GB2527071A

GB2527071A - A tensile overload protection system for offloading systems

Info

Publication number: GB2527071A
Application number: GB1410310.5A
Authority: GB
Inventors: James Straker; Brian Blenkinsop; Colin Rutherford
Original assignee: Techflow Marine Ltd
Current assignee: Techflow Marine Ltd
Priority date: 2014-06-10
Filing date: 2014-06-10
Publication date: 2015-12-16
Also published as: WO2015189580A1; EP3154852B1; GB201410310D0; EP3154852A1

Abstract

A tensile overload protection system is provided for a loading hose (16, Fig 6(a)) of an offloading system 18. The tensile overload protection system comprises at least one first tether 104, having a first end and a second end that are coupleable between a predetermined segment 106 of a hose string and a hose string support structure 20, so as to transfer a tensile load above a predetermined threshold from the hose string to the at least one first tether. The tensile overload protection system further comprises a first connection member (108, Fig 8) that is connectable to the hose string and comprises at least one first anchor point adapted to receive and fix the first end of the at least one first tether, and a second connection member 112 that is operatively coupleable to the hose string support structure and comprises at least one second anchor point (118, Fig 10) adapted to receive and fix the second end of the at least one first tether.

Description

A TENSILE OVERLOAD PROTECTION SYSTEM FOR OFFLOADING SYSTEMS

The present invention relates generally to the field of oil and gas production, and towards offloading and storage facilities. In particular, the present invention relates to an overload protection system for offloading facilities offshore and onshore.

Introduction

A floating production, storage and offloading [FPSO) unit is a floating vessel used by the offshore oil and gas industry for the processing of hydrocarbons and for storage of oil. An FPSO vessel is designed to receive hydrocarbons produced from nearby platforms or subsea template, process them, and store oil until it can be offloaded onto a tanker or, less frequently, transported through a pipeline. FPSOs are preferred in frontier offshore regions as they are easy to install, and do not require a local pipeline infrastructure to export oil. FPSOs can be a conversion of an oil tanker or can be a vessel built specially for the application. A simplified FPSO 10 and offloading tanker 12 is shown in Figure 1, where the tanker 12 is moored to the FPSO 10 via a hawser 14, and the hose string 16 provides a fluid connection between the FPSO 10 and the tanker 12 allowing, for example, crude oil to be transferred from the FPSO to the tanker.

The offloading of crude oil from an FPSO vessel to a shuttle tanker is often facilitated via offloading systems 18 that are integrated into the hull of the FPSO 10. As shown in an example in Figure 2, the offloading system 18 may consist of a rotating hose reel 20 accommodating hose(s) that can be deployed overboard and connected to the tanker 12 to facilitate the offloading process. The hose string 16 is connected to the offloading reel 20 at a gooseneck connection 22 secured by a bolted flange (not shown).

The nature of the offloading procedure and the close proximity of the FPSO 10 and tanker 12 create a significant risk of oiL spillage that may he caused by hose rupture.

One of the ways in which this risk is mitigated, is to confine the offioading operation into a strictly controlled offloading zone or sector. The position of the shuttle tanker 12 relative to this zone is close]y monitored. in the event that this position cannot be maintained, emergency disconnection procedures of the hose string 16 are automatically initiated. Thus, in the unlikely event of failure of the safety systems employed during offloading an emergency breakaway coupling connecting the hose string 16 and the gooseneck connection 22 of the reel 20 will automatically shut off and disconnect the hose 16 when the vessels drift apart to the point that tension in the hose 16 becomes significantly greater than that of normal operation.

Offloadinu System -Exuansion of Offloadin2 Zone Examples of typical offloading zones 24, 25 defined around an FF50 10 are shown in Figures 3 [a) -[d), The offloading zones 24, 25 are defined from an analysis of the predominant environmental conditions for the specific proposed location in which the FPSO 10 is operational. In the event the conditions change during the oftloading process to the point that the tanker position cannot he maintained, the tanker 12 will disconnect and can in many cases reconnect safely to the offloading system 18 on the opposite side of the FF50 10.

