API螺纹紧密距测量和中径测量的比较

Comparison between API Thread Stand-off Measurement and Middle Diameter Measurement

API螺纹的紧密距和中径是两个重要的参数,这两个参数的公差互相影响、互相制约,目前传统的方法是将紧密距作为主要控制指标,对中径则不进行直接测量。分析了中径、锥度、椭圆度与紧密距之间的关系,指出采用紧密距控制不能完全反映螺纹的真实状况,不利于对螺纹质量的控制,并通过试验验证了这一结论。简要分析了中径测量的可行性,建议油套管生产厂和油田用户以检测螺纹中径代替紧密距。

Being two critical parameters of API thread, the stand-off and the middle diameter have their tolerances interact and condition each other. Following the conventional measurement method, the stand-off is taken as the main controlled index, whereas no direct measurement is made to the middle diameter. Analyzed here in the article are the relationship between stand-off and such elements as middle diameter, taper and ovality. It is concluded that the actual state of the threads can not be fully identified by means of control of the stand-off, which is no good for control of the thread quality. This theory is also verified by relevant testing activities. In addition, the feasibility of measuring the middle diameter is studied, which leads to a proposal that oil casing makers and oil field end-users substitute middle diameter measurement for stand-off measurement.