VMM Software

The Testers Manual

 Appendix C Structural Integrity and Corrosion

1. Introduction
3. Corrosion Assessment
5.  Failure criteria not within prescribed areas components
The effect of corrosion on the safety of a vehicle depends on the extent of the corrosion and the function of the section or component on which the corrosion has occurred.  

A small amount of corrosion in an important part of a vehicle structure can make a vehicle unsafe where it compromises the load bearing capacity of the structure.   On the other hand, excessive corrosion on non structural sections may have little or no effect on the vehicle’s safety.  
Corrosion of a particular part, such as a door sill, may be very important on one type of vehicle construction, but of less importance on another. This can be seen in figures 1 to 4 at the end of this Appendix, where the shaded portions indicate the important load bearing parts of various 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 and thumb pressure.  
If necessary, the Corrosion Assessment Tool should be used to assess the extent of any corrosion by careful scraping or light tapping of the affected areas.  
It is important that use of the Corrosion Assessment Tool is restricted to ascertaining that the failure criteria are met and not used for heavy scraping or poking of the affected areas.
Excessively corroded metal, or metal treated with filler, emits a duller sound than unaffected metal. It is not permissible to apply heavy impact blows or to use a sharp instrument to probe at the structure


Structural fractures, damage or corrosion not within the ‘prescribed areas’ are dealt with in Section 6 of the Manual.  The diagrams at figures 1 to 4 show the main load bearing members of various types of vehicle construction which need to be considered.
2. Prescribed Areas
4. Failure criteria within ‘prescribed areas’
6.  Highly stressed components
Certain areas of the vehicle structure are particularly important for the safety of a vehicle. Particular attention must be paid to these areas during an inspection.   These areas are:
·  The load bearing parts of the vehicle to which the testable items defined in Sections 2, 3 and 5 of the Inspection Manual are mounted, and
·  any load bearing or supporting structure or supporting panelling within 30cm of the mounting location.
To give an example; during the examination of a seat belt mounting on an inner sill, consideration must be given to the outer sill (or the sill reinforcement if the outer sill is a plastic cover), door pillar, floor panel or any other structural part within 30cm of the component’s mounting point.  It is accepted that it is not possible to assess some of these areas due to the fitment of body trim etc.
To give an example; during the examination of a seat belt mounting on an inner sill, consideration must be given to the outer sill (or the sill reinforcement if the outer sill is a plastic cover), door pillar, floor panel or any other structural part within 30cm of the component’s mounting point.  It is accepted that it is not possible to assess some of these areas due to the fitment of body trim etc.
The severity of general or local corrosion in highly stressed components, such as steering and suspension arms, rods, levers etc. can be assessed by lightly tapping or scraping with the Corrosion Assessment Tool.  

In places inaccessible to the Corrosion Assessment Tool, an alternative blunt instrument may be used.  A highly stressed component should be rejected if corrosion has resulted in serious reduction in the overall thickness of the material, or has caused a hole or split.

Welded repairs to highly stressed components such as steering/suspension arms, rods, levers etc are not normally acceptable, other than where the component is made up of sections that are welded together.  In these cases the repair should appear to be as strong as the original design.
7.  Thin gauge steel pressings
8.  Vehicles with separate bodies
 9.  General guidance
It is common to use thin gauge pressings for certain steering and suspension components, mountings, sub- frames and cross members.   These are designed to have minimal material usage with maximum strength, resulting in hollow or open sections or ‘up facing’ areas in which road dirt impregnated with salt or other chemicals collects causing serious but often very localised corrosion.   These types of components require extra vigilance as there may be little evidence of corrosion on initial inspection, but may reveal severe material failure when looked at more closely.
Some vehicle types have bodies and various mechanical components attached to a separate under frame. The frame is the main load bearing structure with a passenger cell and possibly a separate load bed secured on top of the frame, which may also be load bearing or supportive.  
Excessive corrosion within these body panels should only lead to rejection if the failure criteria are met for:
·  Prescribed areas, or
·  is likely to adversely affect the correct functioning of the braking or steering, or
·  body security.
The presenter should be advised of any corrosion or damage which has not yet reached the stage where it meets the criteria for rejection.   However, it may be necessary to refuse to test the vehicle if excessive damage or corrosion could result in injury or further damage to the vehicle and/or testing facility.
10.  Acceptable methods of repair  
 11.    Unacceptable methods of repair
 12.    Testable items mounted to plastic structures
It is essential that repairs to corroded or damaged areas are properly carried out. This requires that suitable materials of appropriate gauge or thickness are used for repairs.   Additionally:

·  Any plating or welding extends to a sound part of a load bearing member.

·  the repair must appear to be virtually as strong as the original structure with only continuous seam welding being acceptable for patch repairs (even if the patch extends beyond the prescribed area).

·  spot welded joints are acceptable where the original panel has been replaced to an existing spot welded flange (provided the original defective panel flange has been removed).  Stitch or plug welding is acceptable as an alternative to spot welding in these cases.  

·  MIG brazing, a combination of adhesive bonding and riveting, or amalgamations of these with other joining methods may be the vehicle manufacturers recommended method of repair.  Such repairs must therefore be accepted unless they are clearly inadequate.
Gas brazing, soldering, adhesive bonding, fibre reinforcement and body filler are bonding processes and are not regarded as strong enough for repairs to load bearing members although they are normally adequate for other repair work.   It is accepted that it is sometimes difficult to identify the repair method after the repair has been covered in paint or underseal.  If the method of repair is in doubt the tester should pass and advise.
Testable items, such as steering racks, sub frames and seat belts, are sometimes mounted directly to plastic structures that do not have metal reinforcement.  

Non-metallic structures must be assessed on their merits. Evidence of weakness such as cracks, separation or delamination within a ‘prescribed area’ or a component flexing on its mounting to the extent that it is clear that it is likely to work loose or break away are reasons for rejection.
 13.    Repairs to non-metallic load-bearing structures
 14.   Panel removal or replacement with different materials
Repairs to non-metallic structures are not acceptable within prescribed areas.  Any repairs outside of these areas should be as strong as the original structure.
On a vehicle of integral construction the strength and stiffness of the whole structure may be seriously affected by any panel being removed or replaced by a panel of different material.  

If it is considered that a modification has significantly reduced the original strength and stiffness of the structure, the tester should fail the vehicle under the appropriate section.  If there is doubt about the effect of the modification the tester should pass and advise.  

It is unacceptable for plastics to replace or reinforce corroded or weak metal in prescribed areas and load bearing sections
Issue Date: 01 January 2012