TASK 70-24-00-110-033
1 . General.
Chemical etching is primarily used on stationary weldments as a preliminary step before fluorescent-penetrant inspection. Smeared surface material, caused by operations such as benching of welds, can mask cracks and flaws in metal parts preventing identification during the inspection process. Etchants are selected to remove this extraneous material and open the flaws to detection. The etchants are classified in the following text by their application to specific metals; however, other applications may be made when authorized by the Shop Manual. Chemical etching may be done by one of two methods: TASK 70-24-01-110-034, Swab Etching Procedure, or TASK 70-24-02-110-035, Dip Etching Procedure.
2 . Classification.
Subtask 70-24-00-110-331
A.Etchants of the following classes shall be used only on the metals listed, unless otherwise specified by the Engine/Shop Manual.
(1)Swab Etchants. Refer to TASK 70-24-01-110-034, Swab Etching Procedure.
Class A: Magnesium alloys
Class B: Titanium alloys
Class C: (Schantz Reagent)
Maraging Steels (Marage 250, etc.), Low Expansion Alloys (INCOLOY 903, 907, 909; Thermospan, etc.), All Stainless Steels (300's, 400's, PH Series, etc.), Iron Superalloys (A286, V57, etc.), Turbine Airfoil Nickel Superalloys (INCONEL 738; Rene' 77, 80, 125, 142, N5, etc.), Non-Turbine Airfoil Nickel Superalloys with Chromium Content less than 20% (INCONEL 600, 718; Rene' 41, 88DT, 95, 104; UDIMET 500, 700, etc.), Non-Turbine Airfoil Nickel Superalloys with Chromium Content greater than 20% (HASTELLOY X; INCONEL 601, 625, 939; MA754, etc.), Cobalt Superalloys (HS188, L605, MarM 509, X40, etc.).
Class D: Cancelled. Replaced by Class C. Use Class C when Class D is specified.
Class E: Carbon and Low Alloy Steels (4340, 9310, etc.), Maraging Steels (Marage 250, etc.), bearing and gear alloys.
Class F: Aluminum alloys.
Class G: High chromium superalloys.
Class H: Copper-Cobalt-Beryllium Alloy (B11H49 or B11H68) - Solution Heat Treated, Copper-Cobalt-Beryllium Alloy (B11G25, B11H49, or B11H68) or Copper-Nickel-Silicon-Chromium Alloy (B11G48) - Age Hardened.
(2)Dip Etchants. Refer to TASK 70-24-02-110-035, Dip Etching Procedure.
Class G: Inconel 718