NOTE : You must remove the pipe from the aircraft to do this procedure.
____
(1) Clean the pipe
(a) If the tube is painted (for stainless steel tubes):
1 Remove the paint with grade 400 emery cloth from the full
_ circumference of the tube along a sufficient length around the damage area.
(b)
Clean the outside of the tube with CLEANING AGENTS (Material No. 11-026).
(c)
Flush the inside of the tube with CLEANING AGENTS (Material No. 11-026). Do the operation three or four times to remove all grease from the tube.
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Preparation of the Damage Area Figure 273/TASK 20-23-11-991-072- 12 (SHEET 1)
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(d)
Flush the tube with water.
(e)
Let the tube dry in ambient air.
(2)
Identify the location of the damage
(a)
Blow dry compressed air, at a pressure of approximately 10 bar (145.0377 psi), through the tube.
(b)
Soak the outer surface of the tube in water or apply a leak detection product to see the leak.
(c)
Grind the surface of the tube along the full length of the crack to identify the damage area.
(d)
Accurately identify each end of the crack. The identification mark must not be more than 2 mm (0.0787 in.) on each side of the length of the crack.
(3)
Prepare the damage area for the repair
(a) With a 2-cut milling cutter, make a groove along the length of the defect plus 5 mm (0.1968 in.) on either side of the crack.
NOTE : Use a 2-cut milling cutter with the characteristics:
____
- 40 teeth,
- cut angle: 110 Deg.,
- DIA.: 15 mm (0.5905 in.),
- width: 1.8 mm (0.0708 in.) or 2 mm (0.0787 in.) or 2.2
mm (0.0866 in.).
1_ The shape of the tool gives the width of the groove.
2_ The cutter must almost go through the tube wall (95% of the
thickness).
NOTE : If the cutter goes through the wall, the opening (at____
the inner surface) must not be more than 0.2 mm (0.0078
in.) on a length of a few millimeters.
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(4) Clean the prepared area
(a)
For stainless steel tubes:
(b)
For titanium alloy tubes: 1 Remove dust with CLEANING AGENTS (Material No. 11-026).
1_ Clean the area with a clean stainless steel wire brush.
NOTE : Make sure that you use a clean stainless steel wire____
brush.
NOTE : Make sure that you do not cause damage to the pipe____
around the prepared area.
2_ Remove dust with CLEANING AGENTS (Material No. 11-026).
NOTE : Do not use a compressed air gun to remove dust.____
_ NOTE : Do not use a compressed air gun to remove dust.
____
(5) Weld the tube (T. I. G. welding process)
(a) Do the gaseous protection NOTE : The welding torch gives protection to the outside of the
____ tube.
1 Blow a neutral gas inside the tube with a flow rate of 4 to 10
_ l/min. for a sufficiently long time (about 10 min. for a long pipe). Decrease the flow rate to 4 l/min. during the welding operation.
(b) Weld the tube NOTE : Make sure that the welding equipment parameters are the
____ same as those used on the test specimen.
1 For stainless steel 21-9-6 tubes:
_
-use Z2 CND 20-10-3 filler metal. 2 For titanium alloy TA3V2.5 tubes:
_ -use T40 filler metal.
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(c) Stop the gaseous protection
1_ Outside the tube:
- continue the argon flow for at least one minute after
welding.
2_ Inside the tube:
- continue to blow the inert gas through the tube for one
minute after welding.
(6) Inspection of the repaired area
(a) Do a visual inspection of the weld bead
1 Make sure that the width of the weld bead is:
_
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