Method of connecting tubular members in offshore structures

Abstract

Two adjacent pipe flanges are secured by a plurality of clamp units, where each clamp unit, in order to receive the adjacent flanges in its receptacle, is thermally expanded.

Claims

1. A method of connecting tubular members, each tubular member having a radially outward projecting flange at its end for connecting the tubular members end-to-end, the method comprising: positioning two of the tubular members end-to-end with their flanges aligned and abutting each other, thereby forming adjacent flanges; providing a plurality of clamp units and securing the adjacent flanges to each other by positioning the clamp units on various predetermined segments of the adjacent flanges; wherein each clamp unit has a base comprising a first portion from which jaws extend to form a receptacle therebetween for receiving and containing one of the predetermined segments, wherein a width (W) across the receptacle between the jaws is too small for the receptacle to receive the predetermined segment of the adjacent flanges when the first portion of the base is at ambient temperature; for receiving the predetermined segment of the adjacent flanges in the receptacle, heating the first portion of the base and by expansion of the first portion increasing the width (W) and positioning the clamp unit with the predetermined segment of the adjacent flanges in the receptacle while the width (W) is increased; then, decreasing the width (W) and pressing the adjacent flanges together due to contraction of the jaws; wherein the increasing of the width (W) is achieved by thermal expansion of the first portion during the heating of the first portion, and wherein the decreasing of the width (W) is achieved by reducing a temperature of the first portion to ambient temperature and by a corresponding thermal contraction of the first portion.

2. The method according to claim 1, wherein the base has a second portion remote from the jaws, the second portion mechanically connected to the first portion; and wherein the method comprises causing more thermal expansion of the first portion than the second portion by the heating and correspondingly changing an angle between the jaws due to an uneven thermal expansion of the base with a larger increase of the width (W) of the receptacle at an edge of the receptacle distal to the first portion.

3. The method according to claim 2, wherein the first portion and the second portion of the base are portions of a metal block, and wherein the method comprises increasing the temperature in the first portion more than in the second portion by the heating of the first portion.

4. The method according to claim 2, wherein an insulating space is provided between the first portion and the second portion of the base for preventing or delaying transfer of thermal energy from the first portion to the second portion during the heating.

5. The method according to claim 2, further comprising: providing the predetermined segment of the adjacent flanges with a profile having a thickness that increases from a smallest to a largest thickness (T.sub.max) over a distance (D) in an outward radial direction; providing the receptacle with a corresponding internal profile with increasing width (W) to a maximum width (W.sub.max=T.sub.max) towards the base over a corresponding distance (D); and increasing an angle between the jaws due to the uneven thermal expansion of the base causing a larger increase of the width of the receptacle at the edge than closer to the first portion, for passing the edge of the receptacle over the predetermined segment at a position of the largest thickness (T.sub.max).

6. The method according to claim 5, wherein the thickness of the predetermined segment increases linearly from the smallest to the largest thickness (T.sub.max) over the distance D.

7. The method according to claim 1, wherein the predetermined segment of the adjacent flanges has a largest thickness (T.sub.max) and wherein the width (W) is increased by the heating to at least (T.sub.max) for fitting the clamp unit over the predetermined segment.

8. The method according to claim 1, wherein the jaws, prior to heating, have parallel sides towards the receptacle and provide a constant width (W.sub.0) across the receptacle when the first portion is at ambient temperature, wherein the predetermined segment has a constant thickness (T.sub.0>W.sub.0), and wherein the width (W) of the receptacle is increased to larger than the thickness T.sub.0.

9. The method according to claim 1, wherein at least one of the jaws has a convex curved surface on a side towards the receptacle with an extreme position that defines a minimum width (W.sub.min) of the receptacle; wherein the minimum width (W.sub.min) of the receptacle is increased by the thermal expansion such that the flanges pass the convex curved surface.

10. The method according to claim 9, wherein the extreme position of the convex curved surface is closer to the base than to an edge of the receptacle opposite the first portion.

11. The method according to claim 9, wherein the convex curved surface is a projection extending over only a part of a length of the receptacle when measured in a direction along a polar angle () about a central axis of the tubular member when the clamp unit is mounted on the adjacent flanges.

12. The method according to claim 1, wherein at least one of the jaws has a convex curved surface on a side towards the receptacle; wherein the method comprises: increasing the width (W) of the receptacle by the thermal expansion to receive only a part of the predetermined segment between the jaws but not enough for the predetermined segment to pass an extreme position of the convex curved surface towards a predetermined final location of the predetermined segment inside the receptacle, wherein the extreme position defines a minimum width (W.sub.min) of the receptacle; advancing the clamp unit with an advance force that overcomes an elastic force of the jaws and pressing the jaws away from each other for the predetermined segment to pass the extreme position, then increasing the elastic force of the jaws at the extreme position by reducing the temperature of the first portion to ambient temperature.

