3. The higher the working pressure of the oxygen is, the greater the danger and the lower the maximum allowable flow rate become. The working pressure is divided into 6 kinds in Table 1:
①Oxygen pipelines with a working pressure less than and equal to 0.1MPa have a low risk of fire and belong to a low-pressure oxygen pipeline; the flow rate is determined according to the pressure drop of the pipeline system.
②Oxygen pipelines with working pressure between 0.1MPa and 1.0MPa, the maximum allowable oxygen flow rates of carbon steel and austenitic stainless steel oxygen pipelines are 20m/s and 30m/s, which are newly added according to the needs of shipbuilding, machinery and other industries.
③ Oxygen pipelines with working pressure between1.0MPa and 3.0MPa, the maximum allowable flow rate of carbon steel and austenitic stainless steel oxygen pipelines are 15m/s and 25m/s, which are commonly used oxygen pressure ranges in steel, metallurgy and other industries. After practical tests for more than 10 years, it has been verified that as long as the oxygen flow rate is strictly controlled according to this, the oxygen pipeline can operate safely and economically. The data is scientific and reliable.
④The pressure between 3.0M Pa and 10.0MPa is the oxygen pressure range commonly used in the chemical industry. Using carbon steel pipes that are prone to rust is no longer allowed due to the high oxygen pressure and high risk. For austenitic stainless steel pipes, the impact occasions and non-impact occasions are also scientifically distinguished, and the maximum allowable flow rate is determined according to the limit of the product value of the oxygen pressure and maximum allowable flow rate. For high-risk collision occasions, pv should be less than and equal to 45MPa·m/s; for less dangerous non-collision occasions, pv should be less than and equal to 80MPa·m/s. If the oxygen pressure is the same, the maximum allowable flow rate calculated in the impact occasion is smaller than that in the non-impact occasion; for the same occasion, the higher the pressure is, the lower the calculated maximum allowable flow rate becomes.
⑤ As for the pressure between 10.0MPa and 15.0MPa, oxygen with this pressure is mainly used in the chemical industry. It is an oxygen pressure range newly added to the GB 16912-2008 standard. Of course, carbon steel pipes cannot be used as oxygen pipelines for this oxygen pressure. When austenitic stainless steel pipes are used, the maximum allowable oxygen flow rates are 4.5m/s and 8.0m/s in impact and non-impact situations, and the flow rate control is very small. In fact, this value is also the flow rate calculated by substituting the pressure of 10.0MPa in the previous pressure interval formula.
⑥The pressure greater than and equal to 15.0MPa is mainly used for filling steel cylinders. Carbon steel pipes are not allowed for this high-pressure oxygen. When austenitic stainless steel pipes are used, the maximum allowable oxygen flow rate is set to 4.5m/s for both impact or non-impact situations, which is strictly controlled. The material of the oxygen pipeline directly limits the maximum allowable flow rate of oxygen. Copper and copper alloys (except copper alloys containing aluminum which are combustible under certain conditions), nickel and nickel copper alloys not containing carbon elements only melt at high temperatures but not burn, and there won't be a fire after rubbing and impacting; they are non-diffusion combustion materials, and the fire doesn't spread, which is safe. Therefore, it is used in high-pressure and dangerous parts. The flow rate can be high. Under the condition of pressure being less than and equal to 21.0MPa, the oxygen flow rate is unlimited when the pressure drop is allowed. Carbon steel pipes have low combustion temperatures, fast combustion speeds, poor anti-combustion ability and low maximum allowable flow rates of oxygen, and are used for general parts. The combustion resistance and combustion speed of austenitic stainless steel are between copper and carbon steel, and it does not rust. Therefore, its maximum allowable oxygen flow rate is higher than that of carbon steel pipes and lower than that of copper pipes. It is used for parts with more important, dangerous and oxygen pressure. The burning temperature, burning speed and anti-combustion ability of some metals in oxygen are shown in Table 2.
 
Table 2 The burning temperature, burning speed and anti-combustion ability of some metals in oxygen