islay pipe and pipe technology paper

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OTC 21396 Evaluation Qualification of Electrical Heat Trace Pipe In Pipe for a SS Flow Line and Selection for an Application on a Subsea Field in UK, ISLAY Herve de Naurois, Dominique Delaporte – TOTAL SA, Marc Helingoe, Hugues Greder –TEP UK Copyright 2011, Offshore Technology Conference This paper was prepared for presentation at the Offshore Technology Conference held in Houston, Texas, USA, 2–5 May 2011. This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material does not necessarily reflect any position of the Offshore Technology Conference, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of OTC copyright. Abstract Long tie-backs are increasingly being considered for deepwater field developments with intermediate or smaller reserves and flow assurance issues. The architecture of the Flowline then becomes a key feature of the development. The Total group has reviewed several solutions for flowline optimizion and, among the different technologies available, has identified the Electrical Heat Trace Pipe In Pipe (EHT-PIP) as an interesting option, with higher energy efficiency, which could limit the impact on the host platform. This paper presents the technology of EHT-PIP, and its evaluation-qualification prior its selection for a first application, Islay field, offshore UK. EHT-PIP technology involves the inclusion of heat tracing cables in a standard PIP, between the outer wall of the inner pipe, and the thermal insulation. Once installed, it can be used safely and with good operability in the different required modes (maintaining the fluid temperature above critical points, or as a controlled warm-up, or for heating the fluid during production). For flow assurance reasons (hydrates, wax, pour points), subsea flowlines generally require highly effective insulation but long tie-backs push to the limit the conventional passive insulation solution, unless a dual loop configuration is adopted. Another solution is to implement an active heating system. Various alternatives for this, such as the direct electrical heating systems (DEH) and hot water circulation (HWC), have been analyzed, but they showed poor energy efficiency. They also presented limits for long term usage, either linked to the higher electrical current required – heavy qualification of connection and insulation material, for example- or operational issues-, although past applications include some positive experiences, on short term usage. In comparison, the EHT-PIP, requires significantly lower voltage and offers greater efficiency. However, although it has been proven in surface, the solution is less mature for subsea flowline. Total has undertaken an “Evaluation Qualification” on this emerging technology. This in-house method is used to improve Total’s capacity to select innovative technology, while adequately addressing the risks and uncertainties before an implementation. Several future applications of EHT-PIP were being considered, in the UK (one with a 6-km flowline presenting a hydrate issue, Islay, another 27 km long, etc.) and in another deepwater areas. The assessment resulted in a list of 12 technical uncertainties to be resolved. The corresponding program - RMP (Resolution Management Plan) - was discussed with 2 contractors developing this technology (ITP and Technip), and subsequently executed. The results (with full validation of the thermal model, demonstration of reliability and long-term cable ageing test, etc.) were positive and the technology was considered valid with both contractors design for application on the first full-scale industrial project, ISLAY, for the 6-km flowline. Here, the EHT-PIP will be deployed as a secondary hydrate prevention method. During the life of the field, the system will be operated and monitored at regular intervals. Once proven on this subsea flowline, it will be deployed on 6 similar potential subsea tie-backs, where it could improve the economics, and eliminate methanol injection. The validation of this technology therefore offers to TOTAL a technically and economically optimized solution, for future long subsea tie-backs with greater operability, even with difficult fluids and isolated, distant reservoirs.

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Islay Pipe and Pipe Technology paper on Heat Tracing System

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Page 1: Islay Pipe and Pipe Technology Paper

OTC 21396

Evaluation Qualification of Electrical Heat Trace Pipe In Pipe for a SS Flow Line and Selection for an Application on a Subsea Field in UK, ISLAY Herve de Naurois, Dominique Delaporte – TOTAL SA, Marc Helingoe, Hugues Greder –TEP UK Copyright 2011, Offshore Technology Conference This paper was prepared for presentation at the Offshore Technology Conference held in Houston, Texas, USA, 2–5 May 2011. This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material does not necessarily reflect any position of the Offshore Technology Conference, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of OTC copyright.

