Sinking 1,000 NYC subway cars in the Atlantic to create a reef didn’t go as planned the 2nd time around... the 1st 1000 were carbon steel Redbirds, which didn't corrode. But the stainless steel Brightliners? Different construction method, which didn't withstand the ocean environment

Retired New York City subway cars were deployed 19 miles off Ocean City to create an artificial reef for fish habitat and recreational divers. 

The Brightliners were predicted to last underwater for more than 25 years, but they started to disintegrate only months after they were dropped.

The MTA had good reason to believe the program would succeed. Just a few years prior, it had dropped more than 1,000 Redbird trains in the ocean. They remain on the ocean floor to this day, in part because they were made of carbon steel, which helps prevent corrosion.

As for materials, anything from concrete rubble to reclaimed culverts to damaged telephone poles can do the trick, as long as tires aren’t involved. In the 1970s, for example, more than 2 million passenger tires were bundled together with steel clips and dropped off the coast of Florida to expand the now infamous Osborne Reef. Except the steel rusted away and let millions of tires loose into the ocean. “They’re still picking up tires in Malaysia,” Sheehy says.

Even the best materials can be used in the wrong location. When a series of tanks were deployed off the coast of Maryland, they sank right through the soft sediment. By comparison, World War II tanks at the bottom of the English Channel, where the ocean floor is harder, haven’t budged.

By comparison, Brightliners were made of stainless steel. When the subway cars debuted in 1964, they were a mechanical and aesthetic innovation. The stainless steel made the train cars lighter on the tracks, but this worked against them underwater. Daniel Sheehy, an environmental consultant who’s been studying artificial reefs for more than 50 years, says the project failed for two reasons: first, because the trains’ envelopes were spot-welded, which formed a thin layer between the two metals that led to corrosion. Second, because the corrugated pattern made it easier for undercurrent waves to “grab on to” and further pull the stainless skin apart. “It is important that we learn from these mistakes and improve the process,” he says.

https://www.fastcompany.com/90716245/sinking-1000-nyc-subway-cars-in-the-atlantic-to-create-a-reef-didnt-go-as-planned

http://darkroom.baltimoresun.com/2015/01/next-stop-the-ocean-floor-where-new-york-subway-cars-go-to-retire/#1