15 Questions and Answers on Safe Use of Welding Gas Cylinders

1.Why do gas cylinders have anti-dumping measures?

Answer: Dumping will cause the gas cylinder valve to fall and gas to escape. Due to the huge reaction force of gas leakage, the gas cylinder will rush forward or spin on the ground. If there are people nearby, they will be injured. If it is a flammable gas, it will cause an explosion, which is even more serious!

2.Why should oxygen and acetylene cylinders be stored separately?

Answer: Acetylene is flammable and oxygen is a combustion-supporting substance. If acetylene leaks, it mixes with air and explodes violently when it encounters sparks or open flames. The explosion also damages the oxygen cylinder and leaks oxygen. In this case, the combustion-supporting property of oxygen makes the explosion more violent and uncontrollable. So the two cannot be placed together.

3.Why should the temperature of the bottle not be exposed to the sun?

Answer: The temperature of the acetylene cylinder should not exceed 40 degrees. The boiling point of acetone is 58 degrees. The higher the temperature, the faster the acetone evaporates, and acetylene is precipitated, causing the pressure in the bottle to increase sharply.

4.Why must there be residual pressure in acetylene cylinders and oxygen cylinders?

Answer: Leaving a few kilograms of pressure in the bottle makes the pressure inside the bottle greater than the pressure outside the bottle, which can prevent the influx of other gases and ensure the safety of use. Because the explosion limit of acetylene is very low, it will explode when it reaches a certain temperature if it is mixed with a little air. Therefore, the exhaust port of the acetylene cylinder must have a pressure reducing valve to prevent air from mixing into the bottle, otherwise there will be a risk of explosion the next time it is used. Adding a pressure reducing valve is to prevent the air pressure in the bottle from being lower than the air pressure outside, and to prevent air from flowing back into the acetylene cylinder. The oxygen cylinder should retain a residual pressure of not less than 0.098~0.196MPa gauge pressure. The acetylene cylinder should retain a residual pressure of 49Kpa~98KPa in winter and 196KPa gauge pressure in summer.

5.Why can't oxygen cylinders be contaminated or contacted with grease?

Answer: Because grease, especially those containing unsaturated fats and acids, can easily vaporize and release heat. The reason why oil yarn heads and oil cloths can spontaneously combust is that they undergo oxidation in the air, and the heat is not dissipated. When the autoignition point is reached, it causes spontaneous combustion. However, grease vaporizes slowly in the air, and the heat generated is quickly dissipated, and it is generally not easy to accumulate heat and spontaneously combust.

Because pure oxygen has extremely strong oxidizing properties, it can promote the violent combustion of combustibles. When grease-like substances encounter pure oxygen, their vaporization rate is greatly accelerated. At the same time, a large amount of heat is released. The temperature rises rapidly and will soon cause combustion. If the mouth of the oxygen cylinder is stained with grease, when oxygen is rapidly ejected, the grease will quickly undergo oxidation reaction, and the heat generated by the friction between the high-pressure airflow and the bottle mouth will further accelerate the oxidation reaction. Therefore, grease contaminated on the oxygen cylinder or the pressure reducing valve will cause combustion or even explosion. This is why oxygen cylinders, especially the bottle mouth and accessories that come into contact with oxygen, are strictly prohibited from contacting and contaminating with grease.

6.Why do gas cylinders need to wear bottle caps?

Answer: Because the cylinder valves of steel cylinders are mostly made of copper alloy, which is relatively fragile. Although some are made of steel, their structure is smaller than the bottle body. When they are screwed on the bottle body, a right angle is formed between the bottleneck and the valve joint. It is both the fragile point of the bottle body and the protruding point of the bottle body, which is most susceptible to mechanical damage or external impact. If the gas cylinder falls, falls, rolls or is hit by other hard objects during transportation, storage and use, it is easy to break the connection between the valve joint and the bottleneck.

