Prediction of Failures of Low-Pressure Steam Turbine Disks

1997 ◽  
Vol 119 (4) ◽  
pp. 393-400 ◽  
Author(s):  
C. Liu ◽  
D. D. Macdonald
Keyword(s):  
Stress Corrosion ◽  
Steam Turbine ◽  
Stress Corrosion Cracking ◽  
Wilson Line ◽  
Corrosion Damage ◽  
Low Pressure ◽  
Corrosion Cracking ◽  
Localized Corrosion ◽  
Pressure Steam ◽  
Turbine Disks

Localized corrosion phenomena, including pitting corrosion, stress corrosion cracking, and corrosion fatigue, are the principal causes of corrosion-induced damage in electric power-generating facilities and typically result in more than 50 percent of the unscheduled outages. In this paper, we describe a deterministic method for predicting localized corrosion damage in low-pressure steam turbine disks downstream of the Wilson line, where a condensed, thin electrolyte layer exists on the steel disk surfaces. Our calculations show that the initiation and propagation of stress corrosion cracking (SCC) is not very sensitive to the oxygen content of the steam, but is sensitive to the conductivity of the condensed liquid layer and the stresses (residual and operational) that the disk experiences in service.

Stress Corrosion Cracking of Low-Pressure Steam Turbine Rotor

2011 ◽  
Author(s):  
Liang Yan ◽  
Kazuyoshi Nakajima ◽  
Shuichi Inagaki ◽  
Masao Arimura ◽  
Shigeo Hosoi
Keyword(s):  
Stress Corrosion ◽  
Steam Turbine ◽  
Stress Corrosion Cracking ◽  
Low Pressure ◽  
Turbine Rotor ◽  
Corrosion Cracking ◽  
Sulfur Concentration ◽  
X Ray ◽  
Steam Turbine Rotor ◽  
Pressure Steam

Corrosion cracks were found at the bottom of the first hook of the L-4 stage of a low-pressure steam turbine rotor after about 230,000 hours operation with about 300 times of starts and stops of a thermal power plant. They developed in the circumferential direction, showing a groove line on the bottom surface of the first hook. Cross sectional observation showed that they had branched and blunted shapes, and X-ray cartography analysis results showed that they filled with corrosion products, and sulfur concentration was detected. In order to verify that they were caused by stress corrosion cracking (SCC), bent-beam stress-corrosion tests with four-point loaded specimens (ASTM G40 method) were performed in a 0.25wt%H2SO4+NH4OH solution with a pH controlled at 9.8 to simulate the corrosion environment of the steam turbine, and the test temperature was set at 80°C. After 6,000-hour and 10,000-hour tests, the cross sections of SCC specimens were inspected with a scanning electron microscope (SEM). Branched and blunted cracks were observed and the crack shapes were similar to those of the corrosion cracks occurred in the steam turbine. Sulfur concentration was also observed in the blunted cracks of the specimens by X-ray cartography analysis. Based on the test results, it can be assumed that the corrosion cracks developed from stress corrosion cracking (SCC) in the low-pressure steam turbine. It is thus necessary to periodically inspect not only the L-1, 2 stages of the wet and corrosion zone, but also the L-3, 4 stages of dry and salt zone in low-pressure steam turbines.

Stress Corrosion Cracking of NiCrMoV Steel Welded Joint under Applied Load in Simulated Environment of Low Pressure Nuclear Steam Turbine

2016 ◽  
Vol 853 ◽  
pp. 361-365 ◽  
Author(s):  
Shuo Weng ◽  
Yu Hui Huang ◽  
Fu Zhen Xuan ◽  
Ling Hua Luo
Keyword(s):  
Stress Corrosion ◽  
Steam Turbine ◽  
Stress Corrosion Cracking ◽  
Heat Affected Zone ◽  
Applied Load ◽  
Welded Joint ◽  
Low Pressure ◽  
Corrosion Cracking ◽  
Simulated Environment ◽  
Nicrmov Steel