Abstract Long tie-backs are increasingly being considered for deepwater field developments with intermediate or smaller reserves and flow assurance issues. The architecture of the Flowline then becomes a key feature of the development. The Total group has reviewed several solutions for flowline optimizion and, among the different technologies available, has identified the Electrical Heat Trace Pipe In Pipe (EHT-PIP) as an interesting option, with higher energy efficiency, which could limit the impact on the host platform. This paper presents the technology of EHT-PIP, and its evaluation-qualification prior its selection for a first application, Islay field, offshore UK. EHT-PIP technology involves the inclusion of heat tracing cables in a standard PIP, between the outer wall of the inner pipe, and the thermal insulation. Once installed, it can be used safely and with good operability in the different required modes (maintaining the fluid temperature above critical points, or as a controlled warm-up, or for heating the fluid during production). For flow assurance reasons (hydrates, wax, pour points), subsea flowlines generally require highly effective insulation but long tie-backs push to the limit the conventional passive insulation solution, unless a dual loop configuration is adopted. Another solution is to implement an active heating system. Various alternatives for this, such as the direct electrical heating systems (DEH) and hot water circulation (HWC), have been analyzed, but they showed poor energy efficiency. They also presented limits for long term usage, either linked to the higher electrical current required – heavy qualification of connection and insulation material, for example- or operational issues-, although past applications include some positive experiences, on short term usage. In comparison, the EHT-PIP, requires significantly lower voltage and offers greater efficiency. However, although it has been proven in surface, the solution is less mature for subsea flowline. Total has undertaken an “Evaluation Qualification” on this emerging technology. This in-house method is used to improve Total’s capacity to select innovative technology, while adequately addressing the risks and uncertainties before an implementation. Several future applications of EHT-PIP were being considered, in the UK (one with a 6-km flowline presenting a hydrate issue, Islay, another 27 km long, etc.) and in another deepwater areas. The assessment resulted in a list of 12 technical uncertainties to be resolved. The corresponding program - RMP (Resolution Management Plan) - was discussed with 2 contractors developing this technology (ITP and Technip), and subsequently executed. The results (with full validation of the thermal model, demonstration of reliability and long-term cable ageing test, etc.) were positive and the technology was considered valid with both contractors design for application on the first full-scale industrial project, ISLAY, for the 6-km flowline. Here, the EHT-PIP will be deployed as a secondary hydrate prevention method. During the life of the field, the system will be operated and monitored at regular intervals. Once proven on this subsea flowline, it will be deployed on 6 similar potential subsea tie-backs, where it could improve the economics, and eliminate methanol injection. The validation of this technology therefore offers to TOTAL a technically and economically optimized solution, for future long subsea tie-backs with greater operability, even with difficult fluids and isolated, distant reservoirs.

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Introduction Operators are currently faced with increasing development costs on deepwater fields. Where limited reserves can not justify a stand-alone development, they have to consider subsea tie-back architectures, with the fluids sent to an existing distant process facility, with sufficient treatment capacity, or possibility to accommodate additional capacity. However, these architectures are increasingly complex, particularly in a context of low seabed temperatures and present difficult flow assurance issues, with high pour points and high wax and hydrate appearance temperatures (WAT, HAT). The choice of architecture will then hinge on the design and operability of the production flowline between the satellite fields and the selected host facility. Various solutions can be considered, for preservation in the event of shutdown, restart in safe conditions and normal production operation. They include conventional solutions such as enhanced insulation, as in Pipe in Pipe, continuous injection of chemical additives during production, or displacement of a stabilized fluid in dual loop. All these solution present limitations in complex and longer tie-backs and entail substantial Capex and Opex. Active subsea heating along the flowline has often been regarded as an alternative means of guarentiying flow assurance and operability, in normal production, in shutdown, and in restart operations. It will actively maintain or raise the temperature of the transported fluid above critical values. However, the capacity of conveying thermal energy from the host facility to the flowline has generally been limited. The relatively extensive facilities needed on the selected host curb the overall gain. The poor efficiency of earlier active heating systems was viewed as a serious limitation, to the point that energy efficiency in active heating technology became as an important driver. The review of the various technologies soon proved that active heating by heat tracing, relatively innovative in subsea applications, offers the advantage of higher efficiency, due in part to the optimized localization of the heating source. This paper discusses the comparison, and then the selection, qualification and selection of this EHT PiP technology for a first industrial application on a 6-km flowline in the UK North Sea. This is considered an important step forward in the challenging context of long tie-backs in deepwater oil and gas developments. It is based on physically demonstrating accuracy of the predictive modeling, the construction , and installation of the system, the performance of the design, and the uniform dispersion of heat. The paper also adresses the monitoring of the integrity of the heat traces, and the electrical continuity throughout the construction and installation phases, the efficiency and safe performance in operation, as well as long-term integrity and reliability of the design, with the defined redundancy. This is achieved through a range of studies, laboratory and full-scale tests and validation against test results after a thorough review of potential risks and uncertainties, using a Total in-house methodology. 1- Comparative review of Active Heating Technologies Total considered several field development cases that were at conceptual or pre-project stages, where optimization and limitation of the impact on the host facility had been identified as key factors for the design. One of the cases in the UK North Sea, with severe flow assurance issues combining wax and hydrate management, and a tie-back distance of 27 km to a host platform, was particularly challenging. Additional deck-load capacity on this platform was extremely limited, making it mandatory to identify heating solutions with an optimum energy efficiency compatible with this constraint. A Total team (a transverse group composed of Advanced technology / Innovation, Subsea technology, Electrical experts, Pipeline experts and TOTAL EP UK personnel) undertook to review the issue on behalf of TEPUK. The team reviewed the various active heating solutions available or under development, consulting various contractor companies, including-Subsea 7-ITP, and Technip, to examine the various issues of design, installation, development and qualification of these technologies. It focused on performances, installation, reliability, limitations and achievable efficiency. A specific Capex review was also commissioned, including qualification, testing, construction, installation, operation and maintenance, on a common-ground set of conditions, aimed at a consistent “apple to apple” comparison. It spanned various technologies in the 2 main groups: Hot Water Circulation (HWC, in annulus or in a bundle) and electrical heating (such as DEH – WET, or DEH PIP, or Electrical Heat Trace PIP). It soon appeared that each technology had a number of different, specific limitations, which can be split into 2 broad categories:

