4.1.3 Material selection - part 1
The need for a materials selection strategy has been touched upon briefly in the consideration of CW quality. The objectives of such a strategy are to ensure that the costs associated with leaking condenser tubes are minimised throughout the life of the plant. This can be established by studying the following technical and economic considerations:
- The estimated life of candidate tube materials from test rig trials, manufacturer's literature, experience, etc.
- The predicted number of outages and associated costs.
- The number of retubes required.
- The capital costs of materials and retubing costs.
- Heat transfer efficiency and thermal performance effects.
- Compatibility with other CW system materials.
Experience has indicated that studies of this type yield materials which initially appear to be an expensive choice, but because of their inherently better corrosion-resistant properties show a higher economic return when plant availability and retubing costs are taken into consideration.
As previously illustrated in Fig 4.9, the copper-based tube materials are liable to varying degrees of impingement attack, depending upon the operating conditions. These materials, however, can be usefully employed providing that a good margin of safety is maintained between operating conditions and the impingement attack threshold, and providing that steamside corrosion conditions are satisfied. Where freedom from erosion or steamside corrosion cannot be assured, it is necessary to use a material such as titanium.