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Spectacle blinds u/s and d/s of control valve

  • 1.  Spectacle blinds u/s and d/s of control valve

    Posted 05-04-2020 08:55
    I am studying a P&ID drawing and observed that we have spectacle blinds upstream and downstream of a control valve. Service is high pressure ethylene. What is the purpose of having spectacle blinds on both sides of the control valve? Appreciate your thoughts.

    Nitin Parmaj

  • 2.  RE: Spectacle blinds u/s and d/s of control valve

    Posted 05-05-2020 01:30
    In one of the conditions, blinds are required for both sides of cv. If you want to keep the line in service, while the is control valve being attended by maintenance for any particular problem. But, once control valve is ready, again removal of blinds is required for which  line needs to be positively isolated, depressurized and purged. Till that time plant may be operated with control valve bypass line in service.  Usually this happens only when, waiting till turn around for handing over the control valve is not in the vicinity. Other wise one side blind may be enough, unless specific conditions are involved with this topic.

    Similar situation we have faced for one of the switch condensers, which leaked in PA plants. We have taken shut down of the plant and provided blinds at upstream and down stream. We have kept the plant in operation at low load. After attending the equipment leakage problem, again we have taken plant shut down and removed the blinds. Finally, the equipment was kept in operation and plant was operated at full load.



    KOTTI KUMAR Commission,Revampof
    Ex. Head Plant Operations

  • 3.  RE: Spectacle blinds u/s and d/s of control valve

    Posted 05-05-2020 08:43

    One possibility is to prevent any flow from either the upstream or the downstream sides of the control valve.  The valve can then be safely removed or worked on if maintenance is needed.  A spectacle blind is used so it's apparent that a blind is in the line.

  • 4.  RE: Spectacle blinds u/s and d/s of control valve

    Posted 05-05-2020 08:57
    Spectacle blinds upstream and downstream allow isolating the control valve to remove the valve for service.

  • 5.  RE: Spectacle blinds u/s and d/s of control valve

    Posted 05-06-2020 00:56
    ​Normally Spectacle blinds (SB) are use for positive isolations of equipment during maintenance only. isolation valves has been provided at every control  valves upstream and down stream with bleed drain valve in to drain system or flare for depressurizing. if control valve is required to remove for maintenance then, follow the SOP for isolation procedure and after remove control valves you can install end blind of both side of pipe work during maintenance. so I would suggest SB is not required, how ever if it is provided then could be use for isolation purpose.

    in my experience we use end blinds instead of SB as per SOP and suggest not required to provide during design phase.

    Hiteshkumar Patel PE,CSP


  • 6.  RE: Spectacle blinds u/s and d/s of control valve

    Posted 29 days ago
    There are other considerations. Spectacle blinds stay in place at the location required after being engineered to fit the process conditions. Numerous incidents have occurred when individuals, years after the plant design is started up, selected the wrong end blind which was damaged due to inadequate strength. Some incidents occurred due to the end blinds being corroded or otherwise damaged while in storage or transit. Other times budget restriction prohibit purchasing replacement blinds so lesser alternatives are inappropriately used. This can allow loss of containment resulting in toxic, flammable and physical incidents.

    One can use slip blinds, end blinds, spectacle blinds or line blind devices. New types of devices are often coming on the market. The selection depends on Process conditions, how frequently the location must be blinded, the properties of materials being contained, the projected knowledge of the workforce and owner company culture.

    Gary Koehler