A picture of a cracked steel beam and a bunch of people who think to know the cause(s) of cracking just by looking to a picture, that’s all you need on social media to confuse the person who asked what could have caused the crack. It remains unclear to me how neurons, synapses and other brain matter interact to come to a conclusion on a failure cause - or causes - without performing a proper failure analysis.

Luckily many people who respond ‘suggest’ that this or that ‘could’ have played a role in the cause of cracking; proviso is a wise thing when you don’t know what happened. Others just mention one or two of the many possible causes and create the absurd impression that they could see it on the picture; strange habit. Just by looking to a cracked beam it’s impossible to state that the steel was of bad quality, that the beam was improperly heat treated or that exaggerated stresses were present; you require specific analysis and a correct interpretation of the test results before you can make any such statement.

And than you have an incredible lot of people who confuse quality with patriotism and/or protectionism. Their answer when asked for the cause of failure is simple and clear: It’s Asian or African steel, or expressed otherwise ‘it’s not American steel’, or ‘it’s not European steel’, dependent on their citizenship. It’s beyond me how you can see a steel’s origin without having read the materials certificate.

With the 22 years experience I have as a failure analyst I can guarantee that ‘bad’ steels do not come from one or two specific regions in the world or, as some hard core patriots say, hail from a specific Asian country. Anywhere in the world bad steels are produced or - better said - production errors and flaws in quality control can occur everywhere. What these people stand for is certainly not quality, yet economic protectionism and/or patriotism. Neither of both has ever served quality, reliability or safety of technical objects and installations. Some consider protectionism and patriotism as important economic and social words, yet they have nothing to do with good engineering practice. To the contrary, protectionism and patriotism undermine the possibility to engineer and create the best possible products and installations in the world.

Have you ever considered that – from a technical and quality point of view - the best material for your product and installation is possibly produced in another country than yours?

Quality is not about patriotism or protectionism; quality is in part an attitude of wisely deployed openness to the possibilities and talents of all people in the world.

Frans Vos
General Manager Materials Consult bv

Product: Heat exchanger of the indoor unit of an air conditioning installation
Material: Copper tube bundle in aluminium lamellae cooling fins
Sector: Manufacturing industry, Construction, Air conditioning, Food production
First observation: Leakage of the tube bundle
Analysis procedure: Leakage detection, visual and stereomicroscopic analysis, light optical microscopy, scanning electron microscopy with spectral analysis (SEM-EDS)

Main Conclusions

Through leak detection and stereomicroscopy, several very small leaks were found in the copper tube bundle. Laboratory analysis prevailed that the leakages initiated at the outer wall of the copper tubing and are due to so-called ‘ant nest corrosion’, probably induced by the presence of organic acids.

The attack was doubled by the crevice corrosion effect in the narrow gap between the aluminium fins and the copper tube bundle.

Furthermore spectral analysis of some external wall deposits indicated for the presence of sulfur and chlorine. Sulfur has been detected in all analysed deposits, where in 5 out of 6 cases calcium was detected as well; in many cases this combination indicates for the presence of gypsum (calcium sulphate). The presence of chlorine is limited, yet significantly detected at one position. Chemical compounds that contain sulfur and/or chlorine might have had an enhancing effect on corrosion processes at the specific location where these compounds were present.

As to the client’s question whether formaldehyde could have played a role, it can be mentioned that formaldehyde in contact with atmospheric oxygen readily oxidizes to formic acid, member of the organic acid family. The environmental analysis also showed that tartaric acid, another organic acid, may have contributed to the damage. In particular, the module was placed at a wine producer; tartaric acid is present in grapes, among other things.

Recommendations for repair

Since several leaks were found at different positions in the heat exchanger and the configuration of the bundle does not allow for local repairs, it was necessary to replace the entire heat exchanger package.

Cross-section images of ant nest corrosion of the outer wall of a copper heat exchanger tube (to the left: after polishing, to the right: after etching)

Product: Exterior sills and vertical wall panels
Material: Powder coated aluminium plate
Sector: Construction, real estate
Where? Apartment building, North Sea coastal area
First observations: Grey-white staining and local detachment of the coating
When observed? finishing phase of the building, prior to delivery to the owner
Analysis procedure: Visual and stereomicroscopic analysis, light optical microscopy with classic lighting as well as in darkfield-mode, scanning electron microscopy with spectral analysis (SEM-EDS)

Main conclusions

Corrosion was due to the presence of large gas cavities and an inhomogeneous (size) distribution of barium sulphate crystals in the coatings. 

Due to the varying outdoor temperature the gas cavities will expand and shrink, which subjects the coating to varying stresses. These stress variations, combined with the limited amount of coating material at the cavity positions has led to coating cracks at/near some of the larger cavities. 

It was also observed that several barium sulphate crystals - which are also added in function of gloss optimisation - were quite large compared to the coating thickness. Barium sulphate crystals with a size of one fourth of the coating thickness were regularly observed. At the same time an inhomogeneous distribution of the barium suplhate crystals was observed. At several postions some of the larger barium sulphate crystals were aligned, together forming an almost continuous line from the aluminium substrate to the coating surface, which led to the creation of ideal propagation paths for cracking of the coating. 

The local corrosive attack of the sills and wall panels was subsequently caused by the penetration of marine humidity/moisture through the coating cracks up to the aluminium substrate.

Recommendations for repair

Given the nature of the coating damage described above and as the aluminium was already severely attacked at several positions, it was advised to replace the complete sills and wall panels. Local repair of damaged areas would not have given the guarantee that the remaining original coating areas would not be affected by the observed failure phenomena.

