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Appendix
C Structural Integrity and Corrosion
1.
Introduction
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3.
Assessment
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5.
Highly stressed components
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The
effect of corrosion on the safety of a vehicle depends on
- Its extent
- The function of the section on which it has occurred
A small amount of corrosion on an important part of a vehicle
structure can make a vehicle unsafe where it destroys the continuity
of the load-bearing structure.
On the other hand, heavy corrosion of unimportant sections may
have no effect on the vehicle's safety.
Corrosion of a particular part, such as a body sill, may be
very important on one type of construction, but of less importance
on another. This is shown in figures A to D where the shaded
portions indicate the important load bearing parts of different
typical vehicle constructions. |
Having
identified the important load bearing members and 'prescribed
areas' on a vehicle, the tester should determine whether they
are excessively corroded, firstly by visual inspection and then
by finger/thumb pressure.
If necessary careful scraping or light tapping of the affected
areas with the Corrosion Assessment Tool is permitted.
Excessively corroded metal, or metal treated with filler, emits
a duller sound than does unaffected metal. It is not necessary
to apply heavy impact blows or to use a sharp instrument to
'dig' at the structure. |
The
severity of general or local corrosion in highly stressed steering
and suspension components (eg. arms, rods, levers etc) can be
assessed by lightly tapping or scraping with the corrosion assessment
tool.
A small screwdriver may be used to push and probe, but only
in places inaccessible to the corrosion assessment tool.
A highly stressed component should be rejected if it has been
- seriously reduced in overall thickness by corrosion, or
- local corrosion has resulted in even a small hole or split. |
2.
Prescribed Areas
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4.
Failure criteria
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To
assist with the assessment of corrosion sections 2, 3 and 5
of the manual identify the parts of the vehicle structure which
are particularly important and to which particular attention
must be paid during the inspection.
These are:
- The load bearing parts of the vehicle to which certain testable
items (as specified in section 2, 3 and 5) are mounted.
- Any structure or panelling which is supportive to either the
component mounting or its load bearing member within 30cm of
the mounting location. eg. In the examination of a seat belt
mounting on an inner sill, consideration must be given to the
outer sill, door pillar, floor panel, wheel arch or any other
supportive structure within 30cm of the component mounting point.
Section 6 of the manual deals with structural cracks, fractures,
damage or corrosion not within the 'prescribed areas'. |
Any
part of a load bearing member, or load bearing panelling within
a 'prescribed area', should be rejected if it is weakened by
corrosion to the extent that
- by finger/thumb pressure it does not feel rigid, or
- it crumbles to leave a hole, or
- The Corrosion Assessment Tool
. penetrates, or
. causes the metal component to crumble or disintegrate
(see section6.5 for the vehicle structure not within a prescribed
area).
Severe distortion means distortion considered to reduce the
strength of a component mounting, supporting structure, panelling
or load bearing member significantly. |
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Reproduced from the MOT Inspection Manual by kind permission of
THE VEHICLE INSPECTORATE.
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