- low performance as regards heat loss to the surroundings, especially with the lower insulation and return to the sea. This leads to poor overall efficiency, higher power consumption, and, for the electrical options, to higher voltage requirements , reducing the choice of host. The higher voltage also limit the choice of equipment adequately qualified for long-term continuous operation.

- non-uniformity: non-uniform heating along the flowline leads to complex operational issues in the case of HWC. In addition, both DEH solutions ( WET and PIP) requires careful selection of tubes whose electrical properties will be homogeneous, as the DEH principle relies on the effect of electrical current in the very metal of the inner pipe.

To summarise the results, for the same subsea tie-back case of a 27-km oil flowline, presenting the same flow assurance constraints:

- Hot water circulation (HWC): requires high power energy as well as costly HW tanks - DEH – WET: requires around 8 MW electrical power - DEH PIP: requires between 3 and 4 MW electrical power - ELECTRICAL HEAT TRACED PIP: requires around 1.5 MW electrical power

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Electrical heat trace pipe technology for subsea flowlines This technology, though not yet proven in subsea application, brings potential benefits; it has been studied and proposed in the past by 2 contractors:

- Technip, with various applications for heated pipelines in subsea or arctic conditions. - ITP, with good experience in providing PIP system, with an enhanced insulation performance, (with OHTC

value commonly below 0.5 W/m2.K°) reducing hence the power requirement. Basically, the design in all cases consists of a combination of 2 elements:

- a highly insulated PIP, well known and proven in subsea developments - and the trace heating technology, extensively used in surface installations.

The electrical heat tracing provide heat through Joule resistive effect. The trace system design is based on a 3-phase configuration, applied on 3 separate cores, each conducting one of the three current phases, which are connected at the far end in star connection, where their sum is nil. There is therefore no need for a current return path, as far as this is a balanced system, no additional umbilical cable being then required.

Fig 1 – Schematic of electric arrangement The intrinsic benefit of this configuration is that it separates the active heating system from the pipe-in-pipe insulation system, each then remaining independent and efficiently integrated. The key points are the following two advantages:

HIGHER EFFICIENCY The EHT-PIP is configured with trace heating cables located between the outer surface of the inner pipe and the thermal insulation located in the annulus of the pipe-in-pipe. This ensures optimum delivery of heat, most of which is transferred into the thick metal wall of the inner pipe and from there into the fluid, minimizing passive heat loss. Power consumption is therefore low, enabling this system to reduce power generation requirements on topsides. UNIFORMITY, BETTER CONTROL AND OPERABILITY EHT delivers uniform, continuous heating, the temperature rising progressively and stabilizing asymptotically at an equilibrium temperature, depending exclusively on the controlled power delivered to the system, the external temperature and the U value of the pipe insulation.

In view of the potential advantages, both Technip and ITP significantly developed this technology from the 1990s and each built a full-scale OD Prototype and tested it in the early 2000s. The schematic, below, of the Technip technology shows the heat tracing cables laid in a spiral configuration, the optical fiber and centralizers, and insulation. The company was able to draw on previous studies and realizations as well as on previous experience in the area of IPB (Integrated Production Bundles).

