Corrosion testing cavitation erosion

In considering these tests it should be remembered that the phenomenon of cavitation-erosion is often accompained by corrosion effects and that a synergistic effect may operate between the mechanically and chemically induced forms of attack. In fact the term cavitation-erosion-corrosion may often be more applicable in describing the requirements of a test procedure. The subject has recently been discussed by Wood etal. °. 

D 2809 1989 Test method for cavitation erosion-corrosion characteristics of aluminium pumps with engine coolants... 

Practice for making and using U-bend stress corrosion test specimens Recommended practice for laboratory immersion corrosion testing of metals Method for vibratory cavitation erosion test Practice for recording data from atmospheric corrosion tests of metallic-coated steel specimens... 

The formation of cavitation bubbles depends on the rugosity, which often changes during the test. The rate of cavitational erosion therefore does not remain constant. One generally observes an onset period, followed by a transition period during which the rate of cavitation corrosion passes through a maximum before it reaches a steady value (Figure 10.37). The duration of these periods depends on the material. To compare the results obtained for different materials the transition period must be short relative to the time scale of the experiment. 

Movement of the electrolyte over a metal surface can cause erosion corrosion, impingement, or cavitation. The corrosiveness of the environment will accelerate the degree of corrosion. Standardized methods for evaluating erosion corrosion and cavitation involve immersion testing in the laboratory or operating system. Analysis is typically performed by visual examination and weight loss data. The following standards are commonly used to evaluate susceptibility to erosion corrosion and cavitation ... 

Standard Test Method for Measuring Fretting Corrosion of Osteosynthesis Plates and Screws Standard Test Method for Cavitation Erosion Using Vibratory Apparatus Standard Terminology Relating to Wear and Erosion... 

Incorporation of nanosized SiC particles in the EL NiP matrix increased the hardness from 627 43 to 704 60HVqqj. However, incorporation of micronsized SiC particles increased the hardness to 1669HVqqj. The cumulative mass loss versus time (see Fig. 8.26) due to cavitation erosion corrosion in 3.5% NaCl is found to be very low for EL Ni-P-nano SiC composite coating compared with its coimterpart incorporating micron-sized SiC particles. The EL Ni-P-nano SiC coated specimen exhibits a smooth and uniform surface after the cavitation erosion corrosion test with no visible pits (see Fig. 8.27). The uniform distribution of the nanosized SiC particles in the EL NiP matrix (R 0.95 0.060 pm) inhibits the formation of pits. However, the higher surface roughness (R 1.72 0.051 pm) promotes bubble formation and causes detachment of the SiC particles, which results in the formation of small cavities on the surface of EL Ni-P-micro SiC coated steel (see Fig. 8.27). Hence, it is evident that incorporation of nanosized particles in EL NiP matrix could provide a better cavitation erosion corrosion resistance and inhibit the onset of erosion damage near surface defects. 

Another test described in ASTM D 2809, Test Method for Cavitation Erosion-Corrosion Characteristics of Aluminum Puir ts with Engine Coolants. This test can be used to evaluate automotive water pump materials (aluminum castings) or the abOity of a coolant formulation to prevent metal loss. Chance (Ref... 

Titanium resists erosion—corrosion by fast-moving sand-laden water. In a high velocity, sand-laden seawater test (8.2 m/s) for a 60-d period, titanium performed more than 100 times better than 18 Cr—8 Ni stainless steel. Monel, or 70 Cu—30 Ni. Resistance to cavitation, ie, corrosion on surfaces exposed to high velocity Hquids, is better than by most other stmctural metals (34,35). 

Standard Test Method for Cavitation Corrosion and Erosion-Corrosion Characteristics of Aluminum Pumps with Engine Coolants... 

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