(3)  
Very high temperatures for the ducts.

 (4)  
Very high duct pressures.

 B.  It may be necessary to replace the ducts as an alternative to the duct repair.
 C.  If a duct is badly damaged, you must use the Overhaul Manual.
 D.  This procedure also contains a task to reform the surfaces of the duct flanges while the duct is installed on the airplanes.
 TASK 36-19-15-308-001
 2.  Duct Repair (Fig. 801)
___________
 A.  Repair the ducts with smooth dents
 S 358-002
 (1)  Do one of the steps that follow to repair the ducts with smooth dents:
 NOTE: It is not necessary to repair the duct if the smooth dent
____ does not limit the air flow through the duct.
 (a)  
You can pull a ball mandrell through the area of the duct that has the dent.

 (b)  
You can use an expansion device that is hydraulically or mechanically operated to remove the dent.

 (c)  
You can use hydrostatic pressure in the duct while you lightly hit the edge of the dent with a hammer that is not metal.

 NOTE: Be careful you do not use a pressure that is more
____ than the pressure permitted for the system.
 S 358-003
 (2)  Do these steps to repair the ducts that have scratches, gouges and corrosion:
 (a)  It is not necessary to repair the duct if the scratch, gouge or corrosion is less than 10% of the duct wall thickness.
 NOTE: The change from the base metal thickness must be
____ smooth and rounded. The bottom of the scratch, gouge or corrosion must be smooth and rounded also.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL

0.12 INCH
PRIMARY
RAD MINIMUM
SILICONE RUBBER SHEET

MAXIMUM CRACK LENGTH DUCT REPAIR (EXAMPLE)
MUST NOT BE MORE THAN THE DUCT DIAMETER.
Pneumatic Duct Approved Repairs Figure 801
B74108
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 (b)  Sharp scratches, gouges and corrosions can be repaired. You can remove some of the adjacent metal surface to make the scratch, gouge or corrosion smooth. You can do this if you have the conditions that follow: 1) The thickness of the duct wall at the scratch, gouge or
 corrosion must be a minimum of 90% of the initial
 thickness. 2) The surface of the duct must not be rougher than 40 RMS. 3) The slope of the area must not be more than 1 to 10. 4) The internal and external radii of the area must be not
 less than 0.12 inches. 5) The scratch, gouge or corrosion must be more than 0.25 inches from a primary fusion welded joint. 6) If the damage to the ducts do not have these conditions, replace the ducts.
 TASK 36-19-15-308-014
 3. Temporary Repair of Cracked Ducts (Fig. 801)
_________________________________
 A. General
 (1)  You can temporarily repair ducts that have a crack along the longitudinal axis.
 NOTE: This repair procedure is only permitted for ducts that
____ have a crack along the longitudinal axis. Replace ducts that have a crack along the circumference or have multiple cracks.
 (2)  
A duct with a longitudinal crack that is less than three inches from a flange or pullout also cannot be repaired by this procedure. It must be replaced or repaired in accordance to the overhaul manual.

 (3)  
The repair is temporary and you must replace the duct as soon as possible.

 B. Consumable Materials
 (1)  
Silicone rubber sheet - BMS 1-57GR50A - 0.10 to 0.15 inch thick

 (2)  
Stainless steel sheet - 0.010 inch thick

 (3)  
Adjustable stainless steel clamps - BACC10B

 C. Repair the duct with the crack
 S 328-010
 (1)  
　
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