Fig 2 – Schematic (Technip) and ITP photos of traces laid in parallel. (ITP)

ITP founded their development on their proprietary PiP technology with a higher insulation capacity (OHTC in the region of 0.5 W / m2 K°), achieved with their specific insulation material and low pressure in the annulus. Their selected laying method is in parallel lines or in lazy waves. They have experience in laying this type of PiP arrangement and have teamed up with SS7 for its extensive experience in pipe-laying operations. 2 – Evaluation-qualification of the EHT PIP Technology: requirements and methodology 2.1 Application cases

2 cases were considered for application on the Total UK assets:

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A 6-km gas flowline with a design temperature of 100°C, Islay Islay was seen as a potential candidate, where the technology could be implemented as an alternative/backup to the hydrate mitigation method. Implementing the technology on an industrial scale on Islay would enable it to be selected for other upcoming subsea tiebacks in the area. Islay requires a subsea line of approx. 6 km, tied back between the well head and a subsea manifold. It is subject to potential hydrate formation and flow assurance constraints (with HAT of the order of 20°C):

Hydrate management philosophy is based primarily on transient hydrate inhibition by methanol injection. The drawback is that this relies on methanol, which will be problematic as regards the methanol content in the NGL product and the long-term acceptability of its use. Electrical Heat Tracing PIP appears to be an alternative or backup solution for hydrate management. It is an efficient method for both active heating and hydrate mitigation. Arriving at a subsea manifold (a less common case) means that the power connection will be made initially by a dedicated vessel each time it is required (pending potential installation of an electrical supply line).

A second case was the subsea tie-back of an oil field at a distance of 27 km, with a design temperature of 120°C. This more stringent case, with a complex fluid (high pour point, HAT and WAT), is a representative example of other complex cases to be considered later. Several other potential application cases were also identified outside the North Sea.

2.2 Operating modes Both systems were regarded as capable of coping, with improved efficiency in the range of 80 - 90%, in the following operational modes:

• Temperature maintenance after shutdown (planned or unplanned) to avoid flow assurance problems • Reheating the fluid before a production restart, after it has dropped to sea bed temperature • Additionally, in some cases, during active production – raising/maintaining the temperature of the production fluid above critical values such as WAT, especially later in field life or at turndown conditions, to prevent temperature at the end of the line dropping below a given threshold.

Due to the enhanced thermal efficiency of the passive insulation of EHT-PIP, the power required to achieve the different scenarios above falls in the range of 8 to 30 W/m, (with lower requirement when the OHTC performance is increased). Temperature maintenance operations use less power but occur more frequently. For warm-up operations, where there is a direct relation between the electrical power provided and the rapidity of the warm-up (related to the thermal inertia of the fluids in the flowline), the figures/rating/quantities depend(s) on the acceptable duration. 2.3 Decision to undertake an evaluation-qualification For both application cases, EHT-PIP technology clearly offers significant benefits. It was, however, less mature.

• The review showed that it has been extensively used in onshore applications where the functionality of the system has proved its worth. However, EHT has not been implemented in a full-scale long Subsea flowline.

• The 2 contractors, ITP and TECHNIP, have provided studies of the EHT system, mainly for a subsea environment, leading the technology to an in-depth level of theoretical demonstration. Each had then developed a full-OD (1 joint long) prototype, while their various sub-components have been reviewed and qualified. Offshore installation methods were analyzed (through FEA analysis, simulations, etc.), including the key element of the impact on keeping the thermal efficiency after reeling installation.

• The reasons for this technology having not yet been selected stemmed apparently from the fact that the focus was more on the dual flowline with displacement of stabilized oil, seen as feasible when the tieback length was limited. Also, several PiP designs did not include, until recently, continuity in the PiP annulus.

TOTAL and TEP UK decided to undertake an Evaluation-Qualification program to demonstrate the suitability of this technology, such that it might be selected on long subsea tiebacks. For planning reasons, Islay was chosen as the first industrial-scale case. The system will be tested there at regular intervals, from commissioning and throughout field’s life, before being implemented in other cases. 2.4 Evaluation-Qualification methodology The methodology used, Evaluation Qualification for innovative technology, ProQual, is an internal Total process, designed to identify early in the studies and decision process the elements of performance, maturity and risks and the prime uncertainties, so as to propose a structured approach to resolution of the uncertainties. In other words, it sets out to gain more knowledge and reduce the uncertainties before a new technology is selected, making sure that it has an acceptable confidence rating at each stage of the development studies. It begins with a Technology assessment, which can be summarized in 4 phases as follows:

A - Initial Inputs – Performance and Design Review B - Innovative Items Maturity Assessment C – Potential Risks, Failure Mode Evaluation and Criticality Analysis, and Mitigations D - Resolution Management Plan (RMP) for uncertainties If the assessment concludes on the feasibility and benefit of resolving the uncertainties preventing selection of the technology, the RMP is financed and executed to provide the necessary answers. Then there is an evaluation phase:

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E - Data Collection, Testing, Reliability and Final Assessment.

