2.3 Structure, Frontal-Impact Systems & Corrosion Decisions

Decide whether the load path remains sound

The body is not judged by appearance alone. Its structure maintains suspension geometry, steering and brake mountings, occupant survival space, and restraint loads. Begin with the General Vehicles structure diagram and shaded areas, then use the separate component page when corrosion lies near a seatbelt, brake, suspension, or door mounting.

Main reasons for rejection

Reject where visible damage compromises structural integrity, including deformation, cracking, fracture, insecure sections, or a poor repair. Corrosion decisions on the structure page include:

• an individual area of corrosion larger than 50 mm in diameter in a shaded structural area;
• any corrosion within 150 mm of the top of an A-pillar; and
• corrosion of any size when it has weakened a load-bearing part of the vehicle structure.

These rules must be read together. A small hole can fail if it has weakened a load path. Surface oxidation can pass when sound metal and strength remain. Several nearby patches are assessed as the VIRM directs; do not hide behind an arbitrary circle when the surrounding member is clearly weak.

The frequently repeated phrase “150 mm structural zone around every safety mounting” is not the current structure rule. Other VIRM pages do use 150 mm for particular mountings—for example, specified door, brake, or suspension locations—but their exact reason for rejection must be applied on that page.

How to inspect corrosion

Use adequate lighting and view both sides where accessible without dismantling. Look for swelling seams, perforation, flaking scale, distortion around fasteners, separated spot welds, cracking in underseal, fresh filler, or coatings that conceal a repair. Gentle approved assessment may establish whether metal is sound; destructive testing is not authorised.

Trace the member and ask what it carries. Sills, pillars, rails, crossmembers, floors around mountings, subframe attachment areas, and frontal-impact load paths require careful attention. If a defect is concealed and cannot be decided using the VIRM method, follow the escalation or evidence process rather than making up a pass.

Repairs and frontal-impact features

A repair must use suitable material and workmanship and restore the member’s function. Reject a patch that is insecure, incompletely attached, poorly welded, severely distorted, or already corroding so that integrity is affected. Cosmetic filler or underseal does not replace structural metal.

Check the frontal-impact provisions applicable to the vehicle and its date. Missing or compromised original structural elements, or a modification affecting a frontal-impact system, can require specialist certification. The evidence is the certification listed in the applicable VIRM modification table—typically a valid LVV plate or accepted proof where required. LT400 is a heavy-vehicle repair certificate and is not a universal light-vehicle structural-repair document.

Decision sequence

1. Locate the defect on the VIRM structure illustration.
2. Decide whether it is corrosion, deformation, fracture, or repair workmanship.
3. Measure an individual corrosion area where the 50 mm rule applies.
4. Check the top-A-pillar 150 mm rule.
5. Decide whether load-bearing strength is reduced regardless of size.
6. Open any separate component page for a nearby mounting.
7. Verify required modification or repair evidence before passing.

Scenario

A 35 mm perforation lies in a floor area that appears inside a shaded zone. Size alone might seem below 50 mm, but the hole has spread around a seat mounting and the metal flexes under reasonable load. The separate seat-anchor requirement and the loss of load-bearing strength control: the vehicle is rejected.

Distinguish rust, corrosion damage, and poor repair

Light surface rust can show discolouration while full metal remains; corrosion damage involves metal loss, commonly pitting, swelling, flaking or perforation. Remove only loose contamination by the permitted method. Fresh paint, seam sealer or underbody coating may justify closer visual inspection but is not itself a failure.

For a repaired zone, inspect the edges and adjacent parent metal, attachment continuity, drainage, heat distortion, and whether load paths and component geometry remain credible. A repair can fail for workmanship or remaining weakness even if its patch is larger than the original hole. Conversely, do not demand proof not required by the applicable VIRM route merely because a repair is visible.