CA1237682A - Process and apparatus for sleeve repair of pipe line - Google Patents

Abstract

"PROCESS AND APPARATUS FOR SLEEVE REPAIR OF PIPE LINE"

ABSTRACT OF THE DISCLOSURE
A longitudinally split cylindrical sleeve, consisting of two half shells, is applied to an internally pressurized pipe, to reinforce a section of the pipe wall weakened by an internal or external defect.
One pair of adjacent shell ends are first welded together along their length with the shells in place on the pipe in a relaxed condition. The other pair of adjacent shell ends are equipped with longitudinally extending, outwardly projecting, attached shoulder lugs. A clamp assembly is applied to the shoulder lugs to draw them together and tension the sleeve about the pipe. The clamping force applied to the shoulder lugs is monitored and terminated when the applied stress in the sleeve is approximately equal to the stress exerted on the pipe wall by the internal fluid pressure. The free ends of the shells are then welded together longitudinally while in the tensioned condition. The sleeve/pipe combination forms, in effect, a thick-walled cylinder. The stress arising from the internal fluid pressure is distributed across the cylinder. This effectively lowers the stress at the location of the defect. This, in turn, eliminates the need to apply circumferential fillet welds at the sleeve ends, since further deterioration of the defect (which would lead to leaking of the contained fluid) is arrested.

Description

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2 This invention relates to repairing or reinforcing a cylindrical3 member, sun as a high pressure steel fluid transmission pipe line, by 4 engirdling it with a longitudinally split sleeve. The free ends of the sleeve are welded together longitudinally to form a collar that tightly 6 enwraps said pipe.
7 The invention has an apparatus aspect, pertaining to the 8 clamping means used to tension the sleeve halves or shells (already 9 welded together along one pair of ends) and to hold the shells in that condition around the pipe while the remaining pair of free ends are If welded together.
12 The invention further has a method aspect, relating to the 13 combination of steps used to apply the tensioned sleeve.
14 And it has a product aspect, pertaining to the cylindrical member with the tensioned sleeve applied thereto and fixed there around.

17 The invention was originally conceived as a method for repairing18 steel pipe lines. While not limited to that application, it will now 19 be discussed in connection with that specific application.
Oil and natural gas transmission pipe lines commonly develop 21 defects in the pipe wall, usually in its outer surface. Predominantly, 22 these defects take the form of corrosion pitting, which is initiated when 23 the protective coating on the pipe is damaged and moisture comes into 24 contact with the steel surface of the pipe. The resulting galvanic corrosion cell develops a string of rusty pits of varying depth. In 26 addition to corrosion pitting, there can also be other defects such as dents, 27 gouges, grooves, and cracks, which arise as a result of poor installation I practices, third party acts, or metal fatigue during service.

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1 In cases where the defect is shallow in nature, it is usual 2 to repair the existing pipe rather than to cut out and replace the

3 damaged segment.

4 The type of repair applied to a shallow defect depends on factors such as its orientation, size and depth, the pipe wall thickness, 6 and the maximum operating pressure.
7 If the corrosion is not very extensive, the corrosion product 8 is simply cleaned out and the pits are filled with hard enable mastic or 9 epoxy, to restore the smooth pipe contour. The pipe segment is then rewrapped with new protective coating and placed back in service.
11 If the defect is more serious, it is common practice to 12 apply a full encirclement sleeve to engirdle the defect and reinforce 13 the pipe at the locus of the defect. The present invention is concerned 14 with this sleeve type of repair.
The sleeve repair procedure commences with some of the same 16 steps as those used with the minor defects. That is, the protective 17 coating is removed from the pipe segment to be repaired, the dirt and 18 corrosion products are cleaned out of the pits, and the pits are filled 19 with mastic or epoxy. Then a steel sleeve, split longitudinally into two half shells, is placed around the pipe over the defect. The two 21 half shells aye welded together by a longitudinal butt weld formed along 22 one pair of adjacent ends, with the shells in a relaxed condition. A
23 chain or cable is then tightened around the exterior of the sleeve using 24 a ratchet tensioner, to clamp the sleeve tightly to the pipe. When the shells are clamped in this manner, a slight longitudinal gap still exists 26 between the two remaining free ends of the sleeve. A second longitudinal 27 butt weld is then applied along this gap, to join the free ends end 28 convert the sleeve into a closed collar.

