下接头 meaning in English

lower adaptor
lower contact
lower sub

If it is necessary to have the joints under water, they must be bedded into a box or sleeve which absolutely prevents water from penetrating in .
如果有必要在水下接头，就必须把它们安置于绝对不渗水的密封盒子或套管中。
Thereby , this paper has carried through an in - depth study on wear mechanism between tool joint of drill pipe and casing , problems caused by wear and measures to deal with wear based on researches at home and abroad . the research contents include : in order to reveal mechanism of wear occurred between tool joint and casing , distribution of the contact pressure between the tool joint and casing for different loads was obtained with finite element method . furthermore , the mathematical model of maximum contact pressure and the wear depth on casing was established
所以，本文在国内外研究的基础上，对钻杆与套管摩擦磨损的机理、引发的系列问题及其预防措施进行了深入研究，研究内容主要包括：为探讨钻杆接头与套管摩擦磨损的机理，采用有限元法研究了不同载荷下接头与套管之间接触压力的分布规律，并建立了最大接触压力与磨损量的数学模型。