In order to safely transport gaseous hydrogen between the surface and the underground storage facility, the integrity of downhole pipes is of extreme importance, preventing leakages, ensuring a stable energy supply and protecting the environment. Tubings are used for injecting and withdrawing hydrogen as well as other gases from storage wells, acting as the primary physical conduit and pressure barrier between the underground storage facility and the surface.
The integrity of tubings and their connections can be safely evaluated at the Full-Scale Testing Center of the Institute of Subsurface Energy Systems at the Clausthal University of Technology by means of upscaled make and break (M&B) and sealability tests.
The M&B test has as goal to study the mechanical integrity of the threaded connection. During this test program the connections are subjected to multiple screwing and unscrewing operations. In between, the threads are inspected to determine whether they have suffered plastic deformation or even material loss. The test is considered successful if after up to 9 M&Bs the thread material does not show any damage or signal of galling failure.
The M&Bs are followed by the sealability assessment. In this case the pipe connection is tested to combined loads which are representative to the loads acting on the tubing string during its service. The application of high internal pressure with gaseous hydrogen combined with axial loads, alternating tension and compression, both at ambient and high temperatures, are planned.
The sealability test program is divided into 3 parts: an initial sample sealability assessment in order to ensure the connection is tight at any possible load state scenario it might encounter during its service. Secondly, the storage operation is replicated, inducing cyclic internal pressure with hydrogen for a certain time period, and finally, another sealability test takes place in order to verify the tightness of the connection after the complete load sequences imposed.
The hydraulic integrity of the string is measured by means of a leak detector connected to the threaded connection, which measures the volume of gas flowing through the threads along the test program, making sure that the connection is leak-free and suitable for the storage operations.
Power tongue used for the Make and Break tests
Example of the load steps run during the sealability tests of a pipe connection.
