Collapse of multilayer pipeline?  

Posting by simon powell on April 17, 2008 at 15:29:29.

Hi there,

Various sources suggest multiple layer of polymer tubes, flexible pipes, to improve permeation characteristics. Commonly suggested solutons are Ethyl Vinyl Alcohol (EVOH), Polyamides put on top of Polypropylene, Polyethylene etc. for Hydrogen, Natural Gas, Carbon Dioxide containment or transport. All the graphical stuff and consultancy that comes with it, is very interesting; but all the ambient process conditions (yes packaging is not so complex!) are a minor challenge compared to high processing pressure, and high temperature applications. Then, the proof of the multilayer pudding is in the eating? Please advise on this pipeline issue, guys!

S Powell

          follow up posts
    On 04/17/2008 naren posts: Hi Powell,

    I tried to understand you question, you must be want to know how to deal with gas permeation in plastic pipelines.

    Flexible pipelines used in onshore and offshore pipeline have an annulus which collects the permeated gas and is vented out at the ends. This venting protects the pipeline from collapse due to annulus pressure.

    Nowadays a cheaper [than conventional flexible] composite pipeline is avialable known as RTP [Reinforced Thermo Plastic] which do not have an annulus. To prevent BTEX permeation into enviroment, an aluminium barrier is used as casing with vents at ends.

    Hope this helps.

    Rgds Naren
    [responses: 3]

      On 04/17/2008 simon powell posts: Many thanks Naren,

      My question is indeed related to the relining of an existing steel pipeline for the sake of conveyance of hydrogen gas and/or liquefied petroleum gas.

      Do you have any idea of other essential design considerations, besides the mentioned pressure build-up by permeation into the polymer and swelling pressure by gas/liquid uptake of the plastic liner?

      Moreover, what sort of polymer would be suited for this lining application?

      Simon Powell

      [responses: 2]

        On 04/17/2008 Composite Analytica posts: For a case description regarding a hydrogen diffusion, solubility and permeation into fluoropolymer on top of titanium oxide, please check the case description below. Note that we assume an ideal and tight interface between the two materials. Moreover, realize that swelling pressure is not an issue here, since the solubility of hydrogen is very low and the free volume of the polymer considerable (at least 10 volume percent based on the molar volume of the polymer at 0 Kelvin). Click the following picture:

        I trust this is helpful.

        [responses: 1]

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