Oxygen Valve Leakage Causes and Troubleshooting
1 fault phenomenon
One year after the normal operation of the oxygen pipeline, leakage occurred.
(1) DN250mm oxygen special shut-off valve is not closed. Although the valve is closed, the gas leakage is large at the downstream side flange.
(2) Cracking at the root of the DN100mm oxygen relief valve. The main reason is that the pipeline is located at the outlet section of the piston oxygen compressor, and the vibration is large. The long-term vibration causes the connection between the bottom pipe and the main pipe of the valve to crack, and the medium-pressure oxygen is largely dissipated, resulting in a large potential safety hazard.
Owing to the large amount of oxygen used in the production line and the installation of valves on the 3 sets of 21000m3/h air separation equipment side, the air supply to the oxygen network is cut off. There is no time to eliminate this safety hazard. As a result, a steel clip was temporarily made to temporarily dispose the oxygen pipeline, and a temporary warning zone was set within a range of 10m around.
2 treatment measures and processes
The overhaul of the oxygen production process has been carried out synchronously with the mainline processes such as steelmaking, ironmaking and stainless steel. To deal with the above security risks, the specific treatment measures are:
(1) The original DN250mm oxygen special cut-off valve is used as a section of pipe. The valve is open for a long time; and the flanges on both sides are fastened to ensure that the flange connection does not leak oxygen. A special DN250mm oxygen shut-off valve with a pressure of 614 MPa was installed on the pipeline. This valve was used as a shut-off valve (middle contact valve) for normal operation.
(2) Repair welding cracking pipe, and fix the pipe and valve; replace the 6000m3/h air separation equipment oxygen pipe three-way valve.
Prior to construction, related materials and spare parts were prepared, and equipment such as argon arc welding machines and chain rewinding was transported to the site to degrease and suppress the new oxygen contact valve in advance. The Φ273mm×8mm carbon steel pipe and the 90° stainless steel three-way pipe were used. Valves, 45° elbows, and 45° Y-shaped three-way valves are used for rust removal, degreasing, and grinding of the bevel. According to the pipeline construction site conditions, a removable maintenance platform or scaffolding shall be made at the pipe cutting site and the new oxygen valve. Make new oxygen contact blinds in advance. A stainless steel pipe with a length of about 115m is welded on the flange of the inlet side of the new oxygen connection valve, and a 4MPa, DN250mm flange is welded on the other end of the stainless steel pipe. The original 4MPa, DN250mm oxygen linkage valve north side and east side support beam were removed in advance, and the steel plate at the lower part of the pipeline needs to be removed. The necessary support was provided to the platform to ensure that the removed pipeline could fall vertically. 12mm steel plate is used to make the original oxygen contact valve blind plate, the blind plate outer diameter is slightly larger than the outer diameter of the flange, and the blind plate is drilled according to the size of the flange screw hole and tapped. At the same time, in order to prevent accidents once the gas in the oxygen pipeline cannot be completely eliminated, two blowers are prepared in advance on site to ensure that forced air exchange on the site can be performed in time. Disengage 6000 m3/h air separation equipment 4 sets of oxygen presser oxygen supply valve inner flanges in advance, and leave gaps between the oxygen delivery valve and the flange to provide blow-off points for the networked pipes.
During construction, pressure relief is 2 hours, replacement is 1 hour, pipeline removal is 6 hours, new valves and pipelines are installed for 6 hours, purging is 1 hour, pressure leakage is checked for 1 hour, and air recovery (blind plate and air supply) is resumed for 1 hour The program was organized for construction for a total of 18 hours. After the pressure relief and displacement are completed, the construction personnel cut the pipe obliquely at an outlet of the oxygen press at 6m away from the networked three-way valve and 6m at the oxygen supply pipe of the 6000m3/h air separation plant. And set the baffle in the above two cut-outs to prevent the leakage of oxygen into the pipeline after the flange of the contact valve is disassembled. Dismantle the original oxygen contact valve 6000m3/h air separation equipment side flange screw, disengage the flange, and fix the blind plate on the valve flange to ensure that the blind plate does not fall off. After the dismantling pipeline is vertically dropped, in order to prevent the oxygen from leaking into the pipeline after the disengagement of the connecting valve flange, the baffle disposed at the cut-off position of the two oblique cuts is removed, and the original oxygen connecting valve blind plate is dismantled. The stainless steel pylons and the flanges and the new oxygen liaison valve (valve in the fully open state) are connected to the original oxygen liaison valve flange. After confirming that the flange is tightened, slowly close the new oxygen contact valve and add a blind plate to the 6000m3/h air separation unit side of the new oxygen contact valve.
After the construction is completed, the original pipeline welding port is polished, and the Φ273mm×8mm and 45° elbows on the outlet pipe of the oxygen press and the Φ273mm×8mm and 45° Y-shaped three-way valves on the oxygen feeding pipeline are welded. After the welding is completed, the maintenance personnel, with the cooperation of the crane, connects the outlet flange of the new oxygen connection valve (the flange is welded with the outlet pipe in advance) to the valve. After the connection is completed, the other end of the outlet pipe is welded to the 45° Y-shaped three-way valve, and the oxygen compressor outlet pipe is welded to the 45° Y-shaped three-way valve.
3 implementation effect
After the construction is completed, the air recovery operation is performed. The new oxygen connecting valve blind plate and the oxygen spherical tank blank plate are removed, the oxygen oxygen valve of each oxygen compressor is restored, the new oxygen valve is opened, and the residual nitrogen of the pipeline is replaced with oxygen. After 10 minutes, gas composition tests were conducted at the pipe discharge point, and the oxygen was returned to normal after passing the test. This time, the root pipeline cracking treatment of the oxygen pipeline and the installation of a contact valve were successfully completed.