3- Evaluation-Qualification of the EHT PIP Technology - review of EHT PiP The first four phases, A through D above, of the Evaluation-Qualification concluded that there were no actual showstoppers barring the way of this technology but that a number of important uncertainties needed to be resolved before it could be deployed for use in a Total project. The uncertainties were grouped in 12 areas:

1. Thermal performance of the heat tracing system, including downgraded modes

2. Thermal and mechanical integrity of standard PiP components

3. Thermal integrity of the heat tracing cables

4. Cables and connection design and long-term reliability of same.

5. Potential loss of electrical insulation

6. Bulkhead / T-piece subsea connections, connectors and feeder cables

7. Full-scale model (submitted to reeling or towing ) and thermal tests

8. Cable installation, construction & tests during construction

9. PiP installation (offshore), commissioning and testing

10. Operating modes including downgraded modes

11. Reliability and Redundancy philosophy

12. Thermal tracking and monitoring.

The Resolution Management Plan (RMP) was designed to lift those uncertainties to rest, in the perspective of a detailed design tailored to the two application cases (6-km flowline with a design temperature of 100°C and 27-km flowline at 120°C). It was discussed with the 2 contractors and involved the following tasks: - Further data acquisition, including analysis of potential statistical failure data of cables and connections and

qualification basis obtained from suppliers, and past test results, - Further studies, including thermal design and flow assurance operating requirements, with Electrical Design

finalization, specification and selection of tracing wires, together with detailed fabrication methods (Wire connections and laying method on inner pipe of PIP, etc.), and installation methods including towing and reeling / un-reeling, review of overall reliability and redundancy for ensuring adequate reliability.

- Test campaign, including: - Ageing tests to demonstrate the wire integrity over 20 years of service (accelerated ageing under higher test temperatures – as per Arrhenius law) - Construction of a 12-meter-long prototype (featuring wire installation, monitoring, etc.) for validating the computerized model and investigate all downgraded modes, and demonstrate fabrication .

Its 4 broad objectives were to obtain confirmation of: - the performance of the design, in normal and downgraded mode, where applicable (i.e. working on only one set

of cables), efficiency and operability, heating efficiency and safe use of the system in operation - the predictability and accuracy of the modeling of operational control, uniformity and certainty that no hot spot

would be present in normal or downgraded mode, where applicable - the feasibility of the installation and monitoring of the heat tracing integrity and electrical continuity: the focus

here was to demonstrate the integrity at the different stages of its life, i.e. construction, installation and operation. - the long-term integrity, reliability of the design and adequacy of the chosen redundancy, to check for appropriate

reliability and absence of total failure over a 20-year field life. 4 - Design of the EHT-PiP for ISLAY CASE The design has been established for the 6-km ISLAY flowline, with both contractors. Key elements worthy of note are: The heat tracing - the electrical traces are selected with the objective of providing the requisite high level of reliability and 20-year longevity, including a sparing philosophy with 300% redundancy (i.e. there should be at least 4 triplets of cables installed where the system is to work with only one triplet, even if this results in a longer duration to reheat from seabed temperature). Cable insulation must withstand conditions significantly above the required system voltage. The cable can be laid in various possible arrangements. The arrangement must ensure a limited impact on the OHTC (Overall Heat Transfer Coefficient) and an optimum exchange surface against the flowline to maximize heat transfer efficiency. The subsections are the lengths of PiP which are tobe constructed with insertion of inner pipe into the outer pipe (around 750 m or 1000m) Cable connections at each subsection have been considered as critical, to be thoroughly verified. This conection

