For customers and in publicly funded projects our services include research into transportation pipelines, pipe storage, containers, and tanks along the process chain from steel production to the pipe. Furthermore, we identify property-based criteria for standards and specifications and examine products with established and new testing methods.
Exposure test - hydrogen uptake in pressurized hydrogen gas
The impact of compressed hydrogen on steel can cause hydrogen embrittlement. The required absorption of hydrogen from the gas phase into the steel is not to be expected under normal conditions due to the existing oxide layer. However, under special circumstances, e.g., plastic deformation of the steel and/or activation of the surface in the presence of hydrogen gas, significant hydrogen uptake can occur.
Using exposure tests, steel samples can be loaded in pressurized hydrogen, with various parameters such as surface condition, gas pressure, temperature and exposure time being variable. The hydrogen content in the sample can then be measured using carrier gas hot extraction.
Carrier gas hot extraction – quantitative determination of hydrogen in metals
Carrier gas hot extraction is a method used to determine hydrogen diffusion and concentration in the metal microstructure both quickly and accurately, even with very low hydrogen contents in the ppb-range. The sample to be tested is heated in a specific process to release hydrogen, which is then transported to the thermal conductivity detector with a carrier gas. Depending on the investigation, temperatures of 25 °C to 900 °C can be achieved using an infrared oven. In addition to experiments at constant temperatures, temperature ramps or steps can also be applied to obtain information on differently bound hydrogen. Measurements of large sample pieces (e.g., welded specimens according to ISO 3690) are possible due to the large diameter of the exposure tube. A Bruker G4 Phoenix is available for carrier gas hot extraction measurements. In addition, the Bruker G8 Galileo enables us to determine the total hydrogen in a test piece by means of melt extraction.
Slow strain rate test (SSRT) - Ductility behavior under pressurized hydrogen gas
The “Slow Strain Rate Test” (SSRT) according to NACE TM0198 or DIN EN ISO 7539-7, offers the possibility of testing the effect of a hydrogen atmosphere on the mechanical properties under quasi-static loading. By using a very low strain rate, the hydrogen is given the opportunity to permeate into the steel and diffuse to critical points in the microstructure. The test can be carried out on various sample geometries (smooth, notched, round or flat tensile specimens) under conditions close to real-life (pure gaseous hydrogen or as a mixture with methane or natural gas). As a comparison, tests are carried out in a nitrogen atmosphere under identical conditions.
The evaluation is based on changes in the ductility properties depending on the test environment, including the reduction of area ratio (RAR) and the plastic elongation at fracture ratio (EPR) of the samples after fracture.
Fatigue test - cyclic tests for fatigue strength evaluation
Pipes, tanks, and vessels are exposed to pressure fluctuations during operation. This can lead to fatigue and damage the material and has a significant impact on service life. To simulate the pressure fluctuations in the component, these are reproduced in the test by applying cyclic loads. Material fatigue can thus be determined in alternating load tests, which are evaluated using fatigue strength concepts according to Wöhler and allow component design. This requires a database that also includes the influence of hydrogen on fatigue.
For tests in a hydrogen atmosphere, alternating load tests are carried out on tensile specimens. In addition to the crack propagation, the test results also include the crack initiation phase, which enables a design close to the actual component properties. By varying the applied stress amplitude, the cyclic tests can be used to estimate the fatigue strength as a function of the number of cycles.
Fracture mechanics - fracture toughness, crack growth rate
The design of components for the hydrogen economy is currently based on fracture mechanics concepts. The determination of the required characteristic values will also be decisive for qualification and acceptance in the future (ASME B31.12, DVGW G463). The focus here is on crack propagation behavior (ASTM E647) and fracture and crack toughness (ASTM E1820 / ISO 12135).
The crack propagation behavior is determined under cyclic loading in the elastic range of the material as the crack propagation rate da/dN. It quantifies how fast a crack can grow under cyclic loading in a hydrogen atmosphere. The crack toughness KJIC is determined by means of a crack resistance curve (J-R or CTOD-R) under load with partial unloading for elastic-plastic material behavior. The characteristic value represents the resistance to the opening of an existing crack. In combination with a concept for fracture mechanics service life analysis, a conservative estimation of the allowable service life of a component is achieved based on these characteristic values.
KIH test - standardized material qualification
The design of pipelines for the transportation of hydrogen can be based on a fracture mechanics service life analysis. An important part of this analysis is the limit criterion in the form of the required toughness. The KIH test in accordance with ASME B31.12 provides a qualification value based on this criterion as a threshold factor for stress intensity. The effect of pressurized hydrogen on potential crack propagation under constant deformation or load is determined. For this purpose, fatigue precracked fracture mechanics specimens are brought to a certain load level and then exposed to pure hydrogen at a specified pressure (e. g., 100 bar) for a period of 1,000 hours. After exposure, the sample is cracked open, and the fracture surfaces are analyzed for any crack propagation using scanning electron microscopy (SEM).
Internal pressure test - component behavior under static/cyclic internal pressure
To answer critical safety-related questions regarding the use of materials under pressurized hydrogen conditions, we carry out component tests on pipe materials of various dimensions and examine, for example, what effect the hydrogen medium has on bursting behaviour.
The bursting behavior is analyzed using comprehensive instrumentation with pressure sensors and strain gauges as well as recording the test with high-speed cameras. The fracture surface analysis enables meaningful diagnostics. We take a holistic view of material behavior, environmental conditions, and stress, determine characteristic values in accordance with the customer and consider external influences such as defects introduced - all under one roof and in accordance with current standards. Important insights have already been gained from bursting tests carried out with hydrogen on fracture behavior and the type of failure. The dimensional range of the burst tests carried out currently lies between an outer diameter of 31.5 mm and 70 mm and wall thicknesses of 0.67 mm to 3.4 mm. The corresponding volume is between 0.1 and 2 liters. The burst pressures vary between 68 bar and 400 bar, depending on the sample dimensions and the material. Further tests are planned in which the test volume will be progressively increased. A test rig for cyclic internal pressure testing with hydrogen is currently under construction, with which pipes and tanks can be tested up to a test pressure of 1,050 bar.
Disc testing - hydrogen embrittlement
Hydrogen embrittlement can significantly shorten the service life of metallic materials. We offer comprehensive disk tests in accordance with DIN EN ISO 11114-4:2017 to test the resistance of your materials to hydrogen embrittlement. Using state-of-the-art technology and precise hardness measurements, we ensure that your components meet the highest safety standards. We help you to select suitable steels − cost-efficiently and in a material-saving manner.