1 fault phenomenon
One year after the normal operation of the oxygen pipeline, leakage occurred.
(1) DN250mm oxygen special shut-off valve is not closed. Although the valve is closed, the gas leakage is large at the downstream side flange.
(2) Cracking at the root of the DN100mm oxygen relief valve. The main reason is that the pipeline is located at the outlet section of the piston oxygen compressor, and the vibration is large. The long-term vibration causes the connection between the bottom pipe and the main pipe of the valve to crack, and the medium-pressure oxygen is largely dissipated, resulting in a large potential safety hazard.
Owing to the large amount of oxygen used in the production line and the installation of valves on the 3 sets of 21000m3/h air separation equipment side, the air supply to the oxygen network is cut off. There is no time to eliminate this safety hazard. As a result, a steel clip was temporarily made to temporarily dispose the oxygen pipeline, and a temporary warning zone was set within a range of 10m around.
2 treatment measures and processes
The overhaul of the oxygen production process has been carried out synchronously with the mainline processes such as steelmaking, ironmaking and stainless steel. To deal with the above security risks, the specific treatment measures are:
(1) The original DN250mm oxygen special cut-off valve is used as a section of pipe. The valve is open for a long time; and the flanges on both sides are fastened to ensure that the flange connection does not leak oxygen. A special DN250mm oxygen shut-off valve with a pressure of 614 MPa was installed on the pipeline. This valve was used as a shut-off valve (middle contact valve) for normal operation.
(2) Repair welding cracking pipe, and fix the pipe and valve; replace the 6000m3/h air separation equipment oxygen pipe three-way valve.
Prior to construction, related materials and spare parts were prepared, and equipment such as argon arc welding machines and chain rewinding was transported to the site to degrease and suppress the new oxygen contact valve in advance. The Φ273mm×8mm carbon steel pipe and the 90° stainless steel three-way pipe were used. Valves, 45° elbows, and 45° Y-shaped three-way valves are used for rust removal, degreasing, and grinding of the bevel. According to the pipeline construction site conditions, a removable maintenance platform or scaffolding shall be made at the pipe cutting site and the new oxygen valve. Make new oxygen contact blinds in advance. A stainless steel pipe with a length of about 115m is welded on the flange of the inlet side of the new oxygen connection valve, and a 4MPa, DN250mm flange is welded on the other end of the stainless steel pipe. The original 4MPa, DN250mm oxygen linkage valve north side and east side support beam were removed in advance, and the steel plate at the lower part of the pipeline needs to be removed. The necessary support was provided to the platform to ensure that the removed pipeline could fall vertically. 12mm steel plate is used to make the original oxygen contact valve blind plate, the blind plate outer diameter is slightly larger than the outer diameter of the flange, and the blind plate is drilled according to the size of the flange screw hole and tapped. At the same time, in order to prevent accidents once the gas in the oxygen pipeline cannot be completely eliminated, two blowers are prepared in advance on site to ensure that forced air exchange on the site can be performed in time. Disengage 6000 m3/h air separation equipment 4 sets of oxygen presser oxygen supply valve inner flanges in advance, and leave gaps between the oxygen delivery valve and the flange to provide blow-off points for the networked pipes.
During construction, pressure relief is 2 hours, replacement is 1 hour, pipeline removal is 6 hours, new valves and pipelines are installed for 6 hours, purging is 1 hour, pressure leakage is checked for 1 hour, and air recovery (blind plate and air supply) is resumed for 1 hour The program was organized for construction for a total of 18 hours. After the pressure relief and displacement are completed, the construction personnel cut the pipe obliquely at an outlet of the oxygen press at 6m away from the networked three-way valve and 6m at the oxygen supply pipe of the 6000m3/h air separation plant. And set the baffle in the above two cut-outs to prevent the leakage of oxygen into the pipeline after the flange of the contact valve is disassembled. Dismantle the original oxygen contact valve 6000m3/h air separation equipment side flange screw, disengage the flange, and fix the blind plate on the valve flange to ensure that the blind plate does not fall off. After the dismantling pipeline is vertically dropped, in order to prevent the oxygen from leaking into the pipeline after the disengagement of the connecting valve flange, the baffle disposed at the cut-off position of the two oblique cuts is removed, and the original oxygen connecting valve blind plate is dismantled. The stainless steel pylons and the flanges and the new oxygen liaison valve (valve in the fully open state) are connected to the original oxygen liaison valve flange. After confirming that the flange is tightened, slowly close the new oxygen contact valve and add a blind plate to the 6000m3/h air separation unit side of the new oxygen contact valve.
After the construction is completed, the original pipeline welding port is polished, and the Φ273mm×8mm and 45° elbows on the outlet pipe of the oxygen press and the Φ273mm×8mm and 45° Y-shaped three-way valves on the oxygen feeding pipeline are welded. After the welding is completed, the maintenance personnel, with the cooperation of the crane, connects the outlet flange of the new oxygen connection valve (the flange is welded with the outlet pipe in advance) to the valve. After the connection is completed, the other end of the outlet pipe is welded to the 45° Y-shaped three-way valve, and the oxygen compressor outlet pipe is welded to the 45° Y-shaped three-way valve.
3 implementation effect
After the construction is completed, the air recovery operation is performed. The new oxygen connecting valve blind plate and the oxygen spherical tank blank plate are removed, the oxygen oxygen valve of each oxygen compressor is restored, the new oxygen valve is opened, and the residual nitrogen of the pipeline is replaced with oxygen. After 10 minutes, gas composition tests were conducted at the pipe discharge point, and the oxygen was returned to normal after passing the test. This time, the root pipeline cracking treatment of the oxygen pipeline and the installation of a contact valve were successfully completed.
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