An unexpected ESD Valve failure mode
  • Vote Up0Vote Down ihg May 2008
    Posts: 3
    I have recently been commissioning a new gas plant which has a number of large (DN250 and larger) Class 600 ball valves from a reputable supplier in ESD and BDV services. As is usual, these have quick exhaust valves fitted to ensure rapid depressuring of the pneumatic piston actuators. Most QE valves have two paths to atmosphere - a restricted one back through the solenoid valve, and the much larger pilot-operated port direct to atmosphere. Even if the QE valve should stick closed, the actuator will normally depressurise, albiet slowly, through the solenoid valve. In this case, several of the valve actuators pressurised, but would not depressurise, even with all tubing disconnected from the QE valve ports! To add to the hazard, attempting to disassemble the QE valve in-situ sent internals rocketing upward, fortunately without the tech being in the way. Inspection of the design revealed that the QE valves were fitted with an internal check valve in the pilot path, preventing backflow through the solenoid from the cylinder, and the mechanical design was such that the force available to open the main valve port was inadequate to overcome stickiness in the valve's piston assembly after the valves sat in the pressurised state for several months prior to the first scheduled proof test. These QE valves are now being replaced by a less sophisticated device.
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  • Vote Up0Vote Down cyoungcyoung May 2008
    Posts: 5
    Thanks ihg,
    Just goes to show that sometimes the simplest solution is the best.  Technology is not always the best answer to the situation. 
    I wonder if others have valves and actuators of similar design?  If so, an inspection may be in order.

    Regards
    Clyde
  • Vote Up0Vote Down spacol May 2008
    Posts: 6
    Yeah.. rela nice one.. . thanks for the reminder, I'll justv have to remind them when we getv to detailed design that simplicity is sometimes the best way to go.....
  • Vote Up0Vote Down onil May 2010
    Posts: 1
    The reliability issues concerning on microelectromechanical systems (MEMS) have steadily developed in recent years. One of the processes to understand MEMS reliability is to know the failure modes of these microdevices. In this chapter, we seek to report on both well known and unknown failure modes of MEMS. Most of the failure patterns are the same in nanoelectromechanical systems (NEMS), because NEMS followed a developmental path similar to that of MEMS in functional design, materials, and fabrication. Therefore, the existing results of MEMS failure modes can be used as a reference to nanoscale system reliability research. The failure modes discussed in this chapter contain stiction, wear, fracture, crystallographic defect, creep, degradation of dielectrics, environmentally induced failure, electric related failure, parasitic capacitance, dampening effects, delamination, and packaging.
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