oxygen cylinder is at least 2000 psi
  • The top opening is smaller than a pencil meaning when damaged, the bottled oxygen becomes like a projectile which can cause devastating property damage or injury.
  • The cylinder should never be used until it’s completely empty, as that makes the other gas to back flow into other bottle or gas line.
  • Always keep the regulator, fittings, and hoses free from grease and oil as they can make the oxygen gas explode under pressure.
  • Chain all bottles to prevent falling, which can cause them to explode.
  • Cap the oxygen bottles anytime your regulator is not attached to the gas valve.
  • Use a new clam style safety cap for your bottle even when the regulator is attached.
  • Never store your oxygen bottles close to flammable materials.
  • Store the oxygen bottled in a place with a minimum height wall of 5-inches and a 30 minute fire rating.
  • Chain the oxygen bottle in a 2-wheel dolly when moving it and don’t roll the bottle with your hands as it can fall and cause injury.
  • Always store the oxygen bottle at a 20 feet minimum distance from other fuel gas cylinders. You could also use a non-combustible barrier 5 feet away and with at least 30 minute fire resistance rating.

What Is Reverse Flow Danger? 

Reverse Flow

Reverse flow is a situation where your oxygen bottle is nearly empty while the other gas is not. For example, your oxygen bottle is almost empty while the acetylene bottle still has some gas. This causes the acetylene gas to flow into the oxygen regulator and hose. A reverse flow can cause an explosion if you light the gasses before completely bleeding off the oxygen.

You can prevent a reverse flow by never using an almost empty oxygen bottle. But what is an empty bottle? A bottle is empty if it has less than 50 psi or less. As an operator, bleed the hoses independently before you light the welding torch and never light both your gasses at once. Only light both at once if you are using a universal pressure torch as it’s specially designed to prevent reverse flow.

What Is Backfire And Flashback Danger?

A backfire is a situation where your welding torch flame is burning back into the torch tip, then get extinguished with a loud pop sound. Backfire happens when there is insufficient gas pressure or the torch touches your work. If backfire happens frequently, it can damage your welding torch.

A flashback is a situation where your flame front cannot extinguish and burns back beyond its mixing chamber via the hoses into the regulator and your gas supply. You can avoid the problem by doing internal checks to ensure the valve works properly or use flashback arrestors. When you encounter a flashback, turn off your oxygen, then turn off the acetylene and allow your units to cool.


There isn’t much difference between welding oxygen and medical oxygen. However, knowing the welding oxygen basics helps you understand the gas better and know how to handle the bottled oxygen when welding. The grading of your bottled oxygen matters and picks the right gas for welding because using oxygen with a higher purity is dangerous. UPS recommends welders to use oxygen grade of 99.2% purity.

Observe all safety measures to prevent fire outbreak or explosions, which can be devastating. Handle the bottled oxygen with extreme care and transport it as advised for safety reasons. The safety guidelines recommended by USP and CGI protects you from fire hazards and other injuries


How Much Are Oxygen Tanks For Welding? 

Filling oxygen tanks will cost you $20 - $35. Owning an oxygen welding gas tank costs $100 - $200.

How Much Does A Bottle Of Oxygen Cost? 

A bottle of oxygen costs $50 per unit for the 330 cubit feet bottle. An oxygen bottle is a pressurized storage vessel made of aluminum and mostly silver colored and has a green top.

What Are The Different Sizes Of Oxygen Tanks For Welding?

Oxygen bottles come in various sizes for portable or static use. The sizes are 20, 40, 60, 80, 120, 244 and 330 cubic feet.

What Is The Difference Between Medical Grade Oxygen And Welding Oxygen? 

The main different is the purity. A medical grade oxygen has a purity of 99.5% while a welding oxygen has a purity of 99.2%. both gasses are bottled the same way but have different filling systems.

What Happens If You Use Oxygen And Don't Need It? 

If you use 50% oxygen or more, your body can’t uptake that much comfortably and this will slow the production rate of red blood cells, making you feel tired as it shuts down your breathing impulse. People breathe because their brains sense the rising levels of carbon dioxide, hence breathe in more oxygen to compensate. This condition is called pulmonary oxygen toxicity.

What Diagnosis Qualifies For Oxygen? 

If you have an arterial blood gas below or at 55mmHg, or your oxygen saturation is less than 88% then you qualify for oxygen. Also, people with chronic obstructive pulmonary disease qualify. The qualification is determined through testing by medical professionals.

What Are The Side Effects Of Being On Oxygen? 

You can experience nasal dryness and skin irritation. Oxygen therapy affects the nasal passage leading to nasal dryness. You can experience skin irritation because of the skin breakdown. The side effects can be overcome by prescription drugs by a doctor like moisturizing products.

Last Updated on May 25, 2021 by weldinghubs

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