NPP operation has a significant influence on the rate of degradation of SSCs. Exposure of a SSC to operating conditions (e. g. temperature, pressure, water chemistry) outside prescribed operational limits could lead to accelerated ageing and premature SSC degradation affecting plant safety and availability. In particular, it is prudent to attempt to control the operating environment of inaccessible SSCs where detection and repair of degradation would be difficult and costly.

Since operating practices influence SSC operating conditions, NPP operations staff have an important role to minimize SSC ageing. They can do this by maintaining operating conditions within prescribed operational limits. Examples of such operating practices are:

• Operation within the prescribed pressure and temperature range and rate of change during startup and shutdown to avoid undue transient stresses and the risk of over-stress (this risk varies, depending on the material’s fracture toughness)

• Performing maintenance according to procedures designed to avoid contamination of metal components with aggressive contaminants (such as lead or other reagents containing halogens)

• Maintaining plant heating, ventilation, and air conditioning in a state that keeps plant environments within prescribed (design basis) conditions

• Maintaining thermal insulation on high temperature lines and equipment in good order.

Moreover, good understanding of SSC ageing facilitates optimization of operating conditions and procedures to reduce the rate of normal ageing degradation of some SSCs, hence increasing safety margins and/or service life.