1 If there is concern that a leak will subsequently develop 2 at the defect, it is common practice to apply a circumferential fillet 3 weld between the pipe and the sleeve at each end of the sleeve. In 4 this manner, a pressure tight vessel is created around the defect, to contain the leak should it develop.
6 To execute the circumferential fillet welds, it is necessary 7 to heat the pipe and the sleeve to the proper welding temperature along 8 the area to be welded In the case of liquid transmission pipe lines, 9 the presence of stationary or flowing liquids significantly affects the cooling rate of circumferential fillet welds. Similarly, in the case of 11 a gas line, the segment being welded must be filled with water or the 12 like, to avoid the possibility of an explosion. The presence of the 3 liquid accelerates the cooling rate. When the cooling rate is too fast, 14 the pipe steel has a tendency to develop martensitic micro structures (hard spots) along the toe of the circumferential fillet weld. This 16 condition, known as embrittlement~ particularly manifests itself in the 17 older pipelines now undergoing repairs which are known to have a higher 18 carbon content than modern pipe steels.
19 Eventually, these welds can fail catastrophically by cracking when they are subjected to severe external stresses imposed by a variety 21 of soil conditions, such as poor backfill compaction following sleeve 22 installation, soil movement from freeze-thaw cycles, and insufficient 23 cover under traveled areas.
24 This problem with circumferential sleeve welding is such that many pipe line companies do not allow this type of sleeve repair 26 to be made on their pipe lines, preferring to cut out and replace the 27 damaged segment instead.

I it 1 To provide a feeling to the reader for the high incidence 2 of these repairs, a pipe line company in Alberta recently replaced a 1/2 3 mile section of pipe that had 16 sleeve repairs in place along its length.
4 However, in balance it needs to be said that there are other long sex-mints of line that are free of sleeve repairs.
6 In summary, the repairs to be made are numerous, they have 7 involved for decades the use of the repair sleeve procedure previously 8 described, and the problem connected with the circumferential fillet 9 weld has not heretofore been solved.

SUMMARY OF TOE INVENTION
11 The present invention has the objective of providing a full 12 encirclement sleeve that so reinforces and joins with the wall of the 3 cylindrical member being encircled that the two together, in effect, 14 become a short thick-walled cylinder. The stress, arising from fluid pressure within the cylindrical member, is distributed throughout the 16 thick-walled cylinder. As a result, the stress level associated with 7 the defect is reduced. This reduction in stress level is sufficient so 18 that the troublesome circumferential welds become unnecessary.
19 More particularly, a longitudinal (lap) weld is first applied in the usual manner along two adjacent ends of the sleeve shells. Each 21 shell is equipped with an outwardly protruding and rigidly attached 22 shoulder lug adjacent its remaining free end. A clamp is used to draw 23 the shoulder lugs together, thereby tensioning the sleeve around the 24 cylindrical member (usually a pipe) until the stress level in the sleeve is substantially equal to that present in the pipe wall (said stress in 26 the wall arising from the fluid pressure within the pipe). At this point, 27 the free ends of the sleeves are welded together, to complete the install 28 lotion of the sleeve.

3~37~2 1 By using a clamp whose applied force can be measured, such 2 as a hydraulic clamp having cylinder means, it is possible to monitor 3 the closing or tensioning force being applied to the shoulder lugs, 4 using a gauge. Therefore it is possible to accurately apply a circumferential tensioning stress to the sleeve that substantially 6 satisfies the equation:

7 S =

8 where S = the circumferential stress to be 9 applied in pounds/inchZ
P = the internal pressure of the pipe 11 in pounds/inch2 12 D = the outer diameter of the emplaced 13 sleeve, in inches 4 t = the wall thickness of the thick-walled cylinder created by the combination of 16 the pipe and encircling sleeve, in inches.
7 In summary then, the sleeve is pretension Ed before the 18 final longitudinal weld is applied. The pre-tensioning is conducted 19 using means whose closing force can be monitored, so that it is known when a desired stress level in the sleeve has been achieved. This 21 stress level is selected so that, when the last weld is applied, the 22 sleeve will thereafter in conjunction with the cylindrical member 23 in effect form a thick-walled cylinder and share the stress acting on the 24 cylindrical member. Preferably the pre-tensioning stress applied satisfies equation (1).

