超高压压裂泵自增强残余应力变化规律研究

Fracturing pump plays a significant role in the exploitation of petroleum,natural gas and unconventional petroleum.And vessels that has a similar structure with pump heads are widely applied in many domains. As an effective way to solve the problems such as the stress concentration, fatigue cracking and short life of ultra-high fracturing pump head,the change rule of the remaining stress of the autofrettage technology is still uncertain.The fracturing pump head has many negative features that it has a complex inner structure,bears a high pressure and has a localized stress concentration.Besides,it is likely to occur fatigue cracking,has a short fatigue life and is hard to be tested.Therefore,this program studies the change rules of the autofrettage remaining stress of the pumping head's inner space under complex stress by the means of theoretical analysis combined with the experimental verification. It studies these from three aspects,namely,the building of the precise model of the elastoplastic damage constitutive relationship of the material,the relaxation rules of the autofrettage remaining stress and the best superstrain degree with the influence of relaxed stress. Through the study,the basic system of the autofrettage theory is formed,which provides the precise technological parameter to the autofrettage technology of the ultra-high fracturing pump and makes the evaluation of the fatigue life of the pumping head after autofrettage more accurate.Though focused on the ultra-high fracturing pump head, the research can be widely used in some other domains like petroleum,chemistry,ships and nuke industry.

压裂泵在石油、天然气和非常规油气开发中有着重要的作用,与泵头体结构类似的超高压容器在很多领域被广泛应用。自增强技术作为解决超高压泵头体应力集中、疲劳开裂、寿命短等问题的有效手段，其残余应力的变化规律尚无定论。本项目针对压裂泵泵头体内腔结构复杂、承受超高压（140MPa）脉动循环内压、局部应力集中并容易出现疲劳裂纹、疲劳寿命低、实验测试难度大等特点，从材料弹塑性本构关系的精确模型建立、自增强残余应力松弛规律、考虑应力松弛影响的最佳超应变度三个方面入手，采用理论分析和实验验证相结合的方法，研究泵头体复杂应力内腔自增强的残余应力变化规律。通过本研究将形成压裂泵泵头体自增强理论方法基础体系，为超高压压裂泵的自增强工艺提供精确的工艺参数，使泵头体自增强后的疲劳寿命估计更加准确。本研究虽然以超高压泵头体为具体研究对象，但其研究成果将在石油、化工、船舶、核工业等领域有着广泛的应用前景。

非常规油气资源开发对压裂机组提出了超高压、大排量和长寿命的更高性能要求。泵头体内腔结构复杂，在脉动循环的超高内压作用下疲劳寿命低，容易导致疲劳开裂。对泵头体实施自增强处理，能够使泵头体内腔产生有利的残余应力，从而使泵头体的承压能力和疲劳寿命都得到大幅度提高。研究泵头体复杂应力内腔自增强残余应力变化规律，是泵头体自增强技术发展和应用的基础课题。基于此，根据泵头体材料力学特性，建立了泵头体材料混合硬化弹塑性本构关系模型。通过开发和运用混合硬化弹塑性本构UMAT，并通过拉伸试验模拟对比，验证了其计算精度；将混合硬化UMAT，应用于3000型超高压三缸压裂泵的泵头体自增强弹塑性有限元分析，获得内腔应力应变分布情况；通过内壁含缺口厚壁圆环和单腔十字交叉孔内腔缩小模型，研究了泵头体自增强残余应力松弛规律；通过泵头体工程应用失效分析和极限工况应力分析，确定泵头体的失效模式属于多轴应力下的高周疲劳。考虑泵头体多轴疲劳临界面和残余应力对疲劳寿命的影响，提出一种以应力集中点多轴疲劳寿命最长为标准的最佳自增强压力确定方法；通过试验测试获得泵头体材料P-S-N曲线，并对自增强泵头体进行了疲劳寿命数值分析。然后对泵头体单腔缩小模型实施液压加压疲劳试验；提出了软硬密封相结合的自紧密封方案，得到了最佳密封结构参数，并用实验验证了密封结构的可靠性。相关研究显示：本项目开发的混合硬化UMAT能很好地模拟出材料的应变硬化和包辛格效应，计算精度高，适合用于泵头体自增强残余应力场的精确分析；在循环载荷作用下，自增强残余应力值最初松弛较快；松弛度达到70%时，残余应力松弛开始变得比较缓慢；自增强处理后泵头体疲劳寿命，可提高到原来的2.6-3.1倍左右；软硬密封相结合的自紧密封方式，可以使泵头体自增强加压达到454MPa以上。研究成果为超高压压裂装备中的泵头体自增强处理工艺参数与过程的选取、自增强疲劳寿命预测和超高压自增强加压设备及密封装置研究提供了科学依据和技术指导。