Recent FF50 developments lead to the consideration of an expanded offloading zone providing an increase of the scope of operation and consequently an increase of the opportunity for the offioading to take place. An expanded offLoading zone 25 also justifies a reduction from two separate offloading systems 18 at opposite sides of the FPSO 10 to a single offloading system 18.

Furthermore, the extent 26 within which an emergency load condition can be seen in the hose string 16 for those systems currently in use are predominantly governed by the size and position of the oflloading zone 24, 25. Consequently, the extent 26 to which an emergency load can be applied to Lhe offloading system via the hose 16 is greatly increased by the extended offloading zone 25.

However, the new conditions provided by the extended offloading zone 25 may impose loading regimes upon the hose 16, specifically the hose connection to the offloading system 18, that have not yet been considered or tested for the currently available equipment, and may go beyond the structural capabffities of the hose 16.

In particular, the new loading regimes imposed by the extended offloading zone 25 are significantly more stringent than the loading regimes imposed by the offloading zone 24 generally applied to similar systems. As a result, currently available hoses 16 are structurally not capable of sustaining the anticipated new load conditions without the severe risk of rupture. A rupture of the hose string 16 during offloading would invariably result in a severe pollution incident through loss of the product (e.g. crude oil) directly into the sea.

Figure 4(a) depicts the sectors (hatched) of the extended offloading zone 25 where new loading regimes may be imposed to the hose strIng 16 during offloading. Figure 4(b), shows an example of a hose string 16, typically consisting of many segments 16A that are joined by flange connections 28, each segment 16A comprising rigid steel end fittings (not shown) coupled to a flexible composite rubber tube. Such an arrangement is capable of withstanding considerable axial load and may also wIthstand bending of the rubber tube to a radius of around four times the dIameter of the flexible tube. However, the hose 16 and its flange connectIon 28 are not capable of simultaneously sustaining large tensile loading and a significant misalignment angle. Thus, its capacity for applied bending moments is severely limited.

In summary, the use of an extended offloading zone 25 significantly increases the area in which the emergency release coupling load could be imposed upon the offloading system 18 via the hose 16. The hose 16 does not have the structural capability of sustaining such potentIal loads throughout the entIre scope of application during offloading.

Accordingly, it is an object of the present invention to provide a system that is adapted to limit the potentially imposed bending moments within the hose string and segments to a predetermined maximum magnitude that is within the permissible range of the minimum bending radius (MBR) of the hose string 16.

Summary of the Invention

Preferred embodiment(s) of the invention seek to overcome one or more of the

above disadvantages of the prior art.

According to a first embodiment of the invention there is provided a tensile overload protection system for a loading hose, comprising: at least one first tether, having a first end and a second end, coupleable between a predetermined segment of a hose string and a hose string support structure, so as to transfer a tensile load above a predetermined threshold from the hose string to said at least one first tether; a first connection member connectable to the hose string and comprising at least one first anchor point adapted to receive and fix said first end of said at least one first tether, and a second connection member operatively coupleable to the hose string support structure and comprising at least one second anchor point adapted to receive and fix said second end of said at least one first tether.

This provides the advantage of a passive tensile overload protection to the hose string by transferring any tensile load above a predetermined magnitude from the hose string to the tether and the offloading reel, therefore) preventing potentially damaging bending moment that may be caused by either an excessive tensile load or a minimum permissible bending radius (within the extended offloading zone). In particular, the overload protection system is functioning in synergy with the offloading system, so as to only deploy and engage the tether(s) when the hose string is stressed above a predetermined magnitude without interfering with the functionality of the offloading system. Thus, the system of the present invention can be permanently installed to the offloading system providing an additional and improved safety mechanism to the hose string.

Advantageously, the first connection member may be adapted to be coupled to any one of the flange members connecting two successive segments of the hose string.