Picture at the top of the blog: Stereomicroscopic enlargement of a failure area

Picture top left: Light optical microscopy, darkfield image of a section zone with cracking of the coating (large white area = corrosion products of aluminium)
Picture top right: Light optical microscopy, darkfield image of a section zone with gas cavities in the coating
Picture bottom left: SEM-BS-image of a section, with the coating on top and corrosion products (dark grey) and aluminium (light grey) below
Picture bottom right: EDS-mapping of barium for the section zone of the SEM-BS-picture / The EDS-mapping for sulphur is similar  
 

Tightly organised in a neat suit, that’s the least you can say about the many delightful types of sushi Japan has brought to the rest of the world. The tight organisation is illustrated by the specific sequence of ingredients by which each sushi has to be built up. The neat suit is represented by the freshness of the ingredients and the stately view emerging from a usually mouth fitting dish.    

Tightly organised and in a neat suit are also the mass of Japanese who brave on a daily base the morning and evening rush in the well organised traffic of Tokio, Kobe or other Japanese metropolis. If you didn’t experience it live, I’m quite sure that news or other media already bombarded your retinas with images of Japanse metros that always seem to be overcrowded, yet being always sharp on time as well. An example of efficient mass transport.

And then when you’re visiting certain Japanese restaurants, you have the combination of both. Sushi that are transported on a conveyer belt, nicely aligned, ‘whether or not en masse’ reaching the hungry stomachs. You probably didn’t realise it, yet the speed and frequency with which your favorite colorful bite is reaching your hungry you is dependent on the time at which you enter the restaurant. Do you arrive at the start of a ‘service’ – as we have to say it nowadays – or almost at the end, another culinary experience will be your share.  

Scenario 1: You arrive at the start of the service. The cooks – obviously also tightly dressed in their white costume – are placing the 20 different types of sushi on the conveyor belt, one by one. It looks like a bead necklace where the differently colored beads follow-up each other in the same color-order over and over again. Is someone taking your favorite sushi from the belt right in front of your nose? It’s no problem, as very soon afterwards that specific sushi’s lookalike will follow, allowing you to nibble it right away. If you arrive at the start of the service you will not at all have to wait a longtime for the precious gem you’re craving for. Sushi pass en masse your nose and there will be no moment at which the mass transport will let your appetite wait, even not if you’re permanently longing for your favorite little dish.

Scenario 2: You arrive quite late in the service. The cooks – still in tight suit, yet possibly with some colorful culinary stains on sparkling white – suffer a little as they see that the number of visitors is already diminishing quite a bit. Hence the conveyor belt is not fully covered with sushi anymore. The cooks are already producing less of those Japanese bites you’re longing for, such avoiding that too much of them would end up their life in the garbage bin. You notice that the situation will be even more complex: 5 out of the 20 sushi are not in favor of the diners that day, so relatively spoken the cooks are making even less of them compared to the other types of sushi. And then you’re of course that one diner with those taste buds that bring you to culinary heaven when you’re eating one of those 5. And to crown it all, there’s also that one specific person that’s sitting at a table that – taking into account the direction of movement of the belt – is nourished before you. Exactly that person that seems to have the same palate that you have, hence that one person that walks with your favorite snack.

Given the late arrival you’re hungry as a bear, yet exactly at that moment the fulfillment of your appetite is hindered by another mass transport regime than the one you would have enjoyed when you would have put your legs under the table one hour before.    

Aside from bringing culinary pleasures and the joy of companionship a delightful diner also starts up a chain of chemical processes in our body. Part of these processes bring you gradually to the glorious feeling of saturation. When you arrive early, your favorite bites may quite rapidly bring you to that state of ‘I’m full’. When you arrive late, than it will take some more time before the feeling of saturation rejoices you, even more if you’re always going to wait for that one out of those five from twenty.

When you arrive early, reaching the state of saturation will not be controlled by the quantity and frequency of the different sushi that pass your table. When you arrive late, you’ll have to wait and reaching your vibe of saturation will be controlled by the quantity and frequency of that one type of sushi that makes your mouth water and makes you longing for ‘one more of the same’.

When you arrive early, the chemical processes that lead to saturation are not controlled by the sushi mass transport. When you arrive late, it will only be through sushi mass transport controlled processes that you will arrive at the my-stomach-is-full feeling.

It’s the same with many chemical reactions. An example: The risk of intergranular corrosion of stainless steels is largely influenced by whether the diffusion of chromium atoms through the steel structure is mass transport controlled or not. A chromium mass transport controlled situation can e.g. lead to so-called ‘sensitisation’ in the heat affected zone (HAZ) of a weld. If the HAZ of a stainless steel weld is sensitised, the risk of intergranular corrosion rises considerably from the moment water or another electrolyte would come into contact with the sensitised area.

Do you want to learn more on corrosion, welding and/or their mutual relation? Mail to This email address is being protected from spambots. You need JavaScript enabled to view it. or teL. +32.16.40.21.53. WELCOME !

To conclude:

In all industrial and societal sectors many processes are mass transport controlled. Energy production, pharmacy, biology, food production and consumption (hurray to sushi and also more and more Spanish tapas on a transport belt) and, not to forget, transport. The latter is not only about metro systems in Japan, yet also about

When driving by car or by train runs smoothly without delay, no mass transport controlled process is nibbling from your valuable time.

Trapped in slow traffic or a traffic jam? Then you’re suffering from a mass transport controlled transportation process.

To finalise a tip for your weekend or holidays: When you go to amusement parks, choose those attractions where there’s (almost) no mass transport controlled shuffling in the waiting line, unless queuing is one of your hobbies.  

Have fun !