PREVOST H3-41 Maintenance Manual page 838

STRUCTURE INSPECTION PROCEDURE
The thickness of main carbon steel parts on rear & front sub-frames, drive axle cradle and tag axle beam
must be at least 1/8 inch (0.125") (3mm). There are two options to properly monitor the wall thicknesses:
1- Using an ultrasonic wall thickness gauge.
2- Drilling holes and measuring wall thickness.
1- Structural Inspection Procedure Using Ultrasonic Wall Thickness Gauge
The ultrasonic wall thickness gauge has to be used on bare metal. The surface where the gauge
will be put on has to be cleaned of rust, paint or other material. If the thickness is more than 1/8
inch (3mm), repaint the cleaned surface to prevent corrosion from occurring on this spot.
Use a grinder or another tool to remove
rust or paint on the spot to check. The
gauge has to be placed on the center of
the cleaned spot. The gauge has to be
perpendicular to the surface to get an
accurate measure.
Inspection using ultrasonic wall thickness
gauge is recommended over drilling holes
because it minimize risk of altering the
vehicle structure.
2- Structural Inspection Procedure Using Drilled Holes
Drill a ¼ inch (6 mm) diameter hole in the most corroded wall of the part being checked. Use a
caliper to measure the thickness of the drilled metal. Wall thickness should be at least 1/8 inch
(0.125") (3mm). Drilled hole must then be welded (filled with metal) and repainted after
measurement to prevent water infiltration and corrosion from occurring around the hole.
Clean/remove flaking rust on frame. Drill
hole in the most corroded wall. The hole
must be welded after to prevent corrosion
and water infiltration. Filled hole must be
painted to prevent corrosion.
CAUTION
Holes and welding can increase the risk of
crack initiation. Ultrasonic wall thickness
gauge method is recommended.
FIGURE 6: CLEANED SPOT ON STRUCTURAL MEMBER
FIGURE 7: HOLE DRILLED IN STRUCTURAL MEMBER
MI15-18 / Page 4 / 6
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