1 To accomplish these ends, there it provided a novel 2 clamp assembly for tensioning the sleeve. The clamp assembly 3 comprises a preferably rectangular frame forming a generally central opening or window. The window is configured to permit the sleeve shoulder lugs to project there through. One 6 end of the frame bears against the rear surface of the first 7 shoulder lug. Means, such as a hydraulic cylinder or a 8 tensioning screw, is mounted on the other end of the frame 9 for biasing the second shoulder lug toward the first lug.
The frame and biasing means thus together cooperate to fix 11 the first lug while forcing the second lug toward it, thereby 12 tensioning the sleeve around the pipe. The two free ends of 13 the sleeve are left exposed by the window, so that the last 14 weld may be applied. Restraining members are provided to connect the frame with each shoulder lug, to prevent the 16 moment exerted by the biasing means on each lug from rotating 17 it inwardly.
18 Broadly stated, the invention in one aspect 19 comprises, in combination, an internally pressurized and stressed high pressure fluid transmission pipe line having a 21 surface defect; and a pair of externally applied full 22 encirclement shells forming a sleeve extending around the 23 pipe line at the defect, said shells having first been I longitudina71y welded together along their second ends while on the pipe line, said shells having an inside diameter 26 substantially equal to the outside diameter of the pipeline, 27 so that substantially the entire inside surface of the sleeve 28 is in contact with the outside surface of the pipe line, said 29 shells having a length such that their first ends do not come into abutment when the shells are emplaced on the pipe line 1 and their second ends are welded together, said shells having 2 been tensioned by drawing their first ends together 3 sufficiently, without bringing them into abutment, so that 4 the stress in the shells is substantially the same as that in the underlying wall segment of the pipeline, said shells 6 having been longitudinally welded together along their first 7 ends while so tensioned.
8 In another broad aspect, the invention comprises a 9 process for reinforcing an internally pressurized and stressed cylindrical member, said member having a defect in 11 its wall, comprising: mounting a full encirclement sleeve, 12 comprising a pair of discrete sleeve shells, around the 13 member over the defect, each shell having first and second 14 ends and an outwardly projecting lug attached thereto adjacent the first end of the shell, said lug extending 16 substantially the full width of said first end, said first 17 ends of the shells being overlapped, said shells being of an 18 internal diameter substantially equal to the outside diameter 19 of the cylindrical member and having a length such that, when their second ends are welded together and their first ends 21 are pulled toward each other, tension will be applied to the 22 shells without the first ends of the shells coming into 23 abutment; welding the second ends of the shells together;
24 applying increasing clamp force to the lugs to draw them toward each other and tension the sleeve, whereby 26 substantially the entire internal surfaces of the shells are 27 in contact with the outside surface of the cylindrical 28 member, said force being generally evenly applied along the 29 length of the lugs; simultaneously restraining the lugs against inward pivoting movement to maintain the sleeve ends .
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1 in substantial alignment; measuring the force being applied 2 and stopping the drawing together of the lugs when the sleeve 3 has been tensioned a predetermined amount and stress in the 4 underlying portion of the cylindrical member has been reduced; maintaining said sleeve in said tensioned condition 6 and welding the first ends of the shells together; and 7 relaxing said clamping force.

- pa -~3~7i~ 2 1 The specific best mode of the invention is now described 2 for exemplifications in connection with the following drawings.

