PIPE CONNECTION

According to the present invention, there is provided a pipe length with an integral connector for connecting the length of pipe to another such pipe length so as to form a fluid transport system.

Fluid transport systems are known for conveying materials, such as liquids and gasses, with common examples including fuels such as gas and oil. The systems may include oil and gas pipelines for conveying fuel over thousands of miles. The tubular conduits used in fluid transport of fuel may be made of different metals, including steel, iron, copper and aluminium.

For the larger diameter pipes, typically 1 to 1.5m metres (around 40 inches) in diameter, used in the transport of fuel, welded joints are commonly used. However, welded joints have the disadvantage of requiring skilled workers as well as having negative health and safety and environmental implications. For example, construction of a gas or oil conveying pipeline, are typically made from approximately 12 metre (40 feet) long lengths of steel pipe with a diameter of 1 to 1.5 metres and conventionally use welded joints. Each joint can take a skilled team a whole day to make, when taking into consideration, the deployment of equipment at the joint location and inspection of the joint by X-ray equipment. Also, around 1 in 10 of such welded joints will have to be repaired after an inspection. This makes oil and gas pipelines expensive and time consuming to construct. Welded joints are difficult to disconnect, for

example, for repair or maintenance, with such disconnection often causing damage to the pipes.

A further problem is that the temperature of the pipeline, as it is constructed and before it begins fluid transport, the tie-in temperature, may be significantly different from its temperature when fluid is moving through the pipeline, the working temperature. When the pipeline is being constructed and before use it will be at the ambient temperature of its local environment, which depending on its latitude and the seasons can vary greatly. However, once fluid is being transported by the pipeline, the pipeline will be at, or closer to, the temperature of the fluid passing through it, particularly for oil pipelines. Once in use the working temperature of an oil pipeline generally stays relatively constant, as compared to the variation between the tie-in temperature and the working temperature. For example, for the trans-Alaska pipeline system, the minimum tie in temperature can fall to -6O ⁰ F and the maximum working temperature can rise to 145 ⁰ F.

The differences in temperature cause a metal pipeline to either thermally expand or thermally contract. For example, each 40 foot length of steel pipe will typically expand by .031 inches with each 1O ⁰ F rise in temperature and will typically contract by 0.31 inches with each 1O ⁰ F drop in temperature. For example, for the trans-Alaska pipeline system, longitudinal expansion of a typical 720 foot section of above ground pipeline between tie-in temperature and operating temperature was around 9 inches. This problem can be

overcome by the use of pipeline bellows or by the use of systems for regulating pipeline temperature, which are expensive to install and maintain.

According to the present invention, there is provided a pipe length comprising: a first insert end formed with at least one through slot extending in a direction substantially parallel to a longitudinal axis of the pipe length; a second opposite coupling end for receiving an insert end of a second such pipe length, said coupling end comprising at least one through hole extending from an external surface of the coupling end through to an internal surface of the coupling end; a sealing arrangement for sealing an insert end of such a second pipe length within the coupling end; and at least one fixing element, the or each fixing element extending through a corresponding one of the through holes in the coupling end for engaging slideably within a slot of such a second pipe length so that an insert end of a second pipe length is slideable within the coupling end on thermal expansion or contraction of such a second pipe length. Therefore, the pipe lengths can be fitted together without additional coupling collars to form a pipeline. They are quick and easy to fit and maintain, as compared to a welded joint and accommodate thermal expansion and contraction of the pipeline. The length of the slots can be selected to match the expected amounts of thermal contraction and expansion during the lifetime of the pipeline.

The seal arrangement may comprise a first annular seal within the coupling end for sealing around an insert end of such a second pipe length and may, for example, be located at a position between the fixing element(s) and an

end surface of the coupling end. The seal arrangement may also comprise at least one second seal between the coupling end and the or each fixing element. .

The coupling end may have a longitudinal axis of symmetry and the or each fixing element may be substantially concentric with a line extending in a direction substantially radially of the axis. There may be a threaded engagement between the or each fixing element and associated housing through hole.

The or each of the slots in the insert end may be tapered so that the slot is wider at the external surface of the insert end than at the internal surface of the insert end. The tapered slot may have curved tapered end surfaces. In this case, an end of the or each fixing element which slideably engages the slot may be tapered to match the taper of the slots in the insert end. This complimentary tapering of the side faces of the slots and the portions of the fixing elements which engage the slots prevents shearing of the fixing elements.

