Chloride pitting

Some duplex alloys have even better pitting resistance than type 316 and should be considered in severely pitting media. Titanium is virtually immune to chloride pitting and cupro-nickel alloys are used for condensers where sea-water is the coolant high pitting resistance in this duty is claimed for Cu-25Ni-20Cr-4-5Mo. 

Four hundred-series alloys are resistant to chloride stress corrosion cracking, but not chloride pitting. Accordingly, they are rarely used in aqueous chloride services. However, superferritic ... 

Many low- to moderate-strength aluminum alloys (primarily in the 1000-, 3000-, 5000- and 60(X)-series) have useful corrosion resistance. They are used in mildly corrosive atmospheres (such as those offshore or at seacoasts and for cable trays and fins on air cooler tubes). Several 5000-series alloys are moderately resistant to chloride pitting and find applications in clean seawater and other aqueous chloride services. They are very resistant to corrosion by wet CO2 and are compatible with organics such as acetic acid. 

Aluminum and alloys are not suitable for (1) alkalis, (2) acids at pH 4.5, and (3) mercury, which can be a significant risk in some liquified natural gas operations. The heat treatable, high-strength aluminum alloys of the 2000- and 7000-series are rarely used because of environmental cracking susceptibility. Aluminum and its alloys are susceptible to chloride pitting and to concentration cell problems such as crevice corrosion and under-deposit corrosion. 

Super austenitic stainless steels, such as AL-6XN and 254SMO alloys, have high resistance to localized corrosion. Chloride pitting and crevice corrosion in these alloys is very low due to the presence of high molybdenum content (>6%) and nitrogen additions. Steels with higher nickel content exhibit better resistance to stress corrosion cracking than austenitic stainless steels. 

Rafey, SAM, Ahd El Rehim, SS. 1996. Inhibition of Chloride Pitting Corrosion of Tin in Alkaline and Near Neutral Medium hy Some Inorganic Anions. Electrochim. Acta, 42, 667. 

SS Contains 16% chromium, 10% nickel and 2% molybdenum. Molybdenum increases corrosion resistance and improves chloride pitting resistance. 

Gamer, A., The Effect of Autogenous Welding on Chloride Pitting Corrosion in Austenitic Stainless Steels, Corrosion, Vol. 35, No. 3, 1979, pp. 108-113. 

In industrial or marine atmospheres, or from contamination with highway deicing salts, chloride pitting may occur. If the contamination is severe, overall rusting may occur rather than localized pitting. 

Types 405 and 409 have approximately the same resistance to chloride pitting as type 410, whereas higher alloyed types such as 430 are more resistant. 

Table 7.2 provides the chemical composition of this alloy. This is a low-carbon alloy with molybdenum added to improve chloride pitting resistance. It is virtually immune to chloride stress corrosion cracking. The alloy is subject to 885°F (475°C) embrittlement and loss of ductility at subzero temperatures. 

The chloride pitting resistance of this alloy is similar to that of type 316 stainless steel and superior to that of types 430 and 439L. Like all ferritic stainless steels, t)/pe 444 relies on a passive film to resist corrosion, but exhibits rather high corrosion rates when activated. This characteristic explains the abrupt transition in corrosion rates that occur at particular acid concentrations. For example, it is resistant to very dilute solutions of sulfuric acid at boiling temperature, but corrodes rapidly at higher concentrations. 

The chemical composition of alloy 29-4C is shown in Table 8.3. This alloy has improved general corrosion resistance to chloride pitting and stress corrosion cracking in some environments. The absence of nickel reduces the cost. 

This alloy has improved resistance to chloride pitting and stress corrosion cracking and improved general corrosion resistance in some environments. 

This is a chromium-nickel-molybdenum alloy, with its composition shown in Table 8.4. It has excellent resistance to chloride pitting and stress corrosion cracking environments. It finds use in the chemical processing and utility industries. 

Alloy 2OM0-4 has outstanding corrosion resistance to chloride pitting and crevice corrosion with good resistance to sulfuric acid and various other acidic environments. 

The approximate 50/50 ferrite-austenite structure provides excellent chloride pitting and SCC resistance, with roughly twice the yield strength of the standard austenitic grades. 

Ferralium exhibits good corrosion resistance to a variety of media, with a level of resistance to chloride pitting and SCC. The following corrosion rates of Ferralium 255 have been reported ... 

Pre-modem times, i.e., the 1980s, may be considered a real boom in MIC studies. By the 1980s the impact of stagnant hydrotest conditions on inducing MIC (or more accurately, microbially assisted chloride pitting corrosion) into stainless steel at chloride ion concentrations as low as 200 mg per litre was quite... 

Thickness, density, porosity, type (homogeneous or layered), and color should be noted. When only a limited amount of deposit is available, replication tape is a useful method of removing it. Polyvinyl chloride (PVC) or other chloride-containing tapes should not be used on stainless steels, which are susceptible to chloride pitting and stress cracking. 

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