TASK 70-24-99-990-005
1 . General.
The following chemicals are required for the formulation of etchants used for localized swab and dip tank etching prior to fluorescent-penetrant inspection.
 
Compound*
Strength
 
Acetic Acid (glacial)
99.5% minimum
 
Ammonium bifluoride
Solid 95% minimum
 
Ferric Chloride (FeCl3.6H2O)
Solid 97% minimum FeC13.6H2O
 
Ferric Chloride (FeC13)
Anhydrous solid 97% minimum FeC13
 
Hydrochloric acid
31.5% minimum
 
Hydrofluoric acid
48% minimum
 
Nitric Acid
67% minimum
 
Oxalic acid (C2H2O2 2H2O)
Crystals 99.5% minimum
 
Sodium hydroxide
Pellets or flakes
 
Sulfuric acid
93% minimum
 
Tartaric acid (C4H5O6)
Crystals 99.5% minimum
 
Hydrogen Peroxide
30 - 35%
 
Water
Distilled or deionized
 
NOTE:
*Chemicals must be technical grade or better. Concentration/strength must be as stated. All concentrations are weight percent.
2 . Instructions.
Subtask 70-24-99-990-051
WARNING:
ALWAYS ADD ACIDS TO WATER WHILE STIRRING. NEVER ADD WATER TO ACIDS. LOCALIZED HEAT OF SOLUTION CAN CAUSE BOILING AND SPATTERING AND COULD BURN YOU. THESE CHEMICALS ARE TOXIC AND CORROSIVE. FOLLOW ALL ENVIRONMENTAL, HEALTH, AND SAFETY REQUIREMENTS AND RECOMMENDATIONS LISTED ON THE MATERIAL SAFETY DATA SHEETS (MSDS) FOR THESE CHEMICALS.
A.Add chemicals in the order and proportions given in the following formulas. Mix each thoroughly before adding the next.
B.Ferric chloride, used in formulating the Class C and G etchants, is usually supplied in lump form. To facilitate mixing, it may be added in molten form (melting point: 37°C or 98.6°F). It may also be crushed and added in granular or powdered form with constant stirring until dissolved. Ferric chloride is extremely hygroscopic; keep unused supply tightly sealed.
NOTE:
Ferric chloride dissolves fastest when hot 150°-190°F (65.6°-87.8°C) water is used.
C.Glacial acetic acid freezes at slightly below room temperature (62°F or 16.6°C). To facilitate pouring and mixing, immerse the container in warm water for a few minutes.
D.Loosen stoppers or caps from full bottles carefully to prevent spurting.
3 . Formulas and Swab Etchants.
Subtask 70-24-99-990-052
WARNING:
THE ACTIVE INGREDIENTS OF ETCHANTS ARE TOXIC AND CORROSIVE. USE IN A WELL VENTILATED AREA, AND WEAR PROTECTIVE CLOTHING, GLOVES AND FACE SHIELD. AVOID PROLONGED BREATHING OF VAPORS AND CONTACT WITH THE SKIN. IF ETCHING SOLUTION GETS INTO EYES, FLUSH THOROUGHLY WITH COOL WATER UNDER EYELIDS AND OBTAIN MEDICAL ATTENTION AT ONCE.
E.The following formulas are based on quantities that, with average usage, are estimated not to last beyond the shelf-life period of the etchant. Larger or small quantities may be mixed, as desired, as long as proportions are equal to those given. The values are nominal. A measurement tolerance of plus or minus 5% of the nominal value is acceptable.
 
Swab Etchants - Table 1
 
CLASS A:
Magnesium Alloys
Oxalic acid or Tartaric acid
Distilled or deionized water
10 grams
90 ml
 
CLASS B:
Titanium Alloys except Titanium Aluminide Alloys
Distilled or deionized water
Nitric acid
Hydrofluoric acid
62 ml
35 ml
3 ml
 
Alternative Mixture
(Class B)
Distilled or deionized water
Nitric acid
Ammonium bifluoride
65 ml
35 ml
9 grams
 
NOTE:
The use of Ammonium bifluoride is a safer alternative to Hydrofluoric acid
 
CLASS C:
Stainless Steels and High Chromium Superalloys
Schantz Reagent
Distilled or deionized water
Sulfuric acid
Hydrochloric acid
Nitric acid
Acetic acid
Ferric chloride (FeCl3.6H2O)*
750 ml
150 ml
1800 ml
500 ml
750 ml
454 grams
(1 pound)
 
Alternative Mixture**
(Class C)
Distilled or deionized water
Sulfuric acid
Hydrochloric acid
Nitric acid
Acetic acid
Ferric chloride (FeCl3 Anhydrous)*
930 ml
150 ml
1800 ml
500 ml
750 ml

272 grams
 
NOTE:
*Add ferric chloride without delay. Refer to Step 2.B. in Subtask 70-24-99-990-051, Instructions.
 
CLASS D:
Cancelled. Replaced by Class C. Use Class C when Class D is specified.
 
CLASS E:
Carbon steels, bearing and gear alloys
Distilled water
Nitric acid
95 ml
5 ml
 
 
CLASS F:
Aluminum Alloys
Distilled or deionized water
Sodium hydroxide
Distilled or deionized water to make
60 ml
20 grams
100 ml
 
CLASS G(1):
High Chromium Superalloys
Ferric chloride (FeCl3·6H2O)***
Distilled or deionized water
Hydrochloric acid
Distilled or deionized water to make
38 grams
23 ml
28 ml
76 ml
 
NOTE:
Let the solution cool to room temperature before adding make-up water. Use distilled or deionized water unless otherwise noted.
 
Alternative Mixture**
Ferric chloride (FeCl3
23 grams
 
[Class G(1)]
Anhydrous)***
 
Distilled or deionized water
38 ml
 
Hydrochloric acid
28 ml
 
Distilled or deionized water
76 ml
 
to make
 
NOTE:
***Refer to Step 2.B. in Subtask 70-24-99-990-051, Instructions.
 
CLASS G(2):
Cancelled. Replaced by Class C. Use Class C when Class G(2) is specified.
 
CLASS H:
Distilled or deionized water
33 ml
 
Nitric acid
22 ml
 
Sulfuric acid
44 ml
 
Hydrochloric acid
0.5 ml (9 drops)
 
CLASS I:
Class F
9 parts
 
Hydrogen Peroxide
1 part
 
NOTE:
**Alternative Mixtures using anhydrous Ferric Chloride (FeCl3) can reduce errors when preparing these solutions.
4 . Formulas for Dip Tank Etchants.
Subtask 70-24-99-990-053
F.For dip etching mix the following chemicals in a polyethylene or polyvinyl chloride rigid tank in order to make 100 gallons (379 liters). Larger or smaller quantities may be mixed, as desired, as long as proportions are equal to those given.
 
Dip Tank Etchants - Table 2
 
Inconel 718
Ferric chloride (FeCl3 anhydrous)*
Distilled or deionized water
Hydrochloric acid (36.5%)
Distilled or deionized water to make
110 Kg
130 Liters
103 Liters
379 Liters
 
NOTE:
*Refer to Step 2.B. in Subtask 70-24-99-990-051, Instructions.