Technical field This invention refers to a pipe threaded joint, pipe used in oil and gas extractive industry.

Background Art There are known several pipe threaded joints, used especially in oil industry, by which fitting between an outside tapered threaded pin and an inside tapered threaded coupling is to be made, the pin and the coupling being fitted with some taper surfaces which effects the packing between inside and outside of the pipe by their contact, as well as some taper surfaces as screwing up blocking shoulders.

The disadvantage of these joints consist in under 100% tensile efficiency in regard to pipe body resistance, diminishing of the sealing capacity under tensile axial load, and, in case of using these pipes in acid environment, there is a danger of disposal of metallic sealing between pin and coupling.

bisclosure of invention Pipe threaded joint, according to the invention, dispose of the disadvantages shown above, by achievement of the contact between pin and coupling on the bottom diameter of the pin thread and the peak diameter of the coupling thread, on the whole length of the thread having asymmetric trapezoidal shape, between pin thread peak diameter and coupling thread bottom diameter being achieved a clearance which is, before mechanical make-up, at least equal to total radial load, which actuate contact pressure between sealing tapered surfaces adjacent to threaded areas ; Follow-up the sealing surfaces adjacent to threaded areas, pin and coupling are provided with other taper surfaces, angle between these surfaces and threaded areas adjacent to the sealing surfaces being less than 90°, preferably between 75° and 85°.

Brief description of drawings Hereinafter are shown two examples for accomplishment of the invention, apropos of figures no. 1,2 and 3 : - Fig. 1, longitudinal section through threaded joint between a pin and a coupling.

- Fig. 2, close-up A of the thread according to Fig. 1.

- Fig. 3, close-up of the sealing provided with non-metallic insertion.

Best mode for Carying Out Pipe threaded joint, according to the first example, consist of a pipe end (1), hereinafter called pin (2), provided with some outside threaded taper surfaces, thread having an asymmetric trapezoidal shape,

and a coupling (3), provided with some inside threaded taper surfaces, contact between threaded taper surfaces of the pin (2) and threaded taper surfaces of the coupling (3) being achieved between some pin (2) thread bottom diameters (a) and some coupling (3) thread peak diameters (b), on the whole length of the thread, between some pin (2) thread peak diameters (c) and some coupling (3) thread bottom diameters (d) being achieved a clearance which is, before mechanical make-up, at least equal to total radial load which actuate contact pressure between pin sealing (e) tapered surface and coupling sealing (f) tapered surface. To eliminate the posibility of damaging the thread by crushing or shearing on axial stress up to the pipe material yield point, the thread has the trapezoidal shape asymmetric with the angle of bearing side (9), measured beside a plane normal to thread axis, at least equal to angle of the thread generatrix beside the pipe axis, but not greater than peak angle of the thread cone, and the difference between peak course of thread and base course of thread, related to 1 mm thread depth, is between 0.2 and 0.3 mm. On these circumstances, between some pin thread bottoms (a) and some coupling thread peaks (b), breeds a binding pressure, which leads to discharging the effect of pin working inside pressure, which is less durable than the coupling, on terms of using in the field some standard pipe specifications, cross area of the pipe becoming critical section of the joint on axial stress.

By axial displacement of the pin into the coupling on make-up, it arises a force between pin sealing (e) tapered surface, adjacent to the thread, and coupling sealing (f) tapered surface, which actuate compression stress into the pin, respective tensile stress into the

coupling, which leads to surface pressures onto contact surfaces and to achieve the sealing, axial displacement continuing until some pin peak displaced taper surfaces (h) follow-up sealing surfaces (f) and having with these an angle less than 90°, preffered values being between 75° and 85°, come into contact with some coupling taper surfaces (i), between these surfaces arising a force which actuate tensions into the pin, respective into the coupling, which on the one hand leads to arising surface pressures onto contact surfaces and to achieve the second sealing and on the other hand contribute to enhancement of pin peak rigidity, so increasing sealing capacity of the joint, without a proportional increase of the pre-load by forced screwing-up.

There is a clearance between pin thread passive side (j) and coupling thread passive side (k). When some compression stresses-which are frequent in service-occur, this clearance is annihilate, emerging the risk of strengthening abatement and disengaging from joint. Surfaces (h) and (i) are so placed that compression stress is absorbed by these, without applying stresses to the fillets of screw.

To assure some uniform contact pressures onto the pin circumference, the ratio between the maximum wall thickness and the minimum wall thickness of the pin peak, under sealing surfaces (e), has values between 0.80 and 0.85.

In the other design version of joint, according to the invention, coupling (3) threads end with a channel (l) performed between threaded area and sealing taper surface; there is a non-metallic insertion (4) placed into this channel, which is chemically resistent to oil products and usual temperatures in wells. Positioning of the channel is so made that, when

screwing up ends, the insert is depressed between the pin and the coupling, achieving an additional sealing for protection of the metallic sealing of the joint.