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Comment by msandford | Hacker News Reader

Sounds 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.

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This 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.

Possibly 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)

Not 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.

Where 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).

I think from a reaction

  2Fe + 3H2O -> Fe2O3 + 3H2

See http://www.madsci.org/posts/archives/2005-12/1134348446.Ch.r...

Yeah, 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...

And 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.

$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.

Since 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.

With a projected lifespan of 150 years [1], that seems pretty reasonable.

[1] http://www.dot.ca.gov/dist4/eastspans/

The 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.

The 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

Well, the construction of the bridge decks and the materials for the bridge was made in China...

"Well, the construction of the bridge decks and the materials for the bridge was made in China by the lowest bidder"

Fixed. In all seriousness there have been some pretty in depth articles on the subject and my biggest take away was that the company they hired did not have experience building bridges like this.

Of course it went to the lowest bidder, that's how business is done. But the lowest bidder in China is a lot worse than the lowest bidder in the US. Thanks to our regulations here, you can count on the lowest bidder to make a decent bridge. In China companies can pad their profit margin by using poor quality steel and workmanship, with no fear of consequences.

It should have gone to the lowest bidder that was able to meet the specifications. Just going to the lowest bidder alone pretty much guarantees trouble.

There were numerous problems specific to this. http://www.sacbee.com/news/investigations/bay-bridge/article...

So are Apple Watches and iPads. Please stop it with this nonsensical nationalism/racism.

It'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

[2] http://www.bloomberg.com/bw/articles/2014-11-16/china-turns-...

[3] http://en.wikipedia.org/wiki/Chinese_drywall

China 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-wonderbridg...

[2] http://world.time.com/2012/08/27/bridge-collapse-in-china-ra...

[3] http://www.nytimes.com/2008/05/25/world/asia/25schools.html?...

[4] http://www.npr.org/sections/parallels/2013/05/14/183635289/F...

Don't forget that lead paint keeps ending up in the toys made in China.

>Please stop it with this nonsensical nationalism/racism.

he didn't said "by Chinese" no "by members of Asian race". His comment is about quality controls and regulation in China which are known to be lax especially in the highly corrupt environment of China (no nationalism/racism here, just check the Transparency International. It is about country, it's political and economical system, not about nationality or race of the people).

... under some of the strictest quality control in the industry. Cutting corners when no one's looking closely enough is international.

Actually 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.

Galvanic corrosion can cause steel to become brittle.

http://en.wikipedia.org/wiki/Hydrogen_embrittlement

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