Tag Archives: Engineering

Predicting release rates of hydrogen from stainless steel

The influence of hydrogen on the structural integrity of nuclear power plant, where water molecules in the coolant circuit can be split by electrolysis or radiolysis to produce hydrogen, has been a concern to engineers for decades. However, plans for a hydrogen economy and commercial fusion reactors, in which plasma-facing structural components will likely be exposed to hydrogen, has accelerated interest in understanding the complex interactions of hydrogen with metals, especially in the presence of irradiation. A key step in advancing our understanding of these interactions is the measurement and prediction of the uptake and release of hydrogen by key structural materials. We have recently published a study in Scientific Reports in which we developed a method for predicting the amount hydrogen in a steel under test conditions. We used a sample of stainless steel as an electrode (cathode) in an electrolysis cell that split water molecules producing hydrogen atoms that were attracted to the steel. After loading the steel with hydrogen in the cell, we measured the rate of release of the hydrogen from the steel over two minutes by monitoring the drop in current in the cell, using a technique called potentiostatic discharge. We used our measurements to calibrate a model of hydrogen release rate, based on Fick’s second law of diffusion, which relates the rate of hydrogen motion (diffusion) to the surface area perpendicular to the motion and the concentration gradient in the direction of motion. Finally, we used our calibrated model to predict the release rate of hydrogen over 24 hours and checked our predictions using a second measurement based on the hydrogen released when the steel was melted. So, now we have a method of predicting the amount of hydrogen in a steel remaining in a sample many hours after exposure during electrolysis without destroying the test sample. This will allow us to perform better defined tests on the influence of hydrogen on the performance of stainless steel in the extreme environments of fission and fusion reactors.

Source:

Weihrauch M, Patel M, Patterson EA. Measurements and predictions of diffusible hydrogen escape and absorption in cathodically charged 316LN austenitic stainless steel. Scientific Reports. 13(1):10545, 2023.

Image:

Figure 2a from Weihrauch et al , 2023 showing electrolysis cell setup for potentiostatic discharge experiments.

Entropy has taken its toll

Leave a reply

I am on vacation so this is the third in a series of ‘reprints’ from my archive of more than 570 posts. It was published in July 2014 under title ‘Engineering archaeology‘. Entropy has done its bit and repainting of our railings is long overdue.

Last week I spent a relaxing day painting the old railings in front of our house. Since I am not a painter and decorator by trade the end result is not perfect but they look much better in shiny black than two-tone rust and matt black. One of the fleurs de lis on our railings had been knocked off when either we moved in or the previous occupiers moved out. It’s a way of life being an engineer, so the shape of the failure surface on the broken railing was bugging me while I was painting the rest. You would expect wrought iron railings to be ductile, i.e. to deform significantly prior to fracture, and to have a high tensile strength. Wrought iron’s properties are derived from its very low carbon content (less than 0.25%) and the presence of fibrous slag impurities (typically about 2%), which almost make it a composite material. It was historically used for railings and gates. However, my broken railing had exhibited almost no deformation prior to fracture, i.e. it was a brittle failure, and the fleur de lis had broken in half on impact with the stone flags. So on one of the rainy days last week, when I couldn’t paint outside, I did a little bit of historical research and discovered that in the late 1790s and early 1800s, which is when our house was built, cast iron started to be used for railings. Cast iron has a high carbon content, typically 2 to 4%, and also contains silicon at between 1 and 3% by weight. Cast iron is brittle, i.e. it shows almost no deformation prior to fracture, so the failure surface tends be to flat and smooth just like in my fleur de lis.

This seems like a nice interdisciplinary, if not everyday, engineering example. It would be vandalism to go around breaking iron railings in front of old buildings. So, if you want Everyday Engineering Examples of ductile and brittle behaviour, then visit a junk shop and buy an old china dinner plate and a set of cutlery. The ceramic of the china plate is brittle and will fracture without deformation – have some fun and break one! The stainless steel of the fork and spoon is ductile and can be easily bent, i.e. it is easy to introduce large deformation, in this case permanent or plastic deformation, prior to failure. In fact you will probably have to bend the fork back and forth repeatedly before it will snap with each bending action introducing additional damage.

