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Intergranular Corrosion Properties of Alloy C276 and Alloy 22/C22

Intergranular Corrosion Properties of Alloy C276 and Alloy 22/C22

ASTM G28A and G28B Corrosion Tests

Development over the past 70 years of the “C” family of alloys has been focussed on improvements in alloy metallurgy, in melting technology and in thermo-mechanical processing. ASTM G28A and G28B tests where developed later as qualitative corrosion tests to verify that the metallurgy, melting process and thermo-mechanical processing had been completed correctly to ensure that the material is in the fully solution annealed condition and is not subject to intergranular corrosion resulting from the presence of  intermetallic / carbide precipitates at the grain boundaries. There is no pass or fail criteria for the tests. The results are agreed between buyers and suppliers.

ASTM G28A

  • Ferric sulphate and sulphuric acid boiling test
  • 50% H2SO4 + 42g/litre Fe2 (SO4)3

ASTM G28B

  • Mixed acid (Sulphuric acid, hydrochloric acid, ferric chloride & cupric chloride) – oxidizing salt boiling test.
  • 23% H2SO4 + 1% HCl + 1% FeCl3 = 1% CuCl2

Published industry accepted corrosion rates for C276 and C22/Alloy 22

Producers

Alloy C276 G28A

(mm per annum)

Alloy C276 G28B

(mm per annum)

Alloy 22/ C22 G28A

(mm per annum)

Alloy 22/ C22 G28B

(mm per annum)

Haynes International

6.10

1.40

0.61

0.178

Special Metals

7.00

1.50

1.50

0.50

ThyssenKrupp VDM

9.00

1.50

0.90

0.17

Results based on taking the average of a minimum of 10 mill test certs/heats

Producers

Alloy C276 G28A

(mm per annum)

Alloy C276 G28B

(mm per annum)

Alloy 22/ C22 G28A

(mm per annum)

Alloy 22/ C22 G28B

(mm per annum)

Haynes International

6.172

Not reported

0.807

0.145

ATI ( Allegheny)

5.985

1.330

0.822

0.151

Special Metals Huntington , U.S.A

4.315

0.736

Special Metals Wiggin, UK

6.835

0.858

1.135

0.143

BGH – Germany

4.050

0.780

ThyssenKrupp VDM

0.809

0.172

Bohler

0.590

0.094

Special Metals

Huntington. U.S.A.

0.821

0.119