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We knew in middle school that hydrogen atom is the lightest element in the periodic table, and it is also the earliest and most element in the universe, accounting for 91.2%.
The nature of hydrogen is active and forms water after combustion. Therefore, hydrogen energy is also a highly anticipated clean energy.
However, hydrogen is not as "clean" as we imagined. It once made the US military's tanker cost 36 million US dollars sink at a rate of 140 ships a month, almost scrapping the California Bay Bridge and preventing hydrogen-energy vehicles from becoming the mainstream.
In order to tame this naughty element, a specialized discipline branch even appeared.
Today, let’s learn about the other side of this strange element that you don’t know.
SS John W. Brown, one of the only four remaining Freewheelers . Image source: wikipedia
During World War II, in order to transport soldiers and supplies, the US military built thousands of oil tankers - Freewheelers (Liberty Ships). However, the Freewheel soon became the scene of the disaster film.
Among the 2710 freewheelers, nearly 1,500 of them had severe cracks. On the cold and turbulent sea, some free wheels even broke into two sections. The most famous of these is the tanker S.S. Schenectady.
Freewheel split in half S.S. Schenectady Image source: wikipedia
On the evening of January 16, 1943, the Swan Island shipyard in Oregon made a loud noise, and the yet-delivered S.S. Schenectady split in half.
Because this is the first ship built by the shipyard, it caused panic. In fact, in March of that year, another Freedom Ship, the Esso Manhattan, also cracked when it entered New York Bay.
Freewheel sinks at a rate of 140 ships a month. The construction cost of the Free Ship was about US$2 million per ship at that time, equivalent to US$36 million now. This shipwreck speed has caused huge losses to the US military. What exactly is the problem?
The free wheel of cracked images source: tf.uni-kiel.de
No one knows the answer during the war, but everyone still found a solution, that is, patches. US shipyards patched steel plates at cracks to prevent further cracking of ships. This method is quite effective, so later these anti-crack steel plates were called crack stop rivet joint (crack arrestor).
After this measure was fully implemented, only 20 freewheelers sank in one month, and the number dropped to one-seventh of the previous one.
After World War II, George Irwin, a physicist at the U.S. Naval Research Laboratory, used data from the Freewheel to conduct research and finally found the murderer who made the ship crack and sink - hydrogen.
It turns out that in the early 20th century, some new welding technologies were invented, such as manual arc welding (SMAW) and welding rod welding. During welding, the heat from the arc or acetylene combustion melts the metal, causing the two pieces of metal to weld together.
Before the emergence of electric welding technology, the metal plates of the ship were spliced with riveting technology. Riveting technology has many disadvantages, such as the need for specially trained technicians, which makes the cost of riveting workers account for one-third of the labor cost of ship assembly. In addition, several metal plates need to be overlapped during riveting, which will not only increase the weight of the hull, but also increase the cost.
Hull Riveting Image source: boat-building.org
Due to the lack of skilled riveting workers, the US federal maritime commissioner asked US shipyards to replace riveting with welding. As a result, the delivery speed of the ship was rapidly improved. Between 1930 and 1937, US shipyards built only 71 ships. However, after using electric welding technology, 5,777 ships were built by American shipyards between 1939 and 1945.
only takes 5 days to build a freewheel. Between 1941 and 1945, 18 US shipyards used welding technology to manufacture 2,710 freewheelings for the US military.
However, what people at that time did not know was that single atomic hydrogen (H) would be produced during welding, and single atomic hydrogen would drill into the metal to form hydrogen (H2).
Hydrogen gathers near metal grains, destroying the metal structure and making the metal bloating brittle. Sometimes hydrogen can accumulate in metals into 18.7 megapas, which is a high pressure of 187 times the surface air pressure. This phenomenon is named hydrogen embrittlement (hydrogen embrittlement).
In addition, at high temperatures, hydrogen atoms absorbed by steel may also form methane gas (CH4) with carbon atoms in steel, making steel decarbonized and brittle, which is called hydrogen corrosion (hydrogen attack).
During use, the welding parts where hydrogen embrittlement and hydrogen corrosion occur easily crack. The heavy objects transported by tankers and the slap of waves will accelerate the expansion of cracks. What's even more terrifying is that the surface of the metal that has already occurred hydrogen embrittlement looks no different from ordinary metals and will not arouse the alertness of manufacturers and users, which increases the risk of hydrogen embrittlement.
