MIL-DTL-87173B
APPENDIX B
APPENDIX B
HEATER TUBE DEPOSIT RATING
B.1 SCOPE
B.1.1 Scope. This appendix provides instructions to conduct and read the heater tube deposit. This
appendix is a mandatory part of the specification.
B.2 APPLICABLE DOCUMENTS. (This section is not applicable to this appendix.)
B.3 VISUAL TEST METHOD
B.3.1 Snap the upper end of the heater tube into the clamp of the adapter for the heater tube.
B.3.2 Push the heater tube against the stop of the adapter tube.
B.3.3 Slide the adapter with the heater tube over the guide rod into the tuberator equipped with a
magnifying glass assembly.
B.3.4 Insert the ASTM color standard into the tuberator.
B.3.5 Rotate the adapter and position the heater tube so the side with the maximum deposit is visible.
B.3.6 Within 30 minutes after completion of the test, visually examine the heater tube in a tuberator.
The entire portion of the test section between the bottom shoulder and the top shoulder of the heater tube
test section shall be carefully examined using a magnifying glass in conjunction with the tuberator for any
signs of discoloration, scratches, or other visually identified defects. When an area of the tube
corresponds visually to an ASTM color standard, that color standard code number shall be recorded. If
the area being rated has a color between two adjacent color standards, it shall be rated as the lighter
(lower number) color standard. (NOTE: It is important that all light bulbs in the tuberator are functioning,
as a change in light intensity can shift the rating significantly.)
(NOTE: The person rating the tube should have normal ability to distinguish between colors; i.e., he
should not be color blind.)
B.3.6.1 In rating the heater tube, the darkest deposits govern and the code number representative of the
darkest section, rather than the average deposit, shall be reported.
B.3.6.2 If a spot or streak is found on the heater tube, it shall be carefully examined under various
lighting conditions using a magnifying glass to determine if it is a deposit, a scratch, or tube defect; (note
that the tube defects should have been found during the pretest inspection of the tube). If the spot or
streak is determined to be a scratch or tube defect, it shall be disregarded. If the spot or streak is a
deposit, it shall be rated against the ASTM color standards, if larger in area than about 0.025 sq cm
(0.004 square inch); i.e., approximately 1.5 mm x 1.5 mm (1/16 inch x 1/16 inch) square or an equivalent
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area. However, a streak deposit shall be ignored if less than 0.8 mm ( /32 inch) wide, regardless of length.
Note that the tube section is about 3 mm (1/8 inch) in diameter; thus, a 1.5 mm- (1/16 inch-) wide spot is
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half the diameter of the tube test section and a 0.8 mm- ( /32 inch-) wide streak is one fourth the diameter
of the tube test section.
B.3.6.3 If the heater tube has deposits which do not match the Color Standards, the following criteria
shall be used.
B.3.6.3.1 If the deposit has peacock (rainbow) colors, rate this as Code P (P for peacock). If some
portion of the deposit does match the Color Standard, it shall be rated.
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