GB2251906A - Wye piece junction for flowlines - Google Patents

Abstract

A Wye piece is contained within a spherical steel structure 10 to accommodate loads due to sub-sea pipeline operating pressures. Fluid transportation and pigging operations are through the internal pipework 13. Varying pipeline diameters, internal and external pressures, temperatures, pigging requirements, internal pipe geometry and materials selection may be accommodated in the design. Volumetric changes to the spherical shell may be compensated by an expanding device (Figs 4, 5 not shown) which separates inert fluid contained in space 11 of the shell from the transported fluid in the pipework 13. Alternatively, pressure loadings may be transferred from the internal pipework 13 to the outer shell 10 by filling the internal space 11 with solid material such as concrete or resin. <IMAGE>

Description

Wye Piece Junction for Pipelines This invention relates to piggable Wye piece junctions for liquid and gas pipelines.

Wye piece junctions allow two pipelines to be merged into a single line for the economic transportation of the fluids to a remote receiving station.

Major features of Wye piece design are 1. Facility to permit pigging of the lines for inspection and cleaning operations.

2. Pressure retention within the geometric boundaries delineated by the pigging requirements.

3. Additional mechanical strength to except externally applied loads due to flowline expansion resulting from temperature and pressure changes, wave and current loads, change in fluid momentum and accidental impacts.

This invention allows Wye pieces to manufactured using conventional pressure vessel fabrication techniques rather than the current methods of casting or forging and boring.

The design, manufacturing and testing process for this invention is considerably cheaper than current alternative methods.

The present invention consists of an outer spherical shell which provides pressure containment and strength to accept externally applied loads. The simple geometric shape allows analysis using a standard pressure vessel design code, eg. BS 5500.

The function of the internal pipework shown in the drawing as two intersecting bends of radius three times nominal pipe diameter is to transport the produced fluids and provide guide passages for running inspection, cleaning and intelligent pigs from the output stations.

To prevent internal corrosion of the sphere, external corrosion of the pipework and provide zero differential pressure cross the pipework the sphere may be filled with a suitable fluid prior to operation. Volume changes within the sphere are compensated by means of an expanding bellows, capsule, piston or flexible bag connected by small bore pipework to the pipeline pressure. A dashpot arrangement may be included on the volume compensating device to prevent rapid cycling with small pressure variations.

Alternatively the space between the internal pipework and the external shell may be filled with a solid material (eg. concrete or resin) to transmit pressure loads to the external shell thus dispensing with the pressure compensation arrangement.

Connection of the internal pipework to the shell compensation rings is dependant on a number of variables within the overall design. Alternative methods of connection include the following to compensate for relative movement between the sphere and internal pipework 1. Sliding seal arrangement to allow relative movement between the internal pipework and sphere.

2. Intermediate device between internal pipework and sphere compensation ring which deflects with relatively small loads.

3. Direct connection of the interal pipework to shell compensation rings. The sphere and internal pipework may be prestressed during manufacture by thermal expansion of sphere and cooling of the internal pipework.

A pipeline or valves may be connected to the Wye piece via a stub and flange connection to the compensation rings as indicated, direct flange connection to the compensation rings or by connection to stubs projecting from the rings.

Figure 1. shows a plan view of the Wye piece sectioned across the centre line.

Figure 2. shows a plan view of the Wye piece.

Figure 3. shows a half sectioned elevation of the Wye piece from the upstream end.

Figure 4. shows sectioned spring loaded sliding seal arrangement between the internal pipework and shell compensation ring.

Figure 5. shows a sectioned half toroidal corrugation between the internal pipework and shell compensation ring.

Referring to the drawing the Wye piece comprises of a spherical shell 10 filled with an inert fluid 11. The transported fluids 12 and pigs (not shown) are carried by the Wye piece pipework 13.

connected to the shell via the rings 14.

Transported fluid 12 passes through the shut of valves 15 via pipe 17 and enters the volume compensating devices 16 (flexible bellows arrangement shown) which expand according to the pressure and volume change in the sphere to equalise pressure across the internal pipework 13. A simple dashpot (not shown) may be included to reduce transient pressure cycling of the volume compensation device.

The sphere is filled with fluid through valve 18 which may also function as a drain valve. Item 19 is a vent valve which is opened during the filling process.

Alternatively the inert fluid 11 may be replaced by a solid material (eg. concrete or resin) to transfer pressure loading from the internal pipework to the outer shell thus dispensing with the volume compensation arrangements.

Two possible alternative means of providing for relative movement between the expanding sphere and internal pipework are shown in figures 4 and 5.

Refering to figure 4, as the spherical shell 10, compensation ring 14 and flange 20 expand the seal assembly 21 loaded by springs 23 slides along the pipework 13.

Refering to figure 5, as the sherical shell 10, compensation ring 14 and flange 20 expand outwards from the pipework 13 the half toroidal corrugation 22 deflects.

The Wye piece would be installed, supported and protected on the seabed by a structural steel frame (not shown) which would also carry associated valving. The design of the structural frame would provide for fixing to the seabed by means of piles, gravity, skirt or grouting techniques.

Claims (10)

1. Wye piece with external spherical shell which provides pressure containment and strength for loads due to pipeline operating pressures and any externally applied loads. The internal pipework is capable of carrying fluids and inspection and cleaning pigs.

2. Wye piece as claimed in claim 1 with volume compensating device to provide eqalising pressure across pipework and separate transported fluid from inert fluid contained between outer shell and pipework.

3. Wye piece as claimed in claim 1 with space between outer spherical shell and internal pipework filled with solid material (eg. concrete or resin) to transmit pressure loads from internal pipework to outer shell.

4. Wye piece as claimed in claims 1, 2 and 3 designed to suit varying pipeline diameters, operating pressures, water depth, temperatures, pigging requirements, external loads, fluid properties, material specifications and internal geometry requirements.

5. A Wye piece substantially as described herein with reference to figures 1-5 of the accompanying drawing.

6. Limited resources required for design, manufacture, quality control of materials and fabrication, testing, maintenance, inspection and repair.

7. Simple connection of valves and pipelines by flange connection or welding via a stub to the shell compensation ring.

8. Environmental security resulting from a double skin construction.

9. Wye piece as claimed in previous claims may be fabricated using conventional fabrication techniques.

10. Wye piece as claimed in previous claims would be supported within a steel framework that is fixed to the seabed.