Propane/Oxygen - from Cylinder to Oxy/Fuel cutting torch

In summary: The tank pressure is the same for all the gas in the tank. You would not be able to tell how much propane is in a tank by looking at the pressure.
  • #1
martijn_tholen
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TL;DR Summary
How to calculate total gas volume for each cylinder based on the consumption ratio of oxy/fuel for cutting torches
For one of our projects we are at present using quite large amounts of gas & oxygen.
What I was trying to figure out was how to calculate the total available amount of gas in a cylinder (be that either Propane/Oxygen or Propylene (Propene)) and then to determine whether or not -given a certain number of cylinders of each- do we have sufficient gas in stock based on their relative consumption ratio.

For example:
we may have 1 oxygen quad (i.e. interconnected cylinders) with 9 cylinders, type: G/G2, with a 50ltr water-volume @ 150bar filling pressure.
we have propane cylinders, type: S/SE, with a 108ltr water-volume @ 10bar filling pressure.
Given that the oxy/fuel consumption ratio when cutting steel for oxygen vs propane is ± 4:1, how many cylinders of propane would I need to end up with an exact ratio between oxygen and propane?

Can I simply use normal gas laws here?
I.e. oxygen, 9 cylinders, each with a volume 50ltr @ 150bar = 67500ltr of oxygen?
and, subsequently for propane, volume 108ltr @ 10 bar = 1080ltr of propane?
i.e. in that case I would need 16 cylinders of propane?
(9 x (150 x 50)) = 67500ltr @ 4:1 = 16875ltr of propane required => 16875 / 1080 = 15.6 = 16 cylinders?

Would that be a correct approach or would I need to take into account a different volume for each gas based on the fact that the propane and oxygen go through a phase transition in the cylinder (i.e. they go from liquid to gas)
Any help would be appreciated.
 
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  • #2
Propane is stored as a liquid. The amount of propane is measured by weight in small tanks, typically less than 20 lbs or so. Larger tanks, at least in the US, are measured in gallons. A good search term to better understand the relationship is propane temperature pressure. Note that the density of liquid propane can vary by 10% over a typical range of ambient temperatures. The gas volume is calculated from the liquid volume.

You can measure the amount of propane by weighing the tanks if you know the tare (empty) weight of the tank. You can also measure the amount by pouring some hot water down the side of the tank. The tank surface temperature changes at the liquid surface level.

Pressurized oxygen tanks have a stated volume, with typical sizes being 80 or 122 cubic feet for welding oxygen. Oxygen at 150 bar is stored as a pressurized gas. The tank pressure tells how much is in the tank.
 
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FAQ: Propane/Oxygen - from Cylinder to Oxy/Fuel cutting torch

1. How do I properly set up a propane/oxygen cutting torch system?

To set up a propane/oxygen cutting torch system, start by securely attaching the propane and oxygen cylinders to their respective regulators. Connect the hoses to the regulators and the torch handle, ensuring all connections are tight and leak-free. Open the cylinder valves slowly, adjust the regulators to the desired pressure (typically around 5-10 psi for propane and 20-40 psi for oxygen), and perform a leak test using soapy water on all connections before igniting the torch.

2. What safety precautions should I take when using a propane/oxygen cutting torch?

Safety precautions include wearing appropriate personal protective equipment (PPE) such as safety glasses, gloves, and flame-resistant clothing. Ensure the work area is well-ventilated and free of flammable materials. Always check for leaks before igniting the torch, and never use oil or grease on oxygen fittings. Be aware of the torch's flame and hot metal, and have a fire extinguisher nearby.

3. How do I ignite and adjust the flame on a propane/oxygen cutting torch?

To ignite the torch, first open the propane valve slightly and use a spark lighter to ignite the gas. Once the propane is burning, gradually open the oxygen valve until you achieve a neutral flame, which has a clear, well-defined inner cone. Adjust the flame by fine-tuning the propane and oxygen valves until you reach the desired flame characteristics for cutting.

4. What is the proper technique for cutting metal with a propane/oxygen torch?

To cut metal, preheat the area to be cut by holding the torch's flame close to the metal until it reaches a bright red color. Once preheated, press the cutting oxygen lever to release a high-pressure stream of oxygen that will oxidize and blow away the molten metal. Move the torch steadily along the cutting line, maintaining a consistent speed and distance from the metal to ensure a clean cut.

5. How do I maintain and troubleshoot a propane/oxygen cutting torch system?

Regular maintenance includes checking hoses and connections for wear and leaks, cleaning the torch tip, and ensuring the regulators are functioning correctly. If you encounter issues such as irregular flame or difficulty igniting, check for obstructions in the torch tip, ensure proper gas pressures, and inspect for leaks. Replace any damaged components and consult the manufacturer's guidelines for specific troubleshooting steps.

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