Intergranular corrosion testing

T.M. Devine and B.J. Drummond, Use of Accelerated Intergranular Corrosion Tests and Pitting Corrosion Tests to Detect Sensitization and Susceptibility to Intergranular Stress Corrosion Cracking in High Temperature Water of Duplex 308 Stainless Steel, Corrosion, Vol 37, 1981, p 104-115... 

Tab. 1 Standard intergranular corrosion tests for austenitic stainless steels (after Ref. [50, 51])...

Figure 7.42 Corrosion potentials of different intergranular corrosion tests [18,19].

Manning, P. E., "Tin Improved Intergranular Corrosion Test for HasteUoy Alloy C-276," Laboratory Corrosion Tests and Standards, ASTM STP 866, G. S. Haynes tmd R. Baboian, Eds., ASTM International, West Conshohocken, PA, 1985, pp. 437-454. 

Thus standard accelerated intergranular corrosion tests have been developed as a quality control test. They are designed to ... 

The most common intergranular corrosion tests are outlined in ASTM A 262 and G 28. Most of these test solutions are strong oxidizing acids or acids with added oxidizers that maintain the specimen at a stable electrochemical potential where accelerated intergranular corrosion will occur in a susceptible material. The test duration is typically 24-120 h, depending on the alloy. Recommended exposure periods for various nickel-base alloys are listed in ASTM G 28 but not in ASTM A 262. Though only austenitic stairrless steels are listed in ASTM A 262, some of the test methods are used for nickel-base alloys. It is important to note that ASTM A 262, Practice A, the cBialic add etch test, is recommended for stainless steels. It is not normally used for nickel-base alloys. 

Metal salts, such as ferric and cupric sulfate, are oxidizing and will passivate stainless steel when added to sulfuric acid. The salt concentration may be controlled so that passivity will occur at a specific chromium concentration. Stainless steels or areas of a stainless surface (such as sensitized grain boundary areas) with lower chromium content will not be passivated. This is the basis for the intergranular corrosion tests for stainless steels. 

The theory and apphcation of intergranular corrosion tests have been discussed in the hterature [//]. The tests included in ASTM A 262, as summarized in Table 1, are frequently used for qucJity control of austenitic stainless steels. These methods detect susceptibility to intergranular corrosion and the test solutions may be quite different than the service environments. These tests are frequently used to evaluate the effectiveness of the heat treatment used prior to shipment of a material. The alloys that may be evaluated by each practice (e.g., T5qjes 304 or 316) are specified as well as the procedure for using the several tests. Comments regarding a few of the tests are useful. 

Use of Accelerated Intergranular Corrosion Tests and Pitting Corrosion Tests to Detect Sensitisation and Susceptibility to Intergranular Stress Corrosion Cracking in High-Temperature Water... 

France, W. D. and Greene, N. D., Some Effects of Ex(>erimental Procedures on Controlled Potential Corrosion Tests of Sensitised Austenitic Stainless Steel , Corros. Sci., 10,379(1970) Tedmon, C. S. (Jr.), Intergranular Corrosion of Austenitic Stainless Steel , J. Electrochem. Soc., 118, 192(1971)... 

British Standard Method for Determination of Resistance to Intergranular Corrosion of A ustenltic Stainless Steels Copper sulphate-Sulphuric acid Method (Moneypenny Strauss Test) BS 5903 (1980)... 

For both heat-affected zone corrosion (intergranular attack) and knifeline attack the heat flux during welding and the time at temperature can critically affect the severity of the attack. Both these factors may vary from one welder to another, and when preparing pieces for corrosion testing not only should fabrication welding conditions be accurately reproduced, but the work of more than one welder should be evaluated. 

Intergranular corrosion of Fe-Ni-Cr alloys has been the subject of a comprehensive review by Cowan and Tedmon who summarised the various tests used for determining susceptibility (Table 19.3). Of these tests. Nos. 1-5, which are regarded as reliable test procedures by the ASTM, have been incorporated into ASTM A262 1986 Recommended Practice for Detecting Susceptibility to Intergranular Attack in Stainless Steel as follows ... 

Table 19.3 Summary of chemical tests used for the determination of susceptibility to intergranular corrosion of iron-nickel Chromium alloys ...

As is the case with other types of corrosion testing, mass-loss determinations may fail to indicate the actual damage suffered by specimens that are attacked intergranularly or in such a manner as dezincification. In such cases, mechanical tests will be required as discussed already in the section on evaluation techniques. 

Test methods for determining electrolytic corrosion with electrical insulating materials Method for determination of resistance to intergranular corrosion of austenitic stainless steels copper sulphate-sulphuric acid method (Moneypenny Strauss test) Specification for electroplated coatings of tin/lead alloys... 

Test method for determining the susceptibility to intergranular corrosion of 5XXX series aluminium alloys by mass loss after exposure to nitric acid (NAMLT test) Practice for liquid sodium corrosion testing of metals and alloys... 

Austenitic stainless steels-determination of resistance to intergranular corrosion. Part 1 Corrosion test in nitric acid medium by measurement of loss of mass (Huey test) Austenitic stainless steels-determination of resistance to intergranular corrosion. Part 2 Corrosion test in a sulphuric acid/copper sulphate medium in the presence of copper turnings (Moneypenny Strauss test)... 

Nickel-based alloys-Determination of resis-ance to intergranular corrosion Corrosion tests in artificial amospheres at very low concentrations of polluting gas(es) Test /. .-sulphur dioxide test for contacts and connectors... 

Cihal and Prazak determined the resistance of 18/8 stainless steel to this type of corrosion. They claimed that the technique could be used on steels which are difficult to test by other methods, including steels of low carbon content, and steels in which stabilising elements are present. By means of potentiostatic curves and light etching at constant potential they confirmed that the extent of intergranular corrosion depended upon the amount of precipitated chromium carbide. 

Corradi and Gasperini claimed that the potentiostatic method was more effective and simpler than the Strauss test for determining intergranular corrosion of stainless steels, and suggested that the method may lend itself for use on finished equipment in service as a non-destructive test. 

Nozzle deterioration caused direct impingement that may have caused higher corrosion Displayed intergranular corrosion "Not tested... 

Tests for aluminum and its alloys consist of intergranular corrosion, stress corrosion cracking and corrosion fatigue as detailed below ... 

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