The material selection of the oxygen pipeline is a vital safety factor. As the working pressure and flow rate of oxygen pipelines increase, the pipeline's materials have also developed from carbon steel and stainless steel to copper, copper alloys, nickel and nickel alloys. See Table 3 for specific selection. Table 3 is quoted from the GB 16912 standard.
 
1. The working pressure of oxygen is divided into the following four kinds in Table 3:
① Oxygen pressure pipelines with pressure less than and equal to 0.6MPa are general low-pressure oxygen pipelines, which are used in many industries.
② Oxygen pressure pipelines with a pressure range between 0.6MPa and 3.0MPa are widely used in steel, metallurgy, shipbuilding, machinery and other industries.

③ Oxygen pressure pipelines with pressure between 3.0MPa and 10MPa are mainly used in the chemical industry, where the oxygen's pressure is high and the requirements for the pipeline's material are high.

④Oxygen pressure pipelines with pressure greater than 10MPa are mainly used in cylinder filling and some chemical industries. The oxygen's pressure is very high and the pipeline's material is strictly limited. Practice has proved that it is convenient and applicable to differentiate the oxygen pipeline based on different pressure.

2. The applications of oxygen are divided into general applications and non general applications in Table 3. Non general applications refer to the range of 5 times the nominal diameter (not less than 1.5 m) after the valve at the frequent operation zone on the distribution main pipe, valve on the main pipe, system branch valve, and inlet valve at the workshop and 5 times the nominal diameter before and after the regulating valve set ( not less than 1.5m each), inside the oxygen pressure workshop, after the release valve, liquid oxygen transportation, oxygen filling stations, important places, dangerous locations, frequent sources of accidents, high-pressure facilities, and the material selection for oxygen pipelines should be paid attention to.

 
Table 3 The table for the material selection of oxygen pipes

 
Please note the following points:

(1) "√" means yes, and "×" means no.

(2) Carbon steel plate coiled welded pipes should be used when the working pressure is less than 0.1MPa and the pipe diameter exceeds the pipe diameter of existing welded steel pipes and seamless steel pipes.
(3) The valves in the table refer to valves for main pipes, valves for branch pipes for systems and valves at the inlet of the workshop.
(4) Stainless steel should be adopted for the oxygen pipeline in the oxygen storage tank area.
(5) Copper alloy pipes with working pressure greater than 3.0MPa do not include aluminum copper alloys.
 

3. The material selection of oxygen pipes

The characteristics of various materials of oxygen pipes are described in Table 3 and you can check Table 3 for more information.

Different applications
① Carbon steel coil welded pipes should be used when the working pressure is less than 0.1MPa and the pipe diameter exceeds the pipe diameter of existing welded steel pipes and seamless steel pipes.
② Welded steel pipes are suitable for general places with pressure less than and equal to 0.6MPa.
③ Seamless steel pipes are suitable for general places with pressure less than and equal to 3.0MPa.
④ Stainless steel welded steel pipes and stainless steel coil welded pipes are applicable to all places with pressure less than and equal to 3.0MPa. For stainless steel coil welded pipes, the welding seam of the inner wall is required to be polished.
⑤ Stainless steel seamless pipes are suitable for all places with pressure less than and equal to3.0MPa, and for general places with pressure greater than 3.0MPa. The oxygen pipeline with pressure greater than 10MPa is used for cylinder filling. The main pipe from the outlet of the high-pressure oxygen compressor or liquid oxygen pump to the filling station is used for a general place and stainless steel pipes can be used. Copper alloy or nickel alloy pipes with large diameters are scarce in resources and expensive, which are seldom used. For the filling station's pipes and oxygen discharged pipes, copper alloy or nickel alloy pipes should be used. Stainless steel seamless pipes are resistant to low temperatures and have good strength, which are suitable for liquid oxygen pipelines.
⑥ Copper and copper alloy extruded pipes, copper and copper alloy drawn pipes, nickel and nickel alloy pipes are suitable for all places and liquid oxygen pipelines with pressure less than and equal to 21MPa due to their excellent flame and explosion resistance and low temperature resistance.
 
4. Within 5 times the nominal diameter of the oxygen valve (not less than 1.5m), the air current is turbulent, and the impact is severe; within the range of 5 times the nominal diameter (not less than 1.5m) before and after the regulating valve set, because the diameter of the oxygen regulating valve is often 1 to 2 grades smaller than that of the pipe. There are reducers before and after, and the flow rate of the valve port can reach subsonic speed. The airflow impact is very violent; the friction heat is serious, and it is a source of frequent burning and explosion accidents. The internal position of the oxygen pressure workshop is important. The flow rate behind the release valve is fast, which is the occasion of the impact. The liquid oxygen pipeline is easy to rust, which is a dangerous part. In these non general places, when the oxygen pressure is less than and equal to 3.0MPa, stainless steel pipes should be used. Welded, coil-welded, seamless pipes are all good. When the oxygen pressure is greater than 3.0MPa, copper and copper alloy or nickel and nickel alloy pipelines should be used. The oxygen storage tank area with pressure less than and equal to 3.0MPa is an important part, and stainless steel pipes should be used for oxygen pipelines in the area. The copper alloy pipe used for oxygen pipelines with pressure greater than 3.0MPa does not include aluminum copper alloys, because it is combustible under certain conditions. For oxygen pipes with pressure less than 0.1MPa, aluminum alloy pipes can be used for oxygen pipes with large diameters, because they are not rusty and resistant to low temperatures, and suitable for the pipe between the air separation equipment and the inlet of a large oxygen compressor.

After the boundary valve of the oxygen plant, after entering the workshop valve, before the regulating valve set, and the oxygen pipeline before and after the regulating valve should be equipped with flame retardant copper pipe sections. When the oxygen regulating valve set does not have a separate valve chamber or protective wall, copper alloy (except aluminum copper alloy) or nickel alloy pipes should be used within the pipeline range of 8 times the nominal diameter of the regulating valve before and after the oxygen regulating valve. In the event of an accident, it can be safely fused and spreading burning can be stopped.
 
Low-temperature resistant stainless steel seamless pipes, copper and copper alloy pipes, nickel and nickel alloy pipes can all be used as liquid oxygen pipelines.