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The time: January 27th, 2017, 7:00 AM local. The place: New York City and environs.

Jormungandr, the Snakebot of Doom, has just finished steamrolling New York City into something more closely resembling a gravel driveway.

Now it has returned to the vicinity of lower Manhattan and is busy extracting any iron or steel that it can find in the rubble in order to convert it into steel railgun ammunition.

It is currently firing the six large railguns in its tail, each shot containing about 6.8 metric tons of steel, at a combined rate of 4 rounds per second. If it has to use its small railguns for self defence, they won't add significantly to the rate at which steel is being consumed.

Jormungandr's mouth is currently ingesting any iron or steel it can find in the rubble in order to resupply its ammunition bunkerage. It is easily able to resupply its ammunition faster than it can expend it provided sufficient steel is nearby.

How long would the steel found in New York City and environs be able to supply Jormungandr's appetite before it has to move on to another source of steel?

Consider this to be the real world, with the exception that over the evening of the 26th until the morning of the 27th, New York has been experiencing severe blizzard conditions, leading to closure of ports, airports and roads.

At the time in question, neither roads, ports or airports have yet reopened.

The blizzard will mean that there are more ships in the ports adjacent to NYC than usual, and that cars cannot readily leave.

By New York City and environs, I mean the area with this definition: https://drive.google.com/open?id=1piz-lZJ_ti3EAnEH7b_LNgIguiQ&usp=sharing

Please account for the quantities of any man-made iron or steel within the area, no matter how large, including any vehicles, shipping, building structural members, railway track, rolling stock and tunnel shoring or lining, with a reasonable justification. The exact amount of steel in each building need not be accounted for.

Small objects such as nails or bolts, unless part of a larger steel structure, may be discounted, as Jormungandr will not bother with anything so trivial. This will rule out its being interested in scavenging from wooden-framed dwellings, but steel framed dwellings are another matter.

EDIT

The world in this question starts out pretty much as the world with which we are familiar. However, the question is, How long can Jormungandr stay here before it needs to move on to another source of steel, and the world being built is one where Jormungandr stayed for x time, firing continuously, then had to leave to find more steel. That world may or may not resemble our own so much, depending upon the magnitude of x.

I want to know X. Can it stay for Hours? Days? Weeks? Months? Years? How many of them?

If Jormungandr stays for 'hours', then the world will be considerably different than if it stays for 'weeks'. Hours means that all that many of the survivors of NYC have to do is sit tight and wait for relief efforts to come to them. Weeks means that the survivors have to become refugees and travel to somewhere where they can get the necessities of life, since Jormungandr isn't going to leave much in the way of the necessities of life for the survivors to use, and how many relief agencies are going to risk coming close to a thing that destroyed US armed forces sent against it so easily?

The longer Jormungandr stays put, the more time humans will have to try to come up with unconventional means to try to destroy it. The longer it stays put, the more likely that humans will discover that the birds have been bugged before it moves on. The longer it stays put, the more likely it is that some idiot may try a massed submarine ICBM launch against it.

So, while, yes, this is a question about a story set in a world, the world-building aspect of the question is that the answer affects how the world changes. Please don't think that just because the question is basically "how much steel is there in NYC, and then divide by 27.2 metric tons per second" that there aren't other implications that will greatly affect that initial, known, world.

MolbOrg
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Monty Wild
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    @JDługosz, Yes, this is "a question about a story set in a world". However, the world-building aspect of the question is that the answer affects how the world changes. Please don't think that just because the question is basically "how much steel is there in NYC, and then divide by 27.2 metric tons per second" that there aren't other implications that will greatly affect that initial, known world. Just because I'm not asking "How will the quantity of steel affect the rest of the story" doesn't mean that I am not thinking about it. Have a look at my edits. – Monty Wild Jun 20 '17 at 02:56
  • How powerful is the snake's sensors? Could it perceive the ducts going under the street? Is it capable of taking the metal frame inside the concrete buildings? – Sasha Jun 25 '17 at 21:39
  • @Sasha, Jormungandr has a great many high-powered broad-band RF emitters and corresponding receivers. It can emit pretty much any form of radar/lidar you can imagine with almost unimaginable power. It is also capable of seismic imaging, so yes, it can detect any manmade object below ground. It is also equipped with 10 metre thick shape-memory-alloy driven tentacles strong enough to lift a 60,000 ton container ship clear out of the water and fold it up like an aluminium can, so, yes, it can gobble up skyscraper frame members like spaghetti. You name it, and if it is steel, it can eat it. – Monty Wild Jun 25 '17 at 21:47
  • Can it recycle it's own ammunition? If so, how efficiently? – Christopher King Jun 26 '17 at 11:28
  • @PyRulez, As a general rule, no, it can't recycle its own ammunition. It's firing steel railgun slugs, which have no cartridge to be recycled, and even if it came across the impact site of one of its non-disintegrating slugs, an impact velocity on the order of 4-8 kilometres per second wouldn't leave much of the slug to salvage. Then, most of its steel slugs disintegrate into thousands of smaller flechettes prior to impact in order to maximise damage - very little in this world is so tough that it would require the attention of a single railgun slug that big. – Monty Wild Jun 26 '17 at 21:24

2 Answers2

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Right, this will be a very rough estimation since I'm not an engineer.