The coupling end may comprise an abutment positioned to be engageable with an end face of such an insert end at maximum thermal expansion of the pipe length. Thus, when the pipe length is not at maximum thermal expansion there may be a gap between the end face of the insert end and the abutment.

The present invention also provides a pipeline, for example an oil or gas pipeline, comprising at least two pipe lengths of the type described above. In this case the coupling end of the first pipe length may slideably receive the insert end of the second such pipe length, the sealing arrangement may seal the insert end of the second pipe length within the coupling end; and the or each fixing element of the coupling end of the first pipe length may extend through a corresponding one of the through holes so as to slideably engage within a corresponding slot of the second pipe length, such that the insert end of the second pipe length is slideable within the coupling end of the first pipe length on thermal expansion or contraction of such a second pipe length.

The present invention also provides a method of installing a pipeline of the type described above comprising the steps of: slideably locating the insert end of the second pipe length within the coupling end of the first pipe length so that the slots of the insert end are aligned with the through holes of the coupling end; and fixing the or each of the fixing elements within the through holes of the coupling end of the first pipe length so that they slideably engage the slots of the insert end of the second pipe length.

For a pipeline in which the tie-in temperature and working temperature of the pipeline are similar, the method may comprise the additional step of positioning the insert end within the coupling end so that the fixing elements slideably engage a central portion of the slots. With the fixing elements in this position the connection between the pipe lengths can accommodate both thermal expansion and thermal contraction.

For a pipeline in which the tie-in temperature is higher than the working temperature of the pipeline, the method may comprising the additional step of positioning the insert end within the coupling end so that the fixing elements slideably engage an end region of the slots which end region is located remote to the end face of the insert end. With the fixing elements in this position the connection between the pipe lengths can accommodate the thermal contraction of the pipe lengths when the pipeline is first used. The length of the slots are selected to accommodate the thermal contraction when the pipeline first works and also any subsequent thermal contraction or expansion predicted during the lifetime of the pipeline.

For a pipeline in which the tie-in temperature is lower than the working temperature of the pipeline, the method may comprise the additional step of positioning the insert end within the coupling end so that the fixing elements slideably engage an end region of the slots which end region is located proximal to the end face of the insert end. With the fixing elements in this position, the connection between the pipe lengths can accommodate the thermal expansion of the pipe lengths when the pipeline is first used. Again, the length of the slots are selected to accommodate the thermal expansion when the pipeline first works and also any subsequent thermal contraction or expansion predicted during the lifetime of the pipeline.

The invention will now be described by way of example only and with reference to the accompanying schematic drawings, wherein:

Figure 1 shows a partial longitudinal cross-section through two pipe lengths according to the present invention coupled at tie-in where the working temperature is the same as the tie-in temperature;

Figure 2 shows a partial longitudinal cross-section through two pipe lengths according to the present invention coupled at tie-in where the working temperature is lower than the tie-in temperature; and

Figure 3 shows a partial longitudinal cross-section through two pipe lengths according to the present invention coupled at tie in where the working temperature is higher than the tie-in temperature.

Like parts are represented by like numerals in each of the Figures.

Figure 1 shows an insert end (2) of a first pipe length (4) according to the present invention, coupled within a coupling end (6) of a second pipe length (8) according to the present invention. Each pipe length (4, 8) has a coupling end (6) and an insert end (2) remote from the coupling end. A pipeline is made from a plurality of pipe lengths (4, 8) by connecting the insert end (2) of each pipe length within the coupling end (6) of an adjacent pipe length.

The coupling end (6) of each pipe length (8) is formed with an increased internal diameter, external diameter and wall thickness, as compared to the remainder of the pipe length. This forms an annular shoulder or abutment (10) in the internal surface of the pipe length (8). The internal diameter of the coupling end (6) is dimensioned to smoothly receive the insert end (2) of

another of the pipe lengths (4) so that the insert end (2) fits with close tolerances within the coupling end (6). Adjacent an end surface (12) of the coupling end (6), the internal surface of the coupling end is formed with an annular recess (14) for snugly receiving a first annular seal (16). At the side of the annular recess (14), remote from the end surface (12) the pipe length (8) is formed with four through holes (18), each located at the same distance from the annular recess (14). The four through holes (18) are equally spaced around the circumference of the coupling end (6). Each through hole (18) extends from the external surface of the coupling end (6) to the internal surface of the coupling end. The four through holes (18) are similarly dimensioned, having an outer cylindrical section (18a) adjacent the external surface of the coupling end (6) and an inner internally threaded cylindrical section (18b) adjacent the internal surface of the coupling end (6). The inner cylindrical section (18b) of each through hole (18) has a smaller diameter, sized to fit an externally threaded shank of a fixing element (20), than the outer cylindrical section (18a) of each through hole, which is sized to fit the head of the fixing element. A second annular seal (22) is located against a through hole shoulder (24) formed between the inner (18b) and outer (18a) sections of the through hole (18). Then when a fixing element (20) is fixed within the through hole (18) the second annular seal (22) is fixed between the through hole shoulder (24) and the head of the fixing element.

