Corrosion resistance of 304 stainless steel in desalinated seawater at different temperatures

Galvanized 17-7 stainless steel sheet pipes are heavily corroded in desalinated seawater, so stainless steel is now being considered as a substitute for galvanized steel for desalinating seawater. Austenitic stainless steel has good corrosion resistance, good resistance to pitting corrosion and uniform corrosion, high strength, good toughness, and is widely used in construction, pipelines and so on. At present, the corrosion behavior of stainless steel in seawater has been widely reported, but there is less in desalinated seawater. Research on the corrosion behavior of stainless steel in desalinated seawater pipelinesSignificance. A company's researchers used electrochemical and slow strain rate stretching methods combined with scanning electron microscopy observations to study the corrosion resistance of 304 stainless steel in desalinated seawater, and analyzed the effect of temperature on the corrosion resistance of stainless steel passivation film.The sample was 17-4 stainless steel sheet, chemical composition (mass fraction, %): C0.080, Mn2.000, Si1.000, S0.031, P0.027, Ni8.050, Cr17.500, balance Fe. The size of the electrochemical sample is 10mm× 10mm× 3mm. One side of the copper wire is welded and encapsulated with epoxy resin. The other side is a working surface. It is sanded with 600, 800, 1000 sandpaper, and dried with acetone and dried. Into a dry dish for use. The stress corrosion tensile test was a dumbbell-shaped structure,? 5mm, and the middle test section was 20mm long.The medium is a grade one reverse osmosis desalinated seawater with a Cl- concentration of 312.5 g/m3, a pH value of 7.8-8.2, a conductivity of 0.8 mS/cm, and temperatures of 35, 50, and 70°C, respectively.Electrochemical tests were performed using a Prinception Applied Research Paratat 2273 electrochemical workstation and data was processed using ZVIEW2. The reference electrode is a saturated calomel electrode, the auxiliary electrode is a graphite electrode, and the medium is desalinated seawater. The critical pitting temperature of 304 stainless steel was measured using ASTMG150-1999 (2004). The applied potential in this test was 700mV and the heating rate was 1°C/min.The stress corrosion test was performed using the LETRY Slow Tensile Tester at a slow strain rate with a tensile rate of 1× 10-5 s-1. The test medium was desalinated seawater and the glycerin was used as a blank control. The tensile bars were fractured with a Zeiss Ultra555 scanning electron microscope. Observe and judge the fracture characteristics. The results showed that:(1) Temperature is an important factor influencing the corrosion resistance of 304 stainless steel in desalinated seawater. When the temperature rises from 35°C to 70°C, the charge transfer resistance and pitting corrosion breakdown potential decrease, and the passivation film protection ability decreases. Increased sensitivity. At 35 °C, Eb-Ep is larger, and the self-healing ability of the passivation film after failure is poorer; at 70 °C, Eb-Ep is smaller, and the self-healing ability is stronger after the passivation film is destroyed.(2) The critical pitting temperature of 304 stainless steel in first-grade reverse osmosis desalination seawater is 34.9°C.(3) With the increase of temperature, the strain and the maximum tensile strength of 304 stainless steel gradually decrease. The fracture fracture characteristics develop from brittle fracture to brittle fracture, and the stress corrosion sensitivity increases.

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