OTC.13: Subsea 7 on heated pipelines

Technology is a big focus for Subsea 7 during OTC week, with a raft of speakers from the firm talking on everything from Pipe-in-Pipe (PIP) developments to deepwater solutions. 

The firm’s latest kit—including the Seven Borealis—is also on show at the firm’s booth (1641). 

John Mair, technology development director, spoke to Offshore Engineer about Subsea 7’s latest developments in PIP development, specifically on thermal insulation of subsea pipelines through Electrically Trace Heated PIP technology.

This has been designed for firms looking to address flow assurance issues of long shutdown and start-up conditions (e.g. hydrate formation) and enable longer, more cost-effective single-line tie-back distances.

Subsea 7’s work in this field has led it to complete an in-depth qualification for Total and it is currently working with Noble Energy on a deepwater subsea field that would be dependent on Electrically Trace Heated PIP technology for the field development.

Mair said an integrated project team has been set up in Houston to complete the detailed engineering and discrete qualification of project-specific elements of the Trace Heating system for this project.

But first he explained how the technology has been developed, first through the development of reel-lay of Pipe-in-Pipe design. 

“Over several years, Subsea 7 has undertaken a continuous development program to bring to the market a step-change technology for the thermal insulation of subsea pipelines,” said Mair. 

“To develop the reel–lay solution, we collaborated with our development partner ITP InTerPipe to qualify the most thermally efficient Pipe-in-Pipe technology in the market.

“Initially a series of full-scale thermal performance tests was carried out on a purpose-built rig on a wide range of PIP insulation materials, including measuring the thermal performance before and after the reeling process.

“These tests conclusively demonstrated that the ITP PIP technology was superior to other insulation products. This was achieved by using ITP Izoflex insulation material installed within the Pipe-in-Pipe annulus with a partial vacuum drawdown and the insulation material acting as a continuous centralizer.

“This performance showed a “notouch” cool-down time approximately three times better than other products.

“Another benefit is that with the High-Performance PIP product, a smaller annulus is required for a given U-value. This has the potential for a smaller outer pipe to be used, resulting in considerable cost savings.

“Building upon this design, the next phase in the development program was the qualification and commercialization of an Electrically Trace Heated option.

“Electrically Trace Heated PIP technology combines our High-Performance PIP technology with a low- power electrical heating arrangement to deliver further significantly enhanced flow assurance properties. 

“The electrical heating comprises individual three-phase wiring triplets configured in a star arrangement.

“The space available within the annulus enables a number of circuits to be installed, thereby providing a high level of redundancy.

“The high level of thermal efficiency of our design provides the further benefit of a low power requirement to meet the specified pipeline heat-up time. This enables a low-voltage system to be adopted with the advantage of longer stepout distance and use of field-proven electrical connectors.

“In normal operation, the system provides ‘no-touch’ times of 72 hours or more before the heating system needs to be activated to maintain the flowline above Wax Appearance Temperature (WAT) or Hydrate Appearance Temperature (HAT), with a typical power consumption of 5-10W/m.

“The high-specification insulated heating wires, as part of the qualification, have been subjected to accelerated ageing tests and are located in contact with the outside diameter of the inner pipe and held in place by the insulation material.

“Finite Element analysis has been performed to evaluate the impact on the wires during the reeling process. This has also been validated by simulated reeling trials to demonstrate that no detrimental impact is experienced.”

Mair said the development had been performed in full compliance with DNV Recommended Practice. 

He said interest in High-Performance and Electrically Trace Heated PIP technology is growing, with many operators, including majors and independents, evaluating the potential benefits for projects.

“The nature of the reel-lay installation method is particularly suited to Electrically Trace Heated PIP, since the wires can be installed in long stalks onshore, unlike with J-lay or S-lay,” he added.

The next step will be pipeline fabrication, which will be carried out in one of Subsea 7’s spoolbases, with installation planned by the firm’s flagship reel-lay vessel, the Seven Oceans.

Mair said that in future, enhancements of High-Performance and Electrically Trace Heated PIP may include the incorporation of fibre optic monitoring to track temperature throughout the length of the pipeline.

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