Wednesday, November 18, 2009
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Earlier post "Measures & Technique In Eliminating / Minimizing PWL" discussed about several measures can be considered in eliminating and minimizing PWL for pressure reduction devices. In similar post, Sound Power Level attenuation due to extended "strengthened" pipe has also been presented. This post will focus on approach to estimate combined sound power level (PWL mix) for two or more streams.
In process plant, there will be scenario for two and/or more pressure reduction devices (PRD) downstream piping discharge to a common header. Typical example is blowdown / restriction orifice to flare header. During plant wide total plant blowdown, all blowdown valves may be opened simultaneously or opened in group. Different PRD will results different level of PWL. Now the queries will be :
Mathematically,
PWL Adder
PWL adder is estimated from PWL difference between both stream and the following equations.
If PWL Difference (PWL, diff)
Two Pressure control valves with PWL of 160 dB and 166 dB discharging to a flare header. Calculate combined PWL.
Assumed PWL attenuation due to piping is ignored.
PWL,diff = 166 - 160 = 6 dB
PWL adder = 10 ^ (0.4771 - 0.0795 x 6) = 1 dB
Combined PWL = Maximum PWL + PWL Adder
Combined PWL = 166 + 1 = 167 dB.
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- Subscribes to FREE Hydrocarbon Processing
Earlier post "Measures & Technique In Eliminating / Minimizing PWL" discussed about several measures can be considered in eliminating and minimizing PWL for pressure reduction devices. In similar post, Sound Power Level attenuation due to extended "strengthened" pipe has also been presented. This post will focus on approach to estimate combined sound power level (PWL mix) for two or more streams.
In process plant, there will be scenario for two and/or more pressure reduction devices (PRD) downstream piping discharge to a common header. Typical example is blowdown / restriction orifice to flare header. During plant wide total plant blowdown, all blowdown valves may be opened simultaneously or opened in group. Different PRD will results different level of PWL. Now the queries will be :
- How these PWL are interact between each and other ?
- How to estimate resultant PWL ?
- Are different PWL addition arithmetically ?
Mathematically,
Combined PWL = Maximum PWL + PWL Adder
PWL Adder
PWL adder is estimated from PWL difference between both stream and the following equations.
If PWL Difference (PWL, diff)
- between 0 to 6 dB, PWL adder = 10 ^ (0.4771 - 0.0795 x PWL,diff)
- between 6 to 10 dB, PWL adder = 10 ^ (0.5651 - 0.0942 x PWL,diff)
- between 10 to 14 dB, PWL adder = 10 ^ (0.5432 - 0.092 x PWL,diff)
- more than 14 dB, PWL adder = 10 ^ (0.7794 - 0.1088 x PWL,diff)
Two Pressure control valves with PWL of 160 dB and 166 dB discharging to a flare header. Calculate combined PWL.
Assumed PWL attenuation due to piping is ignored.
PWL,diff = 166 - 160 = 6 dB
PWL adder = 10 ^ (0.4771 - 0.0795 x 6) = 1 dB
Combined PWL = Maximum PWL + PWL Adder
Combined PWL = 166 + 1 = 167 dB.
Related Topic
- Measures & Technique In Eliminating / Minimizing PWL
- Principle in Eliminating & Minimizing AIV Impact
- Energy Input or E-method In Assessing AIV
- Assess AIV with "D/t-method" with Polynomial PWL Limit Line
- Assess AIV with "D/t-method" with Logarithm PWL Limit Line
- Extra Attention to Common Point and Similarity on AIV Failure
- Piping Excitation When Expose to Acoustic Energy
- Acoustic Induced Vibration (AIV) Fatigue
posted by Webworm, 5:55 AM
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