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Oxygen valve leakage and release valve root cracking fault handling
Take the pipeline diameter Φ273mm × 8mm carbon steel pipe, the intermediate contact valve with 4MPa, DN250mm oxygen special globe valve. DN100mm ordinary shut-off valve is installed on the pipeline in front of the liaison valve as an oxygen releasing valve. The valve is installed vertically upright. The root is about 10cm away from the pipe and the root is not fixed by the neck. The upper vent of the valve is led upward by about 80cm. 1, Symptom Oxygen pipeline connected to the normal operation of about 1 year, there was a leak. (1) DN250mm oxygen valve is not strictly closed. Although the valve is closed, there is a large gas leak at the downstream flange. (2) DN100mm oxygen relief valve root cracking. Mainly due to the section of the pipeline just located in the outlet section of the piston oxygen compressor, large vibration, long-term vibration resulting in the bottom of the valve connection pipe and the main pipeline junction cracking, a large number of medium pressure oxygen emissions, security risks. As the production of the main line with a large amount of oxygen, and in the three sets of 21000m3 / h air separation plant side without the valve to the supply of oxygen gas supply network cut off, there is no time to rule out the potential safety hazard. As a result, a steel clip was temporarily made and temporary disposal of oxygen pipelines was carried out. Temporary warning zones were set within a 10m radius. 2, treatment measures and processes Oxygen maintenance process has been with the steelmaking, ironmaking and stainless steel main line maintenance and other processes simultaneously. According to the company's maintenance plan, on September 27, 2006 to deal with the above security risks, the specific measures are as follows: (1) the original DN250mm oxygen special globe valve as a section of the pipeline, the valve is open all year round; and fastening both sides Flange, to ensure that the flange connection does not leak oxygen. In the pipeline to re-install a pressure of 614MPa DN250mm dedicated oxygen valve, the valve as the usual operation of the shut-off valve (intermediate contact valve). (2) Reinforcing pipe shall be used to relieve the crack of pipeline and to fix the pipe and valve in this section; to replace the 3-way valve of oxygen delivery pipe for 6000m3 / h air separation plant. Scheduled maintenance time 18 hours, the specific overhaul construction shown in Figure 1. Prior to the construction, relevant materials and spare parts were prepared, and equipment such as argon arc welding machine and backchain were transported to the site to degrease the newly added oxygen contact valve and suppress the pressure on the Φ273mm × 8mm carbon steel pipe and the 90 ° stainless steel tee Valve, 45 ° elbow and 45 ° Y-shaped three-way valve rust, degreasing, and polished bevel. According to the pipeline construction site situation, at the pipe cutting and new oxygen contact valve at the production of mobile inspection platform or to build scaffolding. Create a new oxygen contact blind valve in advance. A new stainless steel pipe with a length of about 115m is welded to the flange on the intake side of the oxygen contact valve. A flange of 4MPa and DN250mm is welded to the other end of the stainless steel pipe. Cut off the original 4MPa, DN250mm oxygen contact valve north, east support beams, and will remove the lower part of the steel plate removed, while the platform set up the necessary support to ensure that the pipe can be cut off vertically. The original oxygen production with 12mm steel blind plate blind, the outer diameter of the blind is slightly larger than the outer diameter of the flange, the blind plate according to the size of the flange screw hole drilling, and tapping. In the meantime, in order to prevent the accident of the gas in the oxygen pipeline being not completely eliminated, two blowers are prepared at the site in advance to ensure forced exchange of wind on site. In advance to loosen 6000m3 / h air separation plant 4 Oxygen pressure machine oxygen valve inside the flange, and the oxygen valve and the flange left a corresponding gap between the network pipe blowing point. Construction, in accordance with the pressure relief 2 hours, 1 hour replacement, pipe removal 6 hours, the new valve and pipe installation 6 hours, purge 1 hour, suppress leak 1 hour and recovery of air supply (blind and air) 1 hour The construction of the program, a total of 18 hours. After the pressure relief and displacement, the construction workers cut off the pipeline obliquely at the outlet pipe of oxygen compressor 6m away from the networked pipe three-way valve and 6m away from the oxygen delivery pipe of the 6000m3 / h air separation plant. And in the above two cut-off set baffle to prevent the contact valve flange open oxygen leak into the pipeline. Remove the original oxygen linkage valve 6000m3 / h air separation equipment side flange screws, remove the flange, the blind plate fastened to the valve flange to ensure that the blind does not fall off. After the pipe to be demolished is dropped vertically, in order to prevent the oxygen from leaking into the pipe after the contact valve flange is disassembled, the baffle plate provided at the opening of two bevels of the pipe is reserved and the blank of the original oxygen contact valve is removed. Connect the stainless steel stems and flanges with the new oxygen linkage valve (the valve is fully open) to the original oxygen linkage valve flange. After confirming that the flange is fastened, slowly close the new oxygen linkage valve and add the blind on the 6000m3 / h air separation unit side of the new oxygen linkage valve. After the construction is completed, the original pipe weld is polished, and the Φ273mm × 8mm, 45 ° elbow on the outlet pipe of oxygen compressor and the Φ273mm × 8mm, 45 ° Y-shaped three-way valve on the oxygen delivery pipe are welded at the same time. Welding is completed, the maintenance staff in the crane with the new oxygen linkage valve outlet flange (flange and outlet pipe in advance of the welding) connected with the valve. After the connection, the other end of the outlet pipe is welded with the 45 ° Y-shaped three-way valve, and the oxygen compressor outlet pipe is welded with the 45 ° Y-shaped three-way valve. 3, the implementation of the effect After the completion of the construction, the resumption of air supply operation, removal of new contact oxygen blind valve, blind hole oxygen tank, restore the oxygen pressure oxygen delivery valve, open the new oxygen valve, with oxygen on the pipeline residual nitrogen Replacement. After 10 minutes, gas composition tests were performed at the pipe release and the oxygen was returned to normal after passing the test. The oxygen pipeline relief valve root crack processing and installation of contact valve technology transformation success. 4 Conclusion The exclusion of potential safety hazards, one month before the start of construction began to personnel, materials, equipment and technical programs and other preparations. Due to the adequacy of preparatory work, all kinds of situations that may appear on site may be targeted and prevented in advance. The actual progress of construction is completely controllable and slightly ahead of the planned completion of construction.