The insert end (2) of each pipe length (4, 8) is formed, adjacent its end face (28) with four tapered slots (26) which extend from the external surface of the insert end through to the internal surface of the insert end. Each slot (26) is

longer in a direction parallel to the longitudinal axis of the pipe length (4, 8) than in a direction circumferentially around the insert end (2). Each slot (26) is the same distance from the end face (28) of the insert end (2) and each slot conically tapers so that it is wider at the external surface of the insert end than at the internal surface of the insert end. The four slots (26) are equally circumferentially spaced from each other, so that they can be lined up with the through holes (18) and fixing elements (20) of a coupling end (6). The slots (26) are rounded at their ends with a radius of curvature substantially equal to half the width of the slots in the circumferential direction.

The fixing elements (20), through holes (18) and slots (26) are dimension to cooperate. The heads of the fixing elements (20) are dimensioned to fit snugly within the outer sections (18a) of the through holes. The externally threaded sections of the fixing elements (20) are dimension to engage in a screw thread connection within the internally threaded inner sections (18b) of the through holes. The ends of the fixing elements, remote from the heads of the fixing elements, have tapered faces (34) tapering outwardly from a flat circular end face (30) to a main body (32) of an end portion of the fixing element, so that the end faces of the fixing elements are frusto-conical. The main body (32) of the end portions of the fixing elements (20) are dimensioned to pass completely through the through holes (18) and to locate within the slots (26) with the flat end face (30) of the fixing element substantially level with the internal surface of an insert end (2), when an insert end (2) is fitted within the coupling end (6) with the fixing elements fixed within the through holes, as is shown in the Figures. The tapered end surfaces (34)

of the fixing elements taper at the same angle as the slots (26) in the insert end (2) and the diameter of the circular flat end surfaces (30) is substantially the same as the width of the slots (26) in the insert ends at the internal surface of the insert end. Thus, the end faces (30, 34) of the fixing elements (20) are dimensioned to slideably fit within the slots (26) with the tapered end faces (34) engaging tapered side faces (36) of the slots. This tapered face-to- face engagement between the fixing elements (20) and the slot side faces (36) prevents shearing of the fixing elements.

After each pipe length (4, 8) is formed a first annular seal (16) is located within the annular recess (14), a second annular seal (22) is placed within each of the through holes (18) and located against the shoulder (24).

To fit an insert end (2) of the first pipe length (4) within the coupling end of the second pipe length (8), the first pipe length is rotationally aligned with the second pipe length so as to align the slots (26) with the through holes (18). To facilitate this, markers may be formed on or in the external surfaces of the pipe lengths, which markers can then be aligned. The insert end (2) is then pushed into the coupling end (8) until the slots (26) lie below the through holes (18). A fixing element (20) is then fitted within each of the through holes, as is shown in the Figures, so that the second annular seal (22) is trapped between the head of the fixing element and the shoulder (24), the external thread of the fixing element is threadedly connected within the internally threaded portion (18b) of the through hole, and the ends of the fixing element lie within the slots (26). The seals (16, 22) prevent leakage of fluid from the connection between

the two pipe lengths and the fixing elements (20) prevent the removal of the insert end (2) from the coupling end (6), so forming a leak proof and durable pipe connection.

The arrangement of Figure 1 shows the connection between the pipe lengths in a pipeline at tie-in, for a pipeline where the working temperature of the pipeline is similar to the temperature of the pipeline at tie-in. The connection between the pipes is able to accommodate thermal expansion or contraction of the pipe lengths due to variations in temperature during operation of the pipeline. This removes the need for pipe bellow systems or thermal regulation systems in the pipeline. When the connection shown in Figure 1 is made, the insert end (2) is pushed within the coupling end (6) to the position shown in Figure 1. Again external markings formed on or in the insert end can be used to position the insert end (2) by the desired amount within the coupling end. In the position shown in Figure 1 , the ends (32) of the fixing elements (30) are in the centre of the slots (26) in the insert end and there is a gap between the end face (28) of the insert end (2) and the internal shoulder (10) of the second pipe length (8).