13. The method according to claim 12, wherein (W.sub.min) is in a range of 0.5-3 mm smaller than a width necessary for the predetermined segment to pass the extreme position freely into the receptacle.

14. The method according to claim 1, wherein the flanges are provided with a plurality of bolt holes about the tubular member, and the method comprises providing bolts through the bolt holes and tightening the bolts as an additional measure for securing the flanges to each other, wherein the jaws of each clamp unit have recesses that leave areas free around the bolts for tightening the bolts.

15. The method according to claim 1, wherein the heating of the first portion utilizes a heater adjacent to the first portion in between the jaws and the heater is removed prior to mounting the clamp unit on the adjacent flanges.

16. The method according to claim 1, wherein each clamp unit spans an angular segment of the adjacent flanges of no more than of a circumference of the adjacent flanges, and wherein the method comprises positioning at least three clamp units with equal angular distance on the adjacent flanges about the tubular members.

17. The method according to claim 1, wherein a diameter of the tubular member is larger than 2000 mm.

18. The method according to claim 1, wherein a length of the jaws is in a range of 100-400 mm; and the width (W) across the receptable between the jaws is in a range of 200-600 mm.

19. The method according to claim 1, further comprising heating the first portion to a temperature in a range of 150 C.-300 C. for increasing the width (W) in a range of 0.5-3 mm at an edge of the receptacle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in more detail with reference to the drawings, where:

(2) FIG. 1A illustrates two pipe sections with collars;

(3) FIG. 1B illustrates the two pipe sections of FIG. 1A end-to-end;

(4) FIG. 1C illustrates placement of a clamp unit on an angular segment on the collars;

(5) FIG. 1D illustrates two clamp units on the collars;

(6) FIG. 1E illustrates eight clamp units on the collars;

(7) FIG. 2 is a cross sectional view of a clamp unit;

(8) FIG. 3A illustrates a cross sectional view of a clamp unit and adjacent flanges;

(9) FIG. 3B illustrates inclined jaws due to uneven thermal expansion of the base;

(10) FIG. 3C illustrates the final location of the adjacent flanges in the receptacle;

(11) FIG. 4 illustrates a cross section of an alternative embodiment of a clamp unit;

(12) FIG. 5 is an illustration of principles and possible dimensions;

(13) FIG. 6A illustrates a cross section of a clamp unit with a curved surface;

(14) FIG. 6B illustrates a clamp unit with a curved surface blocking access of the flanges despite thermal expansion of the base;

(15) FIG. 7 illustrates curved surfaces as local projections;

(16) FIGS. 8A, 8B, 8C and 8D illustrate various shapes of clamp units and adjacent flanges;

(17) FIG. 9A is a perspective view of clamp units surrounding flanges of two abutting pipe sections;

(18) FIG. 9B is a cross section of the embodiment shown in FIG. 9A;

(19) FIG. 10A illustrates a perspective view of a clamp unit having recesses for bolts that assist with securing flanges of pipe sections; and

(20) FIG. 10B illustrates a cross section of the embodiment shown in FIG. 10A.

DETAILED DESCRIPTION

(21) FIG. 1A shows two tubular structures 1, each of which has a flange 2 at an end 3 of a cylindrical pipe section 4, 4. For example, one pipe section 4 is an end section of an offshore pipe, and the other pipe section 4 is part of a pump that is to be connected to such offshore pipe.

(22) The flange 2 comprises a collar 5 around the pipe section 4 and fastened to an outer surface 6 of the pipe section 4, 4, which is a typical construction. However, the flange 2 could also be fastened to the end 3 of the pipe section 4 in longitudinal extension of the pipe section 4, instead of around the end 3 of the pipe section 4.

(23) The collar 5 has a front side 5A and a rear side 5B, which are parallel, although this is not necessary, as will be explained below with examples. In the shown embodiments, the collar 5 has a circular outline, which is a typical case but not necessary for the invention disclosed herein.

(24) FIG. 1B illustrates the situation where the two pipe sections 4, 4 have been positioned end-to-end with the two flanges 2 adjacent to each other, and the collars 5 facing each other. In the shown sketch, for simplicity, the two collars 5 are abutting each other, although this is not always the case, as there may be positioned a gasket in between the flanges 2. A clamp unit 7 has a base 8 and two jaws 9 extending from one side of the base 8 for providing a receptacle 10 in between the jaws 9.

(25) A segment 11 of the adjacent flanges 2 is taken up in the receptacle 10 by moving the clamp unit 7 over the collars 5, which is illustrated by arrows 12 in FIG. 1C.

