直縫焊管擴徑是一種利用液壓或機械方式從焊管（guǎn）內壁加力使焊管沿著徑向向外擴脹成型的壓（yā）力加工工藝。機械方式比液（yè）壓（yā）方式，設備簡單且效率（lǜ）更高，在世界上最先進的幾條大口（kǒu）徑直縫焊管製管線擴徑工序都被采用，其工藝為： 機械擴（kuò）徑利用擴徑機端部的分瓣（bàn）的扇（shàn）形塊沿徑向擴張，使管坯沿長度方向以步進方式，分段實現全管長塑性（xìng）變形的過程。分（fèn）為5個（gè）階段。
Diameter enlargement of straight seam welded pipe is a kind of pressure processing technology, which uses hydraulic or mechanical method to force the welded pipe from the inner wall to make the welded pipe expand radially outward. The mechanical method is simpler and more efficient than the hydraulic method. In the world, the most advanced expanding process of large diameter straight seam welded pipe line is adopted. The process is that the mechanical expanding expands along the radial direction by using the sector block at the end of the expander, so that the billet can realize the plastic deformation of the whole length of the pipe in a step-by-step manner. It is divided into five stages. 1、初步整圓階段。扇（shàn）形塊打（dǎ）開直到所有扇形塊都接觸到焊管（guǎn）內（nèi）壁，此時步長範圍內焊管內圓管中各點半徑大小都幾乎一（yī）致，焊管得到初步整圓。
1. Preliminary rounding stage. The sector block opens until all the sector blocks touch the inner wall of the welded pipe. At this time, the radius of each point in the welded pipe is almost the same within the step size range, and the welded pipe is initially rounded.
2、名義內徑階段。扇形塊從前段位置開始降低運動速度，直到抵達要求位置，這（zhè）個（gè）位置是質量要求的成品管內圓周位置。
2. Nominal inner diameter stage. The fan-shaped block reduces its motion speed from the front position until it reaches the required position, which is the circumferential position of the finished pipe required by the quality.
3、彈複補償階段。扇形塊在2階段的位置（zhì）開始進一步（bù）將低速度，直到抵達要求位置，這個位置是工藝設計要求的彈複前焊管內（nèi）圓周位置。
3. Rebound compensation stage. The sector block will start at a lower speed at the position of phase 2 until it reaches the required position, which is the circumferential position of the pre-spring welded pipe required by the process design.
4、保壓穩定階段（duàn）。扇形塊在彈複前焊管內圓（yuán）周位置一段時間保持不動，這是設備和擴徑工藝要求的保壓穩定階段。
4. Pressure-holding and stabilization stage. The sector block remains stationary for a period of time in the circumference of the welded pipe before resilience, which is the pressure-holding and stabilizing stage required by the equipment and the expanding process.
5、卸荷（hé）回（huí）歸階段。扇形塊（kuài）從彈複前焊管內圓周位置開始迅速回縮（suō），直到抵達初始擴徑的位（wèi）置，這是擴徑工藝要求的扇形塊最小收（shōu）縮直徑。 在（zài）實際（jì）應用中，工藝簡化中，2、3步驟可（kě）以合並簡化，這對焊管的擴徑質（zhì）量沒有（yǒu）影響。
5. Return stage of unloading. The sector block shrinks rapidly from the circumferential position of the welded pipe before resilience until it reaches the initial enlargement position, which is the minimum shrinkage diameter of the sector block required by the enlargement process. In practical application, 2 and 3 steps can be combined and simplified in the process simplification, which has no effect on the quality of welded pipe diameter enlargement.