The pipe connection shown in figure 1 can accommodate thermal expansion of the pipe lengths (4, 8). When the temperature rises, the pipe lengths expand and the end face (28) of the insert end (2) of the first pipe length (4) moves towards the shoulder (10) of the second pipe length (8). Also the slots (26) in the first pipe length (4) move towards the shoulder (10) of the second pipe length (8), which is accommodated by the movement of the ends (32) of

the fixing elements slideably within the slots (26) towards the ends of the slots remote from the end face (28) of the first pipe length. The pipe connection shown in Figure 1 can also accommodate thermal contraction of the pipe lengths (4, 8). When the temperature falls, the pipe lengths contract and the end face (28) of the insert end (2) of the first pipe length (4) moves away from the shoulder (10) of the second pipe length (8). Also the slots (26) in the first pipe length (4) move away from the shoulder (10) of the second pipe length (8), which is accommodated by the movement of the ends (32) of the fixing elements slideably within the slots (26) towards the end of the slots closest to the end face (28) of the first pipe length.

The arrangement of Figure 2 shows the connection between the pipe lengths in a pipeline at tie-in, for a pipeline where the working temperature of the pipeline is lower than the temperature of the pipeline at tie-in. The connection between the pipes is able to accommodate the thermal contraction the pipe lengths due to the reduction in temperature of the pipe lengths when fluid is first pumped through them. Again, this removes the need for pipe bellow systems or thermal regulation systems in the pipeline. When the connection shown in Figure 2 is made, the insert end (2) is pushed within the coupling end (6) to the position shown in Figure 2 so that the end face (28) of the insert end abuts the internal shoulder (10) of the second pipe length (8). In the position shown in Figure 2, the ends (32) of the fixing elements (30) are located at the end of the slots (26) in the insert end remote from the end face (28).

The pipe connection shown in Figure 2 can accommodate thermal contraction of the pipe lengths (4, 8), when the pipeline is first used. When the temperature falls, the pipe lengths contract and the end face (28) of the insert end (2) of the first pipe length (4) moves away from the shoulder (10) of the second pipe length (8). Also the slots (26) in the first pipe length (4) move away from the shoulder (10) of the second pipe length (8), which is accommodated by the movement of the ends (32) of the fixing elements within the slots (26) away from the end of the slots remote from the end face (28) of the first pipe length.

The arrangement of Figure 3 shows the connection between the pipe lengths in a pipeline at tie-in, for a pipeline where the working temperature of the pipeline is higher than the temperature of the pipeline at tie-in. The connection between the pipes is able to accommodate the thermal expansion of the pipe lengths due to the increase in temperature of the pipe lengths when fluid is first pumped through them. When the connection shown in Figure 3 is made, the insert end (2) is pushed within the coupling end (6) to the position shown in Figure 3 so that there is a gap between the end face (28) of the insert end and the internal shoulder (10) of the second pipe length (8). The gap in Figure 3 between the end face (28) and shoulder (10) is greater than that in Figure 1 to allow for more thermal expansion. In the position shown in Figure 3, the ends (32) of the fixing elements (30) are located at the end of the slots (26) in the insert end closest to the end face (28).

The pipe connection shown in Figure 3 can accommodate thermal expansion of the pipe lengths (4, 8), when the pipeline is first used. When the temperature rises, the pipe lengths expand and the end face (28) of the insert end (2) of the first pipe length (4) moves towards from the shoulder (10) of the second pipe length (8). Also the slots (26) in the first pipe length (4) move towards the shoulder (10) of the second pipe length (8), which is accommodated by the movement of the ends (32) of the fixing elements within the slots (26) towards the end of the slots remote from the end face (28) of the first pipe length.

In a pipeline made from pipe lengths according to the present invention, thermal expansion and contraction of the pipe lengths (4, 8) can be accommodated by the connections between adjacent pipe length insert ends (2) and pipe length coupling ends (6). Each insert end (2) can move further into or out of the coupling end (6) within which it is fitted as required to take account of temperature changes.

The longitudinal length of slots (26) in the insert ends (2) are dimensioned to take into account the maximum amount of thermal expansion or contraction predicted for the lifetime of a pipeline.