GB2116276A

GB2116276A - Pipe joint

Info

Publication number: GB2116276A
Application number: GB08304374A
Authority: GB
Inventors: Bernard Plaquin
Original assignee: Vallourec SA
Current assignee: Vallourec SA
Priority date: 1982-02-18
Filing date: 1983-02-17
Publication date: 1983-09-21
Also published as: ATE21542T1; JPS58152994A; IN159012B; CS107983A2; MX156310A; CS258111B2; EP0089253B1; MY8700267A; NO162167C; AU1160683A; GEP19970670B; DE3365380D1; CA1214481A; BR8300752A; GB2116276B; AU560228B2; DK69383A; SU1602403A3; NO162167B; ES278066Y

Abstract

The invention relates to a joint for steel pipe, which is oil-tight at high pressure, being of the type including at least one pair of slightly conical sealing surfaces arranged at at least one end of the male member or of the female member, and is insensitive to seizure. This joint is characterized by the fact that the first contact 5 of the sealing zone lying at the end of one member occurs against the corresponding sealing surface of the other member and that at the time of this first contact the taper of the sealing surface which is situated at the end of one of the members of the joint is less than the taper of the corresponding sealing surface which is situated on the other member of the joint, the sealing surfaces at the time of tightening the joint, becoming applied against one another with a contact pressure sufficient to ensure oiltightness. <IMAGE>

Description

1 GB 2 116 276 A 1

SPECIFICATION

New joint for steel pipe which is oil tight at high pressure and insensitive to the phenomena of seizure The present invention relates to a new joint for steel pipes and in particular for pipes intended for the oil industry. The invention refers more especially to joints in which oiltightness is ensured by pairs of sealing surfaces of slightly conical shape which come into contact with one another upon tightening up the joint.

In this known type of joint there is employed on the male member a sealing surface the diameter of which is slightly greater than the corresponding diameter of the sealing surface on the female member, so that at the time of tightening up the joint high contact pressures are exerted between the two sealing surfaces, these being pressures which must be sufficient to ensure oiltightness under the highest pressure which the assembly of pipes must withstand.

Known joints of this type may include only one pair of sealing surfaces, situated either at the end of the male member or at the end of the female member. They may equally well include two pairs of sealing surfaces arranged on opposite sides of the threads which are respectively on the end of the male member and on the end of the female member.

Furthermore the conditions of exploitation of oil fields are at present such that one is led to collect the petroleum at greater and greater depths, which makes it essential to achieve joints which remain oiltight at working pressures which may exceed 1,000 kg/CM2.

Again it may likewise happen that one is led to exploit oil fields at great depth, which contain high contents of corrosive agents such as sulphuretted hydrogen or carbon dioxide, and that one is obliged to employ stainless steels containing chromium, nickel as well as other additive elements. These two requirements which are met more and more often simultaneously cause the joints which are known at present, not to give satisfaction. That is, the stainless steels the employment of which is necessary in order to be able to withstand corrosive agents have a natural tendency to seizure which becomes considerably increased by the necessity of employing high contact pressures at the level of the metal sealing 115 surfaces.

This is the reason why the only joints known today which enable this problem to be solved, include very steeply inclinedsealing surfaces (of the order of 309 with respect to the axis of the pipe, a stop for restricting screwing up immediately becoming opposed to further screwing as soon as contact has been obtained at the level of the sealing surfaces. It will be understood that this type of joint is difficult to put 125 into use and to machine, because the stop for restricting screwing up must be positioned extremely precisely with respect to the steeply conical sealing surfaces.

The present invention relates to a metal-to metal oiltight joint which includes slightly conical sealing surfaces and which is oiltight at high pressures without there being any risk of giving rise to seizure phenomena even when these joints are produced from steel or from steel which is stainless or heavily loaded with chromium. with nickel and with other additive elements.

The object of the present invention is a joint for steel pipe, which is oiltight at high pressure, beim, ' of the type including at least one pair of slightly conical sealing surfaces arranged at at least one end of the male member or of the female member, characterized by the fact that the first contact of the sealing zone lying at the end of one member occurs against the corresponding sealing surface of the other member and that at the time of this first contact the taper of the sealing surface which is situated at the end of one of the members of the joint is less than the taper of the corresponding sealing surface which is situated on the other member of the joint, the sealing surfaces at the time of tightening the joint, becoming applied against one another with a contact pressure sufficient to ensure oil- tightness.

