Threaded joint for an oil-well tubing

Abstract

The engineering problem of the claimed invention consists in the increase of operating reliability of the threaded joint, whose coupling has the coating applied by the diffusion galvanizing method, by way of ensuring a proper standard tightness. The technical result of the increase of the inlet cylindrical counterbore length in the internally threaded element by the value of the thread tightness increment caused by galvanizing and determined from the claimed empirical formula consists in increased reliability of the joint under service conditions as the probability of overtightening the joint for the sake of attaining the nominal tightness, as well as damage to the end thread turns projected from the coupling on service are ruled out. This result is attained without consumption of time and funds for re-training of the personnel, publication and delivery of new normative materials to each drilling site, manufacture of new calibrating tools and repair mountings. In its turn, this makes it possible to immediately begin supplying the suggested joints and increase the service life of standard threaded joints of oil-well tubings from 6÷8 to at least 50 screwing/unscrewing cycles. Besides, in case of forced screwing with a standard torque the joint reliability also increases because the threaded part of the externally threaded element is nearly completely hidden inside the counterbore due to the increased counterbore length and thus protected against the mechanical effect of the well medium.

1 . A threaded joint for an oil-well tubing comprising:
 a threaded element with external tapered triangular threading; and   a threaded element with internal threading including:
 a cylindrical recess inlet, and 
 a threaded portion, 
 wherein the threaded portion has at least a coating applied by a thermal diffusion powder galvanizing method, 
 wherein the length of the cylindrical recess inlet is increased by an increment value of tightness caused by the coating, and 
 wherein the increment value ΔA is calculated in accordance with the following formula:
   Δ A=kδ   min   ÷kδ   max , 
 
 wherein k is an empirical coefficient equal to 70, and 
 δ min  and δ max  are minimum and maximum coating thicknesses, respectively. 
   
   
   
       2 . A threaded joint for an oil-well tubing comprising:
 a threaded element with external tapered trapezoid threading; and   a threaded element with internal threading including:
 a cylindrical recess inlet, and 
 a threaded portion, 
 wherein the threaded portion has at least a coating applied by a thermal diffusion powder galvanizing method, 
 wherein the length of the cylindrical recess inlet is increased by an increment value of tightness caused by the coating, and 
 wherein the increment value ΔA is calculated in accordance with the following formula:
   ΔA=kδ min ÷kδ max , 
 
 wherein k is an empirical coefficient equal to 30, and 
 δ min  and δ max  are minimum and maximum coating thicknesses, respectively.