Instructions for selecting special materials for plate heat exchangers and heat exchanger plates

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Materials for plate exchangers and heat exchangers 1: 904L and SUS890L stainless steels. These are austenitic stainless steels that offer a good balance between price and corrosion resistance; they possess excellent corrosion resistance, making them particularly suitable for use in acids such as sulfuric acid and phosphoric acid, as well as halides (containing Cl- and F-). Due to its high contents of Cr, Ni, and Mo, it exhibits excellent resistance to stress corrosion, pitting, and crevice corrosion. Applicable conditions in chlorine-containing media. Material 2 for plate exchangers and heat exchangers: 254 SMO – an ultra-low carbon premium stainless steel that is an improved version of type 316 through an increased Mo content. It possesses excellent resistance to chloride pitting and crevice corrosion, making it suitable for use in saline solutions, inorganic acids, and other media where type 316 cannot be used. Material 3 for plate exchangers and heat exchangers: Titanium. Unalloyed titanium is lightweight, with a density of 4.51; it can naturally form a passivating protective film (Ti2O3), and it possesses \"self-healing\" properties if this film is damaged. As a result, its corrosion resistance is better than that of stainless steel, making it an ideal material for use in environments containing chlorine (Cl- concentration > 200 mg/L, temperature ≤ 130°C). It is practically immune to corrosion in seawater and other chloride-containing solutions (such as CaCl2) at temperatures not exceeding 120°C. Generally, it can be used in seawater at temperatures below 135°C and in saline solutions (NaCl) of various concentrations at temperatures below 165°C. Titanium also exhibits good corrosion resistance in organic acids below its boiling point (such as concentrated nitric acid and concentrated carbonic acid) as well as in dilute alkaline solutions. Titanium has poor corrosion resistance in H2SO4, HCl, HF, aqua regia, and similar substances. In certain concentrated chloride solutions at high temperatures (above 120°C), such as wastewater with a pH > 7 and a chloride concentration > 200 mg/L, gap corrosion or stress corrosion may also occur. At this time, a titanium-palladium alloy should be selected. Material 4 for plate exchangers and heat exchangers: Titanium-palladium alloy. This is an unalloyed titanium to which palladium (0.12%–0.25%) has been added, thereby significantly improving titanium’s corrosion resistance in acidic media (especially under less severe operating conditions). For example, it exhibits good corrosion resistance to nitric acid with a concentration of up to 70%, hydrochloric acid containing oxidizing ions such as Fe+ and Cu+, as well as plating solutions. In addition, it can also be used for dilute sulfuric acid with a concentration of ≤10% and a temperature of ≤70°C. Material 5 for plate exchangers and heat exchangers: Nickel 200. This is a pure nickel sheet containing over 99% nickel. It is mainly used for caustic alkali solutions (such as NaOH, KOH, etc.) with high concentrations (50%–70%) and high temperatures (up to the boiling point). However, it is highly sensitive to crevice corrosion caused by chlorides such as brackish water. Material 6 for plate exchangers and heat exchangers: Hastelloy C-276 boasts excellent corrosion resistance: it is hardly affected by Cl- ； It exhibits excellent corrosion resistance to sulfuric acid at various concentrations, and is one of the few materials that can be used in hot concentrated sulfuric acid ； Widely used in organic acids (such as formic acid and acetic acid), high-temperature HF acid, and hydrochloric acid at certain concentrations (<40%), as well as phosphoric acid (≤50%) ； Chlorides, fluorides, and organic solvents (such as methanol, ethanol). Material 7 for plate exchangers and heat exchangers: Monel 400, a nickel-based alloy consisting of about 70% nickel and about 30% copper. It exhibits good corrosion resistance in media such as non-gassed sulfuric acid with a concentration of 80% or less and a temperature of 50°C to 100°C, HF acid with a concentration of 50% or less and a temperature below 100°C, acetic acid, and caustic alkalis. Particularly suitable for acidic chloride solutions and brackish water and saline water under certain operating conditions ； It has good high-temperature resistance. However, it is not suitable for concentrated sulfuric acid, hydrochloric acid, and nitric acid, and it is highly sensitive to the erosion by mercury (which is sometimes present as an impurity). Material 8 for plate exchangers and heat exchangers: Incoloy 825 is suitable for sulfuric acid at 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 highly sensitive to crevice corrosion caused by chlorides. Furthermore, its stamping performance is also poor, so it is not a commonly used material for sheets. This article is excerpted from Borne Heat Exchanger Mall: http://www.360bhe.cn/news/1080.html