Paper Title
Experimental Study on Tube end Flaring Process for Different Bottom end Surface Textures

In tube end flaring processes, a circular tube of certain length is axially pushed over a conical die to form a flared end. End flaring ratio is calculated from the percentage of increase in elongation of the circumferential bottom end before and after the process. High flaring limit is demanded in various industrial applications. In this study, API 5L seamless pipes with an outer diameter (OD) 33.7 mm and a wall thickness, t = 3.38 mm were tested in the experiment. Specimens measuring a length, l = 90 mm were cut from the long pipes by sawing, turning and abrasive cutting, respectively. The bottom ends of the specimens were prepared for four conditions i.e. as-cut, de-burred, filed and chamfered at external or internal edge, respectively. In the experiment, the specimen is compressed until the bottom end cracks. The circumferential length of the cracked bottom end is measured along the external edge and the percentage of increase is calculated. The results showed that the total elongation for the band sawed specimen with a de-burred edge was the lowest i.e. 37.3%. However, the abrasive cut specimen with a filed edge has recorded the highest total elongation of 54.7%, or 17.4% higher than the lowest one. De-burring the bottom ends of band sawed and lathed specimens with a wire brush lowered the total elongation values. The total elongation for both specimens increases when the external edges are filed in circumferential direction. The micro cracks perpendicular to the external edge of bottom end resulting from the cutting are removed by filing. Since the external edge is subject to the highest tensile stress concentration in circumferential direction during the flaring process, removing the cracks increases the total elongation. In addition, filing also produces line texture parallel to the external end in the bottom end surface. The line texture is favorable for stretching along circumferential direction. Therefore, the total elongation values for the band sawed and the lathed specimens having de-burred edges were significantly increased from 37.3% and 39.9% to 47.9% and 52.8%, respectively with filing along the external edges. Keywords - End Flaring, Tube Forming, Total Elongation, API Pipe, Drift-Expanding Test