US20190061881A1

US20190061881A1 - Modular anchors

Info

Publication number: US20190061881A1
Application number: US16/081,127
Authority: US
Inventors: Michel Pierre Baylot; Emilio NICOLINI
Original assignee: Individual
Current assignee: Shell USA Inc
Priority date: 2016-03-02
Filing date: 2017-03-01
Publication date: 2019-02-28
Also published as: WO2017151780A1; BR112018067516A2

Abstract

A modular anchor comprising: a top cross, wherein the top cross comprises a central tubular pile and one or more arm attachment tubulars and one or more cross arms connected to the one or more arm attachment tubulars and associated methods and systems.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 62/302,428, filed Mar. 2, 2016, which is incorporated herein by reference.

BACKGROUND

The present disclosure relates generally to modular anchors. More specifically, in certain embodiments, the present disclosure relates to modular anchors useful in onshore and subsea applications and associated methods and systems.
Subsea anchors, such as deadman anchors, are used in the offshore technology for anchoring floating objects, such as production platforms, to the seabed. In addition, subsea anchors are also used to secure equipment itself onto the sea bed and also to anchor any subsea mobile vehicles since the azimuth and declination angles can very over a wide range. Subsea anchors may be temporary anchors or permanent anchors. Examples of conventional subsea anchors are described in U.S. Pat. Nos. 9,221,521, 9,114,858, 8,833,287, and 8,561,565, the entireties of which are hereby incorporated by reference.
Conventional deadman anchors used for anchoring floating objects, securing equipment to the sea bed, and anchoring mobile vehicles, often have a high self weight, often in excess of 25 tons. Due to these high weights, these conventional anchors cannot be transported by air but instead must be transported to offshore locations by ship. In addition, these conventional anchors are typically not configurable for different applications, and thus may only be suitable for use for a specific soil types, tensions, and/or compression loads and not interchangeable for other uses. Other lighter weight anchors, for example drag anchors, require a significant displacement after installation, thus excluding their use in many cases.
It is describable to develop an anchor that can easily be configured for use in all soils types and for all kinds of mooring line loads and variable load direction and that can be transported to offshore locations by air. In addition, it is also desirable to develop an anchor that requires a very limited displacement.

SUMMARY

The present disclosure relates generally to modular anchors. More specifically, in certain embodiments, the present disclosure relates to modular anchors useful in onshore and subsea applications and associated methods and systems.
In one embodiment, the present disclosure provides a modular anchor comprising: a top cross, wherein the top cross comprises a central tubular pile and one or more arm attachment tubulars and one or more cross arms connected to the one or more arm attachment tubulars.
In another embodiment, the present disclosure provides a modular anchor system comprising: one or more modular anchors, wherein the one or more modular anchors each comprise: a top cross, wherein the top cross comprises a central tubular pile and one or more arm attachment tubulars and one or more cross arms connected to the one or more arm attachment tubulars, wherein the modular anchor is embedded in a sea floor; one or more tether lines; and subsea equipment, wherein the one or more tether lines are connected to the subsea equipment and the one or more modular anchors.
In another embodiment, the present disclosure provides a method comprising: providing a modular anchor, wherein the modular anchor comprises: a top cross, wherein the top cross comprises a central tubular pile and one or more arm attachment tubulars and one or more cross arms connected to the one or more arm attachment tubulars and embedding the modular anchor into a seafloor.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete and thorough understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings.

FIG. 1 illustrates an unassembled modular anchor in accordance with certain embodiments on the present disclosure.

FIG. 2 illustrates an assembled modular anchor in accordance with certain embodiments of the present disclosure.

FIG. 3 illustrates an unassembled modular anchor in accordance with certain embodiments on the present disclosure.

FIG. 4 illustrates an assembled modular anchor in accordance with certain embodiments of the present disclosure.

FIG. 5 illustrates an unassembled modular anchor in accordance with certain embodiments on the present disclosure.

FIG. 6 illustrates an assembled modular anchor in accordance with certain embodiments of the present disclosure.

FIG. 7 illustrates a modular anchor system in accordance with certain embodiments of the present disclosure.

The features and advantages of the present disclosure will be readily apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the disclosure.