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has been analyzed in depth and the design reviewed as being demonstrated to be technically very sturdy in every respect, and designed for repeated industrial installation in any context, and for easy full testing, with dual contact to resist future deterioration. The subsea power supply arrangement - this comprises a power umbilical and subsea connectors. The umbilical is to provide electrical power and optical signals from the topside to the T-piece arrangement. The connection between the subsea electric supply cables and the Heat Trace PIP line relies on wet mate electric connectors, widely used in various subsea developments in this range of properties. The voltage and power involved in this technology are lower than in other technologies, and fully in line with standard applications. Wet mate connectors with a proven field track record are readily available. Various high-voltage wet-mateable connectors, all with established track records, from various suppliers were reviewed. Tee Piece Design & arrangement: The electric feed-through arrangement supporting the electric wet mate connector(s), called the “T” piece is an important part of the EHT-PIP architecture. Its objective is to maintain the physical barrier which isolates the dry PIP annulus from the sea’s hydrostatic environment while ensuring the electric supply connection, in line with the dual tested barrier concept. The T-piece will incorporate the female part of the connector. A potential leak path, alone or via its integration into the T piece structure, may occur and sea water leaking into the annulus could jeopardize both the thermal insulation of the line and the heat trace circuits. The designs were reviewed in detail to ensure the anticipated dual-seal integrity longevity. Integrity is to be managed in the same way as for the other systems installed and in use for years. The topside control unit - this includes the electrical power generation facility and the control system. It regulates the power supplied to the cables, according to the behavior modeled and validated along the flowline. Further monitoring, in line with the current monitoring of the temperature in the flowline, will corroborate the effective efficiency of the system, in spatially distributed mode via the fiberoptic cables or in integrated mode with the discretely installed temperature sensors. 5 – Full-scale OD prototype The construction of a full-scale OD prototype to the conditions and design of the targeted applications was required to establish constructability, verify the measurements of the current activation parameters, confirm the real efficiency and validate the thermal models. Each contractors constructed a prototype: Technip’s prototype was built and tested in a university laboratory in Edinburgh (Scotland). The salient points of the test campaign can be summarized as follows:

The full-scale OD model was built and thermally tested in both normal and downgraded modes. The results are in line with expectations. Installation of the wires in the selected spiral mode proved effective. The OHTC was confirmed in the anticipated range (approx. 1 W/m2.K). The thermal modeling can be corroborated and calibrated for all operations, confirming adequate thermal behavior in all cases with no occurrence of cold or hot spots.

PIP cross section schematic and full scale Test Model longitudinal view Fig 3

Through the results, the thermal model has been validated, while activating the system in various modes. The modeling cases and the test results gave a positive match:

Fig 4 : Matching beteen predicted curves and experimental data. The thermal model was also run in downgraded modes, and can be validated through results. Correct performance in the various downgraded modes was confirmed (with only two or one set of cables remaining), as well as little or no influence from

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various defects introduced in the system. The absence of any “hot spot” is confirmed, as is a temperature difference limited to 6°C maximum in all cases, irrespective of fluid composition and physical status. The modeling and its confirmation by the results therefore well represent the actual heat distribution along the pipe in all cases, and can well predict the influence of the centralizers, or the temperature variations in various particular modes. Fig5 Examples of computerized thermal analysis results ITP – Subsea7 : Prototypes (actually 2) were built in the ITP facilities in Ranville (North-West France).

Fig 6 : Full scale OD test model prototype longitudinal view (ITP )

Fig 7 : Full scale OD test model prototype photo (ITP )

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ITP also confirmed their CFD modeling in a similar way: The thermal results were in-line with the predicted values, with enhanced OHTC in the order or below 0,5 W/m2.K.

Fig 8: Temperature distribution modelization with power input in one point at bottom of pipe (ITP)

These results allow to confirm the improvement brought by the lower OHTC, in term of increased time before the heat tracing system has to be activated, and reduced power requirement for similar temperature maintenance or reheating operations. The simulations of the modeling were also confirmed by the prototype results, demonstrating, for instance, that even in the downgraded mode with power on only 1 set of wires, the difference in temperature distribution is limited to 5° or 6°C, in the conservative hypothesis of no fluid conduction. 6 – AGEING TEST TO VALIDATE LONG-TERM HEAT TRACE INTEGRITY An important uncertainty element was the long-term integrity of the wires and wire connections between subsections, in particular for the electrical insulation material, with potential deterioration through the time and use. The laboratory testing program was developed to ensure that the heat tracing cables and associated in-line connections will not be detrimentally affected by the conditions to which they will be subjected, in fabrication, construction, installation and then field operation for 20 years. This includes the ability to withstand the voltages (2 kV phase to ground) and the long-term exposure to high service temperatures (up to 120°C), with no detrimental impact on the insulation resistance of cable / connections (identified as the most critical potential long-term downgrading mode). The laboratory test measurements were developed to internationally accepted heat trace standards and subsea umbilical standards. They focused on specific, extensive aging tests measuring the electrical properties before, during (with insulation monitoring) and after the testing, with conditions close to those anticipated. For ITP Subsea7, the ageing tests on the selected traces and connectors were configured to represent annulus operational constraints on the cables.The test protocol was designed to verify the integrity of the material of the wires under the insulation, by simulating accelerated ageing over 20 years’ heating, applying Arrhenius law of increased temperature vs. time.

