Content of halide ions in 2205 steel pipes during use

This post was last edited by dreamforever on 2017-10-12 at 16:50. It can only be determined by conducting salt spray testing; the presence of halogen elements leads to pitting corrosion and stress corrosion, but corrosion is also related to temperature. In our production process, it’s no problem to use duplex steel when a chloride concentration of 600 is involved

1. Effect of Cl- on the corrosion behavior of 2205DSS: It was found that the decrease in pitting potential is the result of the combined effect of Cl- concentration and temperature. In a 0.1 mol/L NaCl solution, the temperature range over which 2205 DSS undergoes passivation to pitting transition is 55–65°C. The corrosion rate is exponentially proportional to temperature and quadratically proportional to HCl concentration. Temperature and Cl- concentration affect not only the pitting rate but also the pitting morphology. When the NaCl concentration is low and the temperature is below the critical pitting temperature, the pitting pits are small and distributed in a hemispherical pattern ； When the NaCl concentration is high and the temperature reaches 70°C, the pitting pits are larger, with a lace-like coating. It was found that the critical pitting temperature of 2205DSS in a 6% FeCl3 + 1% HCl solution is 38°C, and the pitting morphology consists of two types: surface-opening type and surface-closing type. Due to its insidious and highly destructive nature, crevice corrosion of 2205DSS in Cl- containing solutions is one of the most severe types of localized corrosion. Environmental factors can alter corrosion behavior, among which temperature, Cl- concentration, and pH value are the three most important factors. Temperature can alter the electrochemical properties of the passivation film, thereby promoting or inhibiting the nucleation and propagation of crevice corrosion ； The pH value can change the chemical environment of an aqueous solution, affecting the electrochemical characteristics of corrosion ； The hydrolysis of metal elements and the migration of Cl- lead to ion concentration, which lowers the pH value and creates the critical chemical conditions necessary for the nucleation of crevice corrosion. The critical crevice corrosion temperature CCT of 2205DSS in a 4% NaCl solution is approximately 28°C, and the CCT increases linearly with lg. When the pH value is 8.5, CCT reaches its maximum value of approximately 43°C. The passivation film of 2205DSS is very thin, usually less than 5 nm, and can form spontaneously on the surface of stainless steel. It has a dual-layer structure, with an n-type semiconductor on the inner layer and a p-type semiconductor on the outer layer. Stress corrosion cracking SCC is initiated by the breakdown of the passivation film and nucleation of dissolution. Studies have investigated the SCC behavior of 2205DSS in a 26% NaCl solution at 90°C, and it was found that when the potential is below -160 mV (SCE), 2205DSS is insensitive to SCC ； When the potential exceeds -160 mV (SCE), the toughness of 2205DSS decreases significantly, and its susceptibility to SCC increases. Under experimental conditions, the critical potential for SCC occurrence coincides with the pitting potential, indicating that pitting promotes the nucleation of SCC cracks ； At the same time, selective dissolution is also involved in the progression of SCC. 2. Effect of Br- on the corrosion behavior of 2205DSS. Br- and Cl- are common active anions in chemical production; previous corrosion studies have focused mainly on Cl-, with relatively limited discussion on Br-. It was found that SAF2205 has better resistance to Br-point corrosion than 304L and 316L, but is more susceptible to crevice corrosion. The increase in Cr and Mo contents **enhanced the stability of the passivation film, while the addition of trace amounts of N effectively suppressed the development of pitting. However, due to the more severe corrosion conditions in the \"occluded areas\" caused by gaps, the passivation film of SAF2205 can still be damaged by Br-, leading to corrosion; therefore, gaps should be eliminated as much as possible in structural design to reduce the likelihood of gap corrosion. In the acetic acid solution, as the Br- concentration increased (800, 1000, 1200, 1500 mg/kg), the corrosion rate of SAF2205 increased, along with the size of pitting ； In an acetic acid environment, Cl- poses a greater pitting hazard than Br-, as Cl- with a smaller radius can more easily penetrate the passivation film ； The decrease in pH and the concentration of Cl- make the environment inside the etching pores similar to that of HCl, which is more destructive than HBr.

Is this figure from that paper or magazine? Could you tell me?

The current operating temperature is 150°C; please take a look