Selection requirements and acceptance steps of submerged arc steel pipe

1. For pipelines with high requirements for peak regulation, due to the uneven gas consumption of users and frequent fluctuations in pipeline pressure, the alternating stress on the steel pipe is very large, and the existing defects in the pipe will expand under the alternating stress. If you choose For spiral welded steel pipes with many welds and a high probability of defects, the operation of the pipeline will not be guaranteed.

2. The pipeline crosses the seismic fault zone or passes through the local high-intensity earthquake area. Due to the frequent geological activities in these areas, longitudinal or axial alternating stress 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 long-term stress, the accident probability 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 with high requirements for internal and external anti-corrosion layers. Spiral submerged arc welded steel pipes have more weld passes, and the weld reinforcement is generally higher than that of submerged arc steel pipes. When the steel pipes are internally and externally anti-corrosion, the combination of anti-corrosion materials and bare pipes is not as tight as submerged arc steel pipes, and the anti-corrosion effect is not as good as submerged arc steel pipes. The steel pipe is good.

4. For important crossing projects, submerged arc steel pipes should be used. Since future maintenance and management are more difficult than general line sections, it is especially advantageous to use high-performance submerged arc steel pipes.

5. For the weak link of the pipeline, such as hot-simmered elbow pipe, submerged arc steel pipe should be used. Due to the change of direction, the hot-simmering elbow bears greater internal and external forces than 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.

Submerged arc steel pipe acceptance steps:

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 guarantees that the delivered submerged arc steel pipe complies with the rules of the corresponding product standards. The buyer 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 quantity, sampling location, and test method of submerged arc steel pipe shall be by the rules of corresponding product standards. With the consent of the purchaser, hot-rolled seamless submerged arc steel pipes can be sampled in batches according to the number of rolling roots.

5. For the test results of submerged arc steel pipes, when a certain item does not meet the product standards, the unqualified ones should be picked out, and double the number of samples should be randomly taken from the same batch of submerged arc steel pipes to inspect unqualified items. recheck. If the re-inspection results (including any index required by the project test) are unqualified, the batch of submerged arc steel pipes shall not be delivered. For the following inspection items, if the initial inspection fails, re-inspection is not allowed: a. There are white spots in the low-power tissue; b. Microstructure.

6. For the submerged arc steel pipes whose re-inspection results are unqualified (including those whose microstructure is unqualified due to the initial inspection results, and re-inspection is not allowed), the supplier can submit them for inspection one by one; or re-heat treatment (the number of re-heat treatments shall not exceed two times) ), with a new batch presented for inspection.

7. If there is no special regulation in the product specification, the chemical composition of the submerged arc steel pipe shall be checked according to the melting composition.

In the construction of long-distance pipelines, line steel pipes account for a considerable proportion. Under normal circumstances, the investment in line steel pipes accounts for about 35% to 40% of the total project investment. How choose pipes with reasonable prices and high performance are particularly important. Reasonable selection of pipes has a very important impact on saving construction investment, facilitating construction, and operating the pipeline system. Long-distance oil and gas pipeline steel pipes include high-frequency straight seam 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. In China, it is generally limited to steel pipes within Φ406.4mm. In Japan, the largest pipe diameter has reached Φ508mm. There are two types of pipe-making methods for large diameters: spiral submerged arc welding and straight seam submerged arc welding. Spiral welded steel pipe has many disadvantages due to its pipe-making process and forming characteristics, and its proportion in long-distance pipelines is gradually declining. In foreign countries, especially in many European and American countries, the use of spiral submerged arc welded steel pipes as the main steel pipes for lines has been banned. The submerged arc steel pipe is widely used in long-distance oil and gas pipelines with its unique advantages. The advantages are as follows: 1. There is no unwinding process so the base metal has less pitting and scratches. 2. Misalignment, slit, pipe diameter, and perimeter are easy to control and weld. 3. There is no residual stress after pipe expansion to eliminate stress. 4. Since it is a straight weld seam, the weld seam is short, so the probability of defects is small. 5. After the diameter is expanded, the geometric dimension accuracy of the steel pipe is improved, which greatly facilitates on-site welding. 6. The welding seam is a straight line, which has little effect on the coating of anti-corrosion materials.