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July 31 - August 4, 2017

How does rapid depressurization affect lining performance in vessels and line pipe, and how can you identify any failure that might result?

Selected Answers

From Michael Halliwell of Thurber Engineering Ltd. on August 10, 2017:
Thanks I said, I don't have as much experience on them and had only liquids come to mind initially. I can certainly see how the gas/polymer interactions could also cause significant issues.

From Steve Brown of EDF Energy Ltd on August 8, 2017:
One aspect not covered by the previous answer, but which could lead to catastrophic failure, concerns the solubility of gases in polymers, which can be substantial at high pressure. Slow subsequent depressurisation (DP) would lead to simple diffusion/desorption of the gases out of the solid, with probably no effect on mechanical/physical properties. However, rapid DP can lead to catastrophic disruption of polymers, which if viewed (e.g., experimental rig), might show as large volume increase with 'massive' blistering. I have seen this on experiments of various gasket /o-ring polymers, and interestingly, while the materials are clearly 'destroyed' mechanically, they often would return post-experiment back to their original size/shape with little sign of having suffered any distress! The environments were carbon dioxide with pressure reduced from ~40bar to atmosphere in ~20 minutes. Certain polymers/formulations were resistant, while others failed in the manner described, so one can only predict behavior by experiment, I believe. Linings are typically much thinner film polymers than o-rings, and so I would expect linings to be less sensitive to DP. The actual effects are also likely to be very sensitive to gas type/mix, DP range (bar) and DP rate.

From Michael Halliwell of Thurber Engineering Ltd. on August 3, 2017:
I might not be able to help much on the modes of lining failures (I'll throw some ideas out there.), but I can add to how the rapid depressurization can work on the lining system. When pressurized, the tank and piping will experience elastic stretching due to the pressure. The amount of stretch will depend on the pressure contained and the material both tank and piping are made out of. When the pressure is rapidly released, both quickly return to original shape. If they respond at different rates, I suppose there is the potential for delamination and/or cracking of the coating as a result of the pressurization and stretching of the vessel and piping. If it is cyclic, then the stretch and contraction could further crack the lining, delaminate it or even force whatever is in the tank and pipe behind the coating (blisters?) and have it leveraging the delamination,like a freeze-thaw cycle destroys asphalt.

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Tagged categories: Coating failure; Linings; Quality Control

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