In order to determine the stress corrosion cracking susceptibility of NiCrMoV steel welded joint of low pressure nuclear steam turbine, long time immersion tests had been carried out in the form of cylindrical tensile specimens self-loaded to various applied load (0, 0.3YS, 0.6YS and 0.9YS) and exposed in the simulated environment with 180°C, 3.5% NaCl. Coarsen grain heat affected zone reacted preferentially as anode in welded joint, which was caused by the synthetic effects of micro-galvanic corrosion, much more precipitations of carbides and higher content of Cr element. Preferential local corrosion of coarsen grain heat affected zone with the formation of occluded corrosion cell accelerated corrosion rate. In addition, the dissolution rate also increased as the applied load increased.

scholarly journals A Review on the Applications of Acoustic Emission Technique in the Study of Stress Corrosion Cracking

2020 ◽  
Vol 2 (1) ◽  
pp. 1-33
Author(s):  
Luigi Calabrese ◽  
Edoardo Proverbio
Keyword(s):  
Acoustic Emission ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Future Trend ◽  
Corrosion Cracking ◽  
In Situ Monitoring ◽  
Localized Corrosion ◽  
Complex Nature ◽  
Damage Propagation ◽  
Research Activities

The complex nature of the damage evolution in stress corrosion cracking (SCC) leads to explore for new investigation technologies in order to better identify the mechanisms that supervise the initiation and evolution of the damage as well to provide an improvement of knowledge on this critical localized corrosion form during time. Research activities concerning the use of acoustic emission (AE) technique to assess SCC has acquiring considerably relevance in recent decades. The non-invasiveness and the possibility to provide a continuous in situ monitoring of structures and components make this non-destructive technique clearly promising in the field of structural health monitoring. In this concern, this paper aims to be a focused overview on the evaluation of SCC phenomena by AE technique. The main topic of this review is centered on the approaches that can be used in elaborating AE data to better discriminate the mechanisms that contribute to damage propagation in SCC conditions. Based on available literature, investigation approaches assessing AE waveform parameters were classified, evidencing, furthermore, the identified mechanisms that synergistically take place during the material degradation. Eventually, a brief summary and a future trend evaluation was also reported.

Effect of Long-Term Service Exposure on the Localized Corrosion and Stress Corrosion Cracking Susceptibility of Type 347 Stainless Steel

CORROSION ◽  
10.5006/2612 ◽  
2017 ◽  
Vol 74 (3) ◽  
pp. 350-361 ◽  
Author(s):  
K. Ravindranath ◽  
N. Tanoli ◽  
B. Al-Wakaa
Keyword(s):  
Stainless Steel ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Localized Corrosion ◽  
X Ray Diffraction ◽  
Degree Of Sensitization ◽  
Corrosion Susceptibility ◽  
Service Exposure

The paper presents the results of a study conducted on the effects of long-term service exposure of Type 347 stainless steel (SS) on the microstructure and corrosion susceptibility. The material subjected to the study was in service in a petroleum refinery as heater tube at 620°C for 31 years. The microscopic and x-ray diffraction studies of the service-exposed specimen revealed the precipitation of chromium-rich carbides along the grain boundaries. The microstructural changes that occurred as a result of service exposure affected the ductility and toughness of the alloy. The sensitization of the alloy was assessed by scanning electron microscopy and double loop electrochemical potentiodynamic reactivation. The studies have indicated some degree of sensitization in the alloy. The service exposure resulted in a marginal increase in the susceptibility of Type 347 SS to pitting in environments containing NaCl and NaCl + H2S. Environments such as H2SO4 and K2S4O6 at the tested concentrations did not differentiate between service-exposed and solution annealed specimens for their corrosion susceptibility. Slow strain rate testing of Type 347 SS in both the service-exposed and solution annealed conditions showed susceptibility to stress corrosion cracking in environment containing NaCl + H2S, while the alloy did not show susceptibility to SCC in H2SO4 and K2S4O6. The long-term service exposure did not noticeably influence the SCC susceptibility of Type 347 SS under the tested conditions.

