phosphate
1yr ago
AIUI hydrates are less likely to form in dense phase natural gas, which is one of the advantages of this kind of pipeline -- is that right?
No, that would seem to be a disadvantage of a high pressure pipeline based on the methane hydrate phase diagram you linked, looking at the chart as pressure goes up so does methane hydrate formation.
Supercritical methane: above -82 C and 46 bar
NS1/2 Operating from your first link: 2 to 6 C and 220 to 106 bar
Methane hydrate from the phase diagram you linked elsewhere in the thread: NS1/2 is pretty much exclusively operating in the methane hydrate range, at 2 - 6 C it looks like you need to be under maybe 20 bar to be out of the methane hydrate zone.
So if NS 1 has been operating in the methane hydrate zone for 20+ years why has it not had any issues until now? Well if no water is in the gas stream then no methane hydrate can form. And going off of steam tables and partial pressures at the injection state of 220 bar and 6 C the water content is 43 ppm, which does not leave much water at all for methane hydrate formation. Even less if they stuck the gas stream through a final dehydration step.
Given the above I really question the methane hydrate theory, especially in NS2. I could see at least being possible over time in NS1 as a build up they ignored. But still very doubtful, you'd have to assume that the Russians and Germans both ignored it. For NS2 which hasn't ever been sending gas through, any methane hydrate would be forming out of at most 43 ppm of water that was originally in the pipe when pressurized. Which is a very small amount of methane hydrate.
Above is also assuming that the Russians were not adding any kind of methane hydrate inhibitor to their gas. Or doing any further dehydration after compressing and cooling. Either way the gas is very dry to begin with, so there is not much water to form into methane hydrate, so there won't be much methane hydrate.
https://upload.wikimedia.org/wikipedia/commons/b/b4/Methane_Hydrate_phase_diagram.jpg
phosphate
1yr ago
Despite the name, the fluid that flows through a natural gas pipeline is a liquid not a gas, and as a liquid is incompressible (or more accurately comes pre-compressed)
No, any methane in a normal natural gas pipeline is not liquid and will never be a liquid. The critical temperature of methane is -82 C and actual liquid natural gas as made is much colder. It takes special built terminals and a ton of refrigeration and a ton of very expensive insulation. Any methane in a transmission pipeline is either gas or supercritical
Some whacky Tom Clancy-esque scheme involving hundreds of people across half a dozen countries was executed successfully and in complete secrecy outside Hersh's unnamed source? or Russian industrial safety standards being a bit shit?
Iran-Contra? Manhattan Project? US bombing Cambodia? I mean I generally agree with you that complicated conspiracies' are hard to keep secret. But at least you have to admit that maybe your perception is flawed as you have no idea what the success rate is by definition, as they remain a secret and you only hear about the ones that are revealed.
phosphate
1yr ago
The pipes were pressurized but product hadn't been flowing for months which means plenty of time for water to seep in and start forming methane hydrate. IE the liquid natural gas turns into a solid.
Water at 210 ft of pressure does not and will not ever "seep in" to a pipeline at 105 bar / 3500 ft pressure. Any water in NS1/NS2 was what couldn't be taken out at the point of injection / compression.
Just running the numbers based on the source you linked to above its pretty clear that you can rule out methane hydrate.
I) First determine how much water is in the pipeline to begin with. Per your source the gas is injected at 220 bara and 6 C, which we can use to determine the partial pressure of water in the inlet gas. Per the steam table linked below the partial pressure of water vapor at 6 C is 0.00935 bara.
Since the partial pressure of a gas component in a given mixture is its mol fraction * the total pressure we can determine that the mol fraction of water in our gas stream is 0.00935 bar / 220 bar = 4.25E-05.
Conveniently that same Petro Skills blog linked also had another page that calculates the total kmol inside the pipe during storage equilibrium as 12017147 kmol. With the mol fraction calculated above we can determine the total kmol in the pipe at storage equilibrium to be 12017147 kmol * 4.25E-05 = 510.95 kmol = 9197.05 kg of water present in the pipeline at storage equilibrium of 165 bara.
II) Next determine the how much water is actually in any given mass of methane hydrate. Based on the chemical structure given in wikipedia we can determine the mass fraction of water in a given mass of methane hydrate:
methane hydrate -> 4CH4 *23H2O
mass fraction of water:
= [mass methane hydrate] / [(mass methane) + (mass water)]
= [kmol methane * MW methane] / [(kmol methane * MW Methane) + (kmol methane * MW water)]
= [23 mol H2O * (18 kg / kmol)] / [(23 mol H2O) * (18 kg / kmol) + (4 mol CH4) * (16 kg / kmol) ]
= 414 / 478 = 0.866
III) We can use the answers from 1 & 2 to check the feasibility of an accident caused by a methane hydrate plug based on water availability. Just taking your estimate of a 10 ton methane hydrate plug:
10 ton = 20,000 lbs = 9197.05 total kg methane hydrate.
Which contains 9197.05 kg * 0.866 = 7856 kg of water, or 85% of all water in the entire pipeline. For reference the pipeline is 1224 km long, and at a cross section of 1 m2 & density of 900 kg/m3 the total length of that plug would be about 10 meters if a perfect cylinder. Since I think that there is literally no way that 85% of the water in a 1,224,000 meter pipeline would somehow freeze up in a single 10 meter (or 100 m or 500 m) section I think its safe to rule out a 10 ton hydrate plug. Even if it was one ton that's still 8.5% of the water stuck in a 1 meter section.
A pertinent question would be: why does this 10 m section have such wildly different conditions that the other 1224 km of pipe? Even such that its this 10 m section across 2 different 1224 km pipelines? It might be a valve but I'm figuring that they would have mentioned something about a valve. And valves are expensive, especially when they are 1m diameter and cause a large pressure drop and you just spent all of this effort to get 1224 km of pipe down to 6 micron smoothness to reduce pressure drop because you have 490,000 HP of compression. Also I think relatively quickly someone would have pointed out that the explosion happened at a valve location so maybe that had something to do with it. Given that we have not heard about a valve and the huge cost of having one in the first place I think we can rule out a valve. If it was a hole or something in the insulation I think you have to ask why did the hole happen in relatively the same place to two pipelines a mile apart that are ~1200 km long?
Even if it was a more gradual build up on a larger section you still have to answer how all the water ended up in a pretty small section. And the longer the section is the less its going to plug the pipe. And there really isn't enough water to go around, and how did it end all end up freezing in such a relatively small section? If it happened during pressurization they would have caught it then by noticing the massive pressure drop from the plug forming.
But overall there just isn't enough water in the gas to begin with to support the methane hydrate plug hypothesis. Especially since the Germans are on the other end of the pipeline and would have noticed as soon as any significant amount of water started showing up in the gas. Or if there was water being added to the gas. Or if the Russians shut swapped out dry gas with wet when it was shut off. But maybe my math is off, feel free to correct.
I would like to read the original source with the idea though if you have it?
https://www.thermopedia.com/content/1150/
https://petroskills.com/en/blog/entry/april2022-totm-Transportation-of-Natural-Gas-in-Dense-Phase%E2%80%93Nord-Stream-1
http://www.jmcampbell.com/tip-of-the-month/2022/06/nord-stream-long-distance-gas-pipeline-part-3-application-of-basic-and-aga-equations-for-estimating-maximum-gas-flow-in-a-long%E2%80%90distance-pipeline/
https://en.wikipedia.org/wiki/Methane_clathrate
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