DETAILED DESCRIPTION

The description that follows includes exemplary apparatuses, methods, techniques, and/or instruction sequences that embody techniques of the inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details.
The present disclosure relates generally to modular anchors. More specifically, in certain embodiments, the present disclosure relates to modular anchors useful in onshore and subsea applications and associated methods and systems.
One desirable attribute of the modular anchors discussed herein is that they have a modular construction, allowing them to be easily configurable for use in all soils types and for all tension and compression loads. Another desirable attribute of the modular anchors discussed herein is that they may be quickly adjusted to meet local conditions or specific needs. Another desirable attribute of the modular anchors discussed herein is that they may be air freighted to a location in an unassembled configuration and then assembled on site. Another desirable attribute of the modular anchors herein discussed it that they are able to provide the required holding capacity with very limited displacements.
Referring now to FIGS. 1 and 2, FIGS. 1 and 2 illustrate modular anchor 100. In certain embodiments, modular anchor 100 may be a subsea anchor. In certain embodiments, modular anchor 100 may comprise top cross 110, one or more cross arms 120, central skirt 130, and/or one or more cross arm skirts 140. In certain embodiments, as shown in FIG. 1, modular anchor 100 may be in an unassembled configuration wherein the one or more cross arms 120 are not connected to top cross 110, the one or more cross arm skirts 140 are not connected to the one or more cross arms 120, and/or the central skirt 130 is not connected to top cross 110. In other embodiments, as shown in FIG. 2, modular anchor 100 may be in an assembled configuration wherein the one or more cross arms 120 are connected to top cross 110, the central skirt 130 is connected to top cross 110, and the one or more cross arm skirts 140 are connected to the one or more cross arms 120.
In certain embodiments, each component of modular anchor 100 may be of modular construction. In certain embodiments, each component of modular anchor 100, or modular anchor 100 itself, may be capable of being transported by air freight.
In certain embodiments, top cross 110 may comprise a single piece of material. In certain embodiments, not illustrated in FIG. 1, top cross 110 may comprise all of the components of central skirt 130. In certain embodiments, top cross 110 may be constructed out of steel.
In certain embodiments, top cross 110 may comprise central tubular pile 111 and one or more arm attachment tubulars 112. In certain embodiments, not illustrated in FIG. 1, top cross 110 may comprise one or more skirts.
In certain embodiments, top cross 110 may comprise top support 117. In certain embodiments, top support 117 may provide support for one or more structures to be placed upon modular anchor 100. In certain embodiments, top support 117 may allow for a top member 150 to be connected to top cross 110.
In certain embodiments, central tubular pile 111 may comprise a hollow tubular structure. In certain embodiments, central tubular pile 111 may have an outer diameter in the range of from 0.5 meters to 1 meter. In certain embodiments, central tubular pile 111 may have a length in the range of from 0.25 meters to 5 meters. In certain embodiments, central tubular pile 111 may be capable of being connected to central tubular 131 of central skirt 130 when top cross 110 does not comprise all of the components of central skirt 130.
In certain embodiments, the shape of central tubular pile 111 and/or central tubular 131 may permit modular anchor 100 to be self-burying. In certain embodiments, modular anchor 100 may be buried by lowering modular anchor 100 without depressurizing an internal cavity defined by central tubular pile 111 and/or central tubular 131.
In certain embodiments, the one or more arm attachment tubulars 112 may comprise hollow cylinders. In certain embodiments, modular anchor 100 may comprise one, three, four, five, or arm attachment tubulars 112. In certain embodiments, the one or more arm attachment tubulars 112 may be equispaced arranged around a perimeter of top cross 110.
In certain embodiments, the one or more cross arms 120 may each be capable of being connected to arm attachment points 113 of arm attachment tubulars 112 by any conventional means. Examples of conventional means may include bolts and fasteners or welds.
In certain embodiments, not illustrated in FIG. 1 or 2, top cross 110 may comprise attachment point 114. In certain embodiments, attachment point 114 may be located on a top of top member 150. In other embodiments, not shown in FIG. 1, attachment point 114 may be located on a top of top cross 110. In other embodiments, not shown in FIG. 1, attachment point 114 may be located on a surface of central tubular 131. In certain embodiments, attachment point 114 may permit a subsea line or hook to be connected to modular anchor 100 thus allowing modular anchor 100 to be transported from one location to another.
In certain embodiments, cross arms 120 may comprise a single piece of material. In other embodiments, cross arms 120 may comprise one or more modular pieces of materials. In certain embodiments, not illustrated in FIG. 1, cross arms 120 may comprise all of the components of cross arm skirts 140. In certain embodiments, cross arms 120 may be constructed out of steel.
