News
Credibility ,The combination of tensile stress and a specific corrosive environment can cause the stainless steel plate to break. This type of attack is called Stress Corrosion Cracking (SCC). The most common environmental exposure condition that causes SCC in stainless steel is the presence of chloride. Although the degree of stainless steel immunity to chloride SCC is large, the relative resistance of stainless steel plates varies greatly.
Effect of alloy composition:
The relative resistance of chloride SCC depends on the stainless steel series. The austenitic stainless steel series is the most susceptible. The tolerance of SCC to austenitic stainless steels is related to the nickel content.
The austenitic stainless steels that are most susceptible to SCC have a nickel content in the range of 8-10%. Therefore, standard brands such as 304, 304L and 316, 316L are very sensitive to this type of attack. Austenitic grades with higher nickel and molybdenum contents, such as alloy 20, 904L and 6% molybdenum superaustenitic grades have significantly better chloride SCC resistance.
The ferritic stainless steel series includes grades 430 and 444 and is very resistant to chloride SCC. Duplex stainless steels with austenitic, ferrite microstructures have electrical resistance between the austenitic and ferritic grades.
Corrosion test
The relative resistance of the stainless steel to the chloride SCC is usually quantified by using a standard boiling salt solution. The following table summarizes the test results in 26% NaCl (sodium chloride), 33% LiCl (lithium chloride) and 42% MgCl 2 (magnesium chloride) in boiling salt solution. Boiling LiCl and MgCl 2 test solutions are very aggressive with respect to practical use, and only austenitic alloys with compositions close to that of nickel-based alloys will routinely resist cracks in these test solutions.
Table 1: Relative chloride chloride SCC resistance measured in a standard boiling salt solution using a fully immersed U-bend specimen.
(taken from producer data)
Cracked appearance:
The typical crack morphology of chloride stress corrosion cracking consists of branching nucleation cracks. Figure 1 shows the cracks that occur on 6Mo super austenitic stainless steel (N08367) exposed to 0.2% chloride at 500°F (260°C).Figure 1: Typical appearance of chloride stress corrosion cracking
Envirnmental factor:Environmental factors that increase the susceptibility of stainless steel to cracking include higher temperatures, increased chloride content, lower pH, and higher tensile stress levels. Temperature is an important variable. When the stainless steel plate is completely submerged, chloride stress corrosion cracking of the stainless steel plate is rarely seen at temperatures below 60°C.
There is a synergistic relationship between dissolved oxygen and chloride levels. If the oxygen content is reduced to the 0.01-0.1 ppm range, aqueous solutions containing low to moderate chloride levels cannot crack austenitic stainless steels, such as 304L and 316L stainless steels. At room temperature to moderate temperatures, the normal solubility of oxygen in water is 4.5-8 ppm at atmospheric pressure.Source: China Stainless Steel Plates Manufacturer - Yaang Pipe Industry Co., Limited (www.yaang.com)
Tel No:+86-18267732328 / Email:[email protected]
Address:Longwan District, Wenzhou, Zhejiang Province, China.
Copyright Notice © www.yaang.com Yaang Pipe Industry Co., Limited All rights reserved.
Yaang Pipe Industry Co., Ltd. is an international supplier of piping solutions for flange, butt welding fittings, socket welding fittings and threaded fittings. Our products are widely used in different industrial fields, including oil and gas, chemical industry, petrochemical industry, power plant, pulp and paper industry, environmental and water conservancy engineering, engineering projects, etc.