Preliminary Requirements

Procedure

1. SUBTASK 70-21-04-290-001 Sequence of Inspection

   1. This task is applicable to detail carbon seals and/or seal assemblies at final inspection.

2. SUBTASK 70-21-04-290-002 Definitions

   1. The subsequent definitions are specifically applicable to the terms used in this task.

      1. BEARING PADS: On the outer periphery and face of split ring seals, the lands which are interrupted by axial or radial grooves or flutes and by circumferential grooves. See Figure.

      2. BLISTER: A condition that occurs when the coating lifts because of an unsatisfactory bond between the coating and the base material.

      3. BORE: The Inside Diameter (ID) surface against which the piston-ring type (secondary) seals operate.

      4. CARBON CHIPPED EDGES: The accidental removal of small, thin pieces of carbon from the part edges during handling.

      5. COATING CHIPPED AREAS: Mechanical removal of coating to its full depth with the result that the base material is bare.

      6. CLUSTER: Two or more imperfections with a separation of less than 0.031 inch (0.787 mm) from each other.

      7. FLAKING: Missing coating (but not with the result that the base material is bare).

      8. IMPERFECTION: An interruption (non-uniformity) in the usual surface condition of a part (for which an analysis will be necessary to give the condition its correct inspection standard).

      9. SCANT: A local surface on which there is not sufficient material for finish machining to remove the smallest quantity of material. This is usually seen as a difference in surface color or texture. Measure the contour to make sure of this condition.

      10. SCRATCH: A mark of minimum depth (or a linear depression), caused by the movement of a sharp object across the surface (this does not include lay marks from manufacture or repair). See Figure, Areas A.

      11. SEALING SURFACE: A surface that moves against another to prevent the flow of fluid. See Figure. A sealing surface always has a surface finish requirement on an illustration.

      12. VOID: Regular or irregular shaped imperfections where there is no applied material.

3. SUBTASK 70-21-04-290-003 Acceptance Limits (All Parts)

   1. Parts are visually satisfactory when they are within the limits of this task and, as applicable, to those given in the SPM TASK 70-21-01-220-501 and the applicable Engine Manual Inspection sections.

   2. Conditions not specified within this task are not permitted.

   3. The areas shown in Figure are high stress areas. It is necessary, because of part configuration, to do a visual inspection with 7X to 13X magnification to make sure there are no cracks in the high stress areas.

   4. The maximum limit for the permitted imperfections that follow is 30 on the total part. Minimum separation of different sized imperfections must be the value given for the smaller imperfections.

      NOTE

      Mainshaft seals are those seals that have a sealing surface radial width greater than 0.105 inch (2.667 mm) nominal or a sealing surface ID greater than 3.5 inches (88.900 mm).

      1. Mainshaft seals.

         1. No surface cracks are permitted.

      2. Sealing surfaces or edges.

         NOTE

         When you use the stylus to examine a scratch, the stylus must not cause a scratch.

         1. Imperfections on sealing surfaces or edges are permitted if you cannot feel them with a 0.015 - 0.030 inch (0.38 - 0.76 mm) radius stylus.

         2. Imperfections on sealing surfaces and edges (other than bores), which you can feel with a 0.015 - 0.030 inch (0.38 - 0.76 mm) radius stylus, are permitted to the limits of Table 1 and Table 2.

            Table 2. Acceptance Limits for Imperfections On Edges Of Seal Surfaces

            Area	Maximum Extension Into Sealing Surface		Maximum Length, Circumferentially		Maximum Number Of Imperfections For Each Edge
            ID and OD Edges	0.005 inch (0.127 mm) or less		No Limit		No Limit
            ID and OD Edges	0.020 inch (0.508 mm) or 10 percent of sealing surface, whichever is less		0.500 inch (12.700 mm)		Accumulated length not to exceed 1/4 of total edge length
            ID Edges	0.040 inch (1.016 mm) or 25 percent of sealing surface, whichever is less		0.125 inch (3.175 mm)		3 at least 1.000 inch (25.400 mm) apart *
            OD Edges	0.060 inch (1.524 mm) or 30 percent of sealing surface, whichever is less		0.188 inch (4.775 mm)		4 at least 0.750 inch (19.050 mm) apart *
            * ID and OD edge imperfections must not be radially opposite each other.

