Pitting Corrosion Damage for Prediction Useful Life of Geothermal Turbine Blade

Cuevas-Arteaga C; Rodriguez JA; Clemente CM; Rodríguez JM; Mariaca Y

doi:10.12691/ajme-2-6-3

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Pitting Corrosion Damage for Prediction Useful Life of Geothermal Turbine Blade

Cuevas-Arteaga C¹, Rodriguez JA^1,, Clemente CM¹, Rodríguez JM², Mariaca Y¹

¹Centro de Investigación en Ingeniería y Ciencias Aplicadas, (CIICAp), UAEM, Cuernavaca, Morelos, Mexico

²Centro Nacional de Investigación y Desarrollo Tecnológico

Abstract

1. Introduction

2. Experimental Models

Abstract

In the last years, the power industry in México has suffered the consequences of some mechanisms of damage that reduce the efficiency in power generation. These mechanisms of damage originate problems in main components as rotors, nozzle blades and others due to losses of pressure, high vibrations, erosion and corrosion. By the type of work fluid, mixture of water-steam and brine rich in salts, geothermal turbines are in a high corrosion environment. The main forms of damage caused by corrosion in a geothermal turbine are crevice corrosion and pitting corrosion. The latter is a damage mechanism through which the useful life is affected. The blades of the last stage in low pressure (LP) in the geothermal turbines are exposed to corrosion by environment and high load cycles which cause failures by corrosion fatigue, crack initiation and crack propagations. In this work, a methodology for the analysis of the failure by pitting corrosion and its consequences in its useful life was obtained. From the results, it is possible to conclude that this corrosion may influence a mechanism of pitting corrosion, which precedence to stress corrosion cracking and corrosion fatigue.

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Keywords: pitting corrosion, blades of geothermal turbine, useful life, damage mechanisms

American Journal of Mechanical Engineering, 2014 2 (6), pp 164-168.
DOI: 10.12691/ajme-2-6-3

Received December 02, 2014; Revised December 14, 2014; Accepted December 16, 2014

Cite this article:

C, Cuevas-Arteaga, et al. "Pitting Corrosion Damage for Prediction Useful Life of Geothermal Turbine Blade." American Journal of Mechanical Engineering 2.6 (2014): 164-168.

C, C. , JA, R. , CM, C. , JM, R. , & Y, M. (2014). Pitting Corrosion Damage for Prediction Useful Life of Geothermal Turbine Blade. American Journal of Mechanical Engineering, 2(6), 164-168.

C, Cuevas-Arteaga, Rodriguez JA, Clemente CM, Rodríguez JM, and Mariaca Y. "Pitting Corrosion Damage for Prediction Useful Life of Geothermal Turbine Blade." American Journal of Mechanical Engineering 2, no. 6 (2014): 164-168.

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1. Introduction

Different studies have been carried out on geothermal turbine blades for early damage detecting and useful life estimation ^[1]. Phenomena related aerodynamic instability cause changes in amplitude of vibrations. This instability produces failure by mechanical fatigue ^[2]. When the frequency of this aerodynamic instability and, external forces of excitation, coincide with one of the natural frequencies of the blades or group of blades, a condition known as resonance occurs affecting useful life of steam turbines. The environment and the work flow where energy is transformed present another two damage phenomena; erosion and corrosion ^[3]. The corrosion is a very costly damage mechanism that has a major impact on the economies of turbomachinery. There are two types of corrosion; mixed corrosion and localized corrosion. The development of damage due to localized corrosion on geothermal turbine surfaces involves complex interactions between deposits and electrolyte films ^[4].

Different studies show that corrosion process in the blades is induced by environment causing pit, local deformation and finally fatigue cracks ^[5]. Pitting corrosion or pitting is considered to be one of the main degradation mechanisms for many metallic materials subjected to corrosive environment. This corrosion mechanics leads to the crack initiation, crack growth and failure in stress corrosion cracking and under tensile stress in corrosion fatigue in geothermal turbine blades in L-0 stages of low pressure (LP). Blades of last stages present different problems that may contribute to the failure process, but the limited operational lifetimes are primarily attributed to corrosion pit, steam turbine corrosion and deposits’ problems and solutions ^[6]. It is important for the development to analyze this behavior and control these mechanisms of degradation to create experimental and numerical models ^[7]. Experimental and numerical models are used to predict the damage and the useful life of geothermal turbine blades ^{[8, 9]}.

The presence of corrosion pit reduces the fatigue life of the blades. Some models and statistical approaches provide an approximation of these types of damage mechanics and in some cases make it possible to calculate the useful life. In this work experimentally the corrosion rate of 410 stainless steel (410 SS) in presence of cracks and without crack as a function of time at different temperatures was determined.

Numerical models to determine the stress intensity factor were created and useful life was calculated. The damage process calculation consists in four phases: pitting nucleation, pit growth, short crack growth and long crack ^{[10, 11, 12]}.

2. Experimental Models

The blades’ steel for this work was a martensitic grade 12% Cr-Steel. Table 1 shows the mechanical properties of the 410 SS and Figure 1 shows the dimensions of the specimen according to the specifications of the RB200 machine for fatigue^[13]. These specimens were subjected to fatigue, according to ASTM E 647-88a ^[14].

Table 2 shows the frequency values and loading cycles to which the specimens were subjected to fatigue testing.

Table 1. Mechanical Properties 410 SS

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Pitting Corrosion Damage for Prediction Useful Life of Geothermal Turbine Blade

Science and Education Publishing

Pitting Corrosion Damage for Prediction Useful Life of Geothermal Turbine Blade

Abstract

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Cite this article:

1. Introduction

2. Experimental Models

Table 1. Mechanical Properties 410 SS

Table 2. Frequency values and loading cycles specimens

3. Modeling

Table 3. Deterministic variables

Table 4. Random variables for corrosion fatigue life

4. Results

5. Conclusion

Acknowledgement

References

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