First and foremost cars.

According to what I could find online you have about 700K cars in the city, each weighing 4009 pounds (1818.452Kg), so considering that almost all of the car's weight will be metallic components then you have 1,272,916.4 tons.

Add to that the 6,384 subway cars at around 38 tons each for 242,592 tons.

1,2K real trains, each one weighing about 500 tons, for a total of 600,000 tons

For buildings things get a little more complicated, but using the Empire State building as an example, it has 60,000 tons of steel and weights a total of 365,000 tons. So it would give about 16,5% of the total weight in steel, considering that buildings under 30 floors will have half of that we will come to:

47,000 buildings with 24,373 total floors in buildings over 30 floors and 225,203 floors in buildings under 30 floors.

The Empire State building has 102 floors, so that would give about 3,578.5 tons per floor, that would give about 600 ton of steel per floor.

That would give a total of 14,623,800 ton of steel in the bigger buildings and 67,560,900 tons of steel in the smaller ones.

Ships: According to the NY Harbor website there are 351 ships in harbor right now, since OP says the harbor is more filled then usual, I'll hazard a guess and say it will have about 500 ships of considerable size (600.000 tons).

Bridges: According to Wikipedia there are over 2000 bridges and tunnels in New York with an average length of 952,3 meters.

Taking the Brooklyn Bridge as an example, it has an weight of 14,680 tons, with a span of 1.833677 Km and 3084.42 tonnes of steel in it. This would give about 1,682.09 Tons of steel per kilometer. Giving an total of: 3,203,719.27 tons of steel.

Guns: Apparently there are 1,2 million registered guns in NY, so for practicality I'll assume there are 2 millions guns in NY total. I'll consider that they will have an average weight of 0,5kg and add another 0,5kg as ammo for each one. This would bring about 2,000 Tons.

Only that will amass about 387,505,927.67 tons of steel in New York for your snake to feed on. At the rate you specified the snake will devour it all in about 5 and a half months if my calculations are right. 

