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LNG Pipe-in-Pipe Techology
Richard Rankin M.B.
Mick AMEC Paragon Inc.
Houston OGJ Nov 14, 2005

The large number of proposed LNG projects currently vying for public and governmental approval on a global basis has led to an increased focus on associated safety, economic, environmental, and aesthetic issues.

LNG project teams will consider designing LNG terminals using subsea or buried onshore LNG pipelines in an effort to offer safe, robust, cost-effective, and environmentally and visually appealing alternatives to more traditional technology. AMEC Paragon used this approach for the Camisea LPG export terminal offshore Peru.  Using InTerPipe's (ITP) subsea cryogenic pipeline system, AMEC Paragon proposed a marine export terminal design that allowed the client (Pluspetrol SA, Buenos Aires) to obtain critical local approval for the project.  This article discusses the technical, economic, safety, and local acceptance advantages of a terminal based on subsea or buried onshore LNG pipelines.

Public scrutiny

    LNG projects face significant public scrutiny worldwide.  Local populations object to real and perceived safety, environmental, and inconvenience aspects of siting an LNG facility in their communities.  In siting LNG terminals and dealing with the public, potential developers need to be reminded of the basic equation developed by Peter Sandman, a pre-eminent risk communication consultant:

Risk = Hazard + Outrage.

      "Hazard" is the technical risk engineers are trained to assess.  "Outrage" is the public's perception of risk.  "Outrage" is made up of factors such as trust, responsiveness, control, etc.

      Clearly, with the difficulties experienced by developers of some projects in obtaining local approval, a successful approach must balance technical and economic feasibility with political realities specific to each location.  For each project, the "Outrage" factor of the risk equation must be managed as effectively as the "Hazard" factor.

Alterative technology

Fig. 1
    It is technically and economically feasible to transport cryogenic fluids (including LNG and LPG) at typical loading-offload rates (10,000 cu m/hr) over relatively long distances (~10 miles) via straightforward, robust pipe-in-pipe loading lines.

    This feasibility provides wider options for siting an LNG terminal than had previously been available. For projects where there is strong public concern about LNG carriers approaching residential areas, the berth can be moved further offshore. The LNG might also move via pipeline from a berth to an inland location where siting LNG tanks is more acceptable, or to a facility which has waste heat for regasification (refinery, alumina plant, etc.).

     While double-wall and triple-wall pipe-in-pipe options are both thermally and mechanically feasible using ITP's LNG pipe technology, we have chosen to describe the triple-wall option. 
Fig. 1 shows a cross-section of the triple-wall pipe. This design has an inner pipe made of 36% nickel steel, microporous insulation, an intermediate carbon steel pipe, and an outer carbon steel pipe.

     The third pipe outer wall is optional but adds an extra level of mechanical integrity. The ability to employ butt welds, which are both robust and easily inspected--for all girth welds between individual field joints makes pipeline transport of LNG significantly more feasible.

      Additionally since the mechanical properties of ITP's Izoflex insulation make it safe to weld directly over it the field joints are insulated in exactly the same manner as the running pipe, eliminating any cold spots. Elimination of expansion loops or bellows, which are typically required to accommodate the expansion and contraction caused by low operating temperatures (-256o F), also increases both the robustness of the design and the feasibility of this approach.

     Using the 36% nickel steel inner pipe in the pipe-in-pipe design allows expansion loops to be eliminated. The high thermal performance of the ITP insulation system also allows for a compact pipe-in-pipe configuration.

Pipe-in-Pipe technology

    The upstream oil and gas industry has used pipe-in-pipe flowlines for three decades to improve thermal performance.  Quest Offshore Resources Inc. reports almost 400 miles of pipe-in-pipe installed for upstream oil and gas projects between 2000 and 2004.
Lay barges using J-Lay, S-lay, reeled, or towed equipment weld and install these pipes in water depths exceeding 5,000 ft.
ITP's technology uses the same DNV design code (DNV OS-F101 Submarine Pipeline System) employed for oil and gas pipe-in-pipe installations.

High-performance insulation

     Another important, field-proven component of the ITP LNG pipeline is ITP's Izoflex insulation.  It is microporous insulation.

      Unlike other solid insulation materials, microporous insulation has a thermal conductivity lower than the thermal conductivity of still air.  Izoflex have been installed in subsea oil and gas pipelines since 1998.  Currently 105 miles of installed ITP subsea pipe-in-pipe line has this insulation.  An additional 40 miles will be installed in 2006 offshore Angola.