(26) In the illustrated situation, the receptacle 10 is taking up a complete angular segment of the adjacent collars 5. However, the segment 11 that is taken up in the receptacle 10 need not be a complete angular segment of the collars 5 but could also be a portion of the adjacent flanges 2 less than the entire angular segment of the collars 5.

(27) FIG. 1D illustrates a situation where two clamp units 7 have been placed side-by-side on the collars 5. By continuing to position the clamp units 7 side-by-side about the collar 5, the entire collars 5 can be taken up by the multiple receptacles 10, which is illustrated in FIG. 1E.

(28) FIG. 2 illustrates a cross section of a clamp unit 7. The clamp unit 7 has a base 8 and two jaws 9 extending from a first portion 8A of the base 8 for providing a receptacle 10 in between the jaws 9. The distance between the jaws 9 defines a width W of the receptacle 10. In the shown embodiment, the jaws 9 have parallel sides 9A towards the receptacle 10 so that the width W across the receptacle 10 is constant and the width W.sub.e at the outer edge 14 of the receptacle 10 is the same as at any position between the jaws 9. However, as will be explained by examples below, this constant width W need not be the case, as also the rear sides 5B of the collars 5 need not be parallel.

(29) For a varying width W, the width is a function of the position in the receptacle. For example, W is expressed as a function depending on polar coordinates, W=funct (r,), a radial coordinate r and an angular coordinate , the reference for the coordinates being taken from the central longitudinal axis 15 of the pipe section 4, see FIG. 1C for the central axis and the coordinates. In this case, the width W is measured in a direction parallel to the central longitudinal axis 15. However, other expressions for W are possible.

(30) In FIG. 3A, a cross section of the two adjacent collars 5 is show together with a portion of the two pipe sections 4, 4. The front sides 5A of the two collars 5 are exemplified with a step 17 for precise fitting and for avoiding mutual sliding of the collars 5 when a clamp unit 7 is positioned onto the collars 5.

(31) In order for the clamp unit 7 to actually clamp the two flanges 2 towards each other by the collars 5 and keep them in place, the jaws 9 of the clamp unit 7 need to exert pressure on the flanges 2.

(32) The collars 5 of the adjacent flanges 2 have a thickness T, when measured between the parallel outer sides 5B of the collars of the flanges 2, which is slightly larger than the width W of the receptacle 10 of the clamp unit 7. In order to make the width W fit the thickness T, the base 8 is heated by a heat source 16 so that it undergoes thermal expansion. For example, the base 8 is heated from ambient temperatures of 15 C. to more than 150 C., for example in the range of 150 C. to 300 C., for increasing the width W in the range of 0.5-3 mm at the edge of the receptacle.

(33) A typical expansion coefficient for metal, such as steel, is on the order of 10.sup.5 per degree Kelvin. For W=400 mm, a heating by 250 Kelvin from 15 C. to 265 C. results in an expansion of the first portion of 10.sup.5250400=1 mm. For precisely made jaws and collars, this can be sufficient for fitting the clamp unit 7 over the collars 5.

(34) However, an improved method has been found as illustrated in FIG. 3B. In this case, the heating of the base 8 is made such that the base 8 is heated unevenly. The heat is provided to a first portion 8A of the base 8, while the second portion 8B will not be heated or only be heated delayed by thermal conduction from the first portion 8A to the second portion 8B. Due to the higher temperature in the first portion 8A as compared to the second portion, the base 8 will expand unevenly with the largest expansion in the first portion 8A. As a consequence, the jaws 9 are pressed away from each other without maintaining a parallel orientation of the jaws 9. Instead, the jaws 9 get angled with an angle that is defined by the expansion of the first portion 8A relative to the non-expanded second portion 8B.

(35) The angled expansion can be better understood with reference to FIG. 4 in combination with FIG. 5. As illustrated in FIG. 4, the base contains a void 18 in between the first portion 8A and the second portion 8B of the base 8. The void 18 acts as a partial insulation between the first portion 8A and the second portion 8B, delaying the thermal energy transfer from the first portion 8A to the second portion 8B. If the first portion expands in the order of 1 mm, and assuming a distance D of 200 mm between the first portion 8A and the second portion 8B and a length L of the jaws of 400 mm, as illustrated in FIG. 5, it is readily recognized by the simple sketch of FIG. 5 that the gap increases by 4 times the expansion of the first portion. Although, the expansion of 1 mm of the first portion and the dimensions in FIG. 5 are not to scale and neither precise but only rough examples for illustration, it gives an impression of the sizes in typical offshore pipe connections as well as the dimensions of the possible expansions of the width of the receptacle.

