截面畸变对小半径热煨弯管性能的影响

小半径热煨弯管在生产过程中会出现截面趋于椭圆、壁厚减薄或增厚等各种截面畸变,上述缺陷有可能会降低管道的承载能力。为了研究截面畸变对小半径热煨弯管性能的影响,以不同组合工艺参数煨制小半径热煨3D(D表示管道直径)弯管,通过截面几何尺寸分析、畸变分析、理化性能试验、微观组织分析等方法综合分析了3D弯管和常规5D弯管截面畸变、组织性能情况及其关联性。研究结果表明:(1)3D弯管增厚率和减薄率约是5D弯管的2倍,3D弯管圆度是5D弯管的2~4倍;(2)3D弯管截面畸变显著,各部位加热温度差异较大,使得组织形态或含量有所不同,导致3D弯管外弧侧、内弧侧及中性区等各部位力学性能数值分布较为离散;(3)多数弯管内弧侧强度都达不到标准的要求,强度大小顺序分别为弯管外弧侧、弯管中性区和弯管内弧侧,夏比冲击韧性大小顺序与强度恰好相反;(4)随着圆度的增加,内、外弧侧强度呈下降趋势,随着增厚率的增加,内弧侧强度呈下降趋势,随着减薄率的增加,外弧侧强度呈上升趋势。

Effect of cross-section distortion on the performance of small-radius hot-bending bends

While a small radius hot-bending bend is manufactured, various cross-section distortions may occur, such as out of roundness of cross section, and wall thickness reduction or increase. And these defects may deteriorate the bearing capacity of pipelines. In order to study the effect of cross-section distortion on the performance of small radius hot-bending bends, 3D (D refers to pipe diameter) hot-bending bends were manufactured based on different combinations of process parameters. Then, the cross-section distortion, structure properties and their correlation of 3D bends and conventional 5D bends were analyzed comprehensively by means of cross-section geometry analysis, distortion analysis, physical and chemical property test, micro-structural analysis and so on. And the following research results were obtained. First, the wall thickening/thinning rate of 3D bends is about 2 times that of 5D bends, and the roundness of 3D bends is about 2–4 times that of 5D bends. Second, the cross-section distortion of 3D bends is obvious, so its heating temperature varies greatly in different parts, leading to different structure morphologies and contents. As a result, the numerical distribution of mechanical properties of each part of 3D bends (e.g. intrados, extrados and neutral zone) is discrete. Third, the strength at the intrados of most bends doesn't meet the standard, and it is sorted form the higher to the lower as extrados, neutral zone and intrados while the sequence of Charpy impact toughness is right contrary to the strength. Fourth, the strength at intrados and extrados decreases with the increase of roundness. The strength at intrados decreases with the increase of thickening rates. And the strength at extrados increases with the increase of thinning rates.