BODY OF WATER"

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from Italian patent application no. 102018000008658 filed on September 17, 2018, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method and a system for laying a pipeline on the bed of a body of water.

STATE OF THE ART

Hydrocarbon transport pipelines are laid on the bed of a body of water by laying vessels, each of which is configured to assemble the pipeline on board the laying vessel and launch the pipeline as it is assembled. The laying vessel therefore includes assembly equipment and a launch ramp for the so-called S-laying, or a launch tower for the so-called J-laying. The letters "S" and "J" identify the type of laying in relation to the shape taken by the pipeline between the laying vessel and the bed of the body of water. The so-called S-laying is particularly suitable for laying pipelines with high productivity in medium shallow water, whereas the so-called J-laying is suitable for laying the pipeline in deep water.

Generally, the pipeline is flexible enough to adapt to the profile of the bed of the body of water. However, there are situations in which the profile of the bed of the body of water has abrupt changes in slope and the diameter of the pipeline is relatively large, resulting in a reduced flexibility of the pipeline. The combination of the above factors brings about configurations in which the pipeline is partly suspended with respect to the bed of the body of water and the bending moment stresses in the pipeline exceed the threshold values, and for this reason can cause uncontrolled deformation of the pipeline.

Several solutions are known for mitigating the problem described above.

A first solution consists in modifying the profile of the bed of the body of water, before or after laying the pipeline, by means of earthmoving operations that are all the more complex the greater the depth of the bed of the body of water.

A second solution involves the use of supports that modify the resting configuration of the pipeline on the seabed, or of components such as buoys and flexible joints which modify the configuration of the pipeline along the section exhibiting the change in slope (W02011008704, US7963721 ) .

A third solution involves the use of articulated joints that can be inserted in the launching sequence (dummy pipelaying) , hinged together and at the two ends of the pipeline. These ends are hydraulically closed with Y- shaped flanged branches which split the pipeline into two directions with structural and hydraulic continuity (W02017013541 in the name of the applicant) .

A fourth solution consists in a non-continuous launching method comprising the laying of prefabricated pipeline sections that reproduce the profile of the body of water. These pipeline sections are prefabricated, transported floating and sunk in a controlled manner as described in WO 2016/046,805 in the name of the applicant.

A further solution consists in carrying out a controlled, permanent plastic deformation of the pipeline in situ. In the context of launching underwater pipelines, document EP 963,798 in the name of the applicant describes a machine which can be clamped to the pipeline and is movable along the pipeline. The machine comprises a U- shaped frame which can be selectively clamped to the pipeline at a desired position, wheels for positioning the machine precisely along the pipeline, and a central rotation fulcrum comprising two anvils hinged to the frame.

All the available solutions have advantages and disadvantages and the use of one solution in place of another depends on a plurality of conditions that can make one solution technically sound and cost-effective compared to the others .

Making a curved section in situ through controlled plastic deformation has considerable advantages in certain operating conditions, however, it has some limitations due to the possible occurrence of uncontrolled deformations, such as for example the breaking, collapse, or buckling, before making the curved section through the controlled plastic deformation of the pipeline.

OBJECT OF THE INVENTION

The object of the present invention is to provide a method which can mitigate the drawbacks of the prior art.

In accordance with the present invention, there is provided a method for laying a pipeline on the bed of a body of water, the method comprising the steps of:

- assembling a pipeline on a laying vessel;

- launching the pipeline from the laying vessel;

- identifying a zone of the bed of the body of water that causes stresses greater than a threshold value determined for the pipeline;

- progressively laying the pipeline on the bed of the body of water by advancing the laying vessel; and

- making at least one curved section along the pipeline with a curvature concordant with the curvature assumed by the pipeline in proximity to said zone by means of a controlled plastic deformation, when the pipeline is at least partly laid on the bed of the body of water and partly suspended with respect to the bed of the body of water in proximity to said zone.

The present invention allows one or more curved sections to be made during the laying of the pipeline on the bed of the body of water or in a pause between the laying operations. The fact that the pipeline is subjected to a controlled plastic deformation when it is at least partly laid and partly suspended on the bed of the body of water as well as the fact that the curved section has a curvature concordant with the curvature assumed by the pipeline allow the curved section to be made in a stable equilibrium condition. Keeping the pipeline at least partly suspended prevents the stresses on the pipeline from exceeding critical values.