_ _ 4 Figure 1 is a side view of the sleeve having the shoulder lugs mounted thereon;
6 Figure 2 is an end view of the sleeve of Figure l;
7 Figure 3 is a fragmentary expanded side view showing the end 8 portions of the sleeve with the shoulder lugs mounted thereon;
9 Figure 4 is a partly sectional side view showing the end I portions of the sleeve, the shoulder lugs, and the frame and hook-like Al restraining members of the clamp assembly;
12 Figure 5 is a plan view of the clamp assembly;
13 Figure 6 is a sectional view taken along the line AYE of 14 Figure 5;
Figure 7 is a perspective view of the clamp assembly in use 16 and 7 Figure 8 is a schematic illustration of the positioning of 18 the internal and external strain gauges on the test pipe.

2 Figure 1 shows a conventional, longitudinally split sleeve 1 3 comprising two semi-circular, steel shells 2, 3. The shells 2, 3 are 4 formed at their end edges with a lap joint configuration.
The shells 2, 3 are placed on the pipe 4 to encircle the 6 defect to be repaired. As a first step, they are welded together 7 longitudinally along their rear ends 5, 6 in conventional Fashion.
8 A pair of elongate, outwardly projecting shoulder lugs 7, 9 8 are positioned along the front ends 9, 10 of the shells 2, 3. These shoulder lugs I 8 are each affixed to their respective shell, as with Al welds Il. Each shoulder lug 7, 8 provides a rear bearing surface 12, 12 13 against which the clamp assembly 14 will bear.
3 The clamp assembly 14 comprises a rectangular, collar-like, 4 steel frame 15 having a rectangular opening 16 formed therein.
Along the upper end of the opening 16, the upper end portion 16 19 of the frame 15 provides a clamping surface 17 for locking against the 17 rear bearing surface 13 of the shoulder member 8.
. 18 Along the lower end of the opening 16, a base plate 20 is r 19 affixed by bolts 21 to the lower end portion 22 of the frame 15. A
plurality of vertically extending hydraulic cylinders 23 are supported 21 by the base plate 20 and are held in position by straps 24.

!,~' 22 A pair of vertically extending guide rails 25 are formed 23 along the inner surface of the side portions 26, 27 of the -Frame 15. A
24 horizontal push bar 28 is supported by the pistons 29 of the cylinders 23. The push bar 28 has milled slots in each end that engage with 26 the guide rails 25. Thus the cylinders 23 can slide the push bar 28 27 up and down in the frame opening 16 along the guide rails 25, to bias the 28 lower shoulder member 7 of the sleeve 1 toward the upper shoulder member 29 8.

'10 Each of the clamping beam 17 and push bar 28 carries a 2 restraining member 32, 33 respectively for over-arching and engaging 3 the shoulder lug 7 or 8 associated therewith, to restrain the shoulder 4 lug against inward rotational movement. When the clamping bar 17 and

5 push bar 28 bear against the shoulder lugs I 7, the resultant moment

6 would tend -to rotate the outer ends of the shoulder lugs downwardly

7 and inwardly, thus applying additional load to the pipe 4, the restrain-

8 in members 32~ 33 function to prevent such rotation from taking place.

9 A hydraulic pump is used to expand the cylinders 23. A
pressure gauge is attached to the pump, to provide a measure of the Al force being applied to the shoulder members 7~8.

12 Example 13 To demonstrate the invention, a repair was made on a test 14 length of pipe having a defect formed therein.
More particularly, a 15' length of 24" diameter x Q.344"
16 thickness line pipe was provided. The pipe was formed of APT Grade 17 5L-B steel and was closed at its ends.
18 The test pipe was equipped with strain gauges on its inner 19 and outer surfaces. The locations and orientations of the gauges are 20 indicated in Figure 8. A description of the gauges is given in Table 1 I

eye I
2 ` auger Lo anions 3 huge No. Orate ion monitors 4 2 Hoop Internal surface of pipe 90 degrees from the weld seam and remote from 6 the sleeve 7 3 Longitudinal Internal pipe surface stress at the 8 edge of the sleeve 9 6 Woo Pipe internal surface stress under the sleeve 11 7 Hoop Pipe internal surface stress under 12 the sleeve 13 10 Hoop Sleeve stress about 6" from final weld I 11 Hoop Sleeve stress about 12" from -Final weld 12 Hoop Sleeve stress about 24" from final weld 16 13 Hoop Sleeve stress about 24" from final weld 17 14 Hoop Sleeve stress about 12" from final weld 18 15 Hoop Sleeve stress about 6" from final weld 19 16 Longitudinal External pipe surface at edge of sleeve 17 Longitudinal External pipe surface at edge of sleeve 21 19 Longitudinal External pipe surface at edge of sleeve 22 A 12" wide x .5" thick x 24" internal diameter sleeve of 23 APT 516 Grade 70 carbon steel was used. The sleeve was in the form of 242 semi-circular shells.
Thea pipe was pressured internally to 500 psi, without the Slav in place. The stress values noted are set forth in Table II.

