(1) Construction quality problem had been the principle cause of oxygen pipeline explosion.
1) Iron oxide was found in the piping, and rust was found in the molten peeling layer, indicating that the pipeline pickling was not carried out thoroughly;
2) Rust residue and water stains were found in the piping, indicating that there was no passivation treatment after pickling and no nitrogen filling protection when the pipe was not put into operation for a long time after installation;
3) The existence of welding slags and valve processing residue, indicating that the pipeline was not purged thoroughly after the construction. The valves were not removed during the purging, and the corners of valves can not be purged. Valves should be removed and treated separately, and pipes should be purged with short pipe connections.
These construction quality problems, the presence of iron oxide, rust slag, welding slag and other residual foreign matter in the newly installed oxygen pipeline, caused the ignition in the oxygen flow, which provided the basic conditions for the oxygen pipeline explosion accidents.
(2) Unreasonable design of pipe supports, pipe seats and pipeline direction may cause radial vibration and damage of expansion joint.
Radial vibration or displacement in pipeline operation is not fully considered in the design of pipe supports, pipe seats and pipeline alignment. When the pressure in the pipe changes, radial vibration or displacement will occur in the pipeline, so that the expansion joint will also be damaged by radial vibration. When the pressure rises, the expansion joint is crushed and oxygen escapes, forming a high-speed air stream. When the pipe network pressure rises to 2.4 MPa, the expansion joint is broken, and the instantaneous flow rate of oxygen leakage reaches subsonic speed (about 300m/s). The sundries in the pipe are driven by high-speed airflow and have strong friction and collision with the inner wall of the pipe, so that the local overheating of the pipe reaches the ignition point and burns.
Relevant data show that: If the oxygen is mixed with iron oxide or welding slag, when the oxygen flow rate reaches 44 m/s in the elbow, the high temperature can turn the wall of the tube red; If the impurities are coke particles and oxygen flow rate reaches 30 m/s, or the impurities are anthracite and oxygen flow rate reaches 13m/s, the high temperature produced can all burn the tube wall red. Therefore, when the expansion joint is broken, the oxygen flow rate in the pipeline is greatly increased, resulting in the combustion of iron oxide and welding slag left in the pipeline during construction in high purity oxygen, and the steel pipe also burns and melts in pure oxygen.
(3) Lack of safety assurance measures in the design of oxygen pipelines.
In the pipeline design, filters in front of the constant pressure regulating valve were not considered, resulting in welding slag and other sundries cloging the regulating valve, which lead to the failure of timely adjustment of the pressure in the pipe network behind the constant pressure valve, so that the pressure in the pipe network exceeds the normal working pressure.