Why [7 Types of Gas Cylinders]?
In terms of gas to be stored, raw material used, manufacturing method… there are way more than [7 Types of Gas Cylinders] that are available on the market in 2019. Then, how did we come to divide the Gas Cylinder Types in to 7? Please continue to read this post for why and how. Here are brief index for each section of the post:
- Composite Cylinder for Permanent Gases
When we started thinking about this topic for a post to guide our visitors, we did some homework by googling “types and sizes of gas cylinders” and other similar phrases. We also visited the Wikipedia page “Gas Cylinder” for some information. What we found are: most of the posts are either focusing on the types of a particular type of cylinders or just give the size information for the product they can provide. And this has led us to a topic we want to write about: “The Definitive Guide to Gas Cylinder Types and Sizes in 2019”.
So, the first step is to Define “Gas Cylinder”. Here is how “Gas Cylinder” is defined on Wikipedia:
A gas cylinder is a pressure vessel for storage and containment of gases at above atmospheric pressure. High-pressure gas cylinders are also called bottles. Inside the cylinder the stored contents may be in a state of compressed gas, vapor over liquid, supercritical fluid, or dissolved in a substrate material, depending on the physical characteristics of the contents. A typical gas cylinder design is elongated, standing upright on a flattened bottom end, with the valve and fitting at the top for connecting to the receiving apparatus.
The term “cylinder” in this context is not to be confused with “tank“, the latter being an open-top or vented container that stores liquids under gravity.
Slightly different from Wikipedia, the “Gas Cylinder” what we are discussing here are defined as:
A type of portable and refillable pressure vessel for storage and containment of gases at pressure above 0.2 MPa, in a normal environment temperature of (-40～60℃). The contained gases may be in a state of compressed gas, vapor over liquid, supercritical fluid, or dissolved in a substrate material, depending on the physical characteristics of the contents, as long as the product of pressure and volume is not less than 1.0 MPa·L.
There are three major groups of compressed gases stored in cylinders: liquefied, non-liquefied and dissolved gases. In each case, the pressure of the gas in the cylinder is commonly given in units of kilopascals (kPa) or pounds per square inch gauge (PSIG).
Gauge pressure = Total gas pressure inside the cylinder – atmospheric pressure
Atmospheric pressure is normally about 101.4 kPa (14.7 psi). Note that a compressed gas cylinder with a pressure gauge reading of 0 kPa or 0 psig is not really empty. It still contains gas at atmospheric pressure.
- Liquefied Gases
Liquefied gases are gases that can become liquids at normal temperatures when they are inside cylinders under pressure. They exist inside the cylinder in a liquid-vapor balance or equilibrium. Initially, the cylinder is almost full of liquid, and gas fills the space above the liquid. As gas is removed from the cylinder, enough liquid evaporates to replace it, keeping the pressure in the cylinder constant. Anhydrous ammonia, chlorine, propane, nitrous oxide, and carbon dioxide are examples of liquefied gases.
- Non-Liquefied Gases
Non-liquefied gases are also known as compressed, pressurized or permanent gases. These gases do not become liquid when they are compressed at normal temperatures, even at very high pressures. Common examples of these are oxygen, nitrogen, helium, and argon.
- Dissolved Gases
Acetylene is the only common dissolved gas. Acetylene is chemically very unstable. Even at atmospheric pressure, acetylene gas can explode. Nevertheless, acetylene is routinely stored and used safely in cylinders at high pressures (up to 250 PSIG at 21°C).
This is possible because acetylene cylinders are fully packed with an inert, porous filler. The filler is saturated with acetone or another suitable solvent. When acetylene gas is added to the cylinder, the gas dissolves in the acetone. Acetylene in solution is stable.
To meet the variety of gas state and pressure needs, there are different types of Gas Cylinder developed according to the manufacturing method that are Welded Gas Cylinder, Tubular Gas Cylinder, Extruded Gas Cylinder, Deep Drawing & Ironing Gas Cylinder, and Composite Gas Cylinder. As the Tubular Gas Cylinder, Extruded Gas Cylinder and the Deep Drawing & Ironing (a.k.a. DDI) Gas Cylinder are basically the same type of seamless cylinders in terms of raw material, so we can put them into 3 categories:
- Welded gas cylinders
- Tubular/Extruded/DDI Seamless Gas Cylinder
- Composite Gas Cylinder