Filtern
Dokumenttyp
Sprache
- Englisch (6)
Schlagworte
- Heat treatment (6) (entfernen)
Organisationseinheit der BAM
When engineering a Carbon Capture and Storage site (CCS) local corrosion (pitting) of the injection pipe steel may become an issue when emission gasses from oxyfuel power plants are compressed into deep geological layers. This highly corrosive environment arises when the flue gasses, mainly composed of CO2 , are injected into saline aquifer water. Immediately carbonic acid is formed causing corrosive attack of the injection steels. The influence of heat treatment on the local corrosion resistance was demonstrated in laboratory experiments at 60 °C and ambient pressure for three steels X46Cr13 (1.4034), X20Cr13 (1.4021) and X5CrNiCuNb16-4 (1.4543) under a similar liquid corrosive environment as found at a geological onshore CCS-site in the Northern German Bassin.
The influence of heat treatment on pit corrosion needs to be considered to guarantee reliability and safety during the injection of compressed emission gasses – mainly containing CO2 – into deep geological layers (CCS-technology, Carbon Capture and Storage). In laboratory experiments different heat treated steels used as injection pipe with 13% Chromium and 0.46% Carbon (X46Cr13, 1.4034) as well as 0.2% Carbon (X20Cr13, 1.4021) were tested. Also X5CrNiCuNb16-4 (1.4542) was investigated as typical steel used for geothermal pumps. Keeping stable environmental conditions in laboratory experiments the samples were exposed to the distinct synthetic aquifer environment saturated with technical CO2 at a flow rate of 3 l/h for up to 6 months.
Independent of the exposure time the least amount of pits is found on hardened steels with martensitic microstructure where X5CrNiCuNb16-4 shows fewer pits than X46Cr13 and X20Cr13.
Regarding steels with similar Cr-content the higher Ccontent in 1.4034 results in fewer pits compared to 1.4021.
Properties of pipe steels for CCS (carbon capture and storage) technology require resistance against the corrosive environment of a potential CCS-site (heat, pressure, salinity of the aquifer, CO2-partial pressure). The influence of austenitzing in heat treatment routines of two different injection pipe steels (1.4034, X46Cr13 and 1.4021, X20Cr13) was evaluated. Steel coupons were austenitized at different temperatures (900-1050 °C) for different lengths of time (30-90 min) before quenching and annealing prior to long term corrosion experiments (60°C, 100 bar, artificial brine close to a CCS-site in the Northern German Basin, Germany). In general, fewer pits are found on X46Cr13. Comparing steels with 13% chromium each the higher carbon content of X46Cr13 (0.46% C) results in a lower number of pits compared to X20Cr13 (0.20% C). It is found that neither the carbon content of the steels nor austenitizing temperature has much influence, but local corrosion behaviour is most susceptible towards austenitzing time.
Potential of martensitic stainless steel X5CrNiCuNb 16-4 as pipe steel in corrosive CCS environment
(2017)
Pipe steels suitable for carbon capture and storage technology (CCS) require resistance against the corrosive environment of a potential CCS-site (heat, pressure, salinity of the aquifer, CO2-partial pressure). X5CrNiCuNb16-4 has been proven to be sufficient resistant in corrosive environments, but shows rather unusual corrosion behaviour in CCS environment. Therefore differently heat treated coupons of 1.4542 were kept at T=60 °C and ambient pressure as well as p=100 bar for 700 h - 8000 h in an a) water saturated supercritical CO2 and b) CO2-saturated synthetic aquifer environment similar to on-shore CCS-sites in the Northern German Basin. Additionally fatigue tests were performed via push-pull tests with a series of 30 specimens was tested at stress amplitudes between 150 MPa and 500 MPa (sinusoidal dynamic test loads, R=-1; resonant frequency ~ 30 Hz). Best corrosion resistance in the liquid phase is achieved via normalizing prior to exposure and hardening+tempering at 670 °C leads to lowest corrosion rates in the supercritical phase. With no regard to atmosphere discontinuously ellipsoidal surface corrosion regions appear after exposure of 4000 h and more. The endurance limit of X5CrNiCuNb16-4 measured in air is reduced by more than 50% when exposed to CCS environment (maximum number of cycles (10 x 106) at a stress amplitude of 150 MPa) The scatter range TN = 1:34 is disproportionately large contributing to an overall unusual corrosion behaviour.
Carbon Capture and Storage (CCS) is well acknowledged to mitigate climate change. Therefore, pipe Steels suitable for CCS technology require resistance against the corrosive environment of a potential CCS-site, e.g. heat, pressure, salinity of the aquifer, CO2-partial pressure. Samples of different mild and high alloyed stainless injection-pipe Steels partially heat treated: 42CrMo4, X20Cr13, X46Cr13, X35CrMo4 as well as X5CrNiCuNb16-4 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. Main corrosion products analysed on pits are FeCO3 and FeOOH. The carbon content does not show significant influence on the pitting behaviour. Generally, higher chromium Content results in better corrosion resistance. Although X35CrMo17-1 and X5CrNiCuNb16-4 show low surface corrosion rates, their resistance against local corrosion in CCS environment is not significantly better compared to the much less costly Steels X20Cr13 and X46Cr13.