压力容器内壁长期承受高温、高压、腐蚀性介质的作用,易产生裂纹、气孔、腐蚀等缺陷,因此需要对其内壁缺陷开展无损检测与评估。采用磁探针方法,在外加励磁场的作用下,对含有不同尺寸背部缺陷的结构钢试样进行检测,分析检测线上不同区域的磁滞回线,初步提取剩磁B_r和矫顽力H_c来反映缺陷大小。结果表明,缺陷附近的信号会产生明显的波谷特征,并且波谷宽度随着缺陷尺寸的增加而增加。为了进一步准确检测结构钢背部缺陷,笔者提出面积比S_r这一特征值,并与背部缺陷尺寸大小建立了较好的线性关系。该研究结果可以为磁探针法检测压力容器内部缺陷提供指导。

The inner wall of pressure vessels are often subjected to the impact of high temperature, high pressure and corrosive media, which leads to the crack, pores, corrosion and other defects on the inner walls. Therefore, it is necessary to carry out the nondestructive testing and evaluation on the defects at the inner walls of pressure vessels. In this paper, the magnetic needle probe method is used to detect the defects at the back of structural steel samples with different defect sizes under the effect of excitation magnetic field. The hysteresis loops at the testing lines are analyzed, and the remanence B_r and coercivity H_c are extracted preliminarily to reflect the size of defects. It can be found that the magnetic signals near the defects show the obvious valley characteristic, and the width of valley increases with the increase in size of defects. In order to further evaluate the defects at the back of structural steel accurately, the area ratio S_r is proposed as a new characteristic value, and a linear relationship between area ratio S_r and size of defects at the back of structural steel is established. The research results can provide a guidance for the evaluation on the internal defects of pressure vessels by the magnetic needle probe method.