Challenge
Sydney Water supplies potable water, wastewater, recycled water, and stormwater services to over 5 million people in Greater Sydney and the Illawarra, delivering over 1.5 billion litres of water daily. They manage over 200 potable water reservoir tanks, some exceeding 100 meters in diameter. Many of these tanks are decades old with minimal maintenance inspections.
Historic refurbishments of smaller tanks revealed significant degradation of internal linings and tank shells, necessitating the reduction in height of some tanks due to poor wall thickness. This raised concerns about the condition of these assets.
Previous condition assessments involved divers performing close visual inspections, which proved inadequate in identifying areas of steel deterioration.
Solution
Using Pulsed Eddy Current (PEC) techniques, Inspectahire developed a test methodology to take Wall thickness measurements around the circumference of the tank on the highest two Strakes (rows of Plates) to give a general profile of the condition of the carbon steel plates that combine to make up these strakes.
PEC is an inspection technique for inspecting carbon steel objects such as pipes and vessels, without the need for contact with the steel surface. PEC can measure percentage variations in steel thickness through any non-conductive and non-ferromagnetic materials between sensor and surface such as air, insulation material, concrete, plastics, coatings, seawater and marine growth, paint, deposits, oil, composite repairs, fireproofing, “scabs” aluminium sheeting and other non-magnetic insulation covers; so ideal for Corrosion Under Insulation (CUI) applications. In the case of this operation, the Corrosion is under insulation on the inside and thus invisible as it propagates.
Using an EWP (Elevated Work Platform) measurements were taken over the surface of the strakes in an agreed and methodical manner to develop a profile of each section around the circumference of the tank. A colour-coded spreadsheet is generated. to allow the reviewer to quickly find and assess any areas of potential concern. The sample below shows an example table with values depicting the remaining percentage of “good” steel left.
Result
The data provided by Inspectahire enabled Sydney Water to better plan the time, budget, and scope for significant asset interventions on the tanks. Inspectahire's inspections and follow-up consultancy helped focus subsequent work scopes, allowing for faster inspections of larger tanks by targeting areas of concern identified through a correlation between inspection results and visual inspections during tank drainage.
For the latest reservoir tank workover in Sydney’s Western Suburbs, the data has helped define the project scope. Inspectahire has been asked to support the workover by conducting visual inspections of the tank roof support beams, followed by PEC operations to assess material degradation. This aims to reuse the beams for a new roof structure. Additionally, floor scanning to assess the floor plate condition and PEC assessments of the tank skirt will be provided to supply essential data for the tank's reinstatement post-workover.
Inspectahire has now completed multiple campaigns on behalf of Sydney Water on the condition assessments of its assets and has been engaged to provide consultancy, and service provision of inspection to three of Sydney Water’s tier 1 suppliers.
