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API Standard 6A718Proposed New Macro Etchant

Paul Maxwell30 June 2011

Stated Goal:• Add “Dilute Aqua Regia-Heated” Etchant as an approved

etchant for the requirements stated in API Standard 6A718(Sec. 4.2.1.1)

• Current Macro Etchants–Option A: Canada’s Etchant 100 ml H2SO4,100ml HF, 50ml HNO3, 400 ml H2O, Etch at 160°F to 180°F (71°C to 82°C)–Option B: Aqua Regia 200 ml HCl, 100 ml HNO3–Option C: Kalling’s No. 2 200 ml Methanol, 200 ml HCl, 10 g CuCl2–Option D: Hydrochloric-Peroxide H2O2 (30 %) 100 ml, HCl 200 ml, H2O 300 ml, Remove stains with 50 % HNO3

Materials:Alloy 718 Order/Heats utilized in the evaluation:4 orders/heats & associated locations were evaluated for each etchant

W77942/600409 – 1A,1X See photos 1(API 6A718 Option B etch) &

2 (“Dilute Aqua Regia-Heated” etch)

W79943/600382 – 1A, 1X See photos 3(API 6A718 Option B etch) &

4 (“Dilute Aqua Regia-Heated” etch).

W79939/600409 – 2A, 2X See photos 5(API 6A718 Option B etch) &

6 (“Dilute Aqua Regia-Heated” etch).

W74406/600274 – 3A, 3CO See photos 7(API 6A718 Option B etch) &

8 (“Dilute Aqua Regia-Heated” etch)

Materials (Continued)

Etchants Utilized:

Specified - API 6A718 Option B Etchant - Aqua Regia: 200 ml HCL, 100 ml HNO3.

Unheated - Room Temp (72F/23C).

Proposed - “Dilute Aqua Regia-Heated” Etchant: Aqua Regia, 250 ml HCL, 10- 20 ml HNO3 Processing Temp - 140F – 165F.

Test Methodology

• Same orders/heats, locations, and disc specimens utilized.

• Prep the surface of the specimens prior to etching process.

• Etch the specimens utilizing either the API 6A718 Option B etchant or the “Dilute Aqua Regia-Heated” etchant.

• API 6A718 Option B etchant will be unheated (room temp - 72F/23C).

• “Dilute Aqua Regia-Heated” etchant will be heated to 40F to165F.

• Specimen etching time will be approximately 25 to 30 minutes for each etchant type.

• Specimens will be rinsed and air dried.

• Inspect specimen surface to determine if the visual results are similar.

Results:

• Specimens for all four orders/heats reveal same macrostructure results.

• See attached photos regarding visual comparison.

Summary:• Specimens from four Alloy 718 orders/heats and locations were processed

utilizing the API 6A718 Option B etchant and the “Dilute Aqua Regia-Heated” etchant.

• The etchant composition and etching temperature were the only process variables that were changed.

• Visual inspection of the specimens revealed same macrostructure results (see photos).

• Benefits of utilizing the “Dilute Aqua Regia-Heated” etchant include, but are not necessarily limited to, longer time period prior to burning of surface and better repeatability.

• As a result of the items mentioned above, Carpenter is proposing to have the “Dilute Aqua Regia-Heated” etchant balloted as an approved etchant for the requirements stated in API Standard 6A718, Section 4.2.1.1.

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