In particular, the method comprises acquiring signals correlated to the angle and length of the curved section; and comparing the signals with reference parameters .

In this way, whether the curved section actually corresponds to the design parameters is monitored during the construction of the curved section.

In particular, the method comprises transmitting to the laying vessel a signal deriving from the comparison of the angle and length of the curved section with the reference parameters .

The information in real time concerning the construction of the curved section makes it possible to evaluate how to proceed with the laying operations.

In particular, the method comprises calculating a further signal as a function of the said signals for correcting a graph correlated to the stresses generated in the pipeline; and showing the corrected graph on board the laying vessel.

In this way, information concerning the stresses on the pipeline can be obtained in real time and the successive laying operations can be evaluated based on the curved section under construction.

In particular, the method comprises making a plurality of close step bends in said pipeline, said curved section comprising a succession of close bends.

In this way, each bend is only a slight bend comprised in the range between 0° 30' and 1° 30' .

In accordance with a particular embodiment of the invention, the method comprises making at least a first curved section upstream of said zone with reference to the direction of laying of the pipeline and at least a second curved section downstream of said zone.

Generally, the pipeline is in contact with the most critical zone so that it is easier to bend the pipeline upstream and downstream of the critical zone instead of bending the pipeline in the critical contact zone.

In particular, the method comprises making the first and the second curved section when the pipeline downstream of said critical zone is suspended between said critical zone and the laying vessel.

In this way, the pipeline can be bent before the stresses on the pipeline exceed a given threshold value.

In particular, the method comprises laying the pipeline upstream of said zone up to said zone; making the first curved section upstream of the zone; advancing the laying vessel for lowering the level of the pipeline downstream of said zone; making the second curved section downstream of said zone; and laying the pipeline downstream of said zone.

The described sequence allows the pipeline to be clamped with a bending machine .

In accordance with a second embodiment of the present invention, the method comprises laying the pipeline in said zone; keeping in suspension a section of the pipeline upstream of the said zone for reducing stresses on the pipeline by means of at least one support downstream of the said zone, and keeping in suspension the pipeline downstream of the said zone for reducing stresses on the pipeline by means of at least a second support . In this way, pipeline laying operations are not interrupted and the pipeline is curved after the laying thereof .

In particular, the method comprises making the first curved section upstream of the said zone and the second curved section downstream of the zone; and removing the first and the second support.

In this way, the pipeline assumes its final configuration .

Another object of the present invention is to provide a system for laying a pipeline on the bed of a body of water, which is free from the drawbacks of the prior art.

In accordance with the present invention, there is provided a system for laying a pipeline on the bed of a body of water, the system comprising:

- a laying vessel configured for assembling a pipeline, launching the pipeline into the body of water, and progressively laying the pipeline on the bed of the body of water by advancing the laying vessel;

- a ROV configured to monitor the position of the pipeline on the bed of the body of water with respect to a zone of the bed that causes stresses higher than a threshold value determined for the pipeline; and

- a bending machine to be coupled to the pipeline for making, through controlled plastic deformation, at least one curved section along the pipeline which is concordant with the curvature assumed by the pipeline in proximity to said zone, when the pipeline is at least partly laid on the bed of the body of water and partly suspended with respect to the bed of the body of water in proximity to said zone.

In this way, it is possible to estimate the stresses on the pipeline according to the position of the pipeline on the bed of the body of water and intervene with the bending machine before the estimated stresses exceed a threshold value.

In particular, the bending machine comprises an inclinometer and an odometer for acquiring respective signals correlated to the angle and length of the curved section; and the system comprises a microprocessor configured to compare said signals with reference parameters .

In this way, it is possible to check whether the curved section corresponds to the design parameters even during construction.

In particular, the microprocessor is configured to calculate a further signal as a function of said signals and of the reference parameters and transmit the further signal to the laying vessel for correcting a graph correlated to the stresses generated in the pipeline; the laying vessel comprising a display to show the corrected graph on board the laying vessel.

The information provided on board the laying vessel makes it possible to decide how to manage the laying operations .

