Heat-Traced Flowlines

Planned or unexpected shutdowns of a pipeline imply an effluent temperature reduction and a risk or reaching critical temperatures, such as the Hydrate Appearance Temperature (HAT) or the Wax Appearance Temperature (WAT).

The operator will choose to work with fluids at temperature above the HAT/WAT and allow himself a margin to take into account cooling in case of a production stop. Operationally this margin is defined as a number of hours called the “cooldown time” that the operator requires before having to start up a preservation scheme to replace the hydrate-prone fluids inside the flowlines with inert (“dead”) oil.

Hydrate removal from pipeline

For deep water applications, one of the common strategies is to install dual flowlines forming a loop. In case of shutdown, this architecture allows to replace live oil with dead oil and avoid hydrate appearance. A way to reduce the costs would be to remove the loop and be able to maintain the flowline above HAT/WAT in case of a shutdown.

Drawing upon past experience in the North Sea and in West Africa, ITP has developed an Electrically Heat Traced Flowline (EHTF) characterized by its simplicity and low power requirement.

Objectives

The ITP EHTF is designed for Flow Assurance issues of long shutdown and start up conditions (hydrate formation), and allow single line tie-backs (no loop) in order to minimize:

-CAPital EXpenditures (CAPEX)
-OPeration EXpenditures (OPEX)

Concept

The EHTF can be described as follows:

- A Pipe-in-Pipe fabricated with resistive wires wound along the inner pipe length and high-performance Izoflex^TM panels installed on top of the electrical cables.

- Low electrical power input (about 10W/m to maintain the effluent above the HAT or to raise the temperature above the HAT)

The concept has been qualified within a JIP (GPRI Electrically Heat Traced Flowline Joint Industry Projet - 2001) sponsored by CHEVRON, MARATHON, TOTAL, SHELL, CONOCOPHILLIPS and

CHEVRON.

EHTF pipe section

Advantages

The EHTF feature the following advantages:

- A well insulated pipe provides high arrival temperatures and long cool down times (up to 36hours) in passive conditions (without applying the electrical heat tracing).

- The electrical power tracing is used only in case of very long shutdowns: above 24/36 hours which accounts for less than 2% of shutdown conditions.

- The electrical power consumption (about 10W/m or 200kW for 20km) is low compared to other tracing technologies available.

- The technology does not require dedicated and costly generator which adds payload on already space-limited platforms.

- The technology is compatible with shallow, deep and ultra deep water.

Connecting the electrical power