This provides the advantage of improved adaptability and functionality due to integrated flange members suitable for connecting the tether(s).

Preferably, the tensile overload protection system may further comprise at least one first guide member connectable to the hose string and adapted to guidingly support said at least one first tether. Advantageously, the guide member may comprise at least one guide loop. Advantageously, the at least one first guide member may be adapted to be coupled to any one of the flange members connecting two successive segments of the hose string. This provides the advantage of functionally aligning the tether(s) with the longitudinal axis of the hose string ensuring that tensile loads applied to the hose string are transferred directly to the tether(s) and offloading reel, as well as, minimising the risk that any slack of the tether(s) may interfere with any movement of the hose string during offloading.

Advantageously, the at least one second anchor point may be a pivot anchor.

Alternatively, the at least one second anchor point may comprise at least one sheave adapted to operatively receive said at least one first tether.

Advantageously, the second connection member may further comprise a tether stowage adapted to receive and stow any excess portion of said at least one first tether. Preferably the tether stowage may comprise a predetermined groove cut in the hose string support structure adapted to receive and retain any excess portion of said at least one first tether. Additionally, the tether stowage may further comprise a retract mechanism adapted to retract any excess portion of said at least one first tether into said stowage at a predetermined tensile force. This provides the advantage of minimising any slack of the tether(s) when not engaged, i.e. the tensile load on the hose sting is below a predetermined threshold. The threshold is determined by the structural characteristics of the hose string when bent within the limits of the extended offloacling zone and under a tensile load. An automatic retracting mechanism, such as a spring loaded cable retractor, provides the advantage that the tether(s) is kept taut during operation with the tensile load below which the overload protection system is deployed.

Advantageously, the tensile overload protection system may further comprise an overload detector adapted to indicate when the tensile load is above said predetermined threshold and transferred from the hose string to said at least one first tether. Preferably, the overload detector may be adapted to provide any one of a visual and/or audible signal upon deployment of said at least one first tether.

Advantageously, the visual signal maybe a coloured marking on said excess portion of said at least one first tether. Advantageously, the audible signal may be actuated when the tensile load applied to the hose string exceeds said predetermined threshold. This provides the advantage that an operator or user of the system is informed visually and/or audibly that the tensile load on the hose string has exceeded the predetermined threshold, ensuring that the deployment and engagement of the overload protection system is not missed by the operator(s).

Preferably, the tensile overload protection system may further comprise at least one second tether, having a first end and a second end. Advantageously, the first connection member may further comprise at least one third anchor point adapted to receive and fix said first end of said at least one second tether. The at least one second anchor point may be further adapted to receive and fix said second end of said at least one second tether.

Preferably, the at least one first and at least one second tether are aligned in parallel to the longitudinal axis of at least one hose string segment. This provides the advantage that the hose string and the tether(s) are operatively aligned with the force vector if the tensile load applied to the hose string.

Preferably, the at least one first tether and/or said at least one second tether may be made of a flexible element having a tensile strength that is higher than the tensile strength of the hose string.

Advantageously, the flexible element may be formed from any one of a metal, a synthetic rope or a composite material having a predetermined tensile strength that is higher that the tensile strength of the hose string.

Preferably, the length of said at least one first and/or second tether may be so as to allow a predetermined maximum tensile load and respective predetermined maximum stretch of the hose string before said tensile overload protection system is engaged.

According to a second embodiment of the present invention, there is provided an offloading system comprising a rotataffle hose reel configured to store a hose string, an offloading connection adapted to connect to the hose string, and a tensile overload protection system according to the first embodiment of the present invention.