The comparison between hydrogen-brittle metal (left) and ordinary metal (right) cannot be seen from the appearance. The phenomenon of hydrogen embrittlement was first discovered by W. H. Johnson in 1875. However, before the large number of incidents in the Freewheel, everyone did not know that hydrogen had such strong destructive power. After ascribed the cracked free wheel to hydrogen embrittlement, Owen pioneered the discipline branch of fracture mechanics and material strength, and the construction and manufacturing industries finally began to pay attention to this evil element.
It should be pointed out that until now, researchers have not fully understood the principle of hydrogen embrittlement, nor can they predict when and where the materials will experience hydrogen embrittlement. Therefore, the best way is to prevent it.
As mentioned earlier, electric welding is particularly prone to release hydrogen atoms, because the arc contacts the cellulose coating on the surface of the welding rod or the water vapor in the air, which will produce single-atom hydrogen. Now a material called low hydrogen welding rod has emerged, which can reduce the generation of single hydrogen atoms and is suitable for welding high-strength steel.
Of course, sometimes hydrogen diffuses into the metal during the manufacturing process. The plating and cleaning process may also produce single-atom hydrogen, which may contaminate the metal.
For example, in order to prevent corrosion, some bolts are often coated with cadmium. Single-atom hydrogen may be produced when cadmium is plating. Due to the cadmium plating problem, the US Air Force has set up a standard for low hydrogen embrittlement cadmium plating, requiring contractors to comply with it. To remove hydrogen, the bolt suppliers usually bake the bolts after cadmium plating (such as baking in an environment of 24 degrees Celsius for several hours) to allow the hydrogen to escape from the bolts.
Cadmium plating can prevent corrosion. Image source: milinc
After the true face of hydrogen was revealed, major disasters caused by hydrogen embrittlement are rare now, but they have not completely disappeared.
Between 2014 and 2015, several bolts in the Lidhe Building in the London Financial District were broken due to hydrogen embrittlement.
San Francisco-Oakland Bay Bridge Picture source: wikipedia
In 2013, the San Francisco-Oakland Bay Bridge in the United States was tested for the upcoming opening to traffic. The bridge is the most expensive public building in California's history and the widest bridge included in the Guinness World Records.
However, during the test before opening, the engineer discovered the problem: the safety bolts responsible for erecting the bridge deck on the cement columns appeared cracks after two weeks of testing, making the San Francisco-Oakland Bay Bridge almost become an American broken bridge.
In the test, 30 of the 96 safety bolts were broken. Later I found out that this was caused by hydrogen embrittlement. Replacing the bolts cost the California Department of Transportation $25 million, five times the estimate, causing an uproar in public opinion.
The cross section of the safety bolt in which hydrogen embrittles occurs
The annoying nature of hydrogen has also become one of the biggest obstacles to the widespread use of hydrogen energy. Although hydrogen (H2) cannot be directly absorbed by metal, under certain conditions (such as high pressure), hydrogen molecules on the metal surface will be disassembled into two single atom hydrogen, and then absorbed by the metal, causing hydrogen embrittlement. In other words, long-term storage of high-pressure hydrogen with metal materials is equivalent to raising an irregular time bomb.
In 1988, a 3-kiloliter metal hydrogen tank in Saint-Fons near Lyon, France exploded, and property within a radius of 500 meters was affected. This hydrogen tank was first put into use in 1939, and later testing showed that the explosion was caused by hydrogen embrittlement.
hydrogen energy vehicle Toyota Mirai hydrogen tank Image source: wikipedia
Although the combustion product of hydrogen is only water, these troubles caused by hydrogen make it difficult to produce commercial technologies that can safely compress hydrogen fuel, which has led to the high cost of hydrogen transportation pipelines, and hydrogen energy vehicles have not become the mainstream.
I really didn’t expect you to be like this hydrogen.
let's get a hydrogen, and then the steel cracked.
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Written by | Qijun
Statement: The content of the article is original by Xinhua No. [Everything Magazine]. Please indicate the source when reprinting. Unmarked pictures are from the Internet. If you have any copyright issues, please contact us.
Source: Xinhua No. All Things Magazine
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