1. Due to the arc deviation, local distortion of longitudinal seam welding, The radian and ovality deviation of steel pipe will be difficult to ensure the deviation, and it take the following measures to guarantee.

(1) To design and produce longitudinal seam local arc calibration machine, after welding longitudinal seam, to use machine calibration to ensure its partial arc deviation.

(2) Set up the reasonable steel pipe support to ensure deformation value and ovality of steel pipe.

2. In order to ensure the straightness of the deviation when steel pipe assembling, following measures can be taken.

(1) Improving groove design, adopting asymmetric X groove, leaving no space, cleaning with carbon arc air gouging after the inseam welding, making inside and outside of the weld actual area is almost close to equal, these measures are helpful to reduce the deformation and the residual stress.

(2) Improving welding technology taking small-area welding, especially the first layer of the welding, increasing welding level, to reduce deformation and decrease steel pipe dimension deviation.

(3) Straight tube butt: on the seam welding machine, at first, to adjust clearance, wrong tooth and check dimension as a whole, the, if qualified, to weld as a whole.

(4) Bent pipe assembly: pipe bending is a special socket, the overshoot of dimension error will bring certain difficulties to installment and therefore it requires the whole assembly.