Corrosion, section loss and connection failure on plant structures: inspection and repair scopes

Equipment

Pipe racks and supports, conveyor gantries, access platforms, stairs and handrails, transfer-house steel, tank internals and the secondary steel around boilers and turbine decks — hot-rolled sections, plate, grating and bolted or welded connections, protected by a coating system.

Failure modes

General corrosion and section loss where coatings have failed; crevice corrosion at bolted connections and under gusset plates; corrosion under insulation on pipe supports; cracked welds at fatigue-loaded connections; deformed members from impact or outage lifts; and grating and handrail deterioration that fails the access before the structure.

Common causes

Coating systems past their life; water traps in the geometry; chemical and ash-water spray; vibration from conveyors and fans; overloading from added pipework and equipment; and no structural inspection regime.

Inspection

Walk the structure with a checklist by member; photograph and mark defects; measure remaining thickness with ultrasonics where section loss is visible; check bolt condition and tightness; test suspect welds by dye penetrant or magnetic particle; assess grating and handrails for compliance. Grade each defect so the repair scope can be prioritised.

Maintenance

Maintain the coating system before it fails; keep drainage clear so water does not stand on steel; remove ash and fines that hold moisture; and inspect at a fixed interval so section loss is trended, not discovered.

Repair

Define the scope member by member: replace members below the design section, plate or sister damaged members, replace bolts and connections, repair welds, and re-coat to a specified system after preparation to ISO 8501-1. Repairs on live plant are planned with temporary supports, a lifting plan and a fall-protection plan, and welded repairs are made under qualified procedures.

Replacement

Replace whole structures where section loss is general, where the structure no longer suits the loads it carries, or where the cost of piecemeal repair over an outage cycle exceeds a new structure fabricated off-site and erected in the window.

Umbusso capability

Umbusso fabricates and erects structural steel and repairs existing structures under an ISO 3834-2 welding system with AWS D1.1 in scope and CIDB 7ME and 7CE gradings. In September 2022 the company installed and modified structural steel beams inside a water tank at an Eskom power station under confined-space controls.

This article is general technical guidance. Intervals, standards and methods must be confirmed against the current regulation, the manufacturer’s documentation and the site standard before they are applied.