Ageing assets: refurbish or replace?
Probably the oldest conundrum of them all for owners, operators and maintainers is whether to refurbish an existing asset or just replace it. At what point does refurbishment become untenable or uneconomic and the only option left is replacement?
The logical view has to be that replacement of an asset should only become necessary once the asset has reached the end of its useful life. The problem arises when you try to establish when this milestone has been reached?
This is a relatively simple exercise when the asset (such a water control gate or a movable bridge) has all the obvious signs of having little or no time left before it has to be replaced, often exemplified by excessive corrosion, degradation of moving parts or sealing systems and possibly failure of operating equipment to function as required.
The more difficult decision to be made is when there are no obvious signs; how then does one assess the residual life.
When there is an existing set of Operations and Maintenance manuals, these may contain details on the design life of particular pieces of equipment or on the assembly as a whole, for example, a gate may have a design life of 50 years. However, included within the overall gate assembly may be electrical and hydraulic operating equipment which has a design life of 25 years (or an inherent requirement to be re-planted every 25 years).
This leads to the conclusion that it is not a straightforward exercise to determine whether all or just parts of an overall assembly will need either refurbishment or replacement.
Careful assessment of the amount of any corrosion present within a steel structure will permit residual strength calculations to be undertaken using calculations or computer-aided structural assessment techniques such as Finite Element Analysis. Comparison of residual strength vs required strength will provide an absolute indicator as to whether intervention is necessary. It is also worth remembering that the original designer of the structure may have used different, perhaps lower, partial load factors applicable at that time and that the existing structure may therefore not conform to modern standards anyway. This does not mean that the structure will fail, so part of the assessment will always rely on experience and good engineering judgement to make the final call.
Ultimately, the degree of intervention will be determined by the extent of refurbishment needed to achieve the required strength. It should not be forgotten that it may ultimately be more cost-effective to build a replacement than attempt refurbishment.
If the issues raised above are of interest to you, then please contact KGAL to find out how we can assist you. You can find out more about our approach to asset inspection here.