Inspections We Carry Out
CS 450 sets out the inspection and reporting requirements for highway structures on motorways and all-purpose trunk roads, and many local highway authorities follow the same regime. It replaced BD 63/17, which is now withdrawn. The standard defines several types of maintenance inspection, each with a different purpose and level of detail.
| Inspection | What it involves | Typical interval |
|---|---|---|
| General inspection | A visual inspection of all parts of the structure that can be inspected without additional access equipment, recording the physical condition of all visible elements. | Every 24 months |
| Principal inspection | A close examination, within touching distance, of all accessible parts of the structure, using suitable techniques such as hammer tapping and, for weathering steel, repeated thickness measurements. | Every 72 months, or up to 12 years where a risk-based interval is agreed |
| Special inspection | Detailed investigation of a particular element, area or defect that is causing concern, agreed with the Technical Approval Authority. | As required |
| Acceptance inspections | Pre-opening, defects liability, transfer and handback inspections, which take the form of a principal inspection. | At handover points |
Where Coating And Corrosion Expertise Makes A Difference
A principal inspection must record the location, severity, extent and type of all defects. On steel and composite bridges, a large share of those defects are coating breakdown, corrosion and section loss. An inspector who can tell the difference between cosmetic chalking, early underfilm corrosion and active pitting gives the asset owner a far better basis for maintenance planning.
Where a general or principal inspection shows that coating or corrosion needs a closer look, we can extend the scope into a full coating condition survey or an NDT corrosion survey during the same visit, instead of mobilising a second team later.
- Coating breakdown, blistering and rusting recorded against recognised rating scales
- Paint film thickness and adhesion measurements where coating life needs to be predicted
- Ultrasonic thickness readings at bearings, joints, drainage points and hollow sections
- Paint sampling for lead and other hazardous materials ahead of maintenance painting
- Weathering steel patina and residual thickness checks in line with CD 361
Structures We Inspect
CS 450 applies to a wide range of highway structures, not only bridges. We inspect steel, composite and concrete bridges, footbridges, culverts, retaining walls, sign and signal gantries, cantilever masts and other steel highway structures, as well as rail structures for rail asset owners.
Risk-Based Principal Inspection Intervals
CS 450 allows the principal inspection interval to be extended to 8, 10 or 12 years where a risk assessment supports it and the Technical Approval Authority agrees. Some structures are excluded, including special structures, most complex structures, bridges with severe marine exposure, structures over an operational railway and structures in poor condition.
Good-quality condition data is what makes a longer interval defensible. Detailed coating and corrosion records from the last principal inspection give the owner the evidence needed to support, or reject, an extended interval.
Inspection Competence
CS 450 requires inspections to be carried out by competent inspectors and senior inspectors, and requires a certified senior inspector to lead inspections of complex and special structures. The Bridge Inspector Certification Scheme, run by Lantra under National Highway Sector Scheme 31, is the recognised route to certification. We plan every inspection team so it meets the competence requirements for the structure being inspected.
Reports And Records
Inspection records are prepared in the format the asset owner requires, including element condition data used to calculate condition performance indicators on a 0 to 100 scale. Reports include photographs, defect locations, maintenance recommendations and any items needing urgent attention, and are delivered in time for the owner to meet the CS 450 requirement to upload records within six weeks of the inspection.