2 Pipe Wall Stress Values Measured Prior to Sleeve Installation ___ _ _ ___ _ __._~__ __ ____ _ _ 3 Pipe Pressured to 500 psi _. _._. __. __ 4 Gauge No. Stress/Strain Value psi* Zero Check Value psi**
. .___.,_,,.,_, __ 2 internal pipe Wylie (remote from - 240 6 stress - hoop sleeve) 7 3 internal pipe Wylie (at sleeve - 750 8 stress - longitudinal edge) 9 6 internal pipe Wylie (under sleeve) - 90 lo stress - hoop 11 7 internal pipe Wylie (under sleeve) -300 12 stress - hoop * Stress/strain values are strain gauge readings converted to stress by 14 assuming an elastic modulus of 30 x 106 psi.

Pipe pressure was reduced to zero to check the accuracy of the strain 16 gauges (zero check) 17 ** The zero check readings should read between 0 and + 1000 psi to 18 confirm that the strain gauze is functioning within the limits of 19 accuracy.

The pipe was then repressured to 500 psi in preparation of sleeve 21 installation.

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1 The pipe surface over the defect was cleaned and a lubricant 2 was applied to the sleeve area, to facilitate seating of the shells.
3 The shells were positioned around the pipe over the defect area with 4 the shoulder lugs adjacent each other The sleeve gap at the shoulder lugs was maintained at .125" by means of a spacing plate positioned 6 between them. The shells were then snugged down onto the pipe using a 7 chain type ratchet tensioner and the back weld was applied. After the 8 weld cooled, the spacing plate was removed.
9 The frame 15 was then fitted over the shoulder lugs 7, 8 and hydraulic pressure was applied to the push bar 28, until the cylinder Al pressure reached 4500 psi, to tension the sleeve 1 by biasing the12 lower shoulder lug 7 toward the upper shoulder lug 8, said shoulder lug 3 8 being locked in place by the upper end 19 of the frame. The 4500 psi 4 value used was obtained by a calculation in accordance with equation (1), to offset the internal pressure of 500 psi which was maintained in the 16 pipe during installation of the sleeve. This internal pressure was later 17 increased to 1000 psi after welding was complete. The stress values 18 recorded in connection with the test installation are set forth in 19 Table III.

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pipe and Sleeve Stress Values Measured During and wafter Sleeve Installation Sleeve Sleeve eve Sleeve 6 Gauge_ Tensioned Installed Installed Installed 7 2 11640 11790 2580() - 3360 8 3 30750 8850 3735t) 10350 9 6 - 1770 ~030 16890 - 6600 11 lo 19950 32100 35250 22590 12 Al 5760 14700 18000 12510 Negative values denote compression 21 Gauge 2 measures the internal surface tension remote from the I sleeve, and is used as a reference of unrestrained pipe wall stress.
23 Gauge 3 measures the longitudinal pipe surface tension at the 24 edge of the sleeve.
Gauges 6 and 7 measure the internal pipe surface tension under 26 the sleeve.
27 Note: tension measured by these gauges will decrease as the 28 pipe wall stress transfers to the sleeve due to the applied hydraulic 29 force of the clamp. Compare the readings of gauge 2 with gauzes 6 and 7 after sleeve installation at internal pipe pressures o-F 500 psi and 1000 31 psi to note the stress reduction on the pipe wall.