In certain embodiments, cross arms 120 may comprise a cylindrical body 122. In certain embodiments, cylindrical body 122 may comprise a hollow cylinder. In certain embodiments, cylindrical body 122 may be filled with ballast.
In certain embodiments, the one or more cross arms 120 may each comprise a centerpiece attachment point 123 at the end of cylindrical body 122. In certain embodiments, the one or more cross arms 120 may be capable of being connected to top cross 120 at centerpiece attachment point 123 by any conventional means. Examples of conventional means may include bolts and fasteners or welds.
In certain embodiments, the one or more cross arms 120 may each comprise top support 127. In certain embodiments, top support 127 may provide support for one or more structures to be placed upon modular anchor 100.
In certain embodiments, central skirt 130 may comprise a cylinder body 131 and one or more fins 132. In certain embodiments, fins 132 may be connected to cylinder body 131. In certain embodiments, fins 132 may comprise one or more ribs 138. In certain embodiments, fins 132 may comprise one or more ribs 138 spaced apart a distance in the range of from 0.25 meters to 0.75 meters. In certain embodiments, ribs 138 may have a rectangular or triangular shape. In certain embodiments, ribs 138 may extend out from fins 132 a distance in the range of from 0.05 meters to 0.2 meters.
In certain embodiments, cylinder body 131 may be connected to central tubular pile 111, as shown in FIG. 2, by any conventional means. Examples of conventional means may include bolts and fasteners or welds.
In certain embodiments, cross arms skirts 140 may comprise fins 142. In certain embodiments, as shown in FIG. 2, fins 142 may be connected to fins 132 of central skirt 130 and cylindrical body 122 of cross arms 120. In certain embodiments, fins 142 may be connected to fins 132 and/or cylindrical body 122 by any conventional means. Examples of conventional means may include bolts and fasteners or welds.
In certain embodiments, fins 142 may comprise one or more ribs 148. In certain embodiments, fins 142 may comprise one or more ribs 148 spaced apart a distance in the range of from 0.25 meters to 0.75 meters. In certain embodiments, ribs 148 may have a rectangular or triangular shape. In certain embodiments, ribs 148 may extend out from fins 127 a distance in the range of from 0.05 meters to 0.2 meters.
In certain embodiments, fin 142 may have a cross section that matches fins 132.
In certain embodiments, modular anchor 100 may further comprise ballast plates 160. In certain embodiments, ballast plates 160 may comprise steel plates. In certain embodiments, ballast plates 160 may have a trapezoidal shape. In certain embodiments, as shown in FIG. 2, ballast plates 160 may be connected to cylindrical body 122 of cross arms 120 and/or arm attachment tubular 112 of top cross 110 by any conventional means. Examples of conventional means may include bolts and fasteners or welds.
Referring now to FIGS. 3 and 4, FIGS. 3 and 4 illustrates modular anchor 200. In certain embodiments, modular anchor 200 may be a subsea anchor. In certain embodiments, modular anchor 200 may comprise top cross 210, one or more cross arms 220, and one or more grillage plates 230. In certain embodiments, as shown in FIG. 3, modular anchor 200 may be in an unassembled configuration wherein the one or more cross arms 220 are not connected to central top cross portion 210 and the one or more grillage plates 230 are not connected to the one or more cross arms 220. In other embodiments, as shown in FIG. 4, modular anchor 200 may be in an assembled configuration wherein the one or more cross arms 220 are connected to top cross 210 and the one or more grillage plates 230 are connected to the one or more cross arms 220.
In certain embodiments, each component of modular anchor 200 may be of modular construction. In certain embodiments, each component of modular anchor 200, or modular anchor 200 itself, may be capable of being transported by air freight.
In certain embodiments, top cross portion 210 may comprise any combination of features discussed above with respect to top cross portion 110. In certain embodiments, top cross portion 210 may comprise central tubular pile 211, one or more arm attachment tubulars 212, and/or top support 217.
In certain embodiments, central tubular pile 211 may comprise any combination of features discussed above with respect to central tubular pile 111. In certain embodiments, central tubular pile 211 may have an outer diameter in the range of from 0.5 meters to 1 meter. In certain embodiments, central tubular pile 211 may have a length in the range of from 0.25 meters to 1 meter.
In certain embodiments, the one or more arm attachment tubulars 212 may comprise any combination of features discussed above with respect to arm attachment tubulars 112. In certain embodiments, modular anchor 200 may comprise one, three, four, five, or arm attachment tubulars 212. In certain embodiments, the one or more arm attachment tubulars 212 may be equispaced arranged around a perimeter of top cross 210.
In certain embodiments, the one or more cross arms 220 may each be capable of being connected to arm attachment points 213 of arm attachment tubulars 212 by any conventional means. Examples of conventional means may include bolts and fasteners or welds.
In certain embodiments, top support 217 may comprise any combination of features discussed above with respect to top support 117. In certain embodiments, top support 217 may allow for a top member to be connected to top cross 210.
In certain embodiments, not illustrated in FIG. 3 or 4, top cross 210 may comprise an attachment point. In certain embodiments, the attachment point may comprise any combination of features discussed above with respect to attachment point 114.