Consequences of broken bottlenecks or valves: When the oxygen cylinder valve is broken, the 150 kg/cm2 high-pressure gas in the bottle causes the high-pressure gas in the bottle to lose control, causing the high-pressure gas to spray out. The reaction force causes the gas cylinder to rush in the opposite direction, which can damage machinery and equipment, buildings, and even cause casualties; when the acetylene cylinder valve is broken, flammable gas rushes out and forms an explosive gas mixture with air, which explodes when it encounters an open flame. The high-speed gas ejected from the cylinder will cause more serious secondary accidents (such as fire, explosion, poisoning, etc.) depending on the nature of the gas in the cylinder. If the cylinder is filled with flammable gas, the static electricity generated by the intense friction of the high-speed jet or other fire sources may cause combustion and explosion. On the other hand: the cylinder valve is exposed to the outside, and it is easy to be invaded by dust or grease during transportation and storage, which brings danger. Wearing a safety helmet can prevent the contamination and invasion of dust or grease. In order to eliminate the above-mentioned dangers, it is required that the cylinder manufacturing unit is equipped with a safety helmet when it leaves the factory. When using gas, unscrew the safety helmet and put it in a fixed place. After use, put on the bottle cap and tighten it in time, and do not throw it around. Do not forget to wear a safety helmet during transportation and loading and unloading.

7.Why can't acetylene cylinders be collided?

Answer: Collision will cause activated carbon to break, the expansion space will increase, acetylene gas will gather and be in a high-pressure state, which may cause explosion; at the same time, when the temperature rises, gaseous acetylene will polymerize and explode.

8.Why is it required to load and unload gas cylinders gently, and it is strictly forbidden to throw, roll or collide? Answer: If the gas cylinder is subjected to severe collision or impact, an explosion accident will occur, and the consequences will be very serious.

9.Why can't oxygen cylinders be hoisted? Answer: Oxygen cylinders are high-pressure containers. If they are accidentally dropped, they are easy to explode. If transported in large quantities, there are special containers for oxygen cylinders, which are suitable for one-time transportation, loading and unloading of multiple bottles.

10.Why do acetylene cylinders explode?

Answer: The explosion of acetylene cylinders is mainly caused by the rapid rise in temperature and pressure, which causes the decomposition of acetylene.

Characteristics of acetylene decomposition: If after tempering occurs, the temperature of the bottle wall rises (starting from the top of the bottle) or smoke with an abnormal odor escapes from the open bottle valve. This indicates that acetylene has begun to decompose. If the acetylene cylinder is directly affected by flames or radiant heat, there is a risk of acetylene decomposition at any time.

Causes of acetylene decomposition: (1) Welding tempering; (2) External heating (there are burning materials near the acetylene cylinder, and there are tools such as welding guns or cutting guns that have not been extinguished hanging on the cylinder); (3) Acetylene ignites near the cylinder valve or pressure reducer; (4) Severe impact or vibration.

Preventive measures: (1) Install a flame arrester; (2) Do not expose the cylinder to sunlight, heat the cylinder, or place it near a heat source; (3) Do not hang unextinguished welding guns, cutting guns, or other tools on acetylene cylinders; (4) Load and unload the cylinder gently to avoid severe impact or vibration.

11.Why can't oxygen tape and acetylene hose be mixed?

Answer: Oxygen tape is a high-pressure tube, and acetylene tape is a low-pressure tube; in addition, acetylene tubes sometimes produce slight tempering during use, and there will be carbon deposits in the tube. Carbon deposits mixed with oxygen will cause explosions.

12.Why can't gas cylinders be mixed and used?

Answer: If other gases are filled into gas cylinders, violent explosions will occur, and the consequences are very serious.

13.Why should the lower part of oxygen cylinders be insulated when used at the same work site as electric welding?

Answer: To prevent the gas cylinders from being charged. When working with electric welders (this is the premise), the bottom of the oxygen cylinder is padded with insulating materials to prevent the gas cylinders from being charged. Metal equipment such as pipes in contact with gas cylinders must have good grounding devices to prevent static electricity from causing combustion or explosion accidents.

14. Why can't acetylene cylinders be placed on insulators for use?

Answer: The ignition energy of acetylene is only 0.019 millijoules, and a tiny static discharge (a few millijoules) can ignite (detonate) acetylene. When acetylene flows or leaks in the gas pipeline, it will generate static electricity. Any form of static electricity discharge may ignite acetylene. Since acetylene does not require oxygen to burn or explode, it is very likely to explode after ignition. If the acetylene cylinder is directly grounded, it will not carry static electricity, and of course it will not explode naturally.

15. Why should the copper content of the alloy be less than 70% when using copper alloy utensils for acetylene cylinders?

Answer: After acetylene comes into contact with copper and silver for a long time, explosive compounds acetylene copper and acetylene silver 9 will be generated. When subjected to severe vibration or the temperature reaches 110~120℃, it can cause an explosion.