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Pitting Test on Incoloy 825 Materials

1. ASTM G48 Method A: Ferric Chloride Pitting Test

In order to study the pitting resistance of Incoloy 825 in high chloride-ion environments, pitting test shall be conducted in accordance with ASTM G48 Method A. The specimen is a piece of Incoloy 825 plate of 30 mm x 10 mm x 3 mm manufactured to ASTM B424 UNS N08825. It is immersed into 6% FeCl3 solution at 50(±1)°C. Maintain the test solution temperature for 72 hours. Then, remove the specimen , rinse with water and scrub with a nylon bristle brush under running water to remove corrosion products, dip in acetone or methanol, and air-dry. Weigh the specimen to the accuracy of 0.0001g. Analyze corrosion products at the corrosion pit by using SEM and X-ray EDS methods respectively.

The surface macrostructure of Incoloy 825 after pitting test.

The surface macrostructure of Incoloy 825 after pitting test. Several pitting zones can be clearly observed.

2. Actual Chemical Composition of Incoloy 825 Specimen

CSSiMnPNiCrMoNbTiCu
0.00620.00090.310.470.01443.3422.783.280.180.942.04
*All values are by weight percentage.

3. The SEM & EDS Results

The SEM scanned photo of Incoloy 825 corrosion products.

The SEM scanned photo of Incoloy 825 corrosion products.

X-ray EDS analysis result

X-ray EDS analysis to determine chemical composition of the corrosion products of Incoloy 825.

The main elements remaining at the corrosion pit are Fe, Mo, Ti and O while the content of base element nickel is relatively low. It is concluded that oxidizing ions react with Cr & Ni in the corrosive solution. The product of the reaction is dissolved in the solution.

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