During the development of the technique we succeeded to take into consideration the effect of confounding factors (temperature, roughness, etc.), allowing to measure the speed of ultrasonic surface waves with sufficient accuracy for the prediction (0.05%).

Determination of residual life of metal, such as bends (bent pipe elements), is performed using the proprietary technique, based upon the features of propagation of ultrasonic waves on the forming pipe on extended (convex) part of a bend after surface preparation. These two parameters determine the density of creep flow micropores. After it the residual life of metal is calculated using particular dependence.

At present, the technique implemented in "UralORGRES" company Karmanovskaya TPP, as well as Tumenenergo (Production and Repair Services "Tyumenenergo"), Udmurtenergo, Krasnoyarsk TPP-2.

From 1989 to 2002 we examined more than 15 thousand bends of steam pipelines of various sizes on many thermal power plants, discovered more than 100 bends with macro- and micro-cracks, ie at the pre-fracture stage.

The technique is patented and was repeatedly discussed at conferences and in press.

The method is based upon the following facts and theories:

1. There are two states of micro damages of microstructure, which can be observed at metallographic specimen: intercrystalline creep micropores either exist or not.
2. Microdamage, i.e. specific amount of intercrystalline micropores increases over time.
3. Increase of specific amount of intercrystalline micropores over time can be fairly well described by a parabolic function of the power;
4. There is a tolerance of microdamages, which is characterized by a specific maximum number of creep micropores; after reaching the critical state the mechanism of destruction changes : microcracks begin to form and further forming a crack.

Inspection includes:

1. Descaling and grinding of the axial channel to hydraulic roughness (Rz) 10 microns or better.
2. Visual inspection of the channel using the periscope with 4x zoom or more.
3. Ultrasonic testing of metal by immersion method.
4. Eddie current test of axial channel surface.
5. Geometry of channel diameter and calculation of residual deformation.

If any defects detected, the following inspections to be performed:

− capillary (color or fluorescent)penetrant inspection of the channel surface;
− measure the depth of detected cracks;
− determination of the metal state by the surface ultrasonic waves speed variation.

The unique technique provides effective descaling while preserving the metal. As a result, the information on the rotor deformation is preserved. See the picture of helical deformation of the axial channel due to shaft twisting as an example. After the cleaning is done, grinding of the channel providing roughness better than Rz 10 micron. An important advantage of our method is the speed of cleansing, which allows you to prepare the axial channel of the rotor for controls in 5-6 hours.

For detailed information about our methods click here

The unique method of specimen preparation for creep micropores test appeared as a result of research and thanks to микроскопу ММПУ To learn more about etching microporosity read the article of Vladimir Permikin.