In certain embodiments, cross arms 220 may comprise any combination of features discussed above with respect to cross arms 120. In certain embodiments, cross arms 220 may comprise a cylindrical body 222. In certain embodiments, cylindrical body 222 may comprise a hollow cylinder. In certain embodiments, cylindrical body 222 may be filled with ballast.
In certain embodiments, the one or more cross arms 220 may each comprise centerpiece attachment point 223. In certain embodiments, centerpiece attachment point 223 may comprise any combination of features discussed above with respect to centerpiece attachment point 123.
In certain embodiments, the one or more cross arms 220 may each comprise top support 227. In certain embodiments, top support 227 may comprise any combination of features discussed above with respect to top support 127.
In certain embodiments, the one or more grillage plates 230 may comprise grilled steel plates. In certain embodiments, the one or more grillage plates 230 may have a trapezoidal shape. In certain embodiments, the one or more grillage plates may comprise a plurality of parallel bars 231 defining one or more gaps. In certain embodiments, the plurality of parallel bars 231 may be spaced a distance in the range of from 0.05 meters to 0.5 meters apart. In certain embodiments, the plurality of parallel bars 231 may be spaced a distance in the range of from 0.1 meters to 0.25 meters apart. In certain embodiments, the plurality of parallel bars 231 may be spaced a distance of 0.1875 meters apart. In certain embodiments, the one or more parallel bars 231 may be straight bars. In other embodiments, the one or more parallel bars 231 may have a zigzag pattern.
In certain embodiments, as shown in FIG. 4, grillage plates 230 may be connected to cylindrical body 222 of cross arms 220 and/or arm attachment tubular 212 of top cross 210 by any conventional means. Examples of conventional means may include bolts and fasteners or welds.
In certain embodiments, modular anchor 200 may further comprise ballast plates 260. In certain embodiments, ballast plates 260 may comprise any combination of features discussed above with respect to ballast plates 160. In certain embodiments, as shown in FIG. 4, ballast plates 260 may be connected to cylindrical body 222 of cross arms 220 and/or arm attachment tubular 212 of top cross 210 by any conventional means. Examples of conventional means may include bolts and fasteners or welds. In certain embodiments, the one or more grillage plates 230 may be welded or bolted onto the one or more ballast plates 260.
Referring now to FIGS. 5 and 6, FIGS. 5 and 6 illustrates modular anchor 300. In certain embodiments, modular anchor 300 may be a subsea anchor. In certain embodiments, modular anchor 300 may comprise top cross 310, one or more cross arms 320, and one or more skirt plates 330. In certain embodiments, as shown in FIG. 5, modular anchor 300 may be in an unassembled configuration wherein the one or more cross arms 320 are not connected to top cross 310 and the one or more skirt plates 330 are not connected to the one or more cross arms 320. In other embodiments, as shown in FIG. 6, modular anchor 300 may be in an assembled configuration wherein the one or more cross arms 320 are connected to top cross 310 and the one or more skirt plates 330 are connected to the one or more cross arms 320.
In certain embodiments, each component of modular anchor 300 may be of modular construction. In certain embodiments, each component of modular anchor 300, or modular anchor 300 itself, may be capable of being transported by air freight.
In certain embodiments, top cross 310 may comprise any combination of features discussed above with respect to top cross 210. In certain embodiments, top cross 310 may comprise central tubular pile 311, one or more arm attachment tubulars 312, and/or top support 317.
In certain embodiments, central tubular pile 311 may comprise any combination of features discussed above with respect to central tubular pile 211.
In certain embodiments, the one or more arm attachment tubulars 312 may comprise any combination of features discussed above with respect to arm attachment tubulars 212. In certain embodiments, modular anchor 300 may comprise one, three, four, five, or arm attachment tubulars 312. In certain embodiments, the one or more arm attachment tubulars 312 may be equispaced arranged around a perimeter of top cross 310.
In certain embodiments, the one or more cross arms 320 may each be capable of being connected to arm attachment points 313 of arm attachment tubulars 312 by any conventional means. Examples of conventional means may include bolts and fasteners or welds.
In certain embodiments, top support 317 may comprise any combination of features discussed above with respect to top support 217. In certain embodiments, top support 317 may allow for a top member to be connected to top cross 310.
In certain embodiments, top cross 310 may comprise attachment point 314. In certain embodiments, attachment point 314 may comprise any combination of features discussed above with respect to attachment point 214.
In certain embodiments, cross arms 320 may comprise any combination of features discussed above with respect to cross arms 220. In certain embodiments, cross arms 320 may comprise a cylindrical body 322.
In certain embodiments, the one or more cross arms 320 may each comprise centerpiece attachment point 323. In certain embodiments, centerpiece attachment point 323 may comprise any combination of features discussed above with respect to centerpiece attachment point 223.
