Straight Seam Welded Pipe (LSAW) Advanced and Superior

The vast majority of oil and gas pipelines in the world require the use of straight-seam submerged arc welded pipes (LSAW). The improved processes of spiral welded pipe (SSAW) in western developed countries such as Canada, such as pre-welding, precision welding, multi-wire welding, mechanical expansion, etc., are designed with reference to the straight seam submerged arc welded pipe (LSAW) process, which explains The advancement of the straight seam welded pipe (LSAW) pipe making process. Specifically:

1. From a technical point of view, the advantages of straight seam welded pipe (LSAW):

① The base material of the straight seam welded pipe (LSAW) is a single controlled rolled steel plate which is isotropic, and 100% non-destructive testing can be performed;
②The stress state of the straight seam welded pipe (LSAW) after forming is good. Due to the mechanical expansion, the internal stress can be eliminated and the geometric accuracy of the steel pipe can be improved;
③ The internal quality of the straight seam welded pipe (LSAW) is good, because the welding is performed on a flat surface, so the welding conditions, automatic tracking, and non-destructive testing are easy to perform, which makes the weld height low and the accuracy of the internal and external welds high;
④Wide thickness range of straight seam welded pipe (LSAW) is wide, generally 6-25 mm, the maximum thickness can reach 45 mm;
⑤Straight seam welded pipe (LSAW) has good resistance to bending and flattening;
⑥Straight seam welded pipe (LSAW) weld is 60% shorter than spiral welded pipe, and the probability of weld defects is low;
⑦Straight seam welded pipe (LSAW) has high reliability.

According to statistics, the failure rate of foreign straight seam welded pipe (LSAW) gas transmission is 0.05 to 1.44 times/103 kilometers for 50 years, and the failure rate is low. Therefore, it is suitable for application in the second, third, and fourth regions.

2. From the perspective of applying to ocean oil and gas transportation, it is inevitable to focus on the construction of straight seam welded pipe (LSAW). A considerable part of the world’s oil and gas resources are stored in the ocean. From the perspective of natural gas development in the future, it is mainly buried in the ocean in the form of “flammable ice”. It is currently recognized that the total energy of “combustible ice” in the world is 2 to 3 times the sum of all coal, oil, and natural gas in the world. This is also true in my country, and it will be the main source of energy in the future.

In the short term, China is accelerating the pace of oil and gas development in the East China Sea. With the development of oil exploration deep into the ocean, the squashing phenomenon has also occurred due to the combined forces of pressure, impact and bending forces laid on the submarine transportation pipeline. It is the weak link of the spiral welded pipe (SSAW). In order to improve the pipeline transportation capacity and ensure safety, the submarine pipeline develops toward the thick wall direction, so the submarine pipeline mostly uses straight seam welded pipe (LSAW).

From another point of view, due to the difficulty of installing butt welding in pipelines in the ocean, the requirements for the ellipticity, moderateness, bevel protection and cross-section error of the steel pipe are high, otherwise, the operation efficiency will be seriously affected. As a result, LSAW has a higher dimensional accuracy than spiral welded pipe (SSAW), and repair welding is also easy. Therefore, from this point of view, it is also preferred to use straight welded pipe.

3. Long-seam welded pipe (LSAW) is required for coal slurry and ore slurry pipelines. Pipeline transportation of coal and ore powder in the state of “paste” is an effective direction in the international upward movement. Because the residual height of the weld in the spiral welded pipe (SSAW) is a spiral line, the resistance to coal slurry is large, and the pipeline needs a large wall thickness, so Straight seam welded pipe (LSAW) is preferred.

4. Long-seam welded pipe (LSAW) is required for machinery, construction and chemical industry. The valve seats of valves manufactured in the machinery industry are currently processed with forgings for inner holes, which is time-consuming and time-consuming. If you use thick-walled straight seam welded pipes (LSAW), it is much more economical; in addition, the mechanical properties of construction pipes require flattening resistance , Only use straight seam welded pipe (LSAW); chemical pipe also hope to use straight seam welded pipe (LSAW).

(1). Delamination flaw detection of steel plate
The detection of steel plate layering defects is different from the form in which the steel plate manufacturers abroad are responsible for ensuring the quality requirements of users. In foreign countries, usually the steel pipe plant and the steel plate plant belong to a large-scale joint enterprise, and the steel plate plant carries out the flaw detection of the steel plate delamination. Moreover, foreign advanced instruments are fully capable of achieving 100% coverage of the steel plate layered flaw detection. Different from the foreign form, in the production of domestic straight seam submerged arc welded steel pipe, the steel plate layer defect detection is carried out by the steel pipe factory itself. According to the original design, a scan can only completely cover the edge of the steel plate, and the coverage rate of the entire board can reach more than 25%. If you want to achieve 100% coverage of the steel plate layered flaw detection, you need to do a back and forth scan, in this respect there is a certain gap between domestic and foreign.

(2). Detection of welds
Foreign straight-seam submerged arc welded steel pipe production plants attach great importance to and rely on ultrasonic flaw detection of welds. Generally, ultrasonic flaw detection of the entire length of the weld before expansion is used as the internal quality control of the factory. At the same time, it is also equipped with X-ray industrial TV inspection equipment, and its static sensitivity is also high (less than 16%). It is generally used for re-examination of defective parts of ultrasonic flaw detection before diameter expansion. Only a few manufacturers perform steel pipe inspection before diameter expansion Ultrasonic flaw detection of all welds and X-ray industrial TV inspection. After the diameter expansion and water pressure are completed, the ultrasonic automatic flaw detection is mainly used for the full weld seam. At the same time, the ultrasonic hand detection and the pipe end film inspection of the automatic blind detection area at the two ends of the steel pipe are also used.

China’s domestic straight-seam submerged arc welded steel pipe production plant conducts ultrasonic flaw detection and X-ray industrial television flaw detection on 100% of the total length of the weld before and after water pressure. The flaw detection before water pressure is used for internal quality control of the factory, and the flaw detection after water pressure is used for quality assurance and acceptance inspection. Except for a few steel pipe factories, most of the domestic submerged arc welded steel pipe production plants rely more on X-ray industrial TV flaw detection for welds, but the sensitivity of domestic X-ray industrial TV flaw detection equipment is not very high. In comparison, the inspection of steel pipe welds in China is more dependent on the quality of the operator’s work, while the inspection of welds in foreign factories is more dependent on the equipment itself, and the reliability is higher.

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