The more curious will be wondering why some materials are ductile and others brittle. The answer is associated with their microstructures, which in turn is dependent on their constituents, as hinted above. However, I am not going to venture into material science to explain the details. I have probably already given materials scientists enough to complain about because my Everyday Engineering Examples are not directly analogous at the microstructural level to wrought iron and cast iron but they are more fun.

Conflicted about cost-benefit analysis of international conferences

3 Replies

Last week I wrote about my stimulating experience of attending a conference in Orlando, Florida and presenting our recent research to the experimental mechanics community for the first time in four years. Whilst there, I was conscious of the ecological footprint of my trip – the venue was making extensive use of single use plastics on a scale that surprised me. However, my trans-Atlantic flight had an order of magnitude larger impact. It is difficult to find a reliable estimate of the carbon emissions for a return flight between the UK and Florida but 1,267 kg CO2 from the Guardian newspaper website lies between a lower bound estimate of 856 kg CO2 from iata.org and and an upper bound of 2,200 kg CO2 from myclimate.org. This is equivalent to about one-sixth of my annual domestic carbon footprint of 9,000 kg CO2 using the calculator on the World Wildlife Fund website. The UK average footprint is 9,300 kg CO2/capita and the global average is 6,300 kg CO2/capita. The question is whether it is justifiable to generate additional emissions to attend a research conference? The prime motivation of the research that I presented is to support the development of aircraft which are lighter with less embedded carbon and use less energy while also having a longer useful life. Ultimately, supporting the aviation industry to achieve its target of zero-net emissions by 2050. The carbon emissions of the global aviation industry in 2021 were 720 Mt CO2 [see IEA report]; hence, if my research contributes towards one hundredth of a percent reduction in these emissions then this would be 72,000 kg CO2/year. It seems reasonable to cause a tenth of this annual saving each year (7,200 kg CO2/year) for the next ten years in order to deliver the required technology, i.e., committing one year’s savings to achieve an annual saving in perpetuity. The problem is that I do not have a reliable estimate of the carbon footprint of my research activities. I supervised an MSc student a couple of years ago who conducted a carbon audit of the School of Engineering and estimated the carbon emissions due to research alone to be 61,531 kg CO2 excluding heating, lighting and travel. My group might be responsible for 10% of these emissions, i.e., about 6000 kg CO2; hence, adding about 1,200 kg CO2 to interact with other researchers at a conference seems reasonable and within a budget of 7,200 kg CO2. However, it is difficult to find reliable data to use in estimating carbon emissions for these activities and so perhaps the key conclusion is that we need more and better carbon audits to allow more informed decision-making. In the meantime, perhaps attendence at an international conference once every four years is sufficient.

Image: Tayeb Mezahdia

Addressing societal challenges by engaging 100% of society’s intellectual capital

1 Reply

Today is International Women in Engineering Day (INWED). I have written previously about the lack of progress in achieving gender equality in the engineering profession in most Western countries (see ‘Reflecting on the lack of women in engineering’ on March 16^th 2022) and the seismic shift in attitudes required to increase the number of women in engineering at all levels (see ‘A big question for engineers’ on June 8^th, 2016). I can see signs of change locally. My research group has hovered around an equal number of men and women for some years. In the School of Engineering in Liverpool four women have been promoted to be professors in the last four years – though at a reception following an inaugural lecture given by one of the pair of women who were the first female professors in the School, I was gently admonished by a senior female colleague in another school about why it had taken so long. Of course, she is right. Progress is very slow and we need to do better.

Simone de Beauvoir wrote in her book, The Second Sex first published in 1949: ‘Representation of the world, like the world itself, is the work of men; they describe it from their own point of view, which they confuse with absolute truth.’ More than seventy years later, this still appears to be true, at least in the engineering profession who are responsible for the technology everyone uses everyday. About twenty years ago, the then President of the US National Academy of Engineering, Bill Wulf said, ‘As a consequence of a lack of diversity [in engineering] we pay an opportunity cost, a cost in designs not thought of, in solutions not produced’. However, diversity on its own is not enough, we have to be inclusive and treat everyone equally – as we would like to be treated ourselves. If we do not engage women in the engineering enterprise then we ignore 50% of society’s intellectual capital and we cannot hope to solve the challenges facing society, in part because we will be confused about the truth.

Thank you to my two guest editors who reviewed this post for me.

Photo: Author’s research group in 2022.

Realize Engineering

An engineering commentary for everyone on the first Wednesday of every month