What Is a Gas Cylinder?

Gas cylinders are refillable under normal environment (-40 ~ 60 ), with a nominal working pressure of 1.0 ~ 30MPa (gauge pressure) and a permanent volume of 0.4 ~ 1000 L, which contains permanent gas, liquefied gas or dissolved gas. Mobile pressure vessel for gas. ^[1]

Gas cylinders are refillable at normal ambient temperature (-40 to 60 ° C). The nominal working pressure is greater than or equal to 0.2 MPa (gauge pressure), and the product of pressure and volume is greater than or equal to 1.0 MPa · L. Mobile pressure vessels for gases, liquefied gases and liquids with a standard boiling point equal to or lower than 60 ° C. Gas cylinders are widely used, and they are almost inseparable from gas cylinders in both the production and life fields.

Gas cylinders are a kind of pressure-bearing equipment, which has the danger of explosion, and its loading medium is generally flammable, explosive, toxic, and strong corrosion. The characteristics of changing operating environment are more complicated and harsh than other pressure vessels. Once a gas cylinder explodes or leaks, it often causes fire or poisoning, and even causes catastrophic accidents, causing serious property damage, casualties and environmental pollution.

To ensure the safe use of gas cylinders, in addition to requiring it to meet the general requirements of pressure vessels, there are also some special regulations and requirements. ^[2]

I. Classification by manufacturing method

According to the manufacturing method, cylinders can be divided into the following four categories.

(1) Welding gas cylinder

The welding gas cylinder is formed by welding a cylindrical cylinder body welded with a thin steel plate and a head at both ends. Welding gas cylinders are mostly used to contain low-pressure liquefied gases, such as liquefied sulfur dioxide.

(2) Control cylinder

Control gas cylinders are seamless gas cylinders made of seamless steel pipes. The heads at both ends are formed by heating the steel pipe on a special machine tool by spinning or extrusion.

(3) Pushing and stretching cylinders

After heating the steel ingot, the concave head is first punched out, and then drawn into an open preform, and then the top head and the interface pipe are made according to the method of controlling the cylinder.

(4) Winding cylinder

The gas cylinder is composed of an aluminum inner cylinder and an alkali-free glass fiber wound around the outer cylinder with a certain thickness. The role of the aluminum inner cylinder is to ensure the air tightness of the cylinder. The compressive strength of the cylinder depends on the outer wall of the fiberglass shell that is wound into a single body (using epoxy phenolic resin, etc. as the

(1) Nominal working pressure of gas cylinder

For cylinders containing permanent gas, the nominal working pressure refers to the limited filling pressure of the gas contained at the reference temperature (generally 20 ° C). For cylinders containing liquefied gas, the nominal working pressure refers to the upper limit of the gas pressure in the cylinder when the temperature is 60 ° C.

According to the "Cylinder Safety Supervision Regulations" (Guo Fa [2000] No. 250 of the Quality and Technical Supervision Bureau), the nominal working pressure of cylinders has been serialized. The nominal working pressure of a cylinder containing high-pressure liquefied gas shall not be less than 8 MPa. The nominal working pressure of gas cylinders containing toxic and highly toxic liquefied gases should be appropriately increased.

(2) Hydraulic test pressure, design pressure and allowable pressure

The hydraulic test pressure of steel gas cylinders is the pressure test pressure for testing the strength of gas cylinders. According to the "Steel Seamless Gas Cylinders" (GB 5099-1994) and "Steel Welded Gas Cylinders" (GB 5100-2011) It is stipulated that the hydraulic test pressure of the cylinder is 1.5 times the nominal working pressure.

The design pressure of the steel gas cylinder is used to design and calculate the wall thickness of the cylinder body. The design pressure is equal to the hydrostatic test pressure.

The allowable pressure of the gas cylinder is the highest pressure allowed by the gas cylinder, and it should not be less than the medium pressure of the medium in the cylinder at 60 ° C. The allowable pressure of the steel gas cylinder shall not exceed 0.8 times of the hydraulic test pressure.

(3) Nominal volume of gas cylinder

The nominal volume of a gas cylinder refers to the series of cylinder volumes specified in the cylinder regulations and standards. The nominal volume is the same as the nominal working pressure, and is not an accurate actual value. For safety purposes, the actual volume of the cylinder must be greater than the nominal volume with a tolerance of + 5%. It can be seen that although the nominal volume is the nominal value of an appellation, it is strictly restricted and cannot be called casually. For example, a seamless cylinder with a nominal volume of 40L should have an actual volume between 40L and 42L.

For the convenience of management, the nominal volume of gas cylinders in China is divided into three categories: large, medium and small: small volume below 12L (including 12L), medium volume above 12L to 100L (including 100L), large volume above 100L.

The volume of steel seamless gas cylinders is most commonly 40L cylinders, but there are also as small as 0.4L to 80L.

As the volume of steel welded gas cylinders, as the dissolved acetylene cylinders, 40L steel cylinders are the most common, and liquid ammonia and liquid chlorine gas cylinders are the most popular. Because calculated according to the filling coefficient of liquid chlorine of 1.25 kg / L, their media quality is exactly 1 t and 0.5t.

