High-cycle Corrosion Fatigue Research Articles

Low-Frequency Corrosion Fatigue Test Study of Sucker Rods under High-Salinity Well Fluids in Deep CBM Wells

Corrosion fatigue test is the most direct and effective method to study the corrosion fatigue characteristics of sucker rod. At present, the commonly used test method is the high frequency fatigue test, but the working state of sucker rod is typical low-frequency and high-cycle corrosion fatigue, and the test with high frequency will reduce the impact of corrosion. Alloy steel 4330 is widely used in coalbed gas well high strength sucker rod, but the research on its low frequency corrosion fatigue life is relatively few. Therefore, in this paper, the corrosion fatigue test method of axial low-frequency and high-cycle was adopted to study the corrosion fatigue characteristics of 4330 steel sucker rod through the corrosion fatigue test under different typical corrosion media, temperature, and stress levels. The results show that the fatigue life of 4330 sucker rod drops sharply when the Cl− concentration in high salinity well fluid exceeds the threshold value of 155 mg/L. When this threshold is exceeded, the downward trend slows down. It can be seen that the significant factor affecting the corrosion fatigue life of 4330 material is not the concentration of Cl−, but the existence of Cl−. The presence of HCO3− promotes a further decrease in the corrosion fatigue life of the 4330 sucker rod by Cl−. The corrosion fatigue life of 4330 sucker rod decreases with the increase of temperature. When the well fluid temperature is less than 50 °C, the impact is relatively significant. When the well fluid temperature is more than 70 °C, the decline trend of corrosion fatigue life slows down. Based on the fitted S-N curve (stress-fatigue life curve), it is calculated that the fatigue limit of 4330 sucker rod at the stress ratio of 0.6 is 196 MPa in the solution of 10,000 mg/L Cl− at room temperature. These could provide valuable theoretical and technical guidance for design and selection of high-strength sucker rod in high-salinity corrosion well fluid environment.

A Micro-Mechanism-Based Continuum Corrosion Fatigue Damage Model for Steels

A micro-mechanism-based corrosion fatigue damage model is developed for studying the high-cycle corrosion fatigue of steel from multi-scale viewpoint. The developed physical corrosion fatigue damage model establishes micro-macro relationships between macroscopic continuum damage evolution and collective evolution behavior of microscopic pits and cracks, which can be used to describe the multi-scale corrosion fatigue process of steel. As a case study, the model is used to predict continuum damage evolution and number density of the corrosion pit and short crack of steel component in 5% NaCl water under constant stress amplitude at 20 kHz, and the numerical results are compared with experimental results. It shows that the model is effective and can be used to evaluate the continuum macroscopic corrosion fatigue damage and study microscopic corrosion fatigue mechanisms of steel.

Effects of the microstructural characteristics of a metastable β Ti alloy on its corrosion fatigue properties

In the field of biomedicine, preventing the corrosion fatigue of metallic biomaterials for use in hard tissue replacement implants is of paramount importance. Corrosion fatigue of implants is caused by their contact with body fluids, as well as cyclic stresses resulting from body movements. The metallic biomaterials most widely used today are titanium alloys. It is a well known fact that the mechanical behavior of titanium alloys is determined by their chemical composition and thermomechanical processing. This study involved an evaluation of the influence of the microstructure on the corrosion fatigue of Ti–35Nb (wt.%) alloy samples in NaCl 0.9% solution. The samples were subjected to two different cooling rates from β phase field temperatures. The distinct cooling rates resulted in microstructures composed of β and α″ phases (160°C/s) and α, β and ω phases (0.04°C/s). The samples were characterized microstructurally by optical, scanning electron and transmission electron microscopy and X-ray diffraction. Their high-cycle corrosion fatigue properties were evaluated based on fatigue tests in NaCl 0.9% solution, under stresses ranging from 150 to 450MPa. The results suggest that the furnace cooled sample showed lower corrosion fatigue.

Study on the mechanism of high-cycle corrosion fatigue crack initiation in X80 steel

Corrosion fatigue experiments on X80 steel in 3.5% NaCl solution were conducted on a researcher-developed cantilever-bending corrosion fatigue testing machine. The morphology of corrosion pits and the change in the surrounding microstructure were carefully examined using SEM and TEM, and the stress field was simulated using the finite-element method. The results show that the corrosion fatigue crack initiation is due to not only the corrosion pits’ stress concentration effects but also the adhering corrosion products. Corrosion products formed on the surface of slip bands, and the action of corrosion products on fatigue crack initiation was explained using physical models.

05/00649 Strength calculation of NPP equipment and pipelines during operation. Low- and high-cycle corrosion fatigue

05/00649 Strength calculation of NPP equipment and pipelines during operation. Low- and high-cycle corrosion fatigue

Strength calculation of NPP equipment and pipelines during operation. Low- and high-cycle corrosion fatigue

This paper presents empirical equations and design curves for structural steels employed in nuclear power facilities with light water reactors. These equations allow to take into account the effects of cycle asymmetry, water coolant and ductility decrease during operation. The fatigue curves cover the low-cycle and high-cycle regions (up to 10 12 cycles). The equations include the mechanical characteristics of steels under static tension. The coolant effect on steel fatigue is allowed for using a model developed at the Argonne National Laboratory.

