Some of Sunoco’s recent engineering drawings indicate a much higher pressure than previous drawings did. Increasing the pressure in the Dragonpipe (Mariner East pipeline system) would be an important change for several reasons. For Sunoco, higher pressure is a way of forcing more product through a pipeline of a given diameter. But higher pressure also makes leaks more likely; and, if a leak occurs, the amount of product leaked and size of the blast zone would be greater.
That’s why it is alarming to learn that Sunoco has been indicating higher pressures in its recent engineering drawings, submitted to the DEP as part of the permitting process. Typically, these drawing have shown “1480 PSIG” as the “internal design pressure” for the pipe, but some now show “2100 PSIG. You can see an example of this notation on the final page of this document, filed with the DEP.
This change, if it is real, is a big deal. It amounts to a 42% increase in pressure. Based on an informal check with an industry expert, such a pressure would be unusually high, even with brand new pipe.
Perhaps the more likely explanation is that this is a typographic error, and the real design pressure is still 1480 PSIG. But if so, this is unforgivable sloppiness. Pipeline pressure is a critical factor in pipeline safety. To misstate the pressure by 42% in a regulatory filing speaks of a very unprofessional engineering process.
Either way—covert design pressure change or typo—this doesn’t speak well for the way Sunoco is dealing with this project.
I am grateful to the sharp-eyed regulatory team at Clean Air Council for first noticing this and bringing it to my attention.
Dragonpipe Diary 
WOW!
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According to retired Arco exec, 2000 psi is required to maintain a liquid form of contents. If this is a min, what happens to p. with smaller dia. pipes in the same line?
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My understanding is that about 500 psi is required to keep the contents liquid. To keep it liquid at the far end of a run of 7-10 miles between pumps requires something close to 1500 psi at the pump, depending on pipe diameter. (It’s a given that these materials can’t be permitted to volatilize–become gaseous–at any time in their journey from the fracking fields to the plastics plant.)
But your point is well taken: the smallest-diameter pipe will be a bottleneck even if it is possible to pump at higher pressure in a larger line that is connected.
As a practical matter, I understand that the transition between pipe diameters would normally be made at a pumping station, and the pump would control the pressure on the downstream pipe, so the pressure in the pipe of one diameter would not have a direct effect on the pressure in the next. (But these pipelines have never been “normal”.)
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