Tests which have been made by the Applicant Company have revealed that for a reason which it has not been possible to determine with certainty, the joints which exhibit the characteristics which have just been defined above, may be screwed up to apply the sealing surfaces against one another with very high pressures without harmful seizure occurring and with satisfactory oiltightness and with preservation of the good quality of these surfaces, this being even when the members of the joint are produced from steel or alloy heavily loaded with chromium, nickel and other additive elements and consequently have a particular propensity to seizure.

In accordance with the invention the inclinations of the generatrices of a pair of conical sealing surfaces must at the time of first contact have a difference which corresponds with an angular slope of about 0.5 to 2% and preferably lying between about 0.75 and 1 %, which corresponds with an angular difference lying between about 3/10 and 11 /10 degrees and preferably lying between 4/10 and 6/10 degrees.

In accordance with the invention the angular difference between the generatrices of the two sealing surfaces is the greater, the lower the ratio of thickness to diameter of the pipes.

In accordance with the invention the joint advantageously includes a stop for restricting screwing up so that excessive tightening does not engage the male member too deeply in the female member, so exceeding uselessly the necessary contact pressures between the sealing surfaces and risking impairing them.

The present invention may be employed on joints having taper threads or cylindrical threads. It may likewise be employed on joints which include only one pair of sealing surfaces or on those which include two pairs of sealing surfaces arranged one at the end of the male member and the other at the 2 GB 2 116 276 A 2 end of the female member on opposite sides of the threads.

With the aim of letting the invention be better understood, there will now be described by way of illustration and without any restrictive character, a number of embodiments given by way of example and represented in the drawing in which:

- Figure 1 is a diagrammatic section showing how the first contact of the sealing zone lying at the end of one of the members must occur against the conical sealing surface of the other member; - Figure 2 corresponds with Figure 1 but in the case-n which the first contact does not occur in accordance with the invention; - Figures 3 and 4 represent diagrammatically 80 the differences in diameter which the pairs of sealing surfaces must exhibit in order that the first contact shall occur in accordance with the invention; - Figures 5 and 6 represent diagrammatically a 85 joint in accordance with the invention in which the sealing surfaces are situated at the end of the female member; - Figures 7 and 8 represent diagrammatically a joint in accordance with the invention in which the sealing surfaces are situated at the end of the male member; -- 1-igures 9 and 10 represent diagrammatically a joint having a double cylindrical thread and in accordance with the invention, in which the sealing surfaces are situated at the end of the male member; - Figures 11 and 12 represent a joint in accordance with the invention equipped with a frustoconical thread and two pairs of sealing surfaces situated at the end of the female member, - Figures 13, 14 and 15 represent a joint in accordance with the invention equipped with a frustoconical thread and including a first pair of sealing surfaces at the end of the female member and a second pair of sealing surfaces in the vicinity of the end of the male member.

In Figure 1 there is shown diagrammatically 4 57 how the first contact must occur between two sealing surfaces of a joint in accordance with the invention.

In the embodiment shown in Figure 1 the sealing is effected at the end of the male member.

In this Figure are found the male member 1, the 115 female member 2, the frustoconical sealing surface 3 of the male member 1 and the frustoconical sealing surface 4 of the female member 2. In accordance with the invention the first contact between the sealing zone at the end of the male member and the sealing surface on the female member must take place on the frustoconical surface 4 of the female member 2 as is seen shown at 5 in Figure 1.

In Figure 2 is shown the way in which on the contrary the first contact occurs between the end of the male member and the female member in a manner which is not in accordance with the invention. In this case the joint of first contact 5 is of the female member but on the zone which connects this frustoconical surface with the thread.

In Figure 3 the portions are shown again which concern the sealing of the joint as Figure 1. The point 6 has likewise been plotted which is the end of the theoretical line of the generatrix of the conical surface 3 of the male member 1 as well as the point 7 which is the theoretical end of the generatrix of the frustum of the cone of the sealing surface 4 of the female member 2.

