First, the selection requirements for submerged arc steel pipes:
1. For pipelines with high peak-shaving requirements, due to the uneven gas consumption of users, the pipeline pressure fluctuates frequently, and the steel pipes are subjected to large alternating stresses. Existing defects in the pipes will expand under alternating stresses. If spiral welded steel pipes with many welds and high defect probability are selected, the operation of the pipeline will not be guaranteed.
2. The pipeline passes through earthquake fault zones or local high-intensity earthquake areas. Due to the frequent geological activities in these areas, longitudinal or axial alternating stresses will be generated on the pipeline. There are many spiral welds and the defect probability is higher than that of submerged arc steel pipes. Under long-term stress, the probability of accidents in spiral welded steel pipes is much higher than that of submerged arc steel pipes. Therefore, submerged arc steel pipes should be used in such areas.
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 many welds, and the weld excess height is generally higher than that of submerged arc steel pipes. When the steel pipes are subjected to internal and external corrosion protection, the degree of integration of the anti-corrosion material and the bare pipe is not as tight as that of submerged arc steel pipes, and the anti-corrosion effect is not as good as that of submerged arc steel pipes.
4. Submerged arc steel pipes should be used for important crossing and spanning projects. Since future maintenance and management are more difficult than general line sections, the use of submerged arc steel pipes with high performance is particularly obvious.
5. Submerged arc steel pipes should be used for weak links in pipelines, such as hot-bending elbow pipes. Due to the change in direction, the internal and external forces borne by hot-bending elbows are greater than those of general line straight pipe sections. Due to the influence of various factors during the simmering process, its stress is not easy to eliminate. It is a relatively weak link in long-distance pipelines. The use of submerged arc steel pipes with good comprehensive performance can make up for these shortcomings.
Second, acceptance steps for submerged arc steel pipes:
1. The inspection and inspection of submerged arc steel pipes should be carried out by the supplier’s technical supervision department.
2. The supplier guarantees that the delivered submerged arc steel pipes meet the rules of the corresponding product standards. The buyer has the right to inspect and test 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 methods of submerged arc steel pipes shall comply with the rules of the corresponding product standards. With the approval of the buyer, hot-rolled seamless submerged arc steel pipes can be sampled in batches according to the rolling root group.
5. If a certain item of the submerged arc steel pipe test result does not meet the rules of the product standard, the unqualified ones should be selected, and double the number of samples should be randomly taken from the same batch of submerged arc steel pipes for re-inspection of the unqualified items. If the re-inspection results (including any of the requirements of 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. White spots in the macrostructure; b. Microstructure.
6. For submerged arc steel pipes that fail the re-test (including those that fail the initial test and do not allow re-test), the supplier may submit them for inspection one by one; or re-heat treat them (the number of re-heat treatments shall not exceed two times) and submit a new batch for inspection.
7. If the product standard does not make special provisions, the chemical composition of the submerged arc steel pipe shall be inspected according to the smelting 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 investment in the project. How to choose pipes with reasonable prices and high performance is particularly important. The reasonable choice of pipes has a great 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 resistance welded steel pipes, spiral submerged arc welded steel pipes, and submerged arc steel pipes. The diameter range of high-frequency straight seam resistance welded steel pipes is limited. Domestically, it is generally limited to steel pipes within Φ406.4mm, and the largest diameter in Japan has reached Φ508mm. There are two types of pipe making for large diameters: spiral submerged arc welding and straight seam submerged arc welding. Spiral welded steel pipes have many disadvantages due to their pipe-making process and forming characteristics, and their proportion in long-distance pipelines is gradually decreasing. 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 the lines has been banned. Submerged arc steel pipes are widely used in long-distance oil and gas pipelines with their unique advantages. The advantages are as follows: 1. There is no unwinding process, which reduces the pitting and scratching of the parent material. 2. Misalignment, seam opening, pipe diameter circumference, etc. are easy to control and weld. 3. There is 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 dimensional accuracy of the steel pipe is improved, which greatly facilitates on-site welding. 6. The weld is a straight line, which has little effect on the coating of anti-corrosion materials.
Post time: Dec-25-2024