3t~6~2 1 Gauges 10 to 15 indicate hoop tension on the outer surface 2 of the sleeve at various distances from the clamping point and show 3 the stress distribution around the sleeve.
4 Gauges 16, 77 and 19 measure longitudinal surface tension in the pipe near the edge of the sleeve and the values shown indicate the 6 even distribution of stress to the sleeve without excessive localized 7 stress in the pipe wall.
The scope of the invention is set forth in the claims which 9 follow. It will be noted that the clamp assembly has been described with respect to a specific embodiment having a hydraulically driven 11 slid able push bar acting against one shoulder lug while the other 12 shoulder lug is held stationary by a rigid frame connected with the 13 cylinder means. However it would be feasible to use two driven slid able 14 push bars to act simultaneously from above and below on the shoulder lugs and other biasing means, such as a screw, could be used; the clamp 16 assembly is to be interpreted to encompass such alternative embodiments.

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Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN
EXCLUSIVE PROPERTY OR PRIVILEGE: IS CLAIMED ARE DEFINED AS
FOLLOWS:

1. In combination:
an internally pressurized and stressed high pressure fluid transmission pipe line having a surface defect; and a pair of externally applied full encirclement shells forming a sleeve extending around the pipe line at the defect, said shells having first been longitudinally welded together along their second ends while on the pipe line, said shells having an inside diameter substantially equal to the outside diameter of the pipeline, so that substantially the entire inside surface of the sleeve is in contact with the outside surface of the pipe line, said shells having a length such that their first ends do not come into abutment when the shells are emplaced on the pipe line and their second ends are welded together, said shells having been tensioned by drawing their first ends together sufficiently, without bringing them into abutment, so that the stress in the shells is substantially the same as that in the underlying wall segment of the pipeline, said shells having been longitudinally welded together along their first ends while so tensioned.

2. A process for reinforcing an internally pressurized and stressed cylindrical member, said member having a defect in its wall, comprising:
mounting a full encirclement sleeve, comprising a pair of discrete sleeve shells, around the member over the defect, each shell having first and second ends and an outwardly projecting lug attached thereto adjacent the first end of the shell, said lug extending substantially the full width of said first end, said first ends of the shells being overlapped, said shells hying of an internal diameter substantially equal to the outside diameter of the cylindrical member and having a length such that, when their second ends are welded together and their first ends are pulled toward each other, tension will be applied to the shells without the first ends of the shells coming into abutment;
welding the second ends Of the shells together;
applying increasing clamp force to the lugs to draw them toward each other and tension the sleeve, whereby substantially the entire internal surfaces of the shells are in contact with the outside surface of the cylindrical member, said force being generally evenly applied along the length of the lugs;
simultaneously restraining the lugs against inward pivoting movement to maintain the sleeve ends in substantial alignment;

measuring the force being applied and stopping the drawing together of the lugs when the sleeve has been tensioned a pre-determined amount and stress in the underlying portion of the cylindrical member has teen reduced;
maintaining said sleeve in said tensioned condition and welding the first ends of the shells together; and relaxing said clamping force.

3. A process for reinforcing an internally pressurized and stressed high pressure fluid transmission pipe line , said line having a defect in its wall, comprising:
mounting a full encirclement sleeve, comprising a pair of discrete sleeve shells, around the pipe line over the defect, each shell having first and second ends and an outwardly projecting lug attached thereto adjacent the first end of the shell, said lug extending substantially the full width of said first end, said first ends of the shells being overlapped, said shells being of an internal diameter substantially equal to the outside diameter of the pipe line and having a length such that, when their second ends are welded together and their first ends are pulled toward each other, tension will be applied to the shells without the first ends of the shells coming into abutment;
welding the second ends of the shells together;

applying increasing hydraulically induced clamping force to the lugs to draw them toward each other and tension the sleeve, whereby substantially the entire internal surfaces of the shells are in contact with the outsits surface of the pipe line, said force being generally evenly applied along the length of the lugs;
simultaneously restraining the lugs against inward pivoting movement to maintain the sleeve ends in alignment;
measuring the force being applied as it is increased and stopping the drawing together of the lugs when the sleeve has been tensioned sufficiently so that the stress condition in the sleeve is substantially the same as that in the underlying portion of the pipe wall;
maintaining said sleeve in said tensioned condition and welding the first ends of the shells together; and relaxing said clamping force.