BRIEF DESCRIPTION OF THE FIGURES

Further features and advantages of the present invention will be apparent from the following description of non-limiting embodiments thereof, with reference to the figures of the accompanying drawings, wherein:

- Figures 1 to 14 are schematic side elevation views, with parts removed for clarity, of successive steps of laying a pipeline on the bed of a body of water in accordance with a first embodiment of the method object of the present invention; each of the schematic Figures 1 to 14 is associated with one or more graphs which show the stresses on the pipeline estimated as a function of the configuration and structure of the pipeline and of the configuration of the bed of the body of water;

- Figure 15 is a schematic view, with parts removed for clarity, of the system object of the present invention; and

- Figures 16 to 18 are schematic side elevation views, with parts removed for clarity, of successive steps of laying a pipeline on the bed of a body of water in accordance with a second embodiment of the method object of the present invention; each of the schematic Figures 16 to 18 is associated with one or more graphs which show the stresses on the pipeline estimated as a function of the configuration and structure of the pipeline and of the configuration of the bed of the body of water.

PREFERRED EMBODIMENT OF THE INVENTION

With reference to Figure 1, a laying vessel 1 for laying a pipeline 2 on a bed 3 of a body of water 4 is depicted as a whole. The term "pipeline" refers to both a completed pipeline and a pipeline under construction.

The attached Figures show a laying vessel 1 for S- laying; of course, it is understood that the definition "laying vessel" refers to both a laying vessel for S-laying and a laying vessel for J-laying. The laying vessel 1 is equipped to assemble the pipeline 2, progressively launch the pipeline 2, and lay the pipeline 2 as it advances in the direction of travel D1.

Generally, the conformation of the bed 3 is very variable depending on the geographical areas and often there are geological conformations that can induce critical stresses on the pipeline 2. The case illustrated in the attached Figures shows a bed 3 which comprises a zone 5 close to the shore defined by the so-called "continental shelf" and a zone 6 adjacent to the zone 5 and defined by the so-called "continental slope". The zone 5 and the zone

6 meet in a zone 7, which is characterized by a strong change in slope and, in substance, is the tip of a protrusion of the bed 3 and represents a high criticality for the pipeline 2 as it could cause uncontrolled bends in the pipeline 2.

In Figure 1, the pipeline 2 is laid on the zone 5 (continental shelf) up to the zone 7 and is suspended in the body of water 4 between the zone 7 and the laying vessel 1 above the zone 6. The graph C associated with Figure 1 shows the stress on the pipeline 2 according to a predefined scale. Exceeding a threshold value T represents a critical condition for the pipeline 2 which could cause uncontrolled bends in the pipeline 2. In the graph associated with Figure 1, the graph C is below the threshold value T.

In Figure 2, the laying vessel 1 has moved forward and launched a further portion of the pipeline 2 compared to Figure 1. Since the portion of the pipeline 2 suspended between the zone 7 and the laying vessel 1 is larger than that of Figure 1, the graph C correlated to the stress on the pipeline 2 in the zone 7 has a peak P, which corresponds to the zone 7 but is still below the threshold value T .

In Figure 3, the laying vessel 1 has moved further forward and launched a new section of the pipeline 2 compared to Figure 2. Consequently, the peak P in the zone 7 is very close to the threshold value T. The weight of the suspended section of the pipeline 2 also causes the lifting of a section of the pipeline 2 laid on the zone 5 in the proximity and upstream of the zone 7. In practice, the pipeline 2 is pivoting on the zone 7. Under these conditions, continuing with the laying of the pipeline 2 would cause stresses higher than the threshold value T, which could bring about an uncontrolled deformation of the pipeline 2 in proximity to the zone 7. The laying operations are therefore suspended.

The graph C is calculated, through certain algorithms, as a function of the characteristics of the bed 3, the geometrical and structural characteristics of the pipeline 2, and the configuration assumed by the pipeline 2.

To continue the laying operations without causing damage to the pipeline 2 it is necessary to intervene by bending the pipeline 2 in a controlled manner in the zone 7. For this purpose, a support vessel 8 transports a bending machine 9 to the zone 7, and by means of a crane 10 launches the bending machine 9 into the body of water 4 next to the pipeline 2 in proximity to the zone 7.

In Figure 4, the bending machine 9 is clamped to the section of the pipeline 2 which is raised with respect to the zone 5 and in proximity to the zone 7. The launching and positioning operations of the bending machine 9 are assisted and controlled by a ROV 11 as shown in Figures 3 and 4.

