Application conditions of several stainless steels in aqueous solutions containing chloride ions

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1) Type 304 stainless steel. This is the cheapest and most widely used austenitic stainless steel (e.g., for industrial equipment in the food, chemical, nuclear, and other industries). Suitable for general organic and inorganic media. For example, nitric acid with a concentration < 30% and temperature ≤ 100°C, or with a concentration ≥ 30% and temperature < 50°C ； Carbonic acid, ammonia water, and alcohols of various concentrations at temperatures ≤100℃. Poor corrosion resistance in sulfuric acid and hydrochloric acid ； It is particularly sensitive to crevice corrosion caused by chlorinated media (such as cooling water). PRE is 19. 2) 304L stainless steel. Its corrosion resistance and applications are essentially the same as those of 304 stainless steel. Due to its lower carbon content (≤0.03%), it exhibits better corrosion resistance (especially against intergranular corrosion, including in the weld area) and weldability, making it suitable for semi-welded or fully welded PHEs. 3) Type 316 stainless steel is suitable for general organic and inorganic media. For example, natural cooling water, cooling tower water, softened water ； Carbonic acid ； Acetic acid and caustic alkali solutions with a concentration of <50% ； Alcohols and solvents such as propylene glycol ； Dilute nitric acid at a temperature of ≤100℃ (concentration <20%), dilute phosphoric acid (concentration <30%), etc. However, it is not suitable for use with sulfuric acid. Due to its approximately 2% Mo content, it has better corrosion resistance in seawater and other chlorinated media than type 304, and can fully replace type 304. The PRE is 25. 4) 316L stainless steel) S9 M: Its corrosion resistance and applications are basically the same as those of type 316. Due to its lower carbon content (≤0.03%), it also exhibits better weldability and post-weld corrosion resistance, making it suitable for semi-welded or fully welded PHEs. The PRE is 25. 5) Type 317 stainless steel. Suitable for applications that require a longer service life than that of type 316. Due to slightly higher contents of Cr, Mo, and Ni elements compared to type 316, it exhibits better resistance to crevice corrosion, pitting, and stress corrosion. The PRE is 30. 6) AISI 904L or SUS 890L stainless steel; this is a cost-effective austenitic stainless steel that offers an excellent balance between price and corrosion resistance. Its corrosion resistance is better than that of the other materials mentioned, making it particularly suitable for use in acids such as sulfuric acid and phosphoric acid, as well as halides (containing Cl— and F—). Due to the relatively high contents of Cr, Ni, and Mo, it exhibits good resistance to stress corrosion, pitting corrosion, and crevice corrosion. The PRE is 36. 7) Avesta 254 SMO premium stainless steel. This is an ultra-low carbon premium stainless steel that is a modified version of Type 316, with an increased Mo content. It exhibits excellent resistance to chloride-induced pitting and crevice corrosion. It is suitable for use in saline water, inorganic acids, and other media where Type 316 cannot be utilized. The PRE is 47. 8) Avesta 654 SMO is a high-grade stainless steel. It is a ultra-low carbon high-grade stainless steel whose contents of Cr, Ni, Mo, and N are all higher than those in 254 SMO. Its resistance to chloride corrosion is better than that of 254 SMO; it can be used in cold seawater. PRE is 64. 9) RS-2 (OCr20Ni26Mo3Cu3Si2Nb) stainless steel; this is a domestically produced Cr–Ni–Mo–Cu stainless steel. Its resistance to pitting and crevice corrosion is equivalent to that of type 316, while its resistance to stress corrosion is better. It can be used with concentrated sulfuric acid (concentration 90–98%) at temperatures below 80 °C, with an annual corrosion rate of ≤0.04 mm/a. PRE is 29. 10) Incoloy 825(S) is a high-grade stainless steel composed of Ni (40%)–Cr (22%)–Mo (3%). Incoloy is a registered trademark of the International Nickel Co. Suitable for sulfuric acid of various concentrations at low temperatures ； It exhibits good corrosion resistance in caustic alkali solutions (such as NaOH) with concentrations of 50% to 70%, and does not suffer from stress corrosion cracking. However, it is very sensitive to chloride-induced crevice corrosion. Furthermore, its stamping performance is also poor, so it is not a commonly used material for sheets. PRE represents 32 new types of foreign corrosion-resistant alloys: 1) 31 alloy: an improved version of 904L (with increased Mo and N contents); a standard high-grade stainless steel containing 6% Mo (31% Ni-27% Cr-6.5% Mo-32% Fe). Better corrosion resistance in many media than 904L ； In sulfuric acid at concentrations of 20%–80% and temperatures of 60°C–100°C, its corrosion resistance even exceeds that of C-276. The PRE is 34. 2) Alloy 33: A fully austenitized chromium-based premium stainless steel whose corrosion resistance is comparable to that of certain Ni-Cr-Mo alloys such as Inconel 625. In acidic and alkaline media (including nitric acid, and mixtures of nitric acid and hydrofluoric acid), it exhibits good resistance to local corrosion and stress corrosion cracking ； Its corrosion resistance in concentrated nitric acid is much better than that of 304L. For example, it is suitable for sulfuric acid with a concentration of over 96%–99%, a temperature of ≤150°C, and a sulfur oxide content of less than 200 mg/L ； Warm seawater ； Strongly corrosive solution at boiling point with concentration ≤50% ； Phosphoric acid with a concentration of ≤85% and a temperature of ≤150°C, etc. However, it is not suitable for reductive media (such as dilute sulfuric acid, etc.). The price is roughly the same as that of C-276. PRE is 50. 3) C-2000 alloy: A nickel-based alloy developed in the 1990s; its price is similar to that of C-276, and it is one of the materials with the best corrosion resistance among those listed. In media such as sulfuric acid at concentrations below moderate levels, dilute hydrochloric acid, phosphoric acid at concentrations ≤50% at boiling temperature, and hot chlorides, its corrosion resistance is better than that of C-276 and C-22, showing a tendency to replace the C-22 alloy. However, for sulfuric acid with a concentration of ≥70%, its corrosion resistance is inferior to that of C-276. PRE is 764) Alloy 59: In terms of chemical composition, it is similar to C-2000, with the exception that its Ni content is slightly higher (59%), it contains less Fe, and it has no Cu or W; otherwise, the compositions are essentially the same. This is currently the material with the best corrosion resistance, thermal stability, formability, and weldability among nickel-based alloys. Since its commercialization in 1990, it has been widely used in sulfuric acid, hydrochloric acid, hydrofluoric acid, as well as many other media containing chlorine, oxygen, and having a low pH value. PRE is 76, the same as C-2000. Application range of stainless steel in chloride-ion-containing media
Maximum temperature (°C) | Chloride ion content (mg/L)
25 | 100
50 | 430
60 | 430
75 | 430
80 | 430
100 | 430
120 | 430
130 | 160
150 | 430
160 | 163
180 | 163
200 | 169
250 | 904L
300 | 904L
400 | 904L
500 | 904L
750 | 904L
1000 | 904L
1800 | 254
5000 | 254
7300 | 254

Conclusion: Based on the above analysis, to extend the service life of stainless steel in environments containing chloride ions, it is advisable, provided that process conditions permit, to add appropriate corrosion inhibitors or select suitable materials. Non-metallic materials or lining materials may also be considered, so as to achieve optimal economic benefits.