**4. Technical diagnostics of hydro turbines**

The technical condition assessing of hydro turbines is crucial for the estimated assessment of residual life. Such works are performed in accordance with the provisions of the norms and standards [11, 12]. These works include a wide range of studies of actual state of hydraulic turbines by destructive and nondestructive control methods [13]:


In addition to the listed methods of nondestructive testing, stress-strain state studies using strain-gauge methods [14] and optical methods of electronic speckle interferometry [15] are performed.

*Laboratory, Bench, and Full-Scale Researches of Strength, Reliability, and Safety… DOI: http://dx.doi.org/10.5772/intechopen.88306*

This complex of methods and means is used in diagnosing the technical condition of hydro turbines with over standard operating life. Such work was carried out at the abovementioned hydropower stations in recent years. The main attention was focused on the most loaded structures: the impeller, the turbine shaft, the turbine cover, and the blade of guide.

The systematization and classification results of nondestructive testing showed that the main defects of the impeller blades of hydro turbines are:


#### **Figure 3.**

4.Predicting the growth of cracks in the process of operating time for the

6.Resource management due to the choice of optimal operational parameters,

7. Increased interest of resource estimates of hydraulic turbines in the absence of the recommended calculation methods and regulatory requirements for

8.The lack of systematic studies of the residual life of hydro turbines, similar to how it was done for the turbines of thermal and nuclear power plants

Thus, the problem of calculation and experimental evaluation operational state of hydro turbines has a number of unsolved or difficult tasks that require in-depth basic research on the nature of the stress-strain state of hydraulic units, features of damage development mechanisms, and degradation of mechanical properties of

The technical condition assessing of hydro turbines is crucial for the estimated assessment of residual life. Such works are performed in accordance with the provisions of the norms and standards [11, 12]. These works include a wide range of studies of actual state of hydraulic turbines by destructive and nondestructive

• Experimental studies of metal and welded joints (measurement of hardness, determination of mechanical properties, conducting metallographic studies,

• Visual measurement control of geometry, surface defects, and shape defects

• Nondestructive penetration control for substance detection of surface defects

• Ultrasonic thickness gauging of elements and determination of the internal

In addition to the listed methods of nondestructive testing, stress-strain state studies using strain-gauge methods [14] and optical methods of electronic speckle

• Nondestructive ultrasonic testing of structural elements and welds for

5.An increase in the share of the numerical experiment due to partial

purpose of determining the optimal time between repairs

taking into account the capabilities of the power system

service life and criteria for the admissibility of operation

• Analysis of design, maintenance, and repair documentation

and determination of chemical composition)

with the determination of their sizes

detection of internal defects and cracks

stratification of the metal

interferometry [15] are performed.

**44**

• Nondestructive testing of structural elements and welded joints

**4. Technical diagnostics of hydro turbines**

materials.

control methods [13]:

replacement of the model and natural experiments

*Probability, Combinatorics and Control*

*Corrosion damage and cavitation damage metal of impeller blades.*

**Figure 4.** *Cracks in metal of impeller blades.*

**Figure 5.** *Internal defects of impeller blades, detected by ultrasound tomography.*

½ �¼ *<sup>N</sup>* <sup>1</sup> 4*nN*

> *<sup>σ</sup>r*<sup>0</sup> <sup>¼</sup> *γεβ K<sup>σ</sup> σ*�<sup>1</sup>

*Laboratory, Bench, and Full-Scale Researches of Strength, Reliability, and Safety…*

of the medium, scale factor, and surface quality; and *Kσ* is stress

concentration factor.

pattern indicator.

loading cycles.

following formulas:

*dl dN* <sup>¼</sup> *<sup>q</sup>*

**47**

*π* 8

*Kth R*0*:*<sup>2</sup> � �<sup>2</sup>

For single-frequency loading mode

For multifrequency loading mode

8 ><

>:

*Nl* <sup>¼</sup> <sup>1</sup> *nl*

1 þ ð Þ 1 � *β*

is determined by the following formula:

*DOI: http://dx.doi.org/10.5772/intechopen.88306*

*Eec σ<sup>a</sup>* � *σr*0*=*ð Þ 1 þ *σr*�1*r* � �<sup>2</sup>

where *σ*�<sup>1</sup> is fatigue limit of given loading mode; *σ<sup>m</sup>* is stress average of cycle; *σ<sup>a</sup>* is stress amplitude of cycle; *r* is the asymmetry coefficient of the loading cycle; *γ*, *ε*, and *β* are dimensionless coefficients that take into account the influence

The estimated allowable number of loading cycles at blade and blade frequencies

where *N*<sup>0</sup> is the base number of loading cycles and *m* is dimensionless fatigue

where *σai* is stress amplitude at the frequency *ωi*, *ω*<sup>1</sup> is the frequency of reduc-

The total accumulated fatigue damage for the considered loading modes is defined as the sum of the ratios of the actual *Nei* and the calculated loading cycles:

The number of cycles *Nl* at the stage of crack growth is determined by the

2 ð Þ *<sup>m</sup>* � <sup>2</sup> *CY <sup>m</sup>*

> <sup>1</sup> � *<sup>K</sup>*<sup>e</sup> <sup>2</sup> *th* � �<sup>2</sup>

where *q*, *β*, and *μ* are parameters of the cyclic crack growth diagram, *K*e*th* ¼ *Kth=KC* and *K*e*max* ¼ *Kmax=KC* are relative threshold and maximum stress intensity factors, *Kc* is the crack resistance characteristic of steel, *ω* is relative

frequency of loading, and *Kth* is the threshold stress intensity factor.

*Nei*

<sup>2</sup> *σ<sup>m</sup>*

*K*e 2

1 *l m*�2 2 0

� *<sup>K</sup>*e<sup>2</sup>

*max* � *<sup>K</sup>*e<sup>2</sup> *th* � �<sup>2</sup>

� <sup>1</sup> *l* ð Þ *m*�2 2

*max* � *<sup>K</sup>*e<sup>2</sup> *th* � �<sup>2</sup>

*ωμ*<sup>2</sup>

" #

*<sup>d</sup>* <sup>¼</sup> <sup>X</sup> *i*

The influence of the multifrequency component of the loading mode from Karman vortices is taken into account through the reduced stress amplitude:

*σr*<sup>0</sup> *σa* � �*<sup>m</sup>*

½ �¼ *<sup>N</sup> <sup>N</sup>*<sup>0</sup> *nN*

*<sup>σ</sup><sup>a</sup>* <sup>¼</sup> <sup>X</sup>*<sup>n</sup> i*¼1

tion, *α* is dimensionless coefficient taking into account the influence of the multifrequency nature of loading*,* and *nN* is the safety factor by the number of

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi <sup>1</sup> � *<sup>σ</sup>m=*½ � *<sup>σ</sup>* <sup>p</sup> *,*

*<sup>σ</sup>ai*ð Þ *<sup>ω</sup>i=ω*<sup>1</sup> *<sup>α</sup>* (13)

½ � *<sup>N</sup>* <sup>≤</sup><sup>1</sup> (14)

*ωμ*<sup>2</sup>

9 >=

1*=*ð Þ *β*�1

>;

(11)

(12)

(15)

(16)

**Figure 6.** *Distribution corrosion damages of length (a) and depth (b).*

The nature of the defects and damage is presented in **Figures 3**–**5**. Similar defects were detected and investigated previously in the impellers of the Sayano-Shushenskaya HPP and Krasnoyarskaya HPP [6, 7].

Statistical analysis of the nondestructive testing results for cavitation erosion zones allowed determining the main geometrical parameters for these defects: the length, width, and depth (**Figure 6**).