In certain embodiments, the one or more cross arms 320 may each comprise top support 327. In certain embodiments, top support 327 may comprise any combination of features discussed above with respect to top support 227.
In certain embodiments, the one or more skirt plates 330 may comprise skirted steel plates. In certain embodiments, skirt plates 330 may external skirts 331 and internal skirts 332.
In certain embodiments, skirt plates 330 may comprise 4 external skirts 331 arranged in a trapezoidal pattern. In certain embodiments, external skirts 331 may protrude from skirt plate 330. In certain embodiments, external skirts 331 may have lengths in the range of from 0.25 meters to 1 meters. In other embodiments, external skirts 331 may have lengths in the range of from 0.35 meters to 0.7 meters. In other embodiments, external skirts may have length in the range of from 0.55 meters to 0.6 meters.
In certain embodiments, skirt plate 330 may comprise a plurality of internal skirts 332 arranged in a parallel configuration. In certain embodiments, internal skirts 332 may protrude from skirt plate 330. In certain embodiments, internal skirts 332 may have lengths in the range of from 0.05 meters to 0.5 meters. In certain embodiments, internal skirts 332 may have lengths in the range of from 0.1 meters to 0.2 meters. In certain embodiments, internal skirts 332 may be spaced a distance in the range of from 0.25 to 0.5 meters apart from each other. In certain embodiments, each of the internal skirts 332 may be spaced 0.375 meters apart from each other.
In certain embodiments, as shown in FIG. 6, skirt plates 330 may be connected to cylindrical body 322 of cross arms 320 and/or arm attachment tubular 312 of top cross 310 by any conventional means. Examples of conventional means may include bolts and fasteners or welds.
In certain embodiments, modular anchor 300 may further comprise ballast plates 360. In certain embodiments, ballast plates 360 may comprise any combination of features discussed above with respect to ballast plates 260. In certain embodiments, as shown in FIG. 6, ballast plates 360 may be connected to cylindrical body 322 of cross arms 320 and/or arm attachment tubular 312 of top cross 310 by any conventional means. Examples of conventional means may include bolts and fasteners or welds. In certain embodiments, the one or more skirt plates 330 may be welded or bolted onto the one or more ballast plates 360.
Referring now to FIG. 7, FIG. 7 illustrates modular anchor system 1000. In certain embodiments, modular anchor system 1000 may comprise one or more modular anchors 1100, sea floor 1200, one or more tether lines 1300, and subsea equipment 1400.
In certain embodiments, modular anchors 1110 may comprise any combination of features discussed above with respect to modular anchor 100, 200, and/or 300. In certain embodiments, a portion of modular anchors 1110 may be embedded into sea floor 1200. In certain embodiments, the one or more tether lines 1300 may be connected to subsea equipment 1400 and the one or more modular anchors 1100. In certain embodiments, the one or more tether lines 1300 may be utilized to position and keep subsea equipment 1400 on the sea floor 1200.
In certain embodiments, subsea equipment 1400 may comprise a subsea lifting tool. In certain embodiments, the subsea lifting tool may be utilized to positon a piece of subsea equipment while the subsea lifting tool remains on the sea floor. In certain embodiments, the subsea lifting tool may be utilized to position a capping stack over a damaged subsea well head.
In certain embodiments, the present disclosure provides a method comprising: providing a modular anchor and embedding the modular anchor into a seafloor. In certain embodiments, the modular anchor may comprise any combination of features discussed above with respect to modular anchors 100, 200, and/or 300.
In certain embodiments, providing a modular anchor may comprise transporting the modular anchor to a location above a subsea well site. In certain embodiments, the modular anchor may be transported to the location above the subsea well site in an assembled configuration. In other embodiments, the modular anchor may be transported to the location above the subsea well site in an unassembled configuration.
In certain embodiments, embedding the modular anchor into the seafloor may comprise embedding the modular anchor into the seafloor near a subsea well site. In certain embodiments, the modular anchor may be embedded into the seafloor without depressurizing an internal cavity of the modular anchor.
In certain embodiments, the method may further comprise connecting the modular anchor to a piece of subsea equipment. In certain embodiments, the piece of subsea equipment may comprise a subsea lifting tool. In certain embodiments, the piece of subsea equipment may be connected to one or more additional modular anchors.
In certain embodiments, the method may further comprise utilizing the modular anchor and/or the one or more additional modular anchors to position and keep the piece of subsea equipment on the seafloor. In certain embodiments, the method may further comprise using the subsea lifting tool to position a capping stack over a damaged subsea well head.
While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them. Many variations, modifications, additions and improvements are possible.
Plural instances may be provided for components, operations or structures described herein as a single instance. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter.

