Jan, Thanks for the posting. Yes, methane gas will accumulate - due to the permeation through HDPE - in the annular space between HDPE and the old steel pipe (at least when the old steel pipe is tight - then the secondary diffusion due to steel layer will be much slower - this should be checked because the story that follows assumes old but still tight steel). You will need a continuous flow...
Thread: Relining of steel pipes for Methane with HDPE pipes.  |
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Started 3 months ago by Jan
Relining is when you put new HDPE pipe in old Steel pipe. Outside diameter of new HDPE pipe is smaller than inside diameter of old steel pipe. There is a gap between pipes. Question is: Is there a possibility of accumulation of methane which flows in HDPE pipe and will diffuse in the gap between pipes? What is the volume of diffused methane in one year, per meter of pipe, when HDPE pipe ...
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composite agency replied 3 months ago
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Jan replied 3 months ago
Thank you for the reply. Let say that Steel pipe is still tight, and gas due to the permeation through HDPE will accumulate and will create pressure outside of HDPE pipe. After depressurization of HDPE pipe pressure of permeationed methane between HDPE pipe and steel pipe may be so high that HDPE pipe will collapse? Did I understad this correctly? If yes, I will propose to create openings ...
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composite agency replied 2 months, 4 weeks ago
Pressure inside is 6 Bar? Collapse resistance pressure for unaged thin HDPE cylinders is approximated by: Pcollapse = 0.365 * E * (t^2/r^2) with r > > t With E is the Young Moduls of HDPE (08. Gpa, unaged), t is the thickness of the wall (6.3 mm), r is the radius (48.7mm) gives: 48 Bar. Now since the maximum gas pressure in the interface between HDPE and Steel will never exceed the ...
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Jan replied 2 months, 4 weeks ago
Thank you for the explanation. Still I'm interested in the calculation: I just dont understand why is important to know space between HDPE and STEEL, when there is atmospheric pressure and space is ventilated, to prevent cumulation of methane. For me is important volume of diffused methane. Here are the conditions. What is the volume of diffused methane in one year, per meter of pipe, when ...
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composite agency replied 2 months, 4 weeks ago
Jan, OK point taken. You are interested in a worst case gas flux of Methane through HDPE (note that if the Methane accumulates in a non ventilated environment or a ventilated environment with a slower resulting removal rate than the diffusive flux, Methane pressure will build-up in the annulus, which will reduce the flux as a function of time - then the interfacial space and removal rate is ...
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Jan replied 2 months, 4 weeks ago
Thank you for the answer. It helps.
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