The Northern Lights (NL) onshore terminal will initially receive CO2 transported by ship tankers from several industrial source sites located in south-eastern Norway; temporarily store liquid CO2 onshore in tanks at the terminal; and finally transport CO2 via a 12 ¾’’ OD offshore pipeline for injection into the Johansen storage reservoir, located just south of the Troll field. The CO2 injection pipeline will be laid from the shore terminal to a subsea wellhead structure from where the gas will be injected into the reservoir. Presently, demonstrating arrest of longitudinal propagating shear fracture in CO2 transport pipelines is specifically addressed in two international guidelines, ISO 27913 and DNVGL‑RP‑F104. The study reported here aims to develop a robust fracture control methodology unique to the Northern Lights pipeline that confirms and strengthens the fracture arrest criteria available in these guideline documents

The important loading of concern for fracture propagation control of pipelines transporting liquid CO2 stems from the fluid saturation pressure. For the NL pipeline concept study, the highest expected CO2 saturation pressure will occur by depressurization from onshore/shallow water conditions. This pressure is 55.8 bar, which gives an effective loading pressure of 54.8 bar.

Application of the Battelle method without correction led to an arrest pressure of the baseline pipe that is near insensitive to the linepipe material Charpy impact energy (CVN) value. The estimated arrest pressure is \~140 bar for CVN values in the range 100-200 J, or more than 2.5 times the estimated maximum load. Applying factors in accordance with ISO 27913 and DNVGL‑RP‑F104, here 1.2 on the estimated arrest pressure and 1.3 on the estimated load pressure, a wall thickness of \~10 mm is sufficient to arrest a propagating crack. Thus, the baseline pipe with a wall thickness of 15.9 mm has abundant capacity to arrest a propagating crack following the Battelle method.

The Battelle analyses were supplemented by numerical simulations. The numerical models applied in this study are based on SINTEF’s coupled FE-CFD model. The FE-CFD model is built within the framework of the commercial FE software LS-DYNA. The pipe is discretized using shell elements and the surrounding soil or water is discretized using smoothed particle hydrodynamics. The depressurization upstream of the crack-tip and the pressure of the escaping fluid downstream of the crack-tip are calculated using an in-house, one-dimensional CFD solver. The results from the CFD simulation are used to estimate the pressure profiles in the cross-sections both upstream of the crack-tip and on the flaring flaps downstream the crack-tip. The numerical simulations of the baseline pipe positioned on rigid ground with no trench or backfill also resulted in a minimum wall thickness of \~10 mm for a CVN value of 200 J. However, the numerical analysis is more sensitive to the CVN value than the Battelle analysis, and the minimum wall thickness for CVN=100 J is \~11.5 mm. When accounting for soft soil, and especially for cases where the pipe is submerged under water, trenched or backfilled, the capacity is further increased so that the minimum required wall thickness of \~11.5 mm for the 100 J material is conservative.

The main conclusion is that with the given pipe material and diameter, and the given loading conditions, a wall thickness of 15.9 mm, or potentially a wall thickness of 14.4 mm accounting for a 1.5 mm reduction due to corrosion, is enough for arresting a propagating crack. In addition, it is concluded that the BTCM with ISO 27913 or DNVGL-RP-F104 correction factors can provide a good first estimate in pipe design. In this study, however, the arrest pressure saturates for low CVN values indicating limited accuracy. For the NL pipeline, the analyses lead to a robust arrest assessment with significant margin to a critical wall thickness. With these factors now verified for this specific case, the otherwise straightforward fracture arrest methodology is considered fit for use in subsequent FEED and detail design.


Pipeline Fracture Control Concepts for Norwegian Offshore Carbon Capture and Storage

Division / Sponsors: 
Pipeline Systems Division

Paper Proceedings: https://asmedigitalcollection.asme.org/IPC/IPC2020/volume/84447

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