Effect of Mechanical Expanding of Double Submerged Arc Welding Longitudinal Seam Steel Pipe

    At present, the long-distance transportation of oil and natural gas mainly adopts pipeline. Long-distance pipeline pipeline used in the main spiral pipe submerged arc welded pipe(ssaw steel pipe) and double submerged arc welded straight steel pipe(dsaw steel pipe). As the spiral submerged arc welded pipe is based on strip as raw material, wall thickness is limited, in addition to the existence of spiral submerged arc welded pipe longer, greater residual stress, weld reliability is poor and difficult to overcome the shortcomings of dense population area and reliability requirements of the region, large diameter straight seam submerged arc welded pipe has been gradually replaced by spiral submerged arc welded pipe.

    Expanded diameter is a large diameter straight seam submerged arc welded pipe production to ensure the quality of an important process, the standard pipe line pipe submerged arc welded pipe must be expanded process.

    1, Effectively improve the dimensional accuracy of steel pipe

    At present, there are mainly UO, RB, JCO, C and Hu-Metal for the forming of LSAW steel pipes. The steel pipes produced by these five kinds of molding methods have different geometrical accuracy. As the straight seam submerged arc welding in the tube side of the inside and outside welding, and thus under the action of thermal stress in the steel pipe to be bending deformation, and the longitudinal part of the weld shrinkage larger, so that the straightness of steel pipe is seriously affected; In addition, these five kinds of forming the production of steel pipe, the oval are large, especially JCO and C forming steel pipe. Therefore, we must increase the diameter, the whole circle and other processes to improve the geometric accuracy of steel pipe.

    2, Reduce or eliminate in the pipe, the test process caused by the Bauschinger effect

    As the steel pipe in the process of forming and testing will produce the Bauschinger effect, so that the yield strength decreased, and the expansion of steel in the cold hardened, expanded diameter can improve the yield strength of steel, thus reducing the strength to achieve steel requirements while increasing the level of waste caused by sheet metal.

    3, The elimination of steel pipe forming and welding residual stress

    Cold expansion can eliminate the residual stress caused by forming and welding, and improve the distribution of stress in the steel pipe, so as to avoid the occurrence of hydrogen embrittlement and crack in the steel pipe stress concentration area due to the transportation of H2S in oil or natural gas.

    In addition, the diameter of the welding quality and welding performance is also a good test.