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The Mystery of the Brand-New Bay Bridge's Corroded Steel
- msandford 11y agoSounds like they got a bad batch of steel or something. Corrosion doesn't cause steel to become brittle. It weakens it, yes, but it does so by reducing the cross-section. Corrosion doesn't materially alter the bulk properties of the metal, only the amount of metal in the bulk. I get that there's corruption and shortcuts getting taken everywhere on big projects like this. But it's still surprising that better QA/QC isn't done. There's going to be a lot of finger pointing on whose fault this is.
- devindotcom 11y agoYeah, I can imagine lax quality control if you're making... I don't know, a desk or even a house, but a bridge? Whoever dropped the ball put a HELL of a lot of people (and money) in jeopardy - even if the corrosion isn't going to critically affect the structure, it makes one wonder about the quality of the rest of the materials, and the contracts involved...
- Dav3xor 11y agoAnd for people who've never been to San Francisco -- this bridge is a huge huge thing, and any problems with it are a very big deal.
- x0x0 11y ago$6.4B and counting, plus a quarter million vehicles per day; there is no possible alternate way to move that many people. It had to be replaced while the old one was still used.
- simulate 11y agoSince drivers pay the $6 toll only one direction, it will take $6.4B / (125,000 vehicles per day * $6 per car * 365.25 days per year) = 24 years to pay off the bridge with tolls alone.
- aggie 11y agoWith a projected lifespan of 150 years [1], that seems pretty reasonable. [1] http://www.dot.ca.gov/dist4/eastspans/ http://www.dot.ca.gov/dist4/eastspans/
- oh_sigh 11y agoWell, the construction of the bridge decks and the materials for the bridge was made in China...
- sneak 11y agoSo are Apple Watches and iPads. Please stop it with this nonsensical nationalism/racism.
- x0x0 11y agoIt's well known that china has lax safety and quality standards. See for one of many examples the adulterated pet food from china or the milk scandal where china poisoned 300,000 infants [1]. To this day, China's own citizens import milk for their children if they can [2]. Or chinese drywall [3]. It's merely prudent to safety test food and materials imported from China. [1] http://en.wikipedia.org/wiki/2008_Chinese_milk_scandal http://en.wikipedia.org/wiki/2008_Chinese_milk_scandal [2] http://www.bloomberg.com/bw/articles/2014-11-16/china-turns-to-the-u-dot-s-dot-and-australia-to-import-safer-milk http://www.bloomberg.com/bw/articles/2014-11-16/china-turns-... [3] http://en.wikipedia.org/wiki/Chinese_drywall http://en.wikipedia.org/wiki/Chinese_drywall
- prewett 11y agoChina also has had a bunch of spectacular construction failures. My favorite is the Shanghai bridge made out of styrofoam and garbage [1], but there are other, less spectacular examples: [2]. The schools in Sichuan are notable for poor construction, as many schools feel down but adjacent buildings did not. [3] Apparently one builder would tap the cement on inspection, and if it didn't ring right, he would make the contractor redo it. They didn't like him much, but his schools stayed up. Can't find the article, though. Apparently the rebuilding isn't any better [4]. I wouldn't even consider using Chinese construction material. [1] http://www.weirdasianews.com/2010/02/05/shanghai-wonderbridge-trash-collapses/ http://www.weirdasianews.com/2010/02/05/shanghai-wonderbridg... [2] http://world.time.com/2012/08/27/bridge-collapse-in-china-raises-questions-about-safety-of-countrys-road-construction-boom/ http://world.time.com/2012/08/27/bridge-collapse-in-china-ra... [3] http://www.nytimes.com/2008/05/25/world/asia/25schools.html?pagewanted=all http://www.nytimes.com/2008/05/25/world/asia/25schools.html?... [4] http://www.npr.org/sections/parallels/2013/05/14/183635289/Five-Years-After-A-Quake-Chinese-Cite-Shoddy-Reconstruction http://www.npr.org/sections/parallels/2013/05/14/183635289/F...
- gscott 11y agoThe bridge was made in China and assembled here. There were a lot of quality control and cost overrun issues. The Chinese company would kick out the American inspectors.
- MrBuddyCasino 11y agoThe bolts in question were made by an american company. The same issue happened with another bridge before. See https://news.ycombinator.com/item?id=9695276 https://news.ycombinator.com/item?id=9695276
- VLM 11y agoPossibly the journalist mixed two totally separate stories, hydrogen embrittlement and corrosion fatigue. That would fit the symptoms and the journalists visual observations of testing. I suppose H2 damaged steel, could lead to cracks, that when put underwater under tension would cause faster than expected corrosion fatigue like a couple years instead of a couple centuries, they're not totally unrelated. (edited to rephrase corrosion doesn't cause brittleness but brittleness can speed corrosion in the above scheme)
- benzofuran 11y agoNot knowing the particulars of the bridge CP system in place, hydrogen embrittlement is possible but it sounds more like stress corrosion cracking is the major culprit.
- refurb 11y agoWhere would the hydrogen come from in a situation like this? I know aluminum will produce hydrogen under basic or acid condition, but steel doesn't (I think).
- Someone 11y agoI think from a reaction 2Fe + 3H2O -> Fe2O3 + 3H2 See http://www.madsci.org/posts/archives/2005-12/1134348446.Ch.r.html http://www.madsci.org/posts/archives/2005-12/1134348446.Ch.r...
