问 :无损检测 级培训教材《磁粉探伤》中关于形状不规则工件当量直径计算给出了以下两个公式D1=2 Sπ (1 )D2 =Lπ (2 )式中　S——不规则工件的截面积 ,mm2L——不规则工件的周长 ,mm教材中列举的正方形工件当量直径的计算同时采用了以上两种方法 ,那么两种计算法是否都合适 Q: The non-destructive test-grade training textbook “Magnetic Particle Inspection” on the irregular shape of the workpiece equivalent diameter calculation gives the following two formulas D1 = 2 Sπ (1) D2 = Lπ (2) where S - irregular workpiece cut Area, mm2L - perimeter of irregular workpieces, mm teaching materials listed in the square equivalent diameter of the workpiece while using the above two methods, then whether the two methods are suitable