Stainless Steel in Water Solutions Containing Chlorine

1. Stainless steel 304

Stainless steel 304 is the cheapest and most widely used austenitic stainless steel for equipment used for food, chemical, atomic energy and other industry. It is suitable for general organic and inorganic media, for example, nitric acid with concentration less than 30%, temperature less than and equal to 100°C or concentration higher than and equal to 30%, temperature less than 50°C, carbonic acid, ammonia and alcohols with various concentrations and a temperature less than and equal to 100°C. Stainless steel 304 has poor corrosion resistance in sulfuric acid and hydrochloric acid; it is especially sensitive to crevice corrosion caused by media containing chlorine such as cooling water.
 

2. Stainless steel 304L

Stainless steel 304L has the same corrosion resistance and usage as stainless steel 304. Its corrosion resistance, especially resistance to intergranular corrosion and weldability is better due to the lower carbon content (less than and equal to 0.03%), and it can be used for semi-welded or fully-welded PHE.
 

3. Stainless steel 316

Stainless steel 316 is suitable for general organic and inorganic media, such as natural cooling water, cooling tower water, softened water, carbonic acid; acetic acid and caustic lye with a concentration less than 50%, solvents such as alcohols and acetone, dilute nitric acid with a concentration less than 20%, and dilute phosphoric acid with a concentration less than 30%. However, it is not suitable for sulfuric acid. Because stainless steel contains about 2% Mo, it has better corrosion resistance in seawater and other media containing chlorine than stainless steel 304, which can completely replace stainless steel 304. Valves made of stainless steel 316 are widely used in chemical, petrochemical, petroleum, paper, mining, electric power, liquefied gas, food, pharmaceutical, water supply and drainage, municipal, mechanical equipment, electronic industry, urban construction and other fields.
 
4. Stainless steel 316L
Stainless steel 316L has the same corrosion resistance and usage as stainless steel 316. Its weldability and corrosion resistance after welding is also better due to the lower carbon content (less than and equal to 0.03%), and it can be used for semi-welded or fully-welded PHE.
 
5. Stainless steel 317
Stainless steel 317 is suitable for working conditions requiring longer service life than stainless steel 316. The content of Cr, Mo, Ni in stainless steel 317 is slightly higher than that of stainless steel 316, which makes stainless steel 317 have better resistance to crevice corrosion, pitting corrosion and stress corrosion.
 

6. AISI 904L or SUS 890L

AISI 904L or SUS 890L is a kind of cost-effective austenitic stainless steel that has both good price and corrosion resistance. Its corrosion resistance is better than the above materials. It is especially suitable for general sulfuric acid, phosphoric acid and halides. It has good resistance to stress corrosion, pitting and crevice corrosion due to the high content of Cr, Ni and Mo.
 
7. Avesta 254 SMO high-grade stainless steel
This is an ultra-low carbon high-grade stainless steel that has been improved for stainless steel 316 by increasing the Mo content. It has excellent resistance to chloride pitting and crevice corrosion, and is used for media containing salt water and inorganic acid, which can be replaced for SS 316 in media containing watersaline and inorganic acid.
 
8. High-grade Avesta 654 SMO stainless steel
This is high-grade ultra-low carbon stainless steel with Cr, Ni, Mo, and N content higher than 254 SMO. It has better resistance to chloride corrosion than that of 254 SMO and can be used in cold seawater.
 
9. RS-2 (OCr20Ni26Mo3Cu3Si2Nb) stainless steel
This is a domestic Cr-Ni-Mo-Cu stainless steel. Its resistance to pitting and crevice corrosion is equivalent to that of stainless steel 316, while it has better resistance to stress corrosion. It can be used for concentrated sulfuric acid below 80℃ and with a concentration between 90 and 98%, and the annual corrosion rate is less than and equal to 0.04mm/a.
 
10. Incoloy 825 (S)
This is a high-grade stainless steel containing 40% of Ni, 22% Cr and 3% Mo. Incoloy is a registered trademark of the International Nickel Company. It is suitable for sulfuric acid with various concentrations at low temperatures. It has good corrosion resistance in caustic alkali such as NaOH solutions with a concentration of 50% to 70%, and does not produce stress corrosion cracking. However, it is very sensitive to crevice corrosion caused by chloride. In addition, the stamping performance is not very good, so it is not a commonly used material for plates.
 
11. 31 Alloy
It is an improved alloy by increasing the content of Mo and N content in 904L, which is high-grade stainless steel containing 6% of Mo, 31% Ni, 27% Cr, 6.5% Mo and 32% Fe. The 31 alloy has better corrosion resistance in many media than 904L; in sulfuric acid with a concentration of 20% to 80% and a temperature between 60 and 100°C, the corrosion resistance of 31 alloys even exceeds that of C-276.
 
12. 33 alloy
It is a completely austenitized chromium-based high-grade stainless steel, and its corrosion resistance is comparable to Inconel 625 and other Ni-Cr-Mo alloys. In acidic and alkaline media (including nitric acid, a mixture of nitric acid and hydrofluoric acid), it has good resistance to partial corrosion and stress corrosion cracking; the corrosion resistance in concentrated nitric acid is much better than that of 304L. For example, it is suitable for sulfuric acid with a concentration greater than 96% to 99%, temperature less than and equal to 150℃, sulfur oxide content less than 200 mg/L, hot sea water, boiling strongly corrosive solution with a concentration less than and equal to 50%, phosphoric acid with a concentration less than and equal to 85% and a temperature, less than and equal to150℃. However, it is not suitable for reductive media such as dilute sulfuric acid. The price is similar to C-276.
 

13. Alloy 59

Compared with C-2000, the content of Ni in alloy 59 is slightly higher (59%), and Fe lower; there are no Cu and W. Alloy 59 is currently a material with the best corrosion resistance, thermal stability, stampability and weldability in nickel-based alloys. Since its commercialization in 1990, it has been widely used in sulfuric acid, hydrochloric acid, hydrofluoric acid, and media containing chlorine, oxygen and low pH.
 
Material selection table based on the temperature and content of chloride ion