厚壁焊接油井管精密电磁加热隐性缺陷机制及预控

Oil well pipe is the basis for the oil industry, seamless oil well pipe replaced by welded pipe has become the main trend of the world. Deep sea and other harsh environment oil and gas fields for wall thickness and quality performance requirements of oil well pipe are particularly harsh. However, with the oil pipe wall thickness gauge increases, the skin, near and ring effect of electromagnetic heating lead to the phenomenon of weld temperature uneven, macro and micro quality defects resulting in a serious impact on thick welded oil pipe security service. To reveal the microstructure, mechanical properties and residual stress distribution and evolution mechanism of the hidden defects in complex electromagnetic environment of the thick-walled pipe, the project by establishing the whole process of thick-walled pipe welding and heat treatment induction heating magnetic - temperature - microstructure coupled model, precision forecast to achieve the temperature and microstructure field of high-frequency heating cold welding area, burned area, medium frequency heating blind area, repeat area and over heated area, and the introduction of the defect area ratio as a pipe hidden defects quantified evaluation, reveal the influence and mechanism of induction heating welding power、speed and many other parameters and on recessive defects. Not only provide new ideas for quantitative characterization of various types of hidden defect characteristics, differences and mechanisms, but aslo create favorable conditions for the exploration of electromagnetic heating temperature uneven common problems and promote some new discoveries.

油井管是石油工业的基础，焊接油井管替代无缝管已成为世界范围主流趋势，深海等环境恶劣油气田对油井管壁厚规格及质量性能要求尤为苛刻。然而，随着油井管壁厚规格增大，电磁加热集肤、临近和圆环效应导致的焊缝温度不均现象加剧，由此引起的宏微观质量缺陷严重影响了厚壁焊接油井管服役安全。为揭示复杂电磁环境下厚壁焊管焊缝内部微观组织、残余应力及机械性能分布等隐性缺陷产生机理和演化规律，本课题通过建立厚壁焊管焊接和热处理电磁感应加热全过程电-磁-热-组织多场耦合模型，实现高频加热冷焊区、过烧区，中频加热盲区、重复区、过度区内温度场和微观组织的高精度预测，并引入缺陷面积率作为焊管隐性缺陷的量化评价指标，揭示感应加热焊接功率、速度等诸多工艺参数对隐性缺陷的影响规律和作用机理。不仅为量化表征焊管各类隐性缺陷特性、差异和作用机制提供新思路，同时为探索电磁加热温度不均的共性问题和促进一些新的发现创造有力条件。

油井管的质量和性能直接决定了油井的寿命。经过近几十年的发展，我国钢管工业取得了举世瞩目的成就，油井管生产企业有300 多家，年产能达800 万t 以上，但高端产品仍需部分进口，且进口价是出口价的2.6倍，悬殊的价格差也反映出我国产品档次与国外先进水平的巨大差距。本项目建立了焊管焊接过程和热处理过程缺陷面积率的高精度电-磁-热-组织多场耦合模型，对焊接热源和中频热处理热源进行研究，以深入分析隐性缺陷产生机制，从而提高高频焊管的质量。针对管坯焊接过程中运动场、电磁场和温度场的三维耦合仿真计算问题，提出了“节点载荷移动”法，用来等效实际焊接过程中管坯的运动，实现了高频接触焊管电磁加热过程的动态仿真。首次发现了焊管中频加热的“双椭球”结构的热源形貌。发现：1）磁感应强度和感应电流密度在钢管内部沿轴向方向的不对称分布，引发了热源的特殊分布形态，是导致温度场呈“双椭球”状态的根源；2）由于焊缝外、内表面两种不同的热量来源，以及感应线圈和焊管之间的相对运动，导致焊缝内表面最高温度滞后于外表面。由于这种滞后性的存在，势必会在壁厚方向上形成独特的温度场形态，这是引起“双椭球”温度场的直接原因。本项目为后续相关学者进行高频焊管温度场的优化设计，消除残余应力和优化组织结构奠定了基础，同时也为探索电磁加热隐形缺陷产生的根源和演化规律提供了量化参考依据和分析方法。