This summer, four students joined SINTEF Energy Research as summer scientists within the COREu project. One of them was Håkon Hegstad Sæternes, who worked on “Safe Design of CO₂ Pipelines” in work package 2 – Core Technologies. He was under the supervision of Alexandra Metallinou Log and Svend Tollak Munkejord, who both emphasise the value of the program:

“It is very useful for us to have students working with us during the summer. They take on real-life tasks, some of which we don't have the time to complete ourselves. These students can later continue working with us for their master's, and even become our future colleagues working on CCS technologies.”

The Summer Scientist Program at SINTEF Energy Research is a research internship for university students. Participants work on real projects alongside experienced scientists, gaining hands-on experience in state-of-the-art laboratories. The internship typically lasts 6 to 8 weeks, from mid-June to mid-August, and concludes with a conference where the students present their work.

The program gives students an opportunity to contribute to world-leading research, build professional networks, and develop skills useful for future careers in both academia and industry. As part of his internship, Håkon worked on SINTEF’s engineering tool for the safe design of CO₂ pipelines. Below is a summary of the poster he presented at the Summer Scientist Conference in August.

CO₂ capture and storage (CCS) can become an important part of solving the climate crisis. To scale up CCS, an efficient and safe transport system for CO₂ is needed. Pipelines are a cost-effective means of transporting large volumes of CO₂, and it is important that they are safe to use. SINTEF developed an engineering tool that predicts ductile running fractures using the “Battelle Two-Curve Method.” The tool supports two models for fluid calculations: HEM and D-HEM. Previously, the D-HEM model was only available for pipelines transporting CO₂ in liquid phase. New functionality has now been added so that the D-HEM model is also compatible with pipelines transporting CO₂ in gas phase.

When a pipeline is damaged, a so-called running ductile fracture may occur. If the pressure at the fracture zone is high enough, it can drive the fracture further. The fracture then propagates along the pipe, somewhat like a zipper being opened. To prevent this, it is important to design pipelines so that the fracture stops by itself. Being able to predict when a running ductile fracture may occur is crucial for proper pipeline design. It would be costly to manufacture pipes that are unnecessarily thick.

One way to predict whether a running fracture may occur is the Battelle Two-Curve Method. In this method, the propagation speed of the fracture is compared with the speed of the pressure drop wave in the fluid (CO₂). If the fluid curve and the material curve intersect, it means that the pressure from the CO₂ is high enough to drive the fracture further, and there is a risk that a running ductile fracture may occur.

If a CO2-pipe is punctured, the pressure in the pipe will fall and the CO2 will start to boil (if it was originally in the liquid phase) or condense (if it was originally in the gas phase). In the Battelle Two-Curve Method, the fluid curve can be calculated in two different ways. The Homogeneous Equilibrium Model (HEM) assumes that the phase change occurs quickly enough for the flow to remain in thermodynamic equilibrium. This method is widely used. The Delayed Homogeneous Equilibrium Model (D-HEM), on the other hand, accounts for the fact that the pressure drop during a fracture is so fast that the phase change does not occur at thermodynamic equilibrium but is delayed (hence “delayed”). This method provides a better representation of the physics behind the phase change.

Pipelines will be an important part of the transport chain within CCS. A fracture in a pipeline can propagate as a ductile running fracture, and the pipes must be designed to prevent this. The Battelle Two-Curve Method is a way to predict whether a ductile running fracture may occur. The D-HEM model more accurately represents the physics of phase transitions during a sudden pressure drop in CO₂ compared to the HEM model. A key outcome of this work is that the SINTEF engineering tool can now apply the D-HEM model not only for pipelines transporting CO₂ in liquid phase, but also for gas phase transport.