Apr 26

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  • How can problems of "excessive vibration or noise" due to piping strain be avoided on steam turbines?
  • The inlet as well as exhaust steam lines should be firmly supported to avoid strains from being imposed on the turbine.
  • Adequate allowance should be made for expansion of steam pipes due to heat.
  • How  the deposits in turbine be removed?
    • Water soluble deposits may be washed off with condensate or wet steam.

    • Water insoluble deposits are removed mechanically after dismantling the turbine.

    • Experience shows that water soluble deposits are embedded in layers of water-insoluble deposits. And when the washing process is carried out, water soluble parts of the deposit dissolve away leaving a loose, friable skeleton of water-insoluble deposits which then break loose and wash away.

  • How the fatigue damage on high-pressure blades be corrected?
  • Fatigue-damage on high-pressure blades arises due to vibration induced by partial-arc admission. This can be corrected by switching over to full arc admission technique.

    • How the misalignment of Flanges be rectified?

    The bolts holding the flanges together are to be tightened. The coupling is to be checked for squareness between the bore and the face. At the same time axial clearance is to be checked.

    • How the problem of excessive speed variation due to throttle assembly friction be overcome?

    The throttle should be dismantled. Moving parts should be checked for free and smooth movement. Using very fine-grained emery paper, the throttle valve seats and valve steam should be polished.

    • How the problems of vibration and fatigue arise in steam turbine blades?
    • These arise due to flow irregularities introduced because of manufacturing defects, e.g. lack of control over tolerances.
    • System operating parameter, e.g. low flow may excite various modes of vibration in the blades.
  • How does solid-particle erosion occur?
  • Solid-particle erosion, i.e. SPE occurs in the high-pressure blades. And it takes place when hard particles of iron exfoliated by steam from superheater tubes, reheater tubes, steam headers and steam leads strike on the surface of turbine blades.

    • How does the internal efficiency monitoring lead to the detection of turbine deposits?
    • Process heat drop.
    • Adiabatic heat drop.
    • The process heat drop and adiabatic heat drop are obtained from a Mollier-Chart for the corresponding values of steam parameters – pressure and temperature – at initial and final conditions.
  • How is a flyball governor used with a hydraulic control?
  • As the turbine speeds up, the weights are moved outward by centrifugal force, causing linkage to open a pilot valve that admits and releases oil on either side of a piston or on one side of a spring-loaded piston. The movement of the piston controls the steam valves.

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