高钢级套管韧性指标适用性计算方法研究(下)

Research on Calculation Method for Toughness Target Suitability of High Steel Grade Oil Casing(PartⅡ)

利用CEGB-R6安全评价方法,基于材料真应力-应变行为建立了高钢级套管失效评估曲线,对高钢级套管材料的断裂韧性KI与常温冲击功AKV的关系进行了统计研究,根据失效评估技术获得了含缺陷套管韧性指标的适用性计算方法。通过人工预制裂纹、有限元数值模拟和内压爆破全尺寸实验,对韧性指标计算方法进行了有效验证。将所得的计算结果与API Spec 5CT标准规定的韧性指标进行分类对比,指出API标准的韧性计算方法是以防止脆性启裂为设计依据的,由于仅考虑了屈服强度和套管壁厚,而对套管外径、服役中产生的缺陷几何形貌等因素缺乏考虑,因此在实际服役中存在较大的安全隐患。

Based on the true stress-strain behavior of the material and with the CEGB-R6 safety assessment method, the failure assessment characteristic of the high steel grade oil casing is created with which the fracture toughness K1 vs the ambient temperature impact value Akv relationship is studied in an statistical way. And the calculation method for toughness target suitability of defective oil casing is obtained with the failure assessment technique. The calculation method is verified by using such processes as artificial crack, FE numerical simulation and internal-pressure explosion full dimensional experiment. The calculation result is categorically compared with the toughness values as specified in API Spec 5CT. Accordingly, the conclusion is made that the API-specified toughness calculation method is based on the design purpose of preventing occurrence of brittle crack, and only the yield strength and the casing wall thickness are taken into account, while factors concerning the casing such O.D. and the defective geometry as developed during the service are out of the consideration, and thus some considerable potential hazard would exist during actual service of the casing.