Brief Description of the Drawings

Preferred embodiments of the present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which: Figure 1 (prior art) shows a simplified offshore setup for an offloading FPSO in engagement with a tanker; Figure 2 (prior art) shows a commonly used offloading system comprising an offloading reel, gooseneck connection and hose string; Figure 3 (prior art) shows examples of (a) standard offloading zones (b) an extended offloading zone, and (c] & (d) the extent of the offloading zones in (a] and (bJ; Figure 4 shows an example of (a) an extended offloading zone and the regions for limited full-load-application', and (b) and bent section of a typical hose string comprising hose segments and flange connections; Figure 5 illustrates a first embodiment of the overload protection system when operatively coupled to an offloading system; Figure 6 shows a side view of (a] the engaged overload protection system and (b] a schematic diagram of the movement of the tether(s) during movement of the hose string demonstrating that the tether system will remain passive until such times as the hose string is forced out of position through the application of an accidental loading condition; Figure 7 shows (a] a perspective view and (b] a front view of the hose reel, goose neck, hose string and coupled overload protection system including guide members; Figure 8 (a] shows (a) a perspective view and (b] a top view of the flange member coupled to the hose string with a single tether connected to each side of the hose string; Figure 9 shows a detailed (a) perspective view and (b] bottom view of the second connection member integrated in the offloading reel and two tethers anchored to the second connection member; Figure 10 shows (a) a perspective view and (b) side view of a first example of the second anchor point in form of a pivot anchor for two tethers; Figure 11 shows (a) a perspective view and (b] a sectional side view of a second example of the second anchor point in form of a sheave anchor for one tether; Figure 12 shows a schematic diagram of an extended offloading zone and its risk regions during offloading..

Detailed description of the preferred embodiment(s) The exemplary embodiments of this invention will be described in relation to offshore offloading of hydrocarbon fluid. However, it should be appreciated that, in general, the system and method of this invention will work equally well for any other suitable offloading system offshore and onshore.

For purposes of explanation, it should be appreciated that the terms determineç calculate' and computeç and variations thereof, as used herein are used interchangeably and include any type of methodology, process, mathematical operation or technique. In addition, the terms vertical and horizontal refer to the angular orientation with respect to the surface of the earth.

Referring now to Figures 5, 6 and 7, a first embodiment of the overload protection system 100 includes two flexible tethers 102 and 104 that are coupled to the original flange connectors 28 via a flange adaptor 106. The tethers 102, 104 maybe formed from metal wires, or steel ropes or synthetic ropes or any other suitable compound to form a flexible tether 102, 104. The flange adaptor 106 may be a flange member that is coupled between two existing flange connectors 28, but may also be a simple disc member (not shown) compatible with and connectable to the flange connectors 28 of the hose string.

In the preferred example, the flange adaptor 106 is a flange member 106 having an anchor point 108 for each tether 102 and 104 on either side of the hose string 16 (see Figure 8). The anchor points 108 may be pivot anchors allowing the tether 102, 104 to pivot about a pivot axis of the anchor point 108 and align the tether(s) 102, 104 and the hose string axis under tensile load. The pivot anchor may be formed by a simple pin which forms a pivot axis for a ooped end of the tethers 102, 104, or, the anchor points 108 may include a hinge connectable to the ends of the tethers 102, 104 allowing the tethers 102, 104 to move freely about the pivot axis of the hinge.

Any suitable hinge mechanism may be used for the anchor points 108.

Alternatively, the flange adaptor 106 maybe mountable to the outer surface of the existing flange connectors 28. It is understood by the person skilled in the art that any suitable mount that is adapted to provide at east one anchor point 108 for at least one tether 102, 104 maybe used.

A tether guide 110 maybe provided at a more proxima' flange connection aflowing the tethers 102, 104 to be aligned with the thngitudinal axis of the hose string 16.

The tether guide 110 may simple be a guide loop [not shown) attached to a disc member that is operatively coupleable between two flange connectors 28. However, any other guide (e.g. a sheath) suitable to receive and support the tethers 102, 104 may be used. Alternatively, the tether guide 110 may be mounted to the outer surface of the hose string 16.

Referring now to Figures 9 and 10, the second end of the tethers 102, 104 are anchored to the reel structure 20 of the offloading system 18 via a reel anchor 112.

