Research published by the National Physical Laboratory (NPL) and the University
of Birmingham has won the T P Hoar Prize from the Institute of Corrosion, for
the best paper published in Corrosion Science in 2011.
The research looked at the problem of crack formation in disc steel used in
steam turbines in the power industry. Specifically, a combination of
measurement and modelling techniques were carried out to study the transition
from a corrosion pit to a stress corrosion crack. The published results
demonstrate that, contrary to popular belief, cracks form near to the surface of
the steel at the mouth of a corrosion pit rather than at its base.
If a component within a steam turbine fails, it is costly in terms of repair,
downtime and potentially lost energy generation. NPL carries out research to
characterise the evolution of corrosion damage to these components to develop
effective testing methods and framework for life prediction.
In this research a radiography-based technique called X-ray tomography was
used to study the pit-to-crack transition process in detail on specimens of a
medium strength turbine disc steel. This is a non-destructive technique that
allows the interior structure of solid materials to be visualised. The images
obtained clearly show that the majority of the cracks form above the base of the
pits.
Finite element analysis was then used to model the stress and strain around a
corrosion pit. This demonstrated that localised plastic strain occurs just below
the pit mouth, explaining the observed crack formation.
This research improves the understanding of how cracks form under certain
conditions is vital when assessing the lifetime of components within steam
turbines and that of power plants in general. It will also help when designing
and choosing materials for a new generation of more energy efficient and cost-
effective power plants.
The image above shows an X-ray tomography of turbine steel showing
corrosion pits and cracks.
Click link to read the full paper.
of Birmingham has won the T P Hoar Prize from the Institute of Corrosion, for
the best paper published in Corrosion Science in 2011.
The research looked at the problem of crack formation in disc steel used in
steam turbines in the power industry. Specifically, a combination of
measurement and modelling techniques were carried out to study the transition
from a corrosion pit to a stress corrosion crack. The published results
demonstrate that, contrary to popular belief, cracks form near to the surface of
the steel at the mouth of a corrosion pit rather than at its base.
If a component within a steam turbine fails, it is costly in terms of repair,
downtime and potentially lost energy generation. NPL carries out research to
characterise the evolution of corrosion damage to these components to develop
effective testing methods and framework for life prediction.
In this research a radiography-based technique called X-ray tomography was
used to study the pit-to-crack transition process in detail on specimens of a
medium strength turbine disc steel. This is a non-destructive technique that
allows the interior structure of solid materials to be visualised. The images
obtained clearly show that the majority of the cracks form above the base of the
pits.
Finite element analysis was then used to model the stress and strain around a
corrosion pit. This demonstrated that localised plastic strain occurs just below
the pit mouth, explaining the observed crack formation.
This research improves the understanding of how cracks form under certain
conditions is vital when assessing the lifetime of components within steam
turbines and that of power plants in general. It will also help when designing
and choosing materials for a new generation of more energy efficient and cost-
effective power plants.
The image above shows an X-ray tomography of turbine steel showing
corrosion pits and cracks.
Click link to read the full paper.
