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.
2. Prescribed Areas
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. e.g. In the examination of a seat belt mounting location on an inner sill consideration must be given to the outer sill, door pillar, floor panel, wheel arch or any other supportive structure within 30 cm of the component mounting point. Section 6 of the manual deals with structural cracks, fractures, damage or corrosion not within the”prescribed areas”.
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.
4. Failure criteria
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 section 6.5 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.
5. Highly stressed components
The severity of general or local corrosion in highly stressed steering and suspension components (e.g. 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.