Corrosion Protection Failure to Cut Structural Bolts
Structural steelwork bolts were cut down with a grinder after installation, damaging or removing the protective coating from the exposed threaded ends and adjacent nuts. The untreated surfaces have subsequently corroded. Any site cutting or coating damage must be properly prepared and repaired using an approved, compatible corrosion-protection system suitable for the specified environment and original finish.
- NCQLE reference
- NCQLE-2026-00023
- Quality topic
- Defects and corrective action
- Lesson type
- Failure
- Evidence rating
- Experience
- Published
- 2 August 2026
- Last reviewed
- 2 August 2026
Evidence basis: Supported by relevant professional experience. This learning is provided for professional consideration and does not replace project-specific competent advice, statutory duties or contractual requirements.
Context
The issue was identified during an inspection of structural steelwork fixings located in an area exposed to moisture and weathering. The bolts had been shortened on site after installation, leaving the cut threaded ends and damaged areas of the nuts without effective corrosion protection. Visible rusting had developed before the connection was enclosed or completed. The structural bolts had been shortened on site using a grinder after installation. This removed the protective coating from the cut ends and damaged the coating on parts of the exposed threads and nuts. The affected surfaces were not subsequently treated, allowing visible corrosion to develop on the fixings and surrounding steelwork.
The transferable lesson
Any cutting, grinding or adjustment of coated structural fixings can expose unprotected steel and invalidate the intended corrosion-protection system. All damaged areas must be identified, correctly prepared and repaired immediately with an approved coating compatible with the original finish and the environmental exposure conditions. Fixing lengths should be coordinated before installation to minimise unnecessary site cutting.
Recommended action
Specify the correct bolt lengths before installation and avoid unnecessary site cutting. Where shortening is permitted, obtain approval from the structural engineer and follow the fixing manufacturer’s requirements to ensure thread engagement and connection performance are maintained. After cutting, remove sharp edges and corrosion, prepare the exposed metal, and apply an approved compatible repair coating to the cut end, damaged threads, nut and surrounding steelwork. Inspect and record the repair before the connection becomes concealed or inaccessible.
Limitations and application
The repair method will depend on the fixing type, protective finish, connection design and environmental exposure. Site cutting may not be permitted for preloaded, high-strength or proprietary fixings and must not reduce the required thread engagement or affect the connection’s structural performance. Repair coatings must be compatible with the original galvanizing or paint system and must not interfere with tightening, inspection or future removal. The structural engineer, coating manufacturer and fixing supplier should confirm the final treatment.