The high temperature sections of power and combined heat
and power (CHP) boilers are designed for some de facto
expected but finite life. Several significant damage
mechanisms must be taken into account, particularly in
superheaters and reheaters that are designed for creep
but also suffer from thermal degradation, external
erosion and corrosion, and internal steam oxidation that
will gradually increase the metal temperature. As rising
temperature tends to accelerate all damage mechanisms,
major effects can be expected from the internal oxide
growth. The feedback loop is taken into account in
procedures to predict superheater life from known tube
dimensions, time in operation, and other initial data.
The oxide effect can be mitigated by internal cleaning,
but in-service spallation of a relatively thick internal
oxide can also become significant in old plants.
Spallation can create problems but extends the tube life
by keeping the wall cooler than with an adherent oxide.
Examples are shown for boilers with more than 150 000 h
|Conference||BALTICA VIII - International Conference on Life Management and Maintenance for Power Plants|
|Period||18/05/10 → 20/05/10|