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News
High-pressure pipelines are used in high-pressure chemical production processes, and the more important ones are synthetic ammonia production, urea production, methanol production, and petroleum hydrocracking.
In modern industry, high-pressure pipelines are widely used. Many chemical production processes have adopted high pressures of 10 to 100 MPa. The more important ones are synthetic ammonia production, urea production, methanol production, and petroleum hydrocracking. The pipeline connecting the high-pressure chemical production device is an important part of the high-pressure chemical production process system, and it also occupies a large proportion in the whole device. Generally speaking, high-pressure pipelines refer to fluid medium pipelines with a pressure of 10-100MPa, and pipelines with pressures exceeding 100MPa are called ultra-high-pressure pipelines.
Some problems found during high pressure pipeline welding operations are summarized below
1. Verify color codes for tubing, fittings and consumables.
2. Cut the short section and pay attention to the transfer of the logo.
3. Mechanical drilling should be used for the opening of alloy steel pipes with a tendency to hot cracks. Cutting and beveling should also be done mechanically.
4. For pipe fittings with different thicknesses, the inner or outer wall should be chamfered at 15°, and the length of the gentle slope should be 1.5 times the wall thickness.
5. Pipe fittings with ovality should be polished to a good finish.
6. Where there is a preheating requirement before welding, the welding joint of the pipeline must be placed at a height of more than 150mm from the ground to prevent the temperature gradient from dropping sharply.
7. Large grill handle (H01-20) must be used for welding junctions of 2” and below, and a torch cannot be used to prevent unintentional opening of the high-pressure air valve from damaging the base metal of the pipeline.
8. The welding joint of the thick-walled alloy steel pipe above 2” must be preheated by electric heating, and the preheating and heat preservation measures should be able to ensure a stable preheating temperature.
9. The temporary support of the alloy steel pipe assembly welding must be fixed on the hoop. The end of the carbon steel assembly welding fixture should be surfacing with two or more layers of the corresponding alloy steel electrode before it can be spot welded with the alloy steel pipe. The normal preheating method should be used before fixing.
10. The electrode swing does not exceed 3.5 times the core diameter.
11. Welding joints of alloy steel thick-walled pipes should be symmetrically welded, and single-sided multi-layer welding is strictly prohibited. Large-diameter pipeline welds should be welded by multiple welders, and strive to be completed at one time. If it is compelled to stop halfway, the post-heating, slow-cooling and heat preservation work should be done well, and the formal preheating procedure can be used before welding.
12. Welders of high-pressure pipelines should strictly perform the self-inspection procedures of the finished welds to ensure that the welds are plump without lack of flesh, and without deep undercuts and spatters. Only qualified welds can be delivered to the welding quality inspector for joint inspection.
13. The welding ground wire should not be less than 70 square meters, otherwise the current will be unstable. The ground wire should be connected close to the welding seam, and it is strictly forbidden to bridge the control valve and valve of the instrument to prevent the electric spark from damaging the valve core.
14. Welding seam after heat treatment is strictly prohibited.
15. When assembling flanges for high-pressure pipelines, the plumber should ensure that the flange surface is intact, and the ground wire of the welder is strictly prohibited from being overlapped on the flange end surface.
16. The damaged wire of the welder should be wrapped in time to prevent electric sparks from damaging the base metal of the pipeline.
17. Weld scars and arc craters should be ground and repaired before flaw detection and heat treatment.
important hint:
In the welding construction, we must find qualified technicians to operate. If the welding technology of high-pressure pipelines is found to be unsatisfactory after the laying is completed.