            Table 3. Acceptance Limits for Imperfections On Sealing Surfaces

            Maximum Width	Maximum Length		Maximum Distance		Maximum Number Of Imperfections For Each
            Up to 0.010 inch (0.254 mm)	0.030 inch (0.762 mm)		Not Applicable		10, but no more than 3 side by side radially across the surface
            Up to 0.035 inch (0.889 mm)	0.125 inch (3.175 mm) *		1.000 inch (25.400 mm)		3
            * Imperfections must not extend radially across the total face. The above limits do not include those permitted breaking edges given in Table 1.

      3. Coated bores.

         1. Blisters, voids, and scant areas are not permitted.

         2. Scratches are permitted if you cannot feel them with a 0.030 inch (0.762 mm) radius stylus.

         3. Areas to be coated, before coating, must agree with the requirements for nicks and pits in Table 3A and Table 3B.

            NOTE

            Areas referred to in Table 3A and Table 3B appear in Figure, in the section that shows hardface on carbon and in the section that shows chromium plate or hardface on steel.

         4. Coated areas must agree with all the requirements of Table 3A and Table 3B.

            Table 4. Acceptance Limits for Imperfections On Uncoated And Coated Bore Surfaces - Nicks and Pits

            Area	Maximum Surface Dimension		Maximum Number		Maximum Distance
            A	0.020 inch (0.508 mm)		10		1.000 inch (25.400 mm)
            B	No limit (ID after final machining must be equal to, or greater than, Area A diameter)

            Table 5. Acceptance Limits for Imperfections On Uncoated And Coated Bore Surfaces - Chipped or Flaked Areas

            Area	Length x Width		Maximum Number		Maximum Distance
            A	0.031 inch x 0.15 inch (0.787 x 0.381 mm)		3		1.000 inch (25.400 mm)
            B	No limit (ID after final machining must be equal to, or greater than, Area A diameter)

      4. Bearing pads (See Figure).

         1. Nicks and pits on bearing pads are permitted if they are 0.062 inch (1.575 mm) or less across the major surface dimension and their total areas are not more than 1/8 the area of the pad with the damage.

         2. Scratches are permitted if you cannot feel them with a 0.030 inch (0.762 mm) radius stylus.

      5. Surfaces other than sealing surfaces, bores, and bearing pads.

         1. Nicks and pits are permitted to the limits of Table 4.

         2. Scratches are permitted if you cannot feel them with a 0.030 inch (0.762 mm) radius stylus.

            Table 6. Acceptance Limits for Imperfections On All Other Surfaces

            Maximum Number Of Imperfections	Maximum Surface Dimension		Minimum Distance
            10	1/2 the minimum surface dimension or 0.125 inch (3.175 mm), whichever is less		3x the maximum dimension of the imperfection

      6. Edges of non-sealing surfaces.

         1. Nicks are permitted to the limits of Table 5.

            Table 7. Acceptance Limits of Non-sealing Surfaces

            Maximum Extension onto Surface	Maximum Number Of Imperfections For Each Edge	Maximum Circumferential Length
            0.010 inch (0.254 mm) or less	No Limit	No Limit
            Over 0.010 inch (0.254 mm) but less than 0.062 inch (1.575 mm) or 50 percent of non-sealing surface width, whichever is less	5	0.125 inch (3.175 mm)

      7. Carbon surfaces - general.

         1. Bleeding of carbon seal impregnants shows as a white, discolored deposit on the surface of the carbon. This condition is permitted if, at final inspection, there is no build-up of deposit seen above the basic surface of the carbon.

Figure: Section Of Carbon Seal Ring To Show Location Of Bearing Pads And Seal Surfaces Fig. 70-21-04-990-001

Section Of Carbon Seal Ring To Show Location Of Bearing Pads And Seal Surfaces Fig. 70-21-04-990-001



Figure: Sections To Show Hardface On Carbon And Chromium Plate And Hardface On Steel Fig. 70-21-04-990-002

Sections To Show Hardface On Carbon And Chromium Plate And Hardface On Steel Fig. 70-21-04-990-002



Figure: Carbon Ring And Bearing Face Seals - Crack Inspection Fig. 70-21-04-990-003

Carbon Ring And Bearing Face Seals - Crack Inspection Fig. 70-21-04-990-003