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Sunday, May 2, 2010

High frequency acoustic excitation downstream of pressure reducing device potentially results downstream piping failure due to Acoustic Induced Vibration (AIV). Earlier post "Principle in Eliminating & Minimizing AIV Impact" discussed about common principles in minimizing Sound Power level (PWL). Several proposed measures to reduce Sound Power Level at source discussed in "Measures & Technique In Eliminating / Minimizing PWL".

High Risk Area
Piping downstream of AIV source expose to high Sound Power Level, past experiences shown that high risk location is at circumferential piping with high stress concentration and/or asymmetric piping. Typical example are 
  • Welded tee or branch in particular large main pipe with small branch,
  • Main pipe supported vent / drain
  • Main pipe supported instrument connection
  • Welded support
  • Connection (Tee or elbow) subject to thermal cyclic
  • Line / connection subject to sonic flow

The principle is tackling high risk area are minimizing high stress concentration area, reduce asymmetric connection and provide reinforced connection. A few good engineering practices may reduce (but not 100%) risk of AIV problem :
  • Avoid using threadolet fittings

    • Use Sweepolet instead of Weldolet

    • Use forged type Tee and fittings instead of welded type. 
    Welded type connection increases tendencies of localised high stress concentrated area compare to forged type.

    • Use Full Wrap Around reinforcement for welded type tee

    • Reinforce welded pipe support
    • Use thicker pipe wall (strengthen) of main pipe

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    posted by Webworm, 8:40 AM


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