Boiler - Creep Failure
The end of useful service life of the high-temperature
components in a boiler (the superheater and reheater tubes and
headers, for example) is usually a failure by a creep or
stress-rupture mechanism. The root cause may not be elevated
temperature, as fuel-ash corrosion or erosion may reduce the
wall thickness so that the onset of creep and creep failures
occur sooner than expected.
Creep is one of the most
serious high temperature damage mechanisms. It involves
time-dependent deformation and high temperature creep cracking
generally develops in an intercrystalline manner in components
of engineering importance that fail over an extended time. These
include boiler superheater and other components operating at
high temperature, petrochemical furnace and reactor vessel
components and gas turbine blades.
While creep failures are expected for superheaters and reheaters
operating at design conditions, deviations from these parameters
will promote early failures.
Once the condition of the component
has been determined by means of metallurgical examination, the
expected time to failure must be estimated, primarily in order
to schedule future maintenance, inspection activities and to
prevents premature catastrophic fracture or rupture.