In order that the condition in accordance with the invention represented in Figure 1 shall be achieved it is sufficient that the diameter D 1 of the male member at the point 6 is slightly less than the diameter D2 of the female member at the point 7.

It will be understood that under these conditions the first contact of the male member occurs against the frustoconical sealing surface 4 of the female member.

In Figure 4 the case is shown in which the sealing in accordance with the invention occurs at the end of the female member 8, the male member being shown diagrammatically at 9.

The end point of the theoretical line of the generatrix of the frustoconical sealing surface 10 of the female member is shown at 12 whereas the corresponding point of the theoretical line of the gneratrix of the frustoconical surface 11 of the male member is shown at 13. In order that the condition in accordance with the invention shall be achieved it is sufficient that the diameter D'1 corresponding with the point 13 shall be slightly less than the diameter Y2 corresponding with the point 12.

It goes without saying that both in the case of Figure 3 and in that of Figure 4 the difference existing between the diameters D 1, D2 and D'l, D'2 must be sufficiently small to enable a force fit of the two sealing surfaces into one another in order to obtain the contact pressure necessary to the oiltightness which it is desired to impart to them.

In Figure 5 a joint in accordance with the invention is shown, in which the sealing surfaces are situated on the outside of the pipe at the end of the female member 8. The thread 14 is shown diagrammatically, which enables the assembly of the two tubular members, as well as the stop 15 created inside the female member, against which the end of the male member comes to bear in order to avoid excessive screwing up of the joint.

Figure 6 repeats on a larger scale the portion V1 from Figure 5. It represents the joint at the instant at which the end of the female member 8 comes into contact at 5 with the frustoconical sealing surface 11 of the male member 9 in accordance with one of the characteristics of the invention.

In Figure 6 there are shown at A1 and A2 the angles which the generatrices of the frustoconical sealing surfaces 11 of the male member 9 and 10 of the female member 8, make with respect to the axis of the pipe.

not situated on the frustoconical sealing surface 4 130 In accordance with the invention the slope A2 1 3 GB 2 116 276 A 3 of the sealing surface 10 which lies at the end of the female member 8 is less than the slope A1 of the sealing surface 11 on the male member 9 which is separated from the end of the male member by the whole length of the threads 14.

That is shown in Figure 6 by the fact that the angle A1 is greater than the angle A2, which at the time at which first contact occurs at 5, leaves between the two sealing surfaces 10 and 11 an angle 8 equaltoAl-A2.

It is clear that when screwing up is continued so that the end of the male member 9 comes into contact with the stop 15, this angular difference 8 tends progressively towards zero, the sealing surface 10 of the female member becoming 80 completely applied against the sealing surface 11 of the male member.

In Figure 7 an embodiment of the invention is shown in which the sealing occurs inside the joint at the end of the male member 1 which at the end of tightening up comes to bear against the stop 15 for restriction of screwing up, which is situated on the female member 2.

As may be seen in Figure 8 which represents on a larger scale the portion VIII from Figure 7, the first contact of the male member 1 occurs at 5 against the frustoconical sealing surface 4 of the female member 2.

As has been shown on the drawing and in accordance with the invention the angle A1 which 95 the generatrix of the sealing surface 3 which is at the end of the male member 1, makes with the axis of the pipe, is less than the angle A2 which the generatrix of the surface 4 of the female member, makes with the axis of the pipe, the 100 difference A2-AS 1 being represented by the angle 8.

In this case likewise, of course, when the joint has been tightened up and the end of the male member 1 has come to bear against the stop for restriction of screwing up 15, the surfaces 3 and 4 are applied against one another along their whole length with the contact pressure which is sufficient to ensure oiltightness even at high pressures.

In Figure 9 is shown, half in axial section, a joint in accordance with the invention in the state screwed home, which includes a cylindrical thread 14 having two stages, a stop for restriction of screwing up 15 arranged at the end of the male member 1 and a sealing zone arranged at the end of the male member and consisting of the sealing surface 3 on the male member 1 and the sealing surface 4 of the female member 2.