+-----------------------+---------------+---------+-------------+
|         Item          | Tons per item |  Count  |    Total    |
+-----------------------+---------------+---------+-------------+
| Car                   |      1.818452 |  700000 |   1272916.4 |
| Subway car            |            38 |    6384 |      242592 |
| Real trains           |           500 |    1200 |      600000 |
| Tall building floors  |         24373 |     600 |    14623800 |
| Short building floors |        225203 |     300 |    67560900 |
| Ships                 |           500 |  600000 |   300000000 |
| km of bridges/tunnels |       1682.09 |  1904.6 | 3203708.614 |
| Guns                  |         0.001 | 2000000 |        2000 |
| Total                 |               |         |   387505927 |
+-----------------------+---------------+---------+-------------+
typesanitizer
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Sasha
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  • There's a factor of 10 error somewhere in your empire state building calculations. 100 (ish) floors * 60 tons/floor only gives you 6000 tons, not the 60000 you started off with above. – JerryTheC Jun 25 '17 at 23:27
  • dammit, gonna recheck my calculations. – Sasha Jun 25 '17 at 23:38
  • I think you got the decimal point in the wrong place when working out the 60 tons/floor - 10% of 3,578.5 is 357.85, so 16% should be around 600 tons rather than 60. – JerryTheC Jun 25 '17 at 23:50
  • Yeah, decimal cases are my bane and nemesis. – Sasha Jun 26 '17 at 01:32
  • What about ships at dock? Have you considered that? At about 60,000 tons laden for a contaier ship, it might be significant. – Monty Wild Jun 26 '17 at 07:46
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    Do handguns add anything significant? What about bridges and tunnels? – Monty Wild Jun 26 '17 at 07:48
  • Interesting calculations. Out of curiosity: do you have any sources you could cite for those numbers? – Secespitus Jun 26 '17 at 10:43
  • @Secespitus mostly wikipedia, I hope that academic standards don't apply here XD – Sasha Jun 26 '17 at 19:48
  • Unless a question asks for hard-science Wikipedia is more than enough, thanks :D – Secespitus Jun 26 '17 at 19:52
  • @Secespitus, Sasha, I wrote this question as hard science, but it wasn't getting any responses and when MolbOrg edited the tag from hard-science to science-based, I let it stand. I'd still like hard-science-ish answers, though but as long as they're sort of justifiable and correct to within an order of magnitude, that's enough. – Monty Wild Jun 26 '17 at 21:32
  • @MontyWild Ah, okay. Didn't realize it was originally a hard-science question, only looked at the current tags. Personally I would say "If you want hard-science be prepared not to get any responses - but if that's what you want then so be it!". But I also remember having read quite a few discussions on Meta about that tag... science-based makes answering easier, so at least you have some input from others now. That's something... I guess? – Secespitus Jun 26 '17 at 21:38
  • @Secespitus, I have to agree with your assessment of the [hard-science] tag. That's why I didn't change it back from [science-based]. Anyway, I just need a plausible number, not an incredibly accurate one. – Monty Wild Jun 26 '17 at 21:46
  • As for ships at anchor, remember that I said that there had been a blizzard the previous night, and the port was closed. The number of ships in port cannot exceed the docking and anchorage capacity of the ports in the area - any ships unable to dock or anchor in a port would be forced to remain well out to sea and try to ride out the storm at sea, manoeuvre around the storm or go to an alternate port, and in any of those cases would not be in NYC. – Monty Wild Jun 26 '17 at 21:51
  • I'm considering 500 ships as basically a wild guess, I could find a site that showed about 350 in the harbor, but I couldn't find anything about how many ships they can service at once. If you know, just tell me and I can change the numbers. – Sasha Jun 27 '17 at 02:27
  • Sasha, recheck your bridges and tunnels calculations, I made it around 3MT of steel, not 3GT. Did you multiply by average length rather than by average length/1000? – Monty Wild Jun 27 '17 at 02:43
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    I'll pretend I had totally see that point and it was an elaborate test. Congratulation, you passed! – Sasha Jun 27 '17 at 03:02
  • @Sasha, could you add numbers for railway tracks (mentioned by OP in question)? Apart from that, it's a very thorough answer :-). Also, the numbers don't seem to add up: I'm getting a total of roughly 88 million not 388 million. Maybe you missed some zeroes with the bridges calculation? Lastly, could you add a nice table for ease of reading? (generating tables: https://senseful.github.io/web-tools/text-table/) – typesanitizer Jun 28 '17 at 16:10
  • My bad, I misunderstood the ship mass to be 600 instead of 600000. The calculations are right then. i've added a table. – typesanitizer Jun 28 '17 at 21:35
  • Note that gun ammunition is made out of brass and lead. Only rarely will a handgun bullet have a steel jacket or core. – Schwern Jul 02 '17 at 17:50
  • Then consider that as miscellaneous pieces of steel like random nails. – Sasha Jul 04 '17 at 01:55
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If given a target, possibly indefinitely.

Assuming the area is quarantined once it shows up and no new sources of steel arrive

Once the area is clean, the size of the railgun rounds will mean its own spent ammunition make up the largest deposits of ferrous metal in the surrounding area. Assuming the thing isn't intelligent, if you can keep it shooting you can keep it chasing its own tail indefinitely.

Separatrix
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  • I wonder where that downvote came from: This answer definitely makes sense. – Burki Jun 26 '17 at 15:05
  • @Burki, probably because it's not in the spirit of the question which is looking for a more calculating answer in terms of the quantity of steel in the city. – Separatrix Jun 26 '17 at 16:34
  • That may be, but since it exposes a flaw in the assumption, it's perfectly valid, and more valid than any calculatuion. But well. – Burki Jun 26 '17 at 17:51
  • The worst part is that you are right! – Sasha Jun 26 '17 at 21:20
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    Uh... No. Jormungandr is firing railgun slugs at 5 to 8.5 kilometres per second. This sort of launch velocity is sufficient for it to hit targets literally on the other side of the world, and at the present, it's launching against Russia and China, It would have to go there to even have a hope of recovering its ammunition, and needing to do so would mean that it had exhausted its local source of supply, and your answer doesn't even attempt to answer that question. – Monty Wild Jun 26 '17 at 21:29
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    @MontyWild Wow, that seems like something that should have been provided in your original post! – sirius_pain Jun 29 '17 at 13:09
  • @sirius_pain In fairness railguns tend to fire high speed projectiles and 7 tonne projectiles are pretty big, so extreme range was to be expected. – Tim B Jul 01 '17 at 17:15
  • @TimB, one could also suggest that many people wouldn't think of railguns in terms of ballistic flight paths – Separatrix Jul 03 '17 at 07:51