Pipe-in-Pipe Technology Expands Onshore for LNG, Ammonia and Hydrogen Transport
By P. LEVESQUE, ITP Interpipe, Paris, France
(P&GJ) — With growing demand for safer, more efficient transport of cryogenic and sensitives fluids, pipe-in-pipe (PiP) systems are moving beyond offshore use and gaining traction onshore. PiP technology is proving its value in complex onshore environments, such as urban zones, buried crossings and cryogenic service.
The author’s company’s solutionsa combine high-performance insulation, self-supporting architecture and real-time leak detection in a compact, mechanically robust design. This article explores how PiP streamlined design enables reliable transport of liquified natural gas (LNG), liquified petroleum gas (LPG), ammonia and even liquid hydrogen (H2)—without the complexity of traditional double-containment systems.
Design philosophy and thermal performance. The core idea behind the system is to keep things as simple and robust as possible. It is a classic PiP configuration, but with a few key improvements. The inner pipe handles the fluid. Around it, a custom-thickness insulation layerb provides the required thermal performance. The insulation is directly in contact with the outer pipe and does not need any discrete spacers or centralizers (FIG. 1).
The lowest conductivity in the market results in extremely compact systems. Depending on the thermal requirements, insulation thickness can vary from 5 mm–60 mm. Despite this small footprint, the thermal performance is excellent, but difficult to match with conventional insulation like rockwool or cryogel. The PiPa routinely achieves U-values around 0.15 watts per square meter Kelvin (W/m²·K) for pipelines ranging from 4 in.–40 in.
Few thermal bridges, strong mechanical properties. Because the insulation is load bearing there is no need for intermediate supports or spacers. This contributes to very low heat loss and makes the system ideal for applications like LNG or LPG transport, where boil-off must be minimized—even during standby periods between vessel loadings.
MECHANICAL BEHAVIOUR AND STRESS MANAGEMENT
Managing thermal contraction from hot/cold fluids. During installation, both the inner and outer pipes are at ambient temperature; however, in most of the author’s company’s applications, the inner pipe will operate far below or above that temperature, often transporting cold fluids such as LPG, LNG, ammonia or liquid H2. At these low temperatures, the inner pipe naturally contracts; meanwhile, the outer pipe stays close to ambient, especially if it is buried.
This difference in thermal behavior causes the inner pipe to shorten relative to the outer pipe. To handle this safely, forged connection pieces are installed at strategic locations. These forged rings link the two pipes to restrict relative displacement, distributing the stress throughout the system in a controlled manner. Without this, cold shrinkage could create significant issues, especially at the elbows (FIG. 2).
The outer pipe acts as a structural guide. Once in operation, the outer pipe does more than just protect the insulation; it acts as a structural guide or stiffener, controlling the movement of the inner pipe over long distances. It keeps everything aligned and reduces end displacements and the associated loads on anchors or supports.
This behavior is particularly helpful for above-ground installations where the pipeline is exposed to daily thermal cycling. In such cases, conventional piping systems often require large expansion loops or flexible lyres to deal with temperature changes. These loops take up space, increase material cost and add complexity. With the author’s company’s design, such loops are avoided entirely—the stiffness of the outer pipe handles it internally. This reduces the length of pipe required, minimizes pressure drop and simplifies the overall layout.
Of course, this applies to normal operating conditions, when both pipes remain mechanically stable and the annular space is at its designed pressure. In case of a leak or abnormal event, the structural behavior will change, and the system must be re-evaluated accordingly. The PiP is designed for such eventualities.
SAFETY AND LEAK DETECTION
Detecting even the smallest leak. One of the most underrated features of the PiP design is its leak detection capability. Because the annular space is completely sealed and maintained at very low pressure (typically around 15 mbar), it becomes an ideal environment for pressure monitoring. Any small increase in pressure is immediately noticeable.
In practice, a sudden rise of 15 mbar–20 mbar—whether over a few seconds or within an hour—is enough to trigger a leak alert. This is much more sensitive and faster than conventional detection systems, which often rely on temperature gradients, mass balance or visual inspections. In many cases, a simple pressure sensor can monitor the pipeline integrity in real time.
From pressure to location: Fiber optics as a backup. Pressure monitoring tells you that something has happened. To locate the problem, a distributed fiber optic sensing systems laid along the pipeline. These systems can detect temperature variations caused by fluid escaping from the inner pipe, allowing the operator to pinpoint the leak location accurately.
This two-layered approach—pressure spike first, location data second—is fast, reliable and does not require complex electronics inside the pipe. It works well even in buried applications or in areas that are difficult to access.
A secondary containment by design. In many projects, clients (or sometimes regulatory bodies) ask for “double containment” systems, especially when transporting hazardous or flammable products. The author’s company’s PiP system can often meet these requirements. Since the outer pipe is designed to be pressure-retaining, it can contain the potential inner pipe leak.