(36) The increase of the width W.sub.e at the outer edge of the receptacle by several mm facilitates the positioning of the clamp unit 7 over the flanges 2, and also assures that not only is the entire predetermined segment of the flange 2 taken up in the receptacle 10, as illustrated in FIG. 3C, but the flanges 2 are also pressed together by the jaws 9, once the temperature of the first portion 8A returns to ambient temperature, and the base 8 undergoes thermal contraction back to its original state. To the extent the thickness T of the collars 5 allows the jaws 9 to contract again, a resulting elastic force from the base 8 on the jaws 9 remains, which presses the flanges 2 together.

(37) In order to increase the elastic force of the clamp unit 7 on the collars 5 of the flanges 2, the embodiments as sketched in FIGS. 6A and 6B have been found useful. In this case, the inner side 9A of one of the jaws 9 or of both jaws 9 is provide with a curved surface 20.

(38) The curved surface 20 is optionally provided as a surface profile in the radial direction on the inner side 9A of the entire corresponding jaw 9. Alternatively, not the entire inner side 9A of the entire corresponding jaw 9 is curved, but the curved surface 20 is provided as a projection on the inner surface 9A of the jaw 9. As a further alternative several of such projections 20 are provided on the inner surface 9A of the jaw, as illustrated in FIG. 7.

(39) The curved surface 20 in FIG. 6A is projecting a distance towards and into the receptacle which is less than the increase in width of the receptacle 10 due to the heating and thermal expansion. Thus, despite the curved surface 20, the clamp unit 7 can be positioned over the adjacent flanges 2 in an easy-sliding motion. However, once the base 8 contracts, the curved surface 20, for example in the form of multiple projections, will result in additional elastic force on the flanges 2 so that long term creep of the material will not lead to an untight connection.

(40) In order to enhance the elastic force from the clamp unit, the curved surface may extend into the receptacle 10 a distance more than the width increase by the thermal expansion of the first portion 8A. In this case, which is illustrated in FIG. 6B, the flanges do not get spaced far enough for the adjacent flanges 2 to be taken up freely into the receptacle 10. In this case, the clamp unit 7 is moved over the flanges until the curved surface 20 prevents further advancing of the clamp unit 7 over the flanges 2. In order to advance the clamp unit 7 further, increased advance force is used to press an extreme position 26 of the curved surface 20 past the location where further advancement is blocked. This advancement can be achieved due to the elastic material of the base 8 and/or the jaws 9, which both typically are made of metal. In this embodiment, the relatively large projection 20 adds to the subsequent elastic force that presses the flanges 2 together.

(41) As illustrated in FIG. 6B, the largest reduction in width of the receptacle 10 due to the curved surface 20 with the extreme position 26 is closer to the base 8 than to the edge of the receptacle 10, which is advantageous in that the resulting pressure on the flanges by the jaws is highest near the base.

(42) FIG. 7 illustrates a possible pattern of projections of the two types 20 or 20. The position and size of the projections as well as type of projections is only used here as an illustrative example and can be provided in different dimensions and configurations.

(43) FIGS. 8A-8D illustrate different examples of combinations of flanges 2 and jaws 9. In FIG. 8A, the adjacent flanges 2 extend in parallel and so do the jaws 9 on opposite sides of the receptacle. In FIG. 8B, the flanges 2, for example the collars of flanges 2, increase linearly in thickness with distance from the pipe section 4. Correspondingly, the width of the receptacle increases linearly with radial distance from the pipe section 4. The increase in thickness of the flanges 2 can also increase non-linearly, for example by curving smoothly. In FIG. 8C, an increase in thickness is step-wise and comprises a shoulder 21 of the flanges 2 behind which the jaws 9 hook for optimum fit. In FIG. 8D, a similar configuration is illustrated as in FIG. 8C, however, with a shoulder 21 that is inclined, which eases mounting of the jaws 9 on the flanges 2, especially the fit to the shoulder 21.

(44) FIGS. 9A and 9B illustrate a further embodiment, where each clamp unit 7 spans only a minor portion of the circumference of the flange 5 on the order of 5-10 degrees of the circle around the pipe section 4. This implies that each clamp unit 7 is less heavy than if the clamp unit spans of the circle as illustrated in FIG. 1E. For ease of insertion, the clamp unit 7 comprises a lifting eye 22, for example for lifting by a crane.

(45) FIG. 10A in perspective view and FIG. 10B in cross sectional view illustrate an embodiment where the clamp unit 7 comprises recesses 25 for giving access to bolt connections 23 that are used as redundant means for pressing the flanges 5 together. In order to optimize the pressure, the clamp units 7 have portions 24 that extend to regions in between the bolt connections 23.