In the preferred example, the reel anchor 112 includes a reinforced segment 114 mounted to the reel drum 20, wherein a pivot anchor is operatively mounted to the inside of the reel drum. A groove 116 in the reinforced segment 114 allows the tethers 102, 104 to pass through the reel drum wall in order to attach to the pivot anchor 118. In the preferred example of the present invention, tethers 102 and 104 share the same pivot anchor 118. The groove 116 may be formed so as to allow any slack tether 102, 104 to be stowed away inside the ree' drum 20. For example, the groove may be S'-shaped so that the slack tethers 102, 104 can be placed inside the reel drum 20.

Alternatively, the reel anchor 112 may include a spring biased retractor (not shown) that is adapted to automatically retract any slack of the tethers 102, 104 keeping the tethers 102, 104 taut even when the overload protection system 100 is not deployed / engaged due to an excessive tensile load. The spring biased retractor (not shown) may be mounted to the tethers 102, 104 between the pivot anchor 118 and the reinforced segment 114 so as to only retract the slack portion of the tethers 102, 104, and to disengage when the overload protection system 100 is depthyed. It is understood by the person skilled in the art, that any suitable retractor mechanism may be used to pull in any slack of the tethers 102, 104. It is understood that the retracting force applied to the tether(s) 102, 104 is less than a predetermined threshold of the tensile load applied to the hose string 16.

Alternatively, the reel anchor 112 may include a sheave 120 mounted inside the reel drum 20 to the reinforced segment 114. When using the sheave 120, only a single tether 102 is required to provide a dual guided tether arrangement running the tether 102 through the sheave 120 and connecting both ends to the anchor points 108 at the flange adaptor 106. A retractor mechanism maybe operatively coupled to the sheave 120 so as to retract any slack of the tether 102 when the overload protection system 100 is not deployed.

In addition, the overload protection system 100 may include an audible and/or visual indicator adapted to provide a visual and/or audible alarm when the tensile load exceeds a predetermined magnitude and the overload protection system 100 is deployed by tautening the tether(s) 102, 104 between the anchor points 108 and 112. A visual marker may be a coloured section of the tether(s) 102, 104 that only becomes visible when the slack of the tether is pulled out of the stowage inside the reel drum 20 at a predetermined tensile load. In addition or instead, an audible signal may be provided when the tensile load applied to the tether(s) 102, 104 exceeds a predetermined magnitude. The audible signal generator maybe actuated via a tensile tester operatively coupled to the tether(s) 102, 104.

During operation and in the event an extreme emergency toad is applied to the hose string 16, the hose catenary will be forced into ahgnment with the direction of the applied load 200 (see Figure 6, hose orientation (i)]. In accordance with the extended offloading zone 25, the direction of this load can be from a large area about the front and sides of the offloading system 18. When the hose string is pulled into alignment with the tensile load path the tether[s) 102, 104 are deployed and tautened against the anchor points 108 and 112 transferring the poteritia][y damaging tensile load from the hose string 16 and goose neck 22 to the hose reel structure 20 of the offloading system 18. At the same time, a coloured section of the tether(s) becomes visible indication the deployment of the overload protection system 100. Consequently) and since the tensile stress within the hose string 16 is limited to a predetermined maximum, the maximum bending moment that may be generated is also limited to not exceed a predetermined magnitude. The predetermined magnitude of the tensile load allowed within the hose string is defined to be well below the structural limitations of the hose string under tensile load and when bent to the MBR. When the tensile load applied to the hose string is below the predetermined threshold, the tether system will go slack and become passive again (see Figure 6, hose orientation (ii)).

Figure 12 shows an example of offloading load cases within the extended offloading zone 25, where the emergency load case applied as ilLS in a first zone 302 immediately behind the central portion of the offloading zone 25 provides perceived risks of drift-off and reverse drift-off. Emergency load cases applied as ALS in a second zone 304 provides the perceived risks of drift-off with reduced probabilir of disconnection failure.

