What is the difference between the two forming processes of submerged arc welding steel pipe
Generally, longitudinal submerged arc welded steel pipes used in petroleum pipeline engineering are manufactured by UOE and JCOE. The conventional production process is that after the steel pipe blank is formed by UO or JCO, pre-welding, internal and external final welding, diameter expansion, nondestructive inspection, pipe end processing, water pressure test, weighing and length measurement, and appearance inspection of steel pipe marks are carried out. Today, let's learn about the characteristics of UOE and JCOE!
In UOE forming process, firstly, the edges of steel plates need to be bevelled, leveled and bent, then pressed into a U-shape by a forming machine, and then bent into an O-shape. After the steel pipes are closed, gas shielded welding is used for pre-welding, submerged arc welding is used for internal and external final welding, and finally the whole pipe body is cold-expanded by a sectional mechanical expanding process. After the steel pipes are formed and welded, a series of inspections are carried out. This technology is the most widely used, mature and recognized production technology of large diameter longitudinal submerged arc welded pipe in the world.
Main features of UOE welded steel pipe:
1) The forming process is separated from the welding process, which belongs to discontinuous single production.
2) Thick-walled steel pipes can be produced, and the maximum wall thickness can reach about 4Omm.
3) Under the same length, the weld length of steel pipe is only half of that of spiral weld, so the probability of weld defects is less.
4) The output is high, and the output of one UOE unit is generally equivalent to the total output of 2~4 spiral welded pipe units.
5) The diameter expanding process is adopted to improve the strength and dimensional accuracy of the steel pipe.
6) UOE steel pipe is straight seam, which makes pipeline laying and maintenance more convenient.
7) The equipment is larger than the spiral welded pipe mill, and the investment cost is high.
Compared with UOE molding method, JCOE molding process has the advantages of relatively low cost, strong process adaptability, small wear of molding die and light molding die, and its technology and products are widely used. JCOE pipe-making process is to form steel plates in the order of J-C-O-forming, pre-weld the steel pipes by gas shielded welding after joint, and then perform internal and external final welding by submerged arc welding. Finally, the whole pipe body is cold-expanded by sectional mechanical expanding process, and finally a series of inspections are carried out.
Main features of JCOE process:
1) Every forming process of JCOE is completed on a large press, which requires high technical requirements for steel pipe shaping operation and takes a long time for the forming unit. Because of multiple molding, compared with UOE process, the processing efficiency is low, but there are fewer molds and lower equipment investment. Therefore, the number of domestic JCOE units is more than that of UOE units.
2) Because JCO is multi-step pressing, the dimensional accuracy of steel pipes is lower than that of UOE, so UOE steel pipes are mostly used in offshore pipelines.
Quality control of JCO molding：
In the JCO forming process, the steel plate is gradually sent into the forming mold by the steel pusher, and it needs to be straightened again before each side is formed, and finally it is processed into a straight slotted steel pipe, and finally it is welded and welded. JCO molding machine generally adopts automatic control, and the molding machine is designed for short stroke, and the maximum pressure can reach 9000t t.. Before changing dies with different diameters, clean up the impurities of the lower die pad to ensure that the lower die pad is flat after being loaded, so as not to affect the accuracy in the thickness direction.
