Industrial chemicals crevice corrosion

The Materials Technology Institute of the Chemical Process Industry (MTI) has identified five corrosion tests for iron- and nickel-based alloys, out of which two concern the resistance to crevice corrosion. The method MTI-2, originating from ASTM G48, involves the use of 6% ferric chloride solution for determining the relative resistance of alloys to crevice corrosion in oxidizing chloride environment. The method MTI-4 uses an increase in neutral bulk Cl- concentration at eight levels, ranging from 0.1 to 3% NaCl, to establish the minimum critical Cl concentration that produces crevice corrosion at room temperature (20-24°C).43,44... 

The relative frequency of occurrence of various corrosion forms depends on the type of industry and environment. One example from the chemical industry is shown in Table 7.1. In the heading we notice the high proportion of corrosion failures. The percentages of crevice corrosion and galvanic ( ) corrosion are surprisingly low. 

The Ni-Cr-Mo alloys are widely used within the chemical process industry. These alloys are resistant to both oxidizing and reducing environments. They resist chloride-induced pitting, crevice corrosion, and S.C.C. In addition, they are easily formed and are weldable. 

Seawater Titanium resists corrosion by seawater up to temperatures as high as 260°C. Titanium tubing, exposed for 16 years to polluted seawater in a surface condenser, was slightly discolored but showed no evidence of corrosion. T itanium has provided over 30 years of trouble-free seawater service for the chemical, oil-refining, and desalination industries. Exposure of titanium for many years to depths of over a mile below the ocean surface has not produced any measurable corrosion. Pitting and crevice corrosion are totally absent, even if marine deposits form. The presence of sulfides in seawater does not affect the resistance of titanium to corrosion. Exposure of titanium to marine atmospheres or splash or tide zone does not cause corrosion. 

To overcome these limitations. Method D measures the critical crevice corrosion temperature, using a multiple crevice assembly (MCA). The test solution is 6 wt. percent FeCl3 acidified with 1 wt. percent HCl. This test method is also referenced in ASTM G 157 for evaluating the corrosion properties of wrought iron- and nickel-based corrosion resistant alloys for the chemical process industries. 

Type 317 stainless steel contains greater amounts of molybdenum, chromium, and nickel than type 316. The chemical composition is shown in Table 10.1. As a result of the increased alloying elements, these alloys offer higher resistance to pitting and crevice corrosion than type 316 in various process enviromnents encoimtered in the process industry. However, they may still be subject to chloride stress corrosion cracking. The alloy is... 

MaterialsTechnology Institute of the Chemical Process industries. Inc. Crevice corrosion, but reoorted as average corrosion rate... 

Crevice corrosion occurs mainly (but not exclusively) on passive materials. The most important problem is the crevice corrosion of stainless steels, nickel-base alloys, aluminum alloys, and titanium alloys in aerated chloride environments, particularly in sea or brackish water, but also in environments found in chemical, food, and oil industries. Other cases of crevice corrosion are also known such as the so-called corrosion by differential aeration of carbon steels, which does not require the presence of chloride in the environment. Also mentioned in the literature is the crevice corrosion of steels in concentrated nitric acid and inhibited cooling water and of titanium alloys in hot sulfixric environments. 

There are large numbers of reported case histories of MIC on stainless steel in water and aqueous waste systems. They are related to different industrial applications such as freshwater storage and circulation systems in nuclear power plants [103, 113,116,142] and cooling water systems in chemical process industries [117,118]. There are basically three cases (a) crevice corrosion under unexpected deposits, (b) sensitivity of pitting and crevice corrosion to trace of H2S, and (c) crevice corrosion in natural seawater. Most of these reports are not well documented concerning the microorganisms involved in the process. However, some general features are... 

This is a localized form of corrosion, caused by the deposition of dirt, dust, mud and deposits on a metallic surface or by the existence of voids, gaps and cavities between adjoining surfaces. An important condition is the formation of a differential aeration cell for crevice corrosion to occur. This phenomenon limits the use, particularly of steels, in marine environment, chemical and petrochemical industries. 

The corrosion resistant properties of alloy A1-6XN show exceptional resistance to pitting, crevice attack, and stress cracking in high chloride concentrations and general resistance in various acid, alkaline, and salt solutions found in chemical processing and other industrial environments. 

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