The secondary containment improves pipeline development risk profile allowing for the development of terminals in port facilities or in congested industrial zones of near population centers.
MATERIALS AND FABRICATION
Not all steels are created equal. When working with cold or cryogenic fluids, the choice of materials becomes critical. For many low-temperature applications, PiP use high-quality alloys such as 36Ni, 304L stainless steel or low-temperature carbon steels (LTCS) compliant with American Petroleum Institute (API) specifications. These materials are selected not just for their mechanical strength, but for their ductility and stability at low temperatures.
Whenever possible, standard pipe sizes are used to simplify procurement and reduce costs; however, customer diameters may also be employed, if needed. In some projects, this approach allows for a more compact layout or reduction in insulation thickness, while still meeting the thermal criteria. This is especially beneficial for horizontal directional drilling (HDD) applications or where buoyancy is a factor.
Double-wall fittings are part of the package. The PiP system does not stop at straight pipe runs—double-wall fittings (bends, tees, reducers) are also manufactured, all designed to maintain the same mechanical and thermal performance.
While most fabrication takes place in the facility in Normandy, France, the production process has also been successfully adapted to other fabrication yards globally. This allows the best-for-project execution methods to be used, optimizing procurement, logistics and fabrication costs.
A controlled fabrication process. PiP sections are manufactured without any welding. The standard process involves assembling pre-cut inner and outer pipes with the insulation in between. This approach enables a fast and repeatable fabrication while maintaining tight dimensional tolerances.
However, some specific components (tees, interface pieces) do require welding. The author’s company’s fabrication yard in Normandy is fully equipped to handle these cases, including all necessary non-destructive testing (NDT) inspections and hydrotesting. Strict fabrication procedures and qualified welding techniques are followed to ensure full compliance with project and regulatory requirements (FIG. 3).
Over time, strong quality control protocols have been established, along with trusted relationships with material suppliers. This ensures the mechanical performance of every component, the repeatability of the process and the traceability of all materials involved. When necessary, the fabrication model can also be applied at other yards worldwide to adapt to project logistics.
FIELD APPLICATIONS AND CASE STUDIES
Buried PiP lines for LPG transfer in a congested zone. One recent installation involved two PiP lines in parallel—one for butane, the other for propane—used for ship loading operations. The project took place in a highly congested industrial zone, surrounded by existing factories, roads and residential areas, requiring the pipeline to be buried.
This system offered a clear advantage. Unlike conventional insulated pipes that would have required casings and support structures, the PiPs could be directly installed underground. The lines were designed to minimize boil-off losses during idle periods, especially between vessel loadings, which could last up to two weeks. The thermal performance, absence of expansion loops and compact footprint of the solution were key to making the project viable.
Transporting ammonia through an existing facility. In another project, an ammonia pipeline had to be installed in the middle of an already-built plant. The existing pipe racks and structural supports were fully occupied, leaving no space above ground.
The solution was to go below. The PiP line was deeply buried, routed under the plant infrastructure. Because the outer pipe protects the insulation and acts as a load-bearing element, there was no need for any external casing or structural reinforcement. The system could be installed using standard trenching methods and HDD while maintaining high thermal performance and mechanical integrity. This allowed the client to avoid major modifications to existing structures or production downtime.
Double containment requirements and HDD river crossing. Some regulatory bodies require double containment for safety and environmental compliance. Thanks to the design, this requirement can be met directly with the PiP system. This kind of solution has been delivered on several projects. One notable case involved a PiP line that had to cross a river via HDD while also meeting double containment standards. The compact geometry, mechanical integrity and sealed annulus volume made it possible. The result is a safe and compliant underground crossing without the need for complex concrete encasement or oversized tunnels (FIG. 4).
Takeaway. The author’s company’s PiP solutiona is simple, efficient and robust, and well adapted to complex environments. Whether for industrial zones, urban crossings or sensitive fluids, the system offers a unique balance between thermal performance, mechanical integrity and ease of installation.
NOTES
a ITP Interpipe’s PiP solutions
b ITP Interpipe’s Izoflex® insulation layer
About the Author
PIERRE LEVESQUE began his career with several years of experience on major onshore projects across Russia, Qatar and Nigeria, gaining valuable international exposure in the oil and gas industry. This global background led him to join ITP Interpipe in 2018 as a project engineer, quickly advancing to the role of engineering manager.
Since then, Levesque has contributed to a wide range of onshore (NH3, LPG, LNG) and offshore projects, initially as an engineer and team lead, and later as a manager. Over the years, he has tackled diverse technical challenges, led multidisciplinary teams and maintained a strong commitment to QHSE standards and client satisfaction. Today, Levesque focuses on developing processes, mentoring young engineers and strengthening technical capabilities and operational excellence within the organization.