Creep Strain Measurements

Residual life of structural components exposed to creep rupture
The stress-to-rupture behaviour of structural components starts at temperatures over 450°C. Operation in excess of the calculated life - as a rule 200,000 operating hours - is possible. This however requires observation of the component with respect to damage to it and to its elongation development - reaching the critical tertiary creeping area.
Structure replica examinations are carried out and creep strain sensors installed on the structural component for determining residual. Readings and assessments are carried out at given intervals of time.
In many cases it was possible to considerably extend the service life.

Creep behaviour
After the relatively short primary creep phase, secondary creep begins. Secondary creep is characterised by increasing linear elongation. The tertiary creep is critical, as the strains grow exponentially.
Seen under a microscope, damage begins to occur in the structure. This can be detected with the aid of structure replica technology and classified in particular categories of damage.

Pipe bends in power stations are particularly affected by creeping, e.g. due to ovalness.

Application of creep strain technology
We use capacitive sensors. They are mounted onto the structural component at particular points. The sensors are protected against outside influences. Before use they are tested in the laboratory for long-term stability and adapted to suit the respective material.