Temperature Maintenance Philosophy to Optimise Electrically Heated Flowline Solutions
- Wegner Alexis (Subsea 7) | Trucy Geraldine (Subsea 7) | Mencarelli Guy (Subsea 7) | Leitch John (Wood) | Geertsen Christian (ITP Interpipe) | Salque Geraldine (ITP Interpipe)
- Document ID
- Offshore Technology Conference
- Offshore Technology Conference, 4-7 May, Houston, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2020. Offshore Technology Conference
- Operability, Shutdowns, Active Heating, EHTF, Heat-Up
- 4 in the last 30 days
- 53 since 2007
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The design of an electrically heated flowline is based on several thermal requirements, which significantly affect the design and the CAPEX of such a solution. In particular, the heat-up criteria which define the minimum duration - usually 48 hrs - required to heat-up a flowline from ambient temperature to the ready-for-restart temperature is often the most demanding one and drives the electrical system requirements in a very conservative way compared to the other heating criteria. The objective of this paper is to demonstrate how the industry could remove this heat-up requirement and adopt a "temperature maintenance operating philosophy" to optimise the design of electrically heated flowlines. Heat-ups from ambient temperature would still be achievable, in less than seven days.
This approach is particularly well suited to heat traced pipe-in-pipe, where the heat lost to the environment is extremely low. For these highly insulated flowlines, the temperature maintenance duty power is significantly reduced, compared to the required power for heat-up phases.
This paper investigates the potential benefits and the feasibility of this change in the design requirements. Initially, impacts on the overall heated flowline design and particularly on the electrical architecture have been assessed as well as the associated CAPEX reduction. Secondly, analyses of the corresponding operating procedures have been conducted to assess feasibility. Finally, OPEX aspects have been taken into account to conclude on the overall interest of the solution.
Case studies show that applying a temperature maintenance philosophy to heat traced pipe-in-pipe would lead to significant CAPEX savings thanks to optimised electrical system design. Regarding shutdown costs, although the results depend on the assumptions considered, the temperature maintenance philosophy appears preferable as it results in lower power consumption and shorter shutdowns, the majority of the time. Furthermore, fewer heat-up phases result in safer procedures with regard to hydrate melting risks while reducing the power applied reduces the electrical stress on the heating system.
All the assessments have been conducted based on Electrically Heat Traced Flowline (EHTF) technology however the same exercise could be performed for other electrically heated flowline technologies and could demonstrate similar benefits.
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