The full-scale evaluation test of a set of high strength premium connection casing specimens was conducted.The purpose of these tests was to evaluate the performance of the new products.During tension increasing to failure test,the abnormal spiral fracture occurred on each specimen.A series of testing and analysis including fracture macroscopic observation, chemical composition analysis, mechanical properties testing, metallographic analysis and SEM analysis were made on one specimen which had abnormal spiral fracture; and geometry measurement, visual examination, mechanical properties testing and metallographic analysis were made on a new specimen which came from the same lot with the former.The mechanical properties results of the two specimens both in compliance with the specified material specification.The new specimen has lower external diameter ovality and higher wall thickness eccentricity.The smaller wall thickness are distributed in a spiral shape same as the abnormal fracture.The fracture originated in the middle of casing wall,and the fracture position had obvious necking.According to fractography and fracture mechanics analysis,the abnormal spiral fracture imputed to metallurgical and geometry defect grown out of casing machining process.