The volume of liquefied petroleum gas cylinders is the largest with 35.5L. Because it is calculated with a filling factor of 0.42 kg / L, this kind of gas cylinder is just filled with 15 kg of liquefied petroleum gas, which is the consumption of an average family for one month.

(4) the maximum and minimum use temperature of the cylinder

The maximum operating temperature of a cylinder is the highest temperature that a cylinder can reach after it has been filled with gas. According to the provisions of "Steel Seamless Gas Cylinders" (GB 5099-1994), "Steel Welded Gas Cylinders" (GB 5100-2011) and "Gas Cylinder Safety Supervision Regulations", 60 ° C is the maximum temperature of gas cylinders. -40 ° C is the minimum operating temperature of the cylinder.

(5) the color of the cylinder

"Cylinder Color" (GB 7144-1999) makes clear the color of gas cylinders. For example: the acetylene gas cylinder is white, the nitrogen gas cylinder is black, the oxygen gas cylinder is light blue, the ammonia gas cylinder is light yellow, the carbon dioxide gas cylinder is aluminum, and so on. ^[3]

The correct filling of gas cylinders is one of the keys to ensure the safe use of gas cylinders. Improper filling, such as gas mixing and overfilling, are dangerous.

Gas mixing refers to the filling of two gases or liquefied gases in the same cylinder. The most common mixing phenomenon is the mixing of combustible gases such as oxygen and combustible gases. For example, the original cylinders filled with flammable gas (such as hydrogen, methane, etc.) have not been treated by replacement, cleaning, etc. Used to fill oxygen. If these two media undergo a chemical reaction under appropriate conditions, a serious explosion accident will result. Therefore, no gas mixing is allowed.

Overfilling is also a common cause of rupture and explosion of gas cylinders. The overfilled gas cylinder is affected by the ambient temperature, especially in the summer, the liquefied gas in the gas cylinder expands rapidly due to the temperature increase, which causes the pressure in the cylinder to increase sharply, causing the cylinder to burst and explode.

To prevent overfilling of cylinders, the following work should be done. The filling work should be performed by a special person, and the filling personnel should receive safety education and assessment on a regular basis; the filling personnel should be conscientious and not leave the post without authorization. At the same time, pay attention to emptying the remaining liquid and verifying the bottle weight. The weighing instrument used for liquefied gas filling shall be calibrated at least once every 3 months, and the maximum weighing value of the weighing instrument used is 1.5 to 3 times the usual value. Press the bottle stand card and record carefully. Filling cylinders should have someone responsible for repeated weighing. If the automatic measuring equipment is installed, the over-quantity can automatically alarm and cut off the valve. ^[1]

Protect the cylinder from heat. Cylinders in use should not be exposed to the sun, not close to the fire source and high temperature area, and should not be less than 10 m away from the open flame; the high pressure steam should not be used to directly blow the cylinder; the use of thermal hydrolysis and open flame baking is prohibited, strictly prohibited Heat the cylinder with a heat source with a temperature exceeding 40 ° C.

Measures should be taken to prevent the cylinder from tipping when it is placed vertically; it should be opened slowly when the valve is opened to prevent the accessories from generating high temperature quickly; The valve and accessories of the bottle must not be contaminated with grease. Do not operate the oxygen cylinder with oil on your hands or gloves.

Residual gas should be left to the end of the cylinder, which is mainly used to prevent accidents caused by mixing with other gases or impurities. Gas cylinders are used in situations where backflow (backfill) may occur, and devices must be provided to prevent backfill, such as check valves, check valves, buffer tanks, etc. Residual oil and gas in liquefied petroleum gas cylinders shall be recovered by facilities with safety measures and shall not be disposed of by themselves.

Strengthen the maintenance of gas cylinders. The paint layer on the outer wall of the gas cylinder is both anti-corrosion and an identification mark, which can prevent misuse and mixing. It is necessary to maintain the integrity of the paint surface and the clarity of the mark. Water mixed in the bottle will accelerate the corrosion of the inner wall of the cylinder, and the cylinder must be dried before filling. Cylinder users shall not change the type of gas filled by themselves or change the color mark of the cylinder without authorization. An application should be made when replacement is really needed, and the cylinder inspection unit is responsible for modifying the cylinder. The unit responsible for the conversion determines whether the cylinder is suitable for the gas to be replaced according to the steel stamped mark and safety status of the cylinder. During the modification, the inside of the gas cylinder should be thoroughly cleaned, inspected, stamped, and inspected, the corresponding accessories should be replaced, and the type, color ring and color of the modified gas should be replaced. ^[1]

The inspection cycle for various types of gas cylinders is as follows.

Cylinders containing corrosive gases shall be inspected every 2 years.

Cylinders containing general gas shall be inspected every 3 years.

Liquefied petroleum gas cylinders have a service life of 15 years and are inspected every 4 years; the last inspection is 3 years.

Cylinders containing inert gas shall be inspected every 5 years.

Cryogenic insulated cylinders shall be inspected every 3 years.

Liquefied petroleum gas cylinders for vehicles are inspected every five years, and compressed natural gas cylinders for vehicles are inspected once every three years. When a car is discarded, if serious corrosion or damage is found in the gas cylinder of the car during use or if its safety and reliability are suspected, it shall be inspected in advance. Cylinders that are in stock and out of service for more than one inspection cycle are inspected before being used. ^[1]