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Project engineering overcomes T&I challenges

By  Global Marine Systems Wednesday, 14 October 2015 11:15
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Shanghai-based SB Submarine Systems (SBSS) completed two subsea power cable installations in Saudi Arabia and Korea, which required highly engineered solutions, due to the nature of the jobs.

Bold Maverick working on KJO project. Images from Global Marine.

SBSS is a joint venture company between Global Marine Systems and China Communication Services, established in 1995, to focus predominantly on the Asian market.

Up in Saudi Arabia, the group had to install inter-platform power cables for the Khafji Joint Operations (KJO) project, an offshore oil development between Saudi Arabia and Kuwait.

In total, the project work scope called for 17 separate cables extending over 70km to be installed infield and between the field and shore. In itself, this was not an overly complex transportation and installation (T&I) package.

However, the notable exception was that one particular 42km cable length, which had to be installed in one piece was too large to be accommodated by a single cable tank of SBSS’s installation vessel, Bold Maverick

The alternative, a carousel was unavailable within the project timeline as well. So, SBSS’s project engineering team was tasked by the joint engineering, procurement, construction (EPC) clients, Technip and Offshore Oil Engineering Co. (COOEC) to provide a solution.

This was initiated with the mobilization of two high-powered sheaves and cable tank top dynamic loading arms. These were positioned above the vessel’s fore and aft static tanks, thus spreading the cable length between the capacities of two tanks. 

The solution called for very detailed planning and modeling of cable positioning and movement. Only by using the firm’s cable lay software, Orcaflex, could SBSS ensure that the bend radii and tensions were not compromised at any point. Orcaflex also helped determine that the tank loading would not in any way affect the critical laying stage further down the line.

A subsequent requirement for the offshore team was that the coordination and positioning of the key cable handling equipment had to be managed with great precision to achieve the front-end engineered outcomes.

However, one of the principal reasons for SBSS’s success in delivering highly engineered solutions is the involvement of key personnel tasked with offshore delivery at an early stage of onshore engineering, so that continuity of solutions is maintained. This certainly paid off in the KJO project in Saudi Arabia, where a triple-core 40kV power cable was both loaded and laid successfully.

The vessel Bold Maverick also completed work in China for the installation of a19.3km subsea cable on the Wenchang oil field in the South China Sea. For this project, SBSS partnered with COOEC to install the cable between the WC 14-3 and 13-6 platforms. With a diameter of 151mm, the power cable was laid up to 122m underwater in complex conditions.

T&I in Korea

SBSS engineers working back deck

In Korea, SBSS provided power cable installation between Anjwa Island and the Hwawon Peninsula on the Korean mainland. This project, in fact is no different from installations for the oil and gas sector and the stringent requirements for working in the 500m zone.

Using the company’s cable vessel, CS Fu Hai, the work scope called for two 154kV power cables to be installed that would provide redundant power connectivity to Anjwa Island. 

The installation had been scheduled subsequent to the excavation of a cable protection trench measuring 8m in width and 2.5m in depth. Here, the requirement was for the two cables to be laid simultaneously and with great accuracy in the same narrow trench. 

Although, the cable route was only 7km in length, the size of the cable in combination with strong tidal currents of up to four knots, and the requirement to lay two cables simultaneously with a separation of 2m maximum, meant this posed unique challenges for the SBSS project engineering team.

Furthermore, the key phase of the project had to be completed in the remaining working season before weather conditions became too adverse. With this in mind, the significant engineering and intricate calculations required for mobilizing the right cable laying spread.

Managing the drop height of such a large cable during loading, and configuring the back deck of CS Fu Hai to accommodate twin line loading and laying (as well as Uraduct application teams aft of the cable tensioners) were compressed into a very tight delivery schedule.

However, by exploiting the combined experience of onshore and offshore project teams in engineering, SBSS was able to meet the complex demands of the customer.

Bonus: T&I in Europe

Loading power cable onto vessel

While complex projects in Asia have required SBSS to provide reliable and flexible project engineering content, its parent company, Global Marine, too, has seen its fair share of engineering demand in Europe.

An example is the T&I of a cable end module (CEM) in the North Sea. Here, Global Marine’s project engineering department was tasked with pre-planning, interfacing with project stakeholders, design engineering and precision installation.

When the contract from Tampnet was awarded to the group in October 2014, the initial concept design for CEM was very different to what was finally deployed. Indeed, the early involvement of the company’s project engineering team in the design phase was a key part of this platform-to-platform fiber optic communications project.

The design changes requested by the project engineers were important to allow installation given the tight parameters set by the client. Essentially, the CEM had to be installed within a set distance of a pre-installed subsea isolation valve (SSIV) to allow jumper cables to be connected by divers at a later date.

Additionally, the operation was to be performed in close proximity to surrounding structures, which added further complications to the offshore execution. Interfacing with a multitude of stakeholders is always an important element in any project, and especially so when different companies are responsible for design, fabrication, installation and hook up.

Throughout the design process, the project engineering team was involved in review meetings with all parties, including the field owner and visited the fabrication yard to ensure the changes incorporated were satisfactory for the CEM T&I project. When engineering the rigging for subsea deployment, it is important to have a contingency for subsea release in the event that the primary system does not work.

For this project, Global Marine engineered a primary, secondary and tertiary method for releasing the CEM rigging, with the primary method, using ROV hooks, successfully working as planned. A further important aspect of installing subsea structures is positioning on the seabed.

On the Tampnet project, tolerances of ±2.5m for position and ±2.5° for heading meant Global Marine use the Sonardyne Ranger 2 USBL (ultra-short baseline) acoustic positioning and tracking system (with transponders fixed to the structure), and EIVA Navipac template software to ensure precise placement. 

Of course, contingency plans are also a pre-requisite when it comes to positioning subsea structures. On this project, the secondary method in place was a second USBL system, while a third strategy was the deployment of pre-installed sandbags to box-in the target area for landing the CEM.

The CEM was installed successfully, achieving all of the necessary installation tolerances. Positioning this subsea structure accurately was a crucial part in the overall delivery of the project, which relied heavily on sound project engineering both in the planning phase and subsequently during marine operations.

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