12.2 The Gasses and Cylinders

Karl Fulton

Cylinders and General Cylinder Safety

Your oxy-fuel setup may be stationary or portable. You will most likely be utilizing a High-pressure oxygen bottle and a fuel bottle. There are shops that will have cryogenic oxygen tanks for a stationary setup.

On the left of the photograph, one worker uses an OFC process to cut rail with two safety observers. Between the worker cutting and the safety observers is a portable cart with a power source and fuel tanks for cutting. The safety observers hold one blo\ue and one red hose away from the person welding.
Figure 12.3. Union Workers Cutting Railroad Rail / Photo Credit: Geof Sheppard, CC BY-SA 4.0
A worker wearing safety gear is setting up a workspace by checking gauges on gas canisters before making cuts.
Figure 12.4. Setting Up the Work Space / Photo Credit: MHM55, CC BY-SA 4.0

Acetylene Cylinders

The acetylene cylinder is probably the most unique fuel bottle that you will come across and the one you will want to be the most cautious with. This is because acetylene will become explosive and extremely shock-sensitive if stored in its free state at 29.4 psi.

Warning

Never use acetylene at a pressure above 15 psi. Acetylene becomes explosive and shock-sensitive as pressure increases. All acetylene regulators will have a warning about this.

Because of these hazards, the acetylene fuel tank is specially designed and can safely compress up to 275 psi in a porous material like fire brick, balsa wood, charcoal, and other materials. In the past, they would use finely shredded asbestos. The purpose of the porous material is to prevent any high-pressure pockets from forming in the tank. The tank is then filled with acetone, and the acetylene is dissolved into this. Acetone is able to dissolve a large amount of acetylene without changing the chemical composition of the gas. The cylinder being filled with liquid acetone makes it imperative to keep the cylinder upright. If not, the acetone can be drawn into the hose and torch. This will contaminate the regulator and hose and affect the flame. If the cylinder has been on its side, make sure to put it in the upright position and let it settle for at least two hours. In addition to the cylinder being filled with porous material and the acetylene being dissolved into acetone, the cylinder is equipped with fusible plugs designed to relieve pressure if the cylinder is exposed to excessive heat.

One disadvantage of acetylene being dissolved into acetone is you will not be able to tell how much acetylene is left by the pressure gauge. The bottle pressure will remain fairly consistent until the majority of the gas is used.

Oxygen Cylinders

Oxygen is a noncombustible gas that is slightly heavier than air, tasteless, colorless, and odorless. It does support the combustion of other elements, this is what makes it useful in welding and cutting. Our atmosphere consists of about 21 percent oxygen and 78 percent nitrogen. The white flaky corrosion on aluminum, rusting of ferrous metals, and discoloration of copper are all examples of oxidation, the chemical reaction that happens when oxygen from the atmosphere comes in contact with these metals.

There are two ways oxygen is collected for commercial use: the liquid air process and the electrolytic process. The liquid air process starts with compressing air and cooling it to a temperature at which it becomes liquid at -375 degrees F. Once this is accomplished, the temperature of the liquid is elevated to approximately -320 degrees F. This allows the Nitrogen to off-gas as the oxygen stays in its liquid form. The liquid oxygen is again elevated in temperature to -297 degrees F, where it becomes gaseous again. This is compressed into bottles and further purified.

The electrolytic process has an electrical current running through water with an alkali acid added. Oxygen collects at the positive terminal and is collected from there.

Most often, oxygen for welding purposes is supplied in seamless steel cylinders. The cylinder will have a removable metal cap to protect the valve head when not in use or during transportation. The valve head is made of bronze and is the most vulnerable point on the bottle. When in operation, this valve must be opened all the way, this is a double seated valve as it will be sealed when all the way open but will leak if only partly opened. The valve is also equipped with a safety fuse plug and disk. This will rupture and release excessive pressure before the bottle itself fails

The cylinder walls are over a 1/4” thick, and the bottle will hold over 2000 psi at 70 degrees F. The 244 FT3 bottle is the most common size, there are larger and smaller bottles available.

Safety around oxygen and oxygen bottles/cylinders

It is important to practice safety around oxygen bottles and cylinders to protect yourself and the people working around you. Here are some safety practices to consider when working with oxygen cylinders:

  • Never weld on any cylinder; this is extremely hazardous
  • Oil and grease should never come in contact with an oxygen cylinder. This can lead to spontaneous combustion and explosion
  • Oxygen is not air and should never be referred to as such. Oxygen should never be a replacement for compressed air. This is extremely hazardous. Never use oxygen to clean off work areas or dust yourself off. This is extremely dangerous.

Attributions

  1. Figure 12.3: 2023 Taunton track renewals (02) cutting the old rail by Geof Sheppard is released under CC BY-SA 4.0
  2. Figure 12.4: Travaux d’excavation dans le section Louis-Hubert/Morgines au Petit-Lancy. Découpage de poutrelle métallique au chalumeau. by MHM55 is released under CC BY-SA 4.0

License

Icon for the Creative Commons Attribution 4.0 International License

Introduction to Welding Copyright © by Washington State Board for Community and Technical Colleges is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.