With reference to Figures 5, 6, and 7, the bending machine 9 performs a series of close bends so as to make a curved section 12 with a curvature concordant with the curvature assumed by the pipeline 2 in proximity to the zone 7 and, in this case, upstream of the zone 7.

The extent of each bend is comprised in the range between 0° 30' and 1° 30', and the step between two successive bends is comprised in the range of 5 - 15 cm. In practice, the bending machine 9 is advanced stepwise along the pipeline 2 until completion of the curved section 12. Each bend and the curved section 12 as a whole are cold and controlled plastic deformations.

During the construction of the curved section 12 the stresses on the pipeline 2 are progressively reduced and the laying operations can be resumed without generating stresses exceeding the threshold value T.

With reference to Figure 8, the bending machine 9 is coupled to the section of the pipeline 2 suspended between the zone 7 and the laying vessel 1 and directly downstream of the zone 7. The operations of laying the pipeline 2 can again be interrupted if the stresses on the pipeline 2 are close to the threshold value T.

In Figures 9 and 10 a curved section 13 with a curvature concordant with the curvature assumed by the pipeline downstream of the zone 7 is made by a method similar to that described with reference to the curved section 12.

With reference to Figure 11, once the curved section 13 has been made, the operations of laying the pipeline 2 are resumed while the bending machine 9 is recovered on board the support vessel 8.

The laying operations are subsequently completed by laying the pipeline 2 along the zone 6, as shown more clearly in Figures 12 to 14. Each of Figures 5 to 14 shows a comparison between the graph Cl correlated to the stresses on the pipeline 2 in the absence of the curved section 12 or of the curved sections 12 and 13, and the graph C correlated to the stresses on the pipeline 2 provided with the curved section 12 or with the curved sections 12 and 13. As a result of these comparisons, the graph Cl has a peak PI well exceeding the threshold value T, whereas the graph C is entirely below the threshold value T.

The described method comprises making curved sections 12 and 13 with a curvature and a length such as to allow stresses on the pipeline 2 in accordance with the design parameters . For this purpose the method comprises measuring the angle and the length of each of the curved sections 12 and 13 while they are under construction; and comparing the angle and length of the curved section with reference parameters .

With reference to Figure 15, the bending machine 9 comprises an inclinometer 14 and an odometer 15 for acquiring data from which to detect the angle and the length of the curved section and transmit respective signals SI and S2 related to the angle and length of the curved section, respectively, to a microprocessor 17, which processes the data and emits a signal S3, which is used to refresh the graph C on a display 18 on board the laying vessel 1, so as to make it possible to evaluate when the operations of launching the pipeline 2 can be resumed without inducing excessive stress on the pipeline.

The transmission of the signals SI and S2 between the bending machine 9 and the support vessel 8 is preferably achieved by means of the ROV 11 and the transmission of the signal S3 between the support vessel 8 and the laying vessel 1 is achieved by telecommunication.

In accordance with an alternative embodiment of the present invention and with reference to Figure 16, the pipeline 2 is laid both along the zone 5 and along the zone 6. In order to limit the stresses on the pipeline 2 and avoid damaging the pipeline 2 during the laying thereof the pipeline 2 is locally supported upstream and downstream of the zone 7 by means of supports 18, in this case represented by buoys. The supports 18 are installed by means of ROVs (not shown) as the laying operations proceed and keep the stresses below the threshold value T and allow the pipeline 2 to form a very large curved section around the zone 7, with portions of the pipeline 2 raised with respect to the bed 3 both upstream and downstream of position 7. As can be seen in Figure 16, the graph C has three peaks P, which correspond to the zone 7 and the positions where the supports 18 are applied.

The bending machine 9 is coupled to the pipeline 2 upstream of the zone 7 to form the curved section 12 and downstream of the zone 7 to form the curved section 13 in accordance with the methods described with reference to the previous Figures. Both the curved sections 12 and 13 have a curvature concordant with the curvature assumed by the pipeline 2 in proximity to the zone 7 and are made by cold plastic deformation.

With reference to Figure 17 and the associated graph C, once the curved sections 12 and 13 have been made, the peak P in the graph C is only found in the zone 7 and is below the threshold value T.

Subsequently, the supports 18 are removed by the ROVs

(not shown) and the pipeline 2 is as shown in Figure 18.

The present invention clearly includes further variants that are not explicitly described, without however departing from the scope of protection of the following claims .