- benzofuran 11y agoThis sounds like a poster child for stress corrosion cracking - which would greatly impact the toughness of the material. Most steels (including stainless) become significantly more brittle under stress when exposed to high chloride environments like seawater while under load - much more than standard fracture mechanics would suggest. Basically there's chloride penetration and then hydrogen generation at the grain boundaries within the metal structure, which significantly reduces the toughness and allows for rapid and catastrophic failure easily.
- krschultz 11y agoActually that's not 100% correct. Most steel is not at risk, but some forms of high strength steel are susceptible to hydrogen embrittlement in salt water. I don't have enough info to comment on this case, and I don't trust the article because the author can't even get stress vs strain right, but it could be the problem here.
- jacquesm 11y agoGalvanic corrosion can cause steel to become brittle. http://en.wikipedia.org/wiki/Hydrogen_embrittlement http://en.wikipedia.org/wiki/Hydrogen_embrittlement
- mapgrep 11y agoMultiple civil engineering professors have been raising concerns over this issue since at least 2013. http://alumni.berkeley.edu/california-magazine/just-in/2014-10-10/bridge-over-troubled-bolts-uc-berkeley-experts-raise-safety http://alumni.berkeley.edu/california-magazine/just-in/2014-... http://alumni.berkeley.edu/california-magazine/summer-2013-new-deal/troubled-bridge http://alumni.berkeley.edu/california-magazine/summer-2013-n...
- kevlened 11y agoRelevant discussion over a year ago: https://news.ycombinator.com/item?id=7866795 https://news.ycombinator.com/item?id=7866795 Senate report: Caltrans ignored shoddy work on Bay Bridge in China and U.S. http://www.sacbee.com/news/investigations/bay-bridge/article2589402.html http://www.sacbee.com/news/investigations/bay-bridge/article... Californians pay for Bay Bridge flaws, but wind farm recoups costs from same contractor http://www.sacbee.com/news/investigations/bay-bridge/article4748610.html http://www.sacbee.com/news/investigations/bay-bridge/article...
- Animats 11y agoThey don't mention the steel supplier. It was Zhenhua Port Machinery Co., in Shanghai.[1] They usually make port cranes, not bridge parts. [1] http://www.sacbee.com/news/investigations/bay-bridge/article2589402.html http://www.sacbee.com/news/investigations/bay-bridge/article...
- batbomb 11y agoThere's a lot of parts in the bridge. The rods aren't supplied from Zhenhua, they are from Dyson Corp. of Ohio. http://www.sfgate.com/bayarea/article/Bay-Bridge-supplier-failed-to-reveal-rods-6037844.php http://www.sfgate.com/bayarea/article/Bay-Bridge-supplier-fa...
- Animats 11y agoOh. Thanks.
- jedmeyers 11y agoVery informative video on the basics of Charpy Impact Test: https://www.youtube.com/watch?v=tpGhqQvftAo&ab_channel=MaterialsScience2000 https://www.youtube.com/watch?v=tpGhqQvftAo&ab_channel=Mater...
- spiritplumber 11y agoI wonder if an electrical circuit has happened between the salt water and the various sections of the bridge...
- stephengillie 11y agoPerhaps during an electrical storm. Unless you think there's a long-term high-voltage short that nobody's noticed? Welders use Phosphoric acid and an electrified scrub brush (electrified lead wrapped with tough cloth, dipped in Phosphoric acid) to scrub welding scorches off of brushed stainless steel. Phosphoric acid on its own will etch stainless steel (and teeth), and electrifying the set dramatically increases the reaction rate, leaving bare metal after a couple of gentle passes.
- benzofuran 11y agoThere's most certainly a cathodic protection system on the bridge for the rebars and supports exposed to seawater, however if pooling water wasn't intended in the lower areas then there was likely no CP active in the area - and the protection of the other members may have accelerated corrosion elsewhere due to stray current interference. edit: It's actually the low voltage corrosion cells that you need to be cognizant of in such a case - most high voltage shorts fail before significant corrosion has taken place. Consumption rates for steel are in the kg/A-yr scale, and the concentration of the current dump is a major factor in general vs acute/pitting corrosion activity.
- spiritplumber 11y agoYeah. If you get this stuff on a new boat or barge, you have to basically send around guys with voltmeters with really long leads, all over the ship... if I was in charge of the bridge I'd do that. It's relatively inexpensive, and either finds the problem or gets rid of one common variable.
- benzofuran 11y agoThis is what I do for a living actually - and concrete / mixed structure corrosion control is unfortunately a lot more expensive and difficult than single structure (ie steel hulled vessels). A typical concrete CP system will be low output but with dozens to hundreds of individually controlled zones and reference electrodes to monitor the system performance.
- redwood 11y agoTo me the fact that the bridge took 15 years to build --- perhaps the longest major bridge project --- is probably related.
- pasbesoin 11y agoI seem to recall one of the cost saving measures, coming with some controversy, being to use Chinese steel, at least in part. Perhaps I am incorrectly remembering this. I would be interested in knowing the source of these components (which the rather long-winded article does not get around to providing).
- mikeyouse 11y agoThe bolts were made in Ohio and finished elsewhere in the U.S. They never left the country.
- comrade1 11y agoThe u.s. seems to be increasingly modeling itself after banana republics and corrupt third-world countries, so it's no surprise that someone shorted the project with bad steel and pocketed the difference.