Keeping tight connections

Throughout the premium connection development project, the OCAS competencies in the areas of fi nite element modelling, advanced knowledge of material behaviour, surface coating development, and full-scale testing have been successfully combined.

Jeroen Van Wittenberghe

As global energy demand increases, the role of natural gas is becoming more important. To explore and produce from natural gas reserves, gas-tight pipeline connections are required. Furthermore, enhanced gas tightness for downhole casing and tubing lines will be needed for carbon capture and sequestration (CCS) as well as underground hydrogen storage projects for the ongoing energy transition.

MOST STRINGENT TESTING QUALIFICATION CONDITIONS

Together with the ArcelorMittal technical team in Houston, OCAS has developed a state-of-the-art premium connection, branded AM-BLADE. The connection design was optimised through extensive fi nite element analysis. In addition, a lot of attention was given to simulating correct preloading conditions, as these are infl uenced by the coeffi cient of friction between the contacting surfaces and the frictional properties of the applied lubricant. This resulted in a premium connection with the highest technical performance while meeting the most stringent testing qualifi cation conditions. The full-scale qualifi cation tests of the AM-BLADE connection have been carried out on the OCAS Tubular Testing System according to the API 5C5 testing standard. During the testing protocol, the connections are subjected to extreme testing conditions – including tension, compression and bending loading combined with internal and external pressure – all at ambient and elevated temperature levels. During the test sequence, the connections’ resistance to galling and their sealability and structural integrity are evaluated.

DOPE-FREE COATING SOLUTION

To exclude the use of polluting thread compound greases, OCAS worked on the development of a dope-free coating solution to replace the use of thread compounds completely. This technology was implemented using a combination of lab-scale testing as well as full-scale qualifi cation testing to qualify the connection design in combination with the dope-free coating. After screening potential candidates for coating the connections (pin and box) on fl at lab samples, a specifi c set-up was built to coat and cure large parts uniformly. Once the methodology was put in place to achieve a smooth, uniform and adherent coating, the test could be validated. The information gathered from these tests is used for the preparation of the engineering fi le to industrialise this new solution.

INSIDE VIEW

In the ArcelorMittal premium connection development program, fi nite element simulations tackled specifi c load cases that combine axial tension and compressive loads with internal and external pressure and even bending in 3D. These load cases are selected from the load points that are described in the testing protocol. The analysis focuses on determining stress hot

It’s exciting to establish a methodology that enables us to optimise processing parameters suitable for the given confi guration and getting it right: a smooth, uniform and adherent coating!

Marc Leveaux

spots during the different load steps and the evolution of contact pressure in the metalto-metal seal and torque shoulder. The latter two values are used to estimate the sealing performance and the probability of galling during connection make-up, respectively. In addition to the sealing performance, fi nite element analysis also enables us to look ‘inside’ a premium connection. Whereas full-scale tests only provide macroscopic observations, FEA results yield the deformations, stresses and strains at any location within the threaded joint. In this way, these FEA analyses results help to speed up and steer the design process.

Finite element analysis is an established numerical tool for developing new design concepts. On top of that, it’s indispensable in supporting our customers with the verifi cation of the performance within complex operational, testing and qualifi cation scenarios.

Maarten Van Poucke