TASK 70-23-12-110-027
1 . General.
NOTE:
TASK 70-23-23-330-008, Removal of Coatings by High Pressure Water Stripping, is an acceptable alternative to the process listed in this procedure, provided that the self substantiation requirements of the TASK are met.
NOTE:
TASK 70-23-24-110-001, Ultrasonic Stripping of Rotating Parts, is an acceptable alternative to the process listed in this procedure, provided that the self substantiation requirements of the TASK are met.
A.This procedure is recommended for the removal of thermal spray coatings from titanium and nickel-based alloy parts. Refer to TASK 70-23-07-110-023, Stripping of Thermal Spray Aluminum Oxide, Non-Ferrous, and Bond Coatings, for procedure covering other materials. The following thermal spray coating systems may be stripped by this procedure.
(1)Alumina/Nickel-Aluminum (Duplex): TASK 70-49-02-340-003, Thermal Spraying Aluminum Oxide - Alumina (Powder), and TASK 70-49-10-340-011, Thermal Spraying Nickel-Aluminum (Powder) and TASK 70-49-33-340-034, Thermal Spraying Nickel-Aluminum (Powder) - Fine.
(2)Alumina/Nickel-Aluminum (Composite): TASK 70-49-22-340-023, Thermal Spraying Alumina/Nickel- Aluminum Composite (Powder).
(3)Copper-Nickel: TASK 70-49-04-340-005, Thermal Spraying Copper-Nickel Alloy (Powder).
(4)Copper-Nickel-Indium: TASK 70-49-05-340-006, Thermal Spraying Copper-Nickel-Indium (Powder).
(5)Molybdenum: TASK 70-49-07-340-008, Thermal Spraying Molybdenum (Powder), and TASK 70-49-08-340-009, Thermal Spraying Molybdenum (Wire).
(6)Nickel-Aluminum: TASK 70-49-10-340-011, Thermal Spraying Nickel-Aluminum (Powder), and TASK 70-49-11-340-012, Thermal Spraying Nickel-Aluminum (Wire).
(7)Nickel-Graphite: TASK 70-49-14-340-015, Thermal Spraying 75:25 Nickel-Graphite (Powder), and TASK 70-49-15-340-016, Thermal Spraying 85:15 Nickel-Graphite (Powder).
(8)Aluminum Bronze: TASK 70-49-25-340-026, Thermal Spraying Aluminum Bronze (Powder), and TASK 70-49-26-340-027, Thermal Spraying Aluminum Bronze (Wire).
2 . Materials.
Subtask 70-23-12-110-271
A.Refer to TASK 70-00-99-800-001, Solution S0001.
3 . Procedure.
Subtask 70-23-12-110-272
A.Parts must be cleaned and masked (if necessary) before stripping is begun. Proceed as follows:
CAUTION:
THIS SOLUTION WILL ATTACK MANY ALLOYS IF USED HOT AT 160°F (71°C). DO NOT ELEVATE THE TEMPERATURE WITHOUT PRIOR APPROVAL.
CAUTION:
THIS SOLUTION WILL ATTACK LOW ALLOY STEELS, HASTELLOY B, HASTELLOY W, AND INCOLOY 903. REACTION WITH THESE MATERIALS IS VERY RAPID. BASE MATERIAL MUST BE COMPATIBLE WITH THIS SOLUTION.
(1)Steam clean parts in accordance with TASK 70-21-03-160-001, Cleaning Method No. 3 - Steam Cleaning, or TASK 70-21-22-110-042, Cleaning Method No. 22 - Light Duty Aqueous Cleaning. Parts other Parts other than titanium may be degreased per TASK 70-21-02-110-002, Cleaning Method No. 2 - Vapor Degreasing.
(2)Mask any metal sprayed areas that are not to be stripped as follows:
NOTE:
Masking may not be required if all coated areas are to be stripped. Paragraphs 3.A.(2). and 3.A.(5) can be ignored in such instances.
(a)Mask metal sprayed areas with masking tape, and seal all part openings with acid-resistant tape.
(b)Dip entire part into Turco No. 537 Bubble-free maskant (Turco Products, Inc.; Joliet, Illinois) or equivalent, and let dry. Repeat until a minimum of 3 coats have been applied.
(c)Trim by cutting through masking tape and maskant around areas to be stripped. Expose only the area to be stripped by peeling away tape and maskant, but do not remove acid-resistant tape/maskant from openings.
WARNING:
NITRIC ACID AND ITS FUMES ARE TOXIC. MIX AND USE IN A WELL VENTILATED AREA, AND WEAR ACID-RESISTANT CLOTHING, GLOVES AND FACE PROTECTION. IF NITRIC ACID CONTACTS THE SKIN, WASH IMMEDIATELY IN CLEAR WATER. A CHARACTERISTIC YELLOW STAINING OF THE SKIN WILL REMAIN AFTER WASHING.
(3)Immerse part in stripping solution at 70 to 150°F or 20 to 65°C so that all areas are completely covered. Typical exposure time to acid is 1.5 to 2.0 hours.
(a)The stripping may be enhanced by the following steps:
1Remove the part from the bath every 20-30 minutes during the strip cycle to enhance the stripping process, especially for the seal teeth areas.
2Scrub the coating by hand with a non-metallic brush, Scotch Brite pad C10-010  , or equivalent.
NOTE:
This intermediate scrubbing removes the layer of reacted coating and re-activates the surface for additional acid stripping.
3Use the high-pressure water rinse [2000 psi max. (13800 kPa)] to remove the reacted coating layer from the part.
NOTE:
A higher 2000 psi (13800 kPa) pressure water wash [3000 psi max. (20685 kPa)] can be used only if uncoated specimens make sure that the stock loss is permitted as specified in ARP 1755.
(4)Remove the part from the tank. Blast off the blackened bond coat with a high-pressure water rinse. Rinse and blow dry. Remove any remaining bond coat by hand, using a stiff brush and flowing water. Make sure that coatings are completely removed. Repeat paragraph 3.A.(3) if necessary.
WARNING:
ACETONE IS HIGHLY FLAMMABLE. TAKE PRECAUTIONS AGAINST FIRE. AVOID PROLONGED INHALATION OF VAPOR.
(5)Peel maskant from part. Use acetone or methyl-ethyl-ketone to remove any maskant or tape that does not peel away readily. Steam clean entire part as directed in TASK 70-21-03-160-001, Cleaning Method No. 3 - Steam Cleaning, then follow with a pure steam "rinse".