Preliminary Requirements

Safety Requirements

WARNING

IT IS THE RESPONSIBILITY OF THE OPERATOR TO OBTAIN AND OBSERVE THE MANUFACTURERS MATERIAL SAFETY DATA SHEETS FOR CONSUMABLE MATERIALS INFORMATION SUCH AS, HAZARDOUS INGREDIENTS, PHYSICAL/CHEMICAL CHARACTERISTICS, FIRE, EXPLOSION, REACTIVITY, HEALTH HAZARD DATA, PRECAUTIONS FOR SAFE HANDLING, USE AND CONTROL MEASURES AND ALSO TO TAKE LOCAL REGULATIONS INTO CONSIDERATION.

Procedure

1. SUBTASK 70-33-77-300-001 Clean the Parts

   1. Clean the parts for between 30 to 90 minutes. Refer to the SPM TASK 70-11-13-300-503.

2. SUBTASK 70-33-77-300-002 Grit Blast the Parts

   1. 

      CAUTION

      WHEN YOU USE A GRIT BLAST PROCEDURE TO REMOVE THERMAL SPRAY COATINGS, CONTAMINATION OF THE GRIT BLAST MEDIA WITH REMOVED COATING OCCURS. IF YOU USE GRIT BLAST MEDIA THAT CONTAINS REMOVED COATING MATERIAL CONTAMINATION TO PREPARE PART SURFACES FOR THERMAL SPRAY COATING, CONTAMINATION OF PART SURFACES AND SUBSEQUENT COATING BOND PROBLEMS WILL OCCUR.

      Lightly grit blast the parts. Refer to the SPM TASK 70-12-09-120-501 for the procedure. Use one of the grits given below:

      CoMat 05-198 ALUMINUM OXIDE, 320-GRIT.

      CoMat 05-197 ALUMINUM OXIDE, 240-GRIT.

      For parts other than turbine airfoils, it is permitted to do the subsequent procedure to remove the ceramic top coat from multiple-layer thermal barrier plasma spray coatings that have a ceramic top coat.

      Abrasive blast with CoMat 05-192 ALUMINUM OXIDE GRIT or CoMat 05-046 ALUMINUM OXIDE GRIT 60 grit aluminum oxide by the procedure in the SPM TASK 70-12-09-120-501 to remove the ceramic top coat. Refer to the SPM TASK 70-12-09-120-501, SUBTASK 70-12-09-120-501.

      It is not permitted to use abrasive blast to remove coatings that are in direct contact with (that is, touch directly) the substrate (that is, the part material), such as hardface coatings, because too much erosion of the substrate can occur and cracks will be more difficult to find during FPI.

      Although the SPM TASK 70-34-18-380-501, SUBTASK 70-34-18-380-501 specifies to use 60 grit aluminum oxide, it is not permitted to do coating removal procedures with blasting equipment that you use for the SPM TASK 70-34-18-380-501 because combination of the SPM TASK 70-34-18-380-501 grit blast media with removed coating removal will occur.

3. SUBTASK 70-33-77-300-003 Mask the Parts

   1. 

      CAUTION

      YOU MUST MASK AREAS OF PLASMA HARDFACE COATINGS WHICH ARE NOT TO BE REMOVED OR DAMAGE WILL OCCUR.

      Wax mask the areas of the parts where the coatings are not to be removed with CoMat 02-038 MASKING WAX COMPOUND (HIGH TEMPERATURE), or CoMat 02-021 MASKING WAX COMPOUND. Refer to the SPM TASK 70-38-24-300-503.

4. SUBTASK 70-33-77-300-004 Remove the Coating

   1. 

      CAUTION

      1. YOU MUST MAKE SURE THAT ALL AREAS OF THE PARTS THAT ARE TO HAVE COATINGS REMOVED ARE BELOW THE SURFACE OF THE SOLUTION.

      2. YOU MUST MAKE SURE PARTS DO NOT TOUCH EACH OTHER.

      3. USE MECHANICAL AGITATION (CORROSION RESISTANT STAINLESS STEEL SOLUTION PUMP, MIXER, OR UP/DOWN LIFT) TO CAUSE CONSTANT MOVEMENT OF THE SOLUTION WHILE THE PARTS ARE IN THE SOLUTION.

      Put the parts into applicable baskets or fixtures. The baskets or fixtures must be made of or have a layer of polyethylene or polypropylene on them.

   2. Put the parts fully into solution code 67 stripping solution (refer to the SPM TASK 70-33-77-100-501) with mechanical agitation for between 2 and 4 hours. The temperature of the solution must be 120 to 160 deg F (50 to 70 deg C). The time taken to remove the coating will change with the solution strength and amount of grit blast. Examine the parts every 2 to 4 hours (23 hours total time maximum).

      NOTE

      Ultrasonic agitation is optional.

      When the parts are put into the stripping solution, the underlying bond coat will go a greenish color. This shows that the removal procedure of the coating has started. When the green color has gone, the coating has been fully removed.

   3. Clean the parts in a flow of cold water for half a minute.

   4. Clean the parts with a compressed air/water spray for half a minute.

   5. Wet abrasive blast the parts if necessary to remove signs of oxidation not removed before. Refer to the SPM TASK 70-12-06-120-501 or SPM TASK 70-12-09-120-501.

   6. Examine the coating. If the coating has not been completely removed do Step to Step until the coating has been removed (23 hours total time maximum).

   7. Clean the parts in hot water for half a minute. The water must be at a temperature of 130 to 160 deg F (54 to 71 deg C).

   8. Air dry the parts for one minute.

   9. If used, remove the masking. Refer to the SPM TASK 70-38-36-380-501.