Effects of surface treatments on high cycle corrosion fatigue of metallic implant materials

Long term corrosion fatigue properties of two materials which are candidates for skeletal implants — cold worked c.p. Niobium and c.p. Tantalum — have been investigated. Fatigue properties have been compared to two implant materials in clinical use — c.p. Titanium and Ti–6Al–7Nb alloy. Constant amplitude fatigue experiments (S–N curves) were performed at ultrasonic frequency (20 kHz) with two different surface structures (ground surface and blasted and shot peened surface) in ambient air and in a corrosive fluid similar to the body fluid in the oral cavity. The endurance limit at 2×10 8 cycles of all materials decreased by 5–20% if they were cycled in corrosive fluid instead of ambient air. The loss of fatigue strength is more pronounced for ground Ti–6Al–7Nb alloy and c.p. Ti than for ground c.p. Nb cw and c.p. Ta cw. Fracture surfaces show a more pronounced embrittlement of ground Ti–6Al–7Nb alloy and c.p. Titanium after cycling in corrosive fluid than ground c.p. Tantalum and c.p. Niobium. A beneficial influence of surface structuring by blasting and shot peening on the fatigue properties was found for all materials in both environments. Fatigue loading using ultrasonic frequency allows one to select appropriate implant materials and to determine their very-high cycle corrosion-fatigue behaviour within reasonable testing times. Though the obtained high-frequency values may not be fully representative of actual in vivo behaviour, they are regarded as useful material characterizing values.

Corrosion fatigue resistance of powder metallurgy and forged duplex stainless steels

The high cycle corrosion fatigue resistance of powder metallurgically (PM) fabricated and hot isostatically pressed (hipped) duplex stainless steels (DSSs) was investigated and compared with that of a conventional forged DSS. Tests were performed in rotating bending fatigue in a chloride and sulphate containing aqueous solution at room temperature. The hipped PM DSSs studied had small grain size and homogeneous microstructure and isotropic properties and thus, their high cycle corrosion fatigue resistance was generally markedly higher than that of the corresponding forged DSS tested in the longitudinal direction. Fatigue cracks were observed to grow preferentially in the ferrite phase and a retarding effect of the austenite phase on corrosion fatigue crack growth was observed both in the hipped PM and wrought DSSs. Slow cooling after solution annealing improved the corrosion fatigue resistance, even though it induced slight second phase precipitation. Localised corrosion attack was observed at inclusion/matrix interfaces, when oxide inclusions were cerium modified (forged DSS). When oxide inclusions were either unmodified or calcium modified (hipped PM DSSs), no localised corrosion attack was observed.MST/3429

Corrosion fatigue resistance of powder metallurgy and forged duplex stainless steels

The high cycle corrosion fatigue resistance of powder metallurgically (PM) fabricated and hot isostatically pressed (hipped) duplex stainless steels (DSSs) was investigated and compared with that of a conventional forged DSS. Tests were performed in rotating bending fatigue in a chloride and sulphate containing aqueous solution at room temperature. The hipped PM DSSs studied had small grain size and homogeneous microstructure and isotropic properties and thus, their high cycle corrosion fatigue resistance was generally markedly higher than that of the corresponding forged DSS tested in the longitudinal direction. Fatigue cracks were observed to grow preferentially in the ferrite phase and a retarding effect of the austenite phase on corrosion fatigue crack growth was observed both in the hipped PM and wrought DSSs. Slow cooling after solution annealing improved the corrosion fatigue resistance, even though it induced slight second phase precipitation. Localised corrosion attack was observed at inclusion/matrix interfaces, when oxide inclusions were cerium modified (forged DSS). When oxide inclusions were either unmodified or calcium modified (hipped PM DSSs), no localised corrosion attack was observed.MST/3429

Fundamental study of microstructure-oriented strength assessment of a spheroidal graphite cast iron. 2nd Report. Corrosion fatigue in 3% hydrochloric acid and synthetic seawater.

Ferrite-base and pearlite-base spheroidal graphite cast irons were prepared to examine corrosion fatigue resistance in 3% hydrochloric acid and synthetic seawater. Rotating bending corrosion fatigue tests were conducted at two rates 3400 rpm and 260 rpm. From the tests in air and two corrosive environments, the following results were obtained : (1) The pearlite-base material (F) showed a fatigue strength stronger than that of the ferrite-base material (A) in the intermediate-cycle fatigue range, irrespective of environment or rotating speed. In the high-cycle fatigue range, the fatigue strengths of both materials asymptotically approached to coincide. (2) Anodic dissolution of graphite and local cathodic dissolution of cementite in pearlite played a primary role in the high-cycle corrosion fatigue process. (3) Those dissolutions described above induced a fatigue process different from that in air and resulted in diminished scatter of the S-n curves.