2016 04 Paper: Using FEA and NDT to Save Repairs

Snowy Hydro requested Quest Integrity to carry out a stress analysis and subsequent critical flaw size calculation on their Main Inlet Valve (MIV), Turbine Top Cover and Spiral Casing at Tumut 1 Power Station.
The main aim of the Finite Element Analysis was to ensure that during the upcoming major refurbishment works, the highest stress areas of the MIV, turbine top cover and spiral casing were identified allowing inspections to be focused in these areas. This also assisted with determining the level of defect repairs required.
A finite element model was constructed of each component and used to determine stress levels to be used to calculate critical crack sizes at highly stressed locations. The finite element analysis revealed:
• The worst loading case for each component in terms of overall stress level.
• The locations of the high stressed areas for both the load rejection and maximum operational load cases.
This information was used during the Tumut 1 refurbishment works to focus NDE examinations and to assist in developing the work scope for the weld repairs.
This paper looks at the move from the old thought process of inspect everything and fix everything, to focus on where the critical areas are and, in conjunction with an overall condition assessment, only perform the repairs where structural integrity is at risk.
Significant time and cost savings were made using this process, by having an inspection regime mapped out prior to start of work and critical flaw sizes identified so that time was not lost deciding where weld repairs were needed.
The paper will also discuss how successful this has been and where improvement can be made for the upcoming Murray 1 unit refurbishments.

• Author: Annette Karstensen, Howard Brown
• Exchange: 2016 - Queenstown Meridian
• Company: Snowy Hydro
• Topic: Asset Condition, Asset Management, Cracks, Design Life, FEA, NDE, Refurbishment
• Key Words: 3D Scanning/Mapping, Crack Assesment, Critical, FEA, MIV, NDE, Spiral Case, computerised