Fig 9 Arrhenius law based Thermal endurance graph.

A full set of tests was run on the integrity, first prior to the exposure, and then at the end of exposure time. The IR of each cable was also periodically measured throughout the test to monitor any potential degradation. The measurements confirmed that the parameters remained constant. The Technip aging tests were conducted in a similar way, in the UK, according to Arrhenius principle of increased temperature and acceleration of exposure time. The loosely coiled cables were heated in a forced convection oven for 28 days at increased temperatures (up to 200°C).

Fig 10 - photos of test arrangement (Technip) .

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Ageing tests equating to 20 years’ service were performed on both cables and concluded on their adequate suitability for all the sample pieces tested. The test results were satisfactory; the measures were as per following table

Table A : test measures results ( Technip)

And the following curves shows the evolution of IR during the test :

Fig 11 Curve of evolution of IR during the test (Technip) No major variations were seen in the cable system, as the insulation of each system was periodically measured throughout the duration of the test (every 2-3 days), plotted here on a logarithmic scale. The IR marks an initial decrease on exposure to high temperature and then stabilizes out for the remainder of the test. When the cable is allowed to return to ambient temperature (on completion of test), the IR measurement recovers its original level. It is well in excess of 100 times the minimum specified value (50MΩ). It may therefore be concluded that the cable would not be degraded by long-term exposure to 120°C (20 years). Definition of a testing protocol for monitoring Integrity and wire condition To ensure that the reliability objective is achieved, it was important to arrange for thorough QA/QC in selecting the wires and their connections, followed by rigorous monitoring. The latter is to start at receipt from the supplier and continue throughout the various steps of installation along the inner pipe. The repeated monitoring and comparison against an initially established baseline will be a means of verifying ongoing integrity during the different steps of the stalks connection. This will be repeatedly tracked during the various phases of offshore installation and commissioning; it will also be used for further tracking during field life operation, such as obtaining a full monitoring across the full project and field life time. This testing protocol will consist in a fixed set of selected and repeatable tests to be run from cables receipt on. It comprises the following tests:

• Continuity Resistance (CR) • Insulation Resistance (IR) • Time Domain Reflectometry (TDR) Additional tests are being reviewed, for potential improvement in this area.

7- Analysis of construction steps and installation Construction The construction method in each contractor program was reviewed step by step, including cable laying methods, cable integrity tests, etc., facilitated by ongoing construction of the prototypes. The overall assembly construction and installation processes were then analyzed specifically with respect to the interfaces related to the wires and the connections. They were subjected to a detailed step-by-step operation and risk analysis, particularly for subsection fabrication, for each scenario. Construction with the Heat Traces transpired as being feasible in both cases. It should imply only a slightly longer construction time in comparison to a standard PiP, which can be covered in non-critical time for the project, thus leaving the possibility for testing and adopting a fallback position at each step.

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Assembly and offshore installation EHT-PIP can be installed in two ways: by reeling or towing. Reeling Reeling is more suitable for longer tiebacks, such as the 27-km distance, where it is expected that three 9-km reeled sections each (or possibly two x 14-km) would be run. It is to be noted that reeling is limited to an inner diameter of 12” or less. Previous reviews pinpointed two points of uncertainty regarding reeling that were addressed in generic mode, but needed to be reviewed for the specific application cases. The first point is the potential deterioration of the thermal system as a result of pipe bending and straightening during reeling and unreeling. To address it, both contractors ran tests consisting of measuring the properties before and after bending (in a Scottish university laboratory, which was able to provide an appropriate test bench). The 12-m prototype was subjected to a full cycle with 3 bending and straightening phases, after which the properties (OHTC in particular) were measured again. The results confirm the continuing thermal performance of the system and the limited impact on the OHTC.

Bending Straightening Fig 12; Test bench photos showing arrangement for bending and straightening. The second point was the potential high stress on the wires and their potential deterioration from the specific stress exerted during reeling and unreeling. It was considered particularly sensitive for the spiral laying configuration proposed by Technip. It was resolved via specific modeling and testing at the base of a Technip subcontractor (Duco) to validate the calculation model of stress on wire during reeling and unreeling through a physical experiment. Spiral installation of the traces on the inner tube was modeled to study stresses in all cases, including reeling or thermal dilatation. A full-scale mockup device was built and measurements were taken, confirming modeling results and the adequacy of the wire’s mechanical properties.

