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In the field of water pipelines, geothermal energy production as well as carbon capture and storage technology (CCS) materials have to provide a high resistance to corrosion and mechanical stress. The combination of cyclic load and corrosive aqueous environment leads to corrosion fatigue of pipes and components (e.g. pumps) and thus inevitably to the reduction of the lifetime of these components. To estimate the reliability of components from adjusted in-situ-laboratory experiments a corrosion chamber was designed and tested with CO2 saturated corrosive aqueous media flowing at a steady rate. Unique feature of this special chamber is its installation directly onto the sample and thus providing flexible usability in almost every testing machine. This allows simultaneous mechanical loading of the sample, operation at temperatures up to 100 °C and exposure to fluid flow of corrosive liquids and gases. The lifetime reduction of AISI 420C (X46Cr13, 1.4034) is demonstrated at T=60 °C, geothermal brine: Stuttgart Aquifer flow rate: 9 l/h, CO2. S-N plots, micrographic-, phase-, fractographic- and surface analysis were applied to obtain sustainable information on the corrosion fatigue behavior. Maximum number of cycles (here 12.5 x 106 cycles to failure) is reached at σa =173 MPa. No typical fatigue strength exists and passive corrosion fatigue may be identified as failure cause.
High-temperature-high pressure stress-strain testing of materials in CO2-containing saline solutions
(2015)
In-situ stress-strain testing under corrosive environment, such as corrosive gasses (e.g. CO2) and highly saline water, is a challenge in testing corrosion fatigue of materials, e.g. for geothermal application or CCS (carbon capture and storage). The first corrosion chamber system was designed for performance at ambient pressure up to 100 °C. The second allows for corrosion fatigue testing at high pressure up to 200 bar and 400 °C. The highly flexible corrosion chambers allow for fast changing and easy alignment of test samples, visual monitoring, CAD-camera monitoring electrochemical measurements, O2-partial pressure or gas partial pressure measurement. Novelty is the fixing of the corrosion chamber directly onto the specimen, that guarantees best fitting and enables the test system to be modified easily suiting a variety of fatigue test machines. All parts of the test system are conforming to the technical rules.
To resist the corrosive geothermal environment during carbon capture and storage CCS -such as: heat, pressure, salinity of the aquifer, CO2-partial pressure, properties of pipe steels-require certain specification. For evaluation samples of differently heat treated high alloyed stainless injection-pipe steels AISI 420 X46Cr13, AISI 420J X20Cr13 as well as X5CrNiCuNb16–4 AISI 630 were kept at T=60 °C and ambient pressure as well as p=100 bar for 700 h up to 8000 h in a CO2-saturated synthetic aquifer environment similar to a possible geological situation in the northern German Basin. Corrosion rates and scale growth are lowest after long term exposure for steels hardened and tempered at 600 °C to 670 °C and pits -indicating local corrosion- decrease in diameter but increase in number as a function of carbon content of the steel. Martensitic microstructure is preferred with respect to these particular conditions.
During carbon dioxide storage technology (carbon capture and storage, CCS) components are exposed to a corrosive environment and mechanical stress, which results in corrosion fatigue and inevitably followed by the a lifetime reduction of these components. In order to gain knowledge upon the corrosion fatigue strength of materials, Samples of high alloyed stainless injection-pipe steels AISI 420 X46Cr13, and X5CrNiCuNb16-4 AISI 630 were tested in a at T=60 °C and ambient pressure in a CO2-saturated synthetic aquifer environment similar to possible geological on-shore CCS-sites in the northern German Basin. Therefore a corrosion chamber applied to a resonant testing machine allowing for “in situ” test conditions was designed and successfully tested. In-situ tension compression experiments were established using a resonant testing machine at a frequency as low as 30 – 40 Hz. In addition technical CO2 was introduced into the closed system at a rate close to 9 L/h to keep stable environmental conditions. Simultaneously electrochemical testing was performed to get information on failure causes and the mechanism of failure during the injection of CO2 into deep geological layers. S-N plots, micrographic analysis, and surface analysis of the fracture surface were applied to obtain sustainable information on the corrosion fatigue behavior of injection pipe steels. Samples used have a surface roughness of Rz = 4, to simulate technically machined surfaces. X46Cr13 reached the maximum number of cycles (12.5 x 106) at a stress amplitude of 173 MPa. X5CrNiCuNb16-4 reached the maximum number of cycles (10 x 106) at a stress amplitude at 150 MPa. The scatter range of X5CrNiCuNb16-4 is very high (1:34); by comparison the scatter range of X46Cr13 is only 1:3.5.
Samples of differently heat treated high alloyed stainless injection-pipe steels AISI 420 X46Cr13, AISI 420J X20Cr13 as well as X5CrNiCuNb16-4 AISI 630 were kept at T=60 °C and ambient pressure as well as p=100 bar for 700 h - 8000 h in a CO2- saturated synthetic aquifer environment similar to possible geological on-shore CCS-sites in the northern German Basin. Corrosion rates and scale growth are lowest after long term exposure for steels hardened and tempered at 600 to 670 °C and pits - indicating local corrosion- decrease in diameter but increase in number as a function of carbon content of the steel. Martensitic microstructure is preferred with respect to this particular CCS-site.
Die Lebensdauer von Bauteilen welche gleichzeitig mechanisch und korrosiv belastet werden kann mit vorhandenen Literaturwerkstoffdaten nicht ausreichend bestimmt werden. So kommt es entweder im Betrieb frühzeitigen versagen, oder einer Überdimensionierung bei der Konstruktion. Um Werkstoffe unter Bedingen der SchwingungsrisskorroSIOn zu prüfen und somit belastbare Materialkennwerte zu bekommen, ist es notwendig diese unter Realbedingungen in hierfür geeigneten Prüfanlagen zu testen.
The commercial usage of latent thermal energy storages primarily depends on the development of a suitable phase change material (PCM). For industrial high temperature applications above 400 °C multicomponent chloride eutectics are promising and therefore discussed seriously. The profound thermodynamic investigation of such eutectics requires a much greater amount of specimen material than conventional calorimeter can handle. Therefore, a special adiabatic calorimeter was developed and designed. With a specimen mass of > 100 g the typical thermodynamic measurements with a commercial calorimeter can be extended by cycle stability measurements, which are often decisive for practical application of PCM. Furthermore, by implementing corrosion specimens inside the calorimeter high temperature corrosion experiments according to ISO 21608 can be performed inside the calorimeter. Adiabatic measuring conditions can be provided by using two separate heating systems. Therefore, the outer “protective system” follows the temperature curve of the inner “measuring system” minimizing the temperature difference between the heating systems and simultaneously preventing heat losses from the measuring systems.
In CCS environment (carbon capture and storage) pipes are loaded statically and/or cyclically and at the same time exposed constantly to the highly corrosive hot thermal water. Experimental procedures such as ambient pressure immersions tests, in-situ corrosion fatigue experiments using a flexibly designed corrosion chamber at ambient pressure and a specially designed corrosion chamber at high pressure. Experimental set-ups for push/pull and rotation bending load are introduced. The corrosion behavior and lifetime reduction of high alloyed steels (X46Cr13, 1.4043), (X5CrNiCuNb16-4, 1.4542) and (X2CrNiMoN22-5-3, 1.4462) is demonstrated (T=60 °C, geothermal brine: Stuttgart Aquifer flow rate: 9 l/h, CO2 ).