A Brief Introduction to Seamless Steel Tubes for Gas Cylinder
What is a gas cylinder ?
A gas cylinder is a pressure vessel for storage and containment of gases at above atmospheric pressure. It can store both flammable gases, such as acetylene, and inert gases such as helium. 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.
Materials of gas cylinder
Gas cylinders can be made from aluminum, steel, alloys, and composite materials. Mechanical strength, corrosion resistance, and impact resistance are critical factors in determining which material is used. Carbon fiber composite cylinders can be very light due to the high tensile strength of carbon fiber, but are more difficult to manufacture. So the alloy steel is the usually used material because of its overall mechanical property and cost. The most common standards are GB/T 18248, EN10297, JIS G3429, EN 10083-3. Though they are different standards in different countries, they have some same steel grades or equivalents. Now let’s take a look at 34CrMo4 of each standard or its equivalent to see their difference.
As you can see, there is a little difference in their chemical composition. But their mechanical properties, tolerance, testing and delivery condition may be different, so all these shall be agreed upon at the time of inquiry and place an order. Except 34CrMo4, 37Mn, 38Mn6, STH21, STH22, 42CrMo4 are also very common materials.
Because gas cylinders store gases under high pressures, it must have excellent tensile strength, corrosion resistance, and impact resistance. So finished pipe are generally tested as below to select the unqualified.
NDT (Non-destructive testing)
ET (Eddy testing)
UT (Ultrasonic testing)