New Item
API Standard 6A718
Proposed New Macro Etchant
Paul Maxwell
30 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 RegiaHeated” 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.
Photo 1
Photo 2
Photo 3
Photo 4
Photo 5
Photo 6
Photo 7
Photo 8