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Thursday, September 4, 2008

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In earlier post "Complicated Tube Rupture Scenario... Nightmare in Sizing a PRD" related to complication of a tube rupture involving many relieving combination. This is a great challenge to a Pressure Relief Device (PRD) designer to provide a correctly sized PRD. For a heat exchanger with low pressure liquid on shell side and high pressure liquid on tube side, pressure surge in one of the thread as discussed in "Tube Rupture : Pressure Relief Valve (PSV) or Rupture Disk (RD) ?"

However, once the rupture is bursted, continuous liquid feeding flare system could be a difficult issue. What can be done ?

The are some ways may consider to handle this situation. The following is one of the way can be considered but still require proper engineering and HAZOP analysis before implementation.

It is recommended to provide a surge vessel on the outlet of rupture disc to capture short term liquid flow. On the surge vessel, there will be a pressure relief valve connected to flare. Apart, provide High-High level trip (LZHH) with two-out-of-three (2oo3) voting on the surge vessel in order to shutdown all the high pressure source.

With above configuration, in the event of tube rupture, high pressure liquid will leak into low pressure side in shell side. Surge pressure may cause rupture disc burst and liquid will discharge into surge drum. Liquid level in surge drum will built up, trigger High-High level trip (LZHH) in surge drum and initiate all Shutdown valves (SDV) closure. This will stop catastrophic failure due to surge pressure and liquid disposal problem.

One shall take note above shutdown configuration may not have proper SIL level for protection. It need further improvement and proper configuration.

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posted by Webworm, 2:06 PM


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