In Figure 10 on a larger scale the portions of 120 the male members 1 and 2 are shown, which surround the sealing zone.

As indicated in Figure 10 and in accordance with the invention the slope of the surface 3 of the male member is less than the slope of the surface 4 of the female member 2.

In the embodiment shown and with a pipe of which the outer diameter is 180 millimetres and the thickness 9 millimetres, produced from a steel having a chromium content higher than 20%, the slope of the sealing surface 3 on the male member, represented by the angle A 1 is equal to 4.25%, whereas the slope of the surface 4 of the female member represented by the angle A2 is equal to 5%, which in accordance with the invention corresponds before tightening up, to a difference of angular slope of 0.75%.

In Figure 11 a particular embodiment of the invention is shown, which includes a joint having a frustoconical thread with sealing surfaces arranged at the end of the female member, which likewise includes a stop 15 for restriction of screwing up, against which the end of the female member 8 comes to bear.

As may be seen in figure 12, the slope of the s;aling surface 10 on the female member 8, which is represented by the angle A2 is equal to 24%, whereas the slope of the sealing surface 11 on the male member 9 is represented by the angle Al which is equal to 25%.

In accordance with the invention the slope of the surface 10 which is at the end of the female member 8 is less by 1 % than the slope of the sealing surface 11 on the male member.

Finally in Figure 13 an embodiment is shown, of a joint in accordance with the invention which includes two sealing zones arranged respectively at the end of the male member 1 and at the end of the female member 2.

In Figures 14 and 15 these two sealing zones are shown on a larger scale.

In Figure 14 may be seen the slopes A' 1 and A12 of the sealing surfaces 11 and 10 and in Figure 15 the slopes A" 1 and A"2 of the sealing surfaces 3 and 4. In accoradnce with the invention A'1 corresponds with a slope of 25% (or 14 degrees), A'2 corresponds with a slope of 24% (or 13. 5 degrees) and A" 1 corresponds with a slope of 5.25% (or 3 degrees) and A112 corresponds with a slope of 6% (or 3.5 degrees).

It will be observed that the difference in angular slope is equal to 1 % in the case of Figure 14 and that in the case of Figure 15 it is equal to 0.75%.

In both cases in accordance with the invention it is the sealing surfaces which are situated at the end of a member 0 0 in Figure 14 and 3 in Figure 15) which have the smaller tapers.

It is quite clear that the embodiments which have been described above are indicated only by way of example and that they might be modified without thereby departing from the scope of the invention.

In particular the invention may be applied to any pipe and is not restricted to certain grades of steel.

Claims

1. A joint for pipes especially of steel or alloy, which is oiltight at high pressure, being of the type including at least one pair of slightly conical sealing surfaces arranged at at least one end of the male member or of the female member, in which pair the first contact of the sealing zone lying at the end of one member occurs against the corresponding sealing surface of the other 4 GB 2 116 276 A 4 member, in which at the time of this first contact the taper of the sealing surface which is situated at the end of one of the members of the joint is less than the taper of the corresponding sealing surface which is situated on the other member of the joint, the sealing surfaces at the time of tightening the joint, becoming applied as a whole against one another with a contact pressure sufficient to ensure oiltightness, the said joint l 0 being insensitive to seizure.

2. A joint as in Claim 1, in which at the time of first contact the generatrices of a pair of conical sealing surfaces have angular differences (B) which correspond with a slope of about 0.5 to 2% and preferably lying between 0.75 and 1 %.

3. A joint as in either of the Claims 1 and 2, which includes a stop for restricting screwing up, which restricts tightening of the joint as soon as the necessary pressures have been obtained between the various points on the sealing surfaces.

4. A joint as in any one of the preceding Claims, which has taper threads.

5. A joint as in any one of the Claims 1 to 3, which has cylindrical threads.

6. A joint as in one of the Claims 1 to 5, which includes two pairs of sealing surfaces arranged one at the end of the male member and the other at the end of the female member on opposite sides of the threads.

7. A joint as in any one of the preceding Claims, in which the angular difference between the generatrices of the two sealing surfaces is the greater, the lower the ratio of thickness to diameter of the pipes.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1983. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.

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