Mock-up and computer model of spirally laid heat trace cables, for stress analysis.

Fig 12: Mock up assembly photo and modeling representation (Technip) . Towing The alternative method of installing EHT-PIP is by towing, an option that offers the possibility of optimizing costs and increasing local content. It does, however, involve having to deal with extensive local logistic considerations. For the Bundle construction, a complete 6-km system could be built onshore and tested before tow-out. The stalks will be assembled into longer strings by welding the subsection inner tubes and then connecting the wires. The integrity of all the components of the trace heating system will be assessed through several checks before sailing, using standardized testing procedures. 8 – Selection for Islay and Conclusions The Evaluation-Qualification work included a thorough assessment of maturity, risks and uncertainties, enabling a coherent uncertainties resolution management plan to be drawn up with the Total team and the 2 contractors, Technip, and ITP SubSea7. It proved that EHT-PIP can be a sound subsea flowline technology, and that both products, such as proposed by Technip, and ITP SubSea7were considered able to be selected in a project such as Islay, for a first application, where it will be possible to

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test it in full scale. This option was included in a call for tender, and after review, it has been decided to include the deployment of this option in the project. One contractor, Technip, was selected for this work, with their proposed design, the selection being based on criteria other than the validation of the technology itself, as both products were considered as suitable technicallyand commercially, and having successfully proven the uncertainties resolution work. Substantial work was performed before the actual selection for the project, but it is considered as having been worthwhile to obtain enhanced answers to the identified uncertainties, explicit or perceived. The doubts centred not only on the main area of electrical design, but also on integration design, fabrication, installation and operation of an EHT-PIP, together with long-term integrity. The review demonstrated that the system provides an improved response to operability issues in contexts involving complex flow assurance constraints:

- the thermal analysis confirmed its high overall efficiency, close to 90%, achieved by maximizing heat transfer to the flowline and minimizing heat loss to the sea

- full-scale prototypes and thermal finite-elements modeling proved the heat tracing system to be fit for purpose and fully validated, as the experimental findings corroborated the model, delivering an enhanced representation of temperature distributions in all the cases, even with complex heating processes and in downgraded modes

- laboratory testing for long-term usage confirmed 20+ years’ integrity, even in high-temperature applications (up to 120°C), a result which, coupled with the 300% redundancy, ensures high reliability (i.e. installation of 4 sets of 3 cables as in the tested design) and demonstrated that, even in the downgraded mode, a single set of 3 cables suffices to heat the contents of the flowline uniformly during active operation.

A number of (project related) issues remain to be addressed during the project, as part of the actual implementation process, and they will be addressed with the selected contractor. Additional work will be undertaken with the alternative contractor, in order to ensure similar type of finalization of details designs and availability of both products for future projects. In conclusion, the review of the work undertaken allows selecting EHT-PIP technology as a potential viable option, even in challenging complex subsea tieback developments. The analysis has confirmed its advantages, in terms of efficiency, operability and low impact on the host platform and has addressed the major uncertainties. In the cases studied, the cost analysis shows that the EHT-PIP improves project economics. With its low electrical power supply requirement, it competes favorably with alternative active heating solutions in CAPEX terms alone. It is a more efficient solution for managing flow assurance on subsea tie-backs, in terms of economic value and energy conservation. It will allow a single line to be used for longer tie-backs and it is a more compact response to space, deck load, and power limitations on the host platform. EHT-PIP can then now be considered as a low energy-consumption heating technology that widens the range of our “Tool box” solutions suitable for long, complex or difficult subsea tie-backs. It improves the feasibility and economics of developing fields with limited reserves distant from previously developed areas. ACKNOWLEDGMENTS The authors would like to thank the Teams and the Management in TOTAL (SCR, ED, RD, TDO TEC), TOTAL UK, as well as in TECHNIP, and ITP - SS7 for their extensive support throughout the Evaluation-Qualification process. NOMENCLATURE EHT-PIP Electrical Heat Tracing Pipe-in-Pipe PIP Pipe-in-Pipe HWC Hot Water Circulation DEH Direct Electrical Heating WAT Wax Appearance Temperature HAT Hydrate Appearance Temperature CFD Computational Fluid Dynamics IR Insulation Resistance OD Outer Diameter [m] CAPEX Capital Expenditure OPEX Operating Expenditure REFERENCES BS EN 60079-30-1, “Electrical resistance trace heating – General and testing requirements: Explosive atmospheres” API 17J, “Specification for Subsea Umbilicals”