The corrosion resistance of duplex steel tee is how many times of ordinary stainless steel and does not have a fixed exact value, because it will be affected by a variety of factors, such as specific steel, corrosive environment, temperature, media concentration, etc.. The following common 2205 duplex steel tee and 304 stainless steel tee as an example, in different corrosive environments for analysis:
Chloride-containing environment: Common stainless steel such as 304 stainless steel is prone to pitting corrosion and stress corrosion cracking in chloride-containing environment. 2205 duplex steel has excellent resistance to chloride pitting and crevice corrosion due to its high chromium, molybdenum and nitrogen content. In some standard pitting resistance tests, the critical pitting temperature (CPT) of 2205 duplex steel is much higher than that of 304 stainless steel, for example, in the ASTM G48 (6% FeCl₃) test, the CPT of 2205 steel may be several times higher than that of 304 stainless steel, which means that 2205 duplex tee is more resistant to pitting corrosion than 304 stainless steel tee under the same chloride environment. The advantage of its corrosion resistance is obvious, but it is difficult to measure it simply by a specific multiple.
Sulfuric acid solution: In sulfuric acid solution, the corrosion resistance of 2205 duplex steel and 304 stainless steel is also different. When the sulfuric acid concentration is low, 304 stainless steel has some corrosion resistance, but as the sulfuric acid concentration and temperature increase, the corrosion rate increases significantly. 2205 duplex steel outperforms 304 stainless steel in solutions with a maximum acid concentration of about 15%, and the advantage is even more pronounced in the range of acid concentrations of at least 40%. Some data suggest that the corrosion rate of 304 stainless steel may be several times that of 2205 duplex steel in sulfuric acid solutions at certain concentrations and temperatures. For example, under certain test conditions, the corrosion rate of 304 stainless steel in a certain concentration of sulfuric acid may reach 0.5mm/year, while 2205 duplex steel may only be 0.1mm/year or so, from the corrosion rate point of view, the corrosion resistance of 2205 duplex steel is about 5 times that of 304 stainless steel, but this is only the result of the specific test conditions, and will change in the actual application due to the specific working conditions. But this is only the result under specific test conditions, the actual application will vary according to the specific working conditions.
Acetic acid solutions: 2205 Duplex also shows good corrosion resistance in organic acids such as acetic acid. 20% of acetic acid boiling, 304 stainless steel corrodes at a rate of about 0.0102 mm/y. 2205 Duplex is dominant in many processes involving high-temperature organic acids, where the rate of corrosion is usually lower than that of 304 stainless steel. But again, it is difficult to say exactly how many times more corrosion resistant 2205 duplex steel is to 304 stainless steel in acetic acid solutions, because this is affected by the concentration of acetic acid, the presence of other impurities, etc.
If the ordinary stainless steel is replaced by 316L stainless steel with better corrosion resistance, 2205 duplex steel tee still has an advantage in resistance to chloride stress corrosion, pitting, etc., but the difference in corrosion resistance in some non-oxidizing acids may be relatively small. In short, the corrosion resistance of duplex steel tee is superior to ordinary stainless steel, the degree of advantage is different in different environments, and it is difficult to accurately describe with a fixed multiple.
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