Claims

1. A modular anchor system comprising:

one or more modular anchors, wherein each of the one or more modular anchors comprise a top cross, wherein the top cross comprises a central tubular pile and one or more arm attachment tubulars and one or more cross arms connected to the one or more arm attachment tubulars, wherein the modular anchor is embedded in a sea floor;

one or more tether lines; and

a piece of subsea equipment, wherein the one or more tether lines are connected to the piece of subsea equipment and the one or more modular anchors.

2. The modular anchor system of claim 1, wherein the one or more arm attachment tubulars comprise four arm attachment tubulars and the one or more cross arms comprise four cross arms.

3. The modular anchor system of claim 1, wherein the central tubular pile comprises a hollow tubular structure.

4. The modular anchor system of claim 1, wherein the one or more arm attachment tubulars each comprise hollow cylinders.

5. The modular anchor system of claim 1, wherein the one or more modular anchors further comprise a central skirt connected to the top cross.

6. The modular anchor system of claim 5, wherein the central skirt comprises a cylinder body and one or more fins.

7. The modular anchor system of claim 5, wherein the central skirt comprises four fins.

8. The modular anchor system of claim 5, wherein the one or more modular anchors further comprise one or more cross arm skirts connected to the one or more cross arms.

9. The modular anchor system of claim 1, wherein the one or more modular anchors further comprise one or more grillage plates connected to the one or more cross arms.

10. The modular anchor system of claim 9, wherein each of the one or more grillage plates comprise grilled steel plates having a trapezoidal shape.