Selection requirements for submerged arc steel pipes:
1. For pipelines with high peak shaving requirements, due to the uneven gas consumption of users, frequent fluctuations in pipeline pressure, and great alternating stress on the steel pipe, the existing defects in the pipe will expand under the alternating stress. For spiral welded steel pipes with many welds and a high probability of defects, the operation of the pipeline will not be guaranteed.
2. When the pipeline passes through the seismic fault zone or passes through the local high-intensity seismic area, due to the frequent geological activities in these sections, the alternating stress in the longitudinal or axial direction will be generated on the pipeline. There are many spiral welds, and the probability of defects is higher than that of submerged arc steel pipes. Under the action of long-term stress, the probability of accidents of spiral welded steel pipes is much higher than that of submerged arc steel pipes. Therefore, submerged arc steel pipes should be used in this area.
3. Submerged arc steel pipes should be used for pipelines that require high internal and external anti-corrosion layers. Spiral submerged arc welded steel pipe has many welds passes, and the residual height of the weld is generally higher than that of submerged arc steel pipe. When the steel pipe is internally and externally anti-corrosion, the combination of anti-corrosion material and bare pipe is not as close as that of submerged arc steel pipe, and the anti-corrosion effect is not submerged arc. Steel pipe is good.
4. For important crossing projects, submerged arc steel pipes should be used. Since the maintenance and management in the future ar more difficult than the general line section, the use of submerged arc steel pipes with high performance is particularly important.
5. For the weak links of the pipeline, such as hot simmering elbow pipes, submerged arc steel pipes should be used. Due to the change of direction, the internal and external force of the hot simmering elbow is larger than that of the straight pipe section of the general line. Due to the influence of various factors during the simmering process, its stress is not easy to eliminate, and it is a relatively weak link in the long-distance pipeline. , the use of submerged arc steel pipes with good comprehensive performance can make up for these deficiencies.
Acceptance steps of submerged arc steel pipe:
1. The inspection and inspection of submerged arc steel pipes shall be carried out by the technical supervision department of the supplier.
2. The supplier shall ensure that the delivered submerged arc steel pipe conforms to the rules of the corresponding product standard. The purchaser has the right to inspect and inspect according to the corresponding product standards.
3. Submerged arc steel pipes should be submitted for inspection in batches, and the batching rules should comply with the rules of the corresponding product standards.
4. The inspection items, sampling quantities, sampling locations and test methods of submerged arc steel pipes are in accordance with the rules of the corresponding product standards. With the agreement of the purchaser, the hot-rolled seamless submerged arc steel pipe can be sampled in batches according to the rolling root group.
5. For the testing effect of submerged arc steel pipes, when a certain item does not meet the rules of the product standard, the unqualified ones should be picked out, and from the same batch of submerged arc steel pipes, double the number of samples should be taken arbitrarily, and the unqualified items should be tested. recheck. If the re-inspection results (including any of the requirements required by the project test) are unqualified, the batch of submerged arc steel pipes shall not be delivered. The following inspection items are not allowed to be re-inspected when the initial inspection fails: a. There are white spots in the low magnification tissue; b. Microstructure.
6. For submerged arc steel pipes with unqualified re-inspection results (including items that have unqualified microstructure in the initial inspection effect and are not allowed to re-inspect), the supplier may submit them for inspection one by one; or re-heat treatment (the number of re-inspection heat treatments shall not exceed twice ), a new batch is proposed for inspection.
7. If the product standard does not make special rules, the chemical composition of the submerged arc steel pipe shall be checked according to the smelting composition.
In the construction of long-distance pipelines, steel pipes for lines account for a considerable proportion. Under normal circumstances, investment in line steel pipes accounts for about 35% to 40% of the total project investment. How choose pipes with reasonable prices and performance is particularly important. A reasonable choice of pipes has a very impont impact on saving construction investment, facilitating construction, and the operation of pipeline systems. Long-distance oil and gas pipeline steel pipes include high-frequency straight seam electric resistance welded steel pipes, spiral submerged arc welded steel pipes, and submerged arc steel pipes. The diameter range of high-frequency straight seam electric resistance welded steel pipe is limited, generally limited to steel pipes within Φ406.4mm in China, and the largest pipe diameter in Japan has reached Φ508mm. There are two forms of pipe making for large diameters: spiral submerged arc welding and straight seam submerged arc welding. Spiral welded steel pipe has many shortcomings due to its pipe-making process and forming characteristics, and its proportion in long-distance pipelines is gradually decreasing. In foreign countries, especially in many of Europe and the United States, the use of spiral submerged arc welded steel pipes as the main body of the line has been prohibited. The submerged arc steel pipe is widely used in long-distance oil and gas pipelines due to its unique advantages. 2. It is easy to control and weld the wrong side, slit, pipe diameter, and circumference. 3. There is basically no residual stress after pipe expansion to eliminate stress. 4. Because it is a straight weld, the weld is short, so the probability of defects is small. 5. After the diameter is expanded, the geometric accuracy of the steel pipe is improved, which greatly facilitates the on-site welding. 6. The welding seam is a straight line, which has little influence on the coating of anti-corrosion materials.