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Corrosion Resistance Of 304 Stainless Steel In Seawater Desalination At Different Temperatures
Jul 26, 2018

Galvanized steel pipes are seriously corroded in desalinated seawater. Therefore, stainless steel instead of galvanized steel is often used as desalination pipeline. Austenitic stainless steel has good corrosion resistance, good resistance to pitting and uniform corrosion, high strength and good toughness. It is widely used in construction, piping and so on. At present, the corrosion behavior of stainless steel in seawater has been reported, but it is less in the desalination of seawater. It is of great significance to study the corrosion behavior of stainless steel in desalination of sea water pipeline. The corrosion resistance of 304 stainless steel in desalination of seawater was studied by using electrochemistry and slow strain rate tensile method and SEM observation, and the effect of temperature on the corrosion resistance of stainless steel passivation film was analyzed.

The test material is 304 stainless steel with chemical composition (mass fraction,%): C0.080, Mn2.000, Si1.000, S0.031, P0.027, Ni8.050, Cr17.500, and the allowance is Fe. The size of the electrochemical specimen is 10mm * 10mm *3mm, one side is welded with copper wire and is encapsulated with epoxy resin. The other side is working face. It is grind with 600, 800, 1000 sand paper respectively, and then blow dry with acetone to remove oil and put it in a dry dish. The stress corrosion tensile test is dumbbell shaped structure, 5mm, and the intermediate test part is 20mm long.

The medium is reverse osmosis seawater desalination. The Cl- concentration is 312.5g/m3, the pH value is 7.8 to 8.2, the conductivity is 0.8mS/cm, the temperature is 35, 50, 70 C, respectively.

Electrochemical tests were carried out using Prinception Applied Research Paratat 2273 electrochemical workstation and data processed by ZVIEW2. The reference electrode is a saturated calomel electrode, the auxiliary electrode is graphite electrode, and the medium is desalination seawater. The critical pitting temperature of 304 stainless steel was measured by ASTMG150-1999 (2004). The added potential of the test was 700mV and the heating rate was 1 /min.

The stress corrosion test was carried out with slow strain rate tensile test by LETRY slow tensile test machine, the tensile rate was 1 x 10-5s-1, the test medium was desalination of seawater, and the glycerol was used to control the blank. The fracture of the tensile rod was observed by ZeissUltra555 scanning electron microscope, and the fracture characteristics were judged. The test results show that:

(1) temperature is an important factor affecting the corrosion resistance of 304 stainless steel in desalination. When the temperature rises from 35 to 70, the charge transfer resistance and the pitting breakdown potential decrease, the passivation film's protection ability decreases and the pitting sensitivity increases. At 35 Eb-Ep, the self recovery ability of the passive film is relatively poor, and the Eb-Ep is smaller at 70. When the passive film is damaged, the self recovery ability is stronger.

(2) the critical pitting temperature of 304 stainless steel in primary reverse osmosis desalination seawater is 34.9 C.

(3) when the temperature rises, the strain and maximum tensile strength of 304 stainless steel gradually decrease, and the fracture fracture characteristics are developed from ductile fracture to brittle fracture, and the sensitivity of stress corrosion is increased.

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