Study on Stress Corrosion Cracking Sensitivity of CrNiMoV Steam Turbine Rotor Steels

2019 ◽  
Vol 795 ◽  
pp. 102-108 ◽  
Author(s):  
Shu Xian Lin ◽  
Yu Hui Huang ◽  
Fu Zhen Xuan ◽  
Shan Tung Tu
Keyword(s):  
Stress Corrosion ◽  
Steam Turbine ◽  
Stress Corrosion Cracking ◽  
Turbine Rotor ◽  
Optical Microscope ◽  
Corrosion Cracking ◽  
Slow Strain Rate Test ◽  
Operation Condition ◽  
Steam Turbine Rotor ◽  
Rate Test

The stress corrosion sensitivities of 25Cr2Ni2MoV, 26NiCrMoV10-10 and 30Cr2Ni4MoV low-pressure rotor steels in simulated nuclear steam turbine operation condition were investigated by slow strain rate test (SSRT), and the stress corrosion cracking (SCC) mechanisms were studied by optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Results revealed that the SCC sensitivity of 25Cr2Ni2MoV steel was highest in 3.5wt.%NaCl solution at 180°C, while the SCC sensitivity of 26NiCrMoV10-10 steel and 30Cr2Ni4MoV steel are similar. The SCC sensitivity of CrNiMoV steam turbine rotor steels could be decreased by the increase of Ni element and the decline of mechanical intensity. Cracks initiate from metal surface and then propagate to the inner metal, which showed a form of transgranular cracking.

scholarly journals Quantitative analysis of localized corrosion in tensile armor wire of flexible riser submitted to sweet stress corrosion cracking testing with crevice

2021 ◽  
Vol 18 ◽  
pp. e2451
Author(s):  
Matheus Porto Trindade ◽  
Ihana Gabriela Conceição de Jesus ◽  
Matheus Mariano da Silva Reis ◽  
Brenno Lima Nascimento ◽  
Fabricio Pinheiro dos Santos ◽  
...  
Keyword(s):  
Quantitative Analysis ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Localized Corrosion ◽  
Flexible Riser

scholarly journals Localized corrosion and stress corrosion cracking of stainless steels in halides other than chlorides solutions: a review

2020 ◽  
Vol 38 (1) ◽  
pp. 1-24
Author(s):  
Mariano A. Kappes
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Pitting Corrosion ◽  
Stainless Steels ◽  
Weak Acid ◽  
Corrosion Cracking ◽  
Localized Corrosion ◽  
Standards And Regulations ◽  
Mo Content ◽  
Industrial Relevance

AbstractFluorides, bromides, and iodides, despite being less common than chlorides, are present in various environments of industrial relevance. Stainless steels suffer pitting corrosion in solutions of all halides except fluorides, which can be understood considering that fluoride is the anion of a weak acid. The aggressiveness of the rest of the halides for pitting corrosion is on the order Cl− > Br− > I− for stainless steels with Mo content below 3 wt.%. Mo is not as effective in inhibiting Br− pitting corrosion as it is for inhibiting Cl− pitting corrosion. Most of those observations were rationalized based on the effect of anions on pit growth kinetics. Sensitized austenitic stainless steel suffers stress corrosion cracking (SCC) in solutions of all halides, albeit chlorides seem to be the most aggressive. Fluoride SCC is relevant for SCC under insulation of stainless steels, and standards and regulations developed to mitigate this problem consider this ion as aggressive as chloride. For the solubilized stainless steels, aggressiveness toward SCC is in the order Cl− > Br−. The SCC of solubilized stainless steels was not observed in solutions of F− and I−, and the possible reasons for this fact are discussed.

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