Corrosion and Corrosion Fatigue of Steels in Downhole CCS Environment—A Summary

Abstract

Static immersion tests of potential injection pipe steels 42CrMo4, X20Cr13, X46Cr13, X35CrMo4, and X5CrNiCuNb16-4 at T = 60 °C and ambient pressure, as well as p = 100 bar were performed for 700–8000 h in a CO2-saturated synthetic aquifer environment similar to CCS sites in the Northern German Basin (NGB). Corrosion rates at 100 bar are generally lower than at ambient pressure. The main corrosion products are FeCO3 and FeOOH with surface and local corrosion phenomena directly related to the alloy composition and microstructure. The appropriate heat treatment enhances corrosion resistance. The lifetime reduction of X46Cr13, X5CrNiCuNb16-4, and duplex stainless steel X2CrNiMoN22-5-3 in a CCS environment is demonstrated in the in situ corrosion fatigue CF experiments (axial push-pull and rotation bending load, 60 °C, brine: Stuttgart Aquifer and NGB, flowing CO2: 30 L/h, +/− applied potential). Insulating the test setup is necessary to gain reliable data. S-N plots, micrographic-, phase-, fractographic-, and surface analysis prove that the life expectancy of X2CrNiMoN22-5-3 in the axial cyclic load to failure is clearly related to the surface finish, applied stress amplitude, and stress mode. The horizontal grain attack within corrosion pit cavities, multiple fatigue cracks, and preferable deterioration of austenitic phase mainly cause fatigue failure. The CF life range increases significantly when a protective potential is applied.

Fatigue corrosion behavior of friction‐welded stainless and carbon steel dissimilar joint

“…On the AISI 304L side, in the MML boundary the maximum hardness of 432.9 ± 0.8 HV 0.1 is measured. This peak of hardness is reached in the austenitic part of the joint and seems to be common in the literature on DMW between austenitic stainless steel and other steels 72,73 . It is mainly attributed to a combination of high plastic deformation, which the mating surface of the steels undergo during the welding process, and to the presence of Mo, which prevents the softening at high temperatures.…”

“…By moving from the contact region towards the stainless‐steel side, it is possible to notice that there is a drop in microhardness to a minimum of ~212 HV 0.1 . This abrupt decrease is related to the growth of new dislocations‐free austenitic grains, thanks to the dynamic recrystallization phenomena that affect this region of the weldment 73 . Then, microhardness is progressively recovered, reaching the average values measured for the AISI 304L.…”

“…This abrupt decrease is related to the growth of new dislocations-free austenitic grains, thanks to the dynamic recrystallization phenomena that affect this region of the weldment. 73 Then, microhardness is progressively recovered, reaching the average values measured for the AISI 304L. From the hardness trend, it can inferred that the heat-affected zone (HAZ) range exceeds the TMAZ range on the stainlesssteel side, while HAZ and TMAZ seem to have the same extension in the ASTM A105 side.…”

“…This peak of hardness is reached in the austenitic part of the joint and seems to be common in the literature on DMW between austenitic stainless steel and other steels. 72,73 It is mainly attributed to a combination of high plastic deformation, which the mating surface of the steels undergo during the welding process, and to the presence of Mo, which prevents the softening at high temperatures. Both aspects cause the work hardening of a very restricted area in MML boundary, 74 producing the microhardness peak.…”

Influence of the Deep Cryogenic Treatment on AISI 52100 and AISI D3 Steel’s Corrosion Resistance

“…This can well explain the trend of Rp values, as the increased number of precipitates increases the corrosion resistance of the X2 sample due to higher nobility of the surface caused by higher number of carbides. For X4 the corrosion resistance decreases despite the increased carbide formation, as the M 7 C 3 are less stable compared to cementite [ 24 , 25 , 26 ]. For steel Y, the microstructural changes after DCT do not only impact the carbide density and their ratio, but also change the content of retained austenite.…”