It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS1. A tensile overload protection system for a loading hose, comprising: at least one first tether, having a first end and a second end, coupleable between a predetermined segment of a hose string and a hose string support structure, so as to transfer a tensile load above a predetermined threshold from the hose string to said at least one first tether; a first connection member connectable to the hose string and comprising at least one first anchor point adapted to receive and fix said first end of said at least one first tether; a second connection member operatively coupleable to the hose string support structure and comprising at least one second anchor point adapted to receive and fix said second end of said at least one first tether.
2. A tensile overload protection system according to claim 1, wherein said first connection member is adapted to be coupled to any one of a flange member connecting two successive segments of the hose string.
3. A tensile overload protection system according to any one of the preceding claims, further comprising at least one first guide member connectable to the hose string and adapted to guidingly support said at least one first tether.
4. A tensile overload protection system according to claim 3, wherein said guide member comprises at least one guide loop.
5. A tensile overload protection system according to any one of claims 3 and 4, wherein said at least one first guide member is adapted to be coupled to any one of the flange member connecting two successive segments of the hose string.
6. A tensile overload protection system according to any one of the preceding daims, wherein said at least one second anchor point is a pivot anchor.
7. A tensile overload protection system according to any one of the preceding daims, wherein said at least one second anchor point comprises at least one sheave adapted to operatively receive said at least one first tether.
8. A tensile overload protection system according to any one of the preceding daims, wherein said second connection member further comprises a tether stowage adapted to receive and stow any excess portion of said at least one first tether.
9. A tensile overload protection system according to claim 8, wherein said tether stowage comprises a predetermined groove cut in the hose string support structure adapted to receive and retain any excess portion of said at least one first tether.
10. A tensile overload protection system according to any one of claims B or 9, wherein said tether stowage further comprises a retract mechanism adapted to retract any excess portion of said at least one first tether into said stowage at a predetermined tensile force.
11. A tensile overload protection system according to any one of the preceding daims, further comprising an overload detector adapted to indicate when the tensile load applied to the hose string exceeds a predetermined threshold and said at least one first tether is engaged.
12. A tensile overload protection system according to claim 11, wherein said overload detector is adapted to provide any one of a visual and/or audible signal upon deployment of said at least one first tether.
13. A tensile overload protection system according to claim 12, wherein said visual signal is a coloured marking on said excess portion of said at least one first tether.
14. A tensile overload protection system according to any one of claims 12 and 13, wherein said audible signal is actuated when the tensile load applied to the hose string exceeds said predetermined threshold.
15. A tensile overload protection system according to any one of the preceding daims, further comprising at least one second tether, having a first end and a second end.
16. A tensile overload protection system according to claim 15, wherein said first connection member further comprises at least one third anchor point adapted to receive and fix said first end of said at least one second tether.
17. A tensile overload protection system according to any one of claims 15 and 16, wherein said at least one second anchor point is further adapted to receive and fix said second end of said at least one second tether.
18. A tensile overload protection system according to any one of claims 15 to 17, wherein said at least one first tether and at least one second tether are aligned in parallel to the longitudinal axis of at least one hose string segment.
19. A tensile overload protection system according to any one of the preceding daims wherein said at least one first tether and/or said at least one second tether are made of a flexible element having a tensile strength that is higher than the tensile strength of the hose string.
20. A tensile overload protection system according to claim 19, wherein said flexible element is formed from any one of a metal, a synthetic rope or a composite material.
21. A tensile overload protection system according to any one of the preceding claims, wherein the length of said at least one first and/or second tether is so as to allow a predetermined maximum tensile load and respective predetermined maximum stretch to be applied to the hose string before said tensile overload protection system is engaged.
22. An offloading system comprising a rotatable hose reel configured to releasably store a hose string, an offloading connection adapted to connect to the hose string, and a tensile overload protection system according to any one of the preceding claims.