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Change the world

22/04/2023

When Dr Hlanganani Siphelele Nyembe was a child in Mahujini, a village in Mtubatuba, KwaZulu-Natal in the 1990s, he saw Eskom employees installing power lines in his village. It was his dream to work for them.

Sadly, his family did not have the funds to send him on an engineering course. Twenty years later, Dr Nyembe has graduated with a PhD in Physics from Nelson Mandela University, in collaboration with the Eskom Power Plant Engineering Institute, established to create a platform for research and postgraduate education between Eskom and South African universities.

The power industry graduate explains that his PhD research project method could help supplement the way Eskom power stations manage their costly turbine rotors. His project focused on rare samples extracted from the 1CrMoV steel (a type of steel that was used to manufacture the turbine rotors used in power stations built in the 1960s to 1980s –  the turbine rotor spins a generator to produce electricity). “These high-pressure turbine rotors are critical components of power plants, and their replacement has significant economic implications.”

One of the major challenges in operating turbine rotors is to avoid creep failure. Creep failure occurs when a material is subjected to constant stress at high temperatures and pressures for a long time, and it deforms irreversibly until it breaks. Turbine rotors are exposed to such conditions during normal operation, and they experience the progressive deterioration of their microstructure and creep resistance. This reduces their service life and increases the possibility of sudden fracture. “To prevent creep failure, it is essential to monitor creep behaviour of turbine rotors and ensure that they do not exceed their creep limit.”

Dr Nyembe explains that to avoid power outages, Eskom used these samples to assess the remaining life and extend the service time of the rotors using conventional methods based on creep cavities and hardness measurements. However, these samples had valuable information that require further investigation.

“In my research project, I used these samples to identify microstructural features that can be used as indicators of creep damage and studied how they evolve with creep damage during rotor service.  I used state-of-the-art microscopes at the Centre for High Resolution Transmission Electron Microscopy (HRTEM) at Mandela University to reveal and study nano-sized features in the structure of these samples. Finally, I used these nano-sized features to develop a microstructural-based creep life assessment of 1CrMoV steam turbine rotors used in power plants.”

According to Dr Nyembe, this microstructural based creep life assessment method could help supplement the way Eskom power stations manage their costly turbine rotors. His research project has developed a microstructural- based life assessment method that is not only applicable to 1CrMoV steel components. This method can also be modified to evaluate the life of low-alloy steel and high chromium steel power plant components.

He explains that his research project aims to refine life assessment models for critical power plant components. “Accurate life assessment models are essential to determine when a component must be safely replaced in a cost-effective manner. By using microstructural analysis to determine the actual creep damage of a component, it can be managed with greater confidence and its life can be significantly extended.” This will contribute to huge potential economic savings by replacing power plant components only when they have reached the end-of-life criterion.

Recently, the Minister of Electricity, Kgosientsho Ramokgopa, announced plans to extend the life of Eskom’s power stations that are reaching their end-of-life criteria to ease load-shedding. “The microstructure-based life assessment method developed in my research project could be useful for accurate prediction of the remaining safe life of those power plants”.

Dr Nyembe said having Dr Johan Westraadt and his team as his promoter for his PhD “has been a great decision, the rewards for the work I've been doing are evident”. He was awarded Best Presentation in the Materials Category at the Eskom Power Plant Engineering Institute’s National Workshop in 2021. This recognition gave him the confidence and motivation to work harder during COVID-19. At the 57th Annual Meeting of the Microscopy Society of Southern Africa in 2022, he earned the “Angstrom/JEOL AWARD for the “Most promising upcoming microscopist” at the Microscopy Society of Southern Africa’s biennial conference in December 2022.

“I am thrilled and excited that my work was recognised with these awards. I cannot wait for my trip to showcase my work at the international Electron Microscopy and Analysis Group (EMAG) conference to be held in Manchester (UK) in July this year.”

Dr Nyembe reflects that after years of being asked the question ‘When are you finishing your studies?’, “I am happy to say that I have completed my PhD. I am also pleased to have been employed as the Microscope Scientist at the Centre for HRTEM.”

His goal is to build his career in microscopy and material characterisation. “As a country, we need to industrialise and become self-reliant. To achieve this, we need more skilled and knowledgeable citizens. I encourage young people to pursue a PhD as it will not only benefit them, but could lead to a better South Africa tomorrow.”

Dr Nyembe will receive his doctorate at the Faculty of Science graduation ceremony on Monday, 24 April 2023.

Contact information
Primarashni Gower
Director: Communication & Marketing
Tel: 0415043057
Primarashni.Gower@mandela.ac.za