AIV Screening Per EI Guidelines

WORK INSTRUCTION

Acoustic Induced Vibration (AIV) Screening

PREPARED BY:

Chan Wei Wen

ACOUSTIC EXERCISE

INDUCED

VIBRATION

(AIV)

SCREENING

1.0 Brief Introduction

The evaluation of potential (AIV) problems is based on the guidelines outlined in Energy Institute publication [Ref.1.]. The screening criteria described below provide guidelines to determine when a detailed evaluation is warranted for gas flow systems. This is NOT used for non-gas flow systems. Liquid flow systems are NOT considered to be potential problems and need not be investigated at all for high acoustic energy. For systems with two-phase flow having gas composing at least 50% of the volumetric flow, use the conservative assumption that the total mass flow rate is gas to evaluate the acoustic energy level. This does not mean that the pressure drops in the line or any other physical property should be recalculated as though the fluid was all vapour.

2.0 Methodology 2.1 AIV First (1st) Screening (ExxonMobil Design Instruction Manual No. 3 [Ref.2.])

Pressure let-down systems meeting any one of the following criteria warrant further detailed evaluation: i) ii) iii)

iv)

Downstream line size 400 mm (16 in) and greater: mass flow rate greater than 91,000 kg/hr (200,000 lb/hr) or pressure ratio greater than 3. Downstream line size 200 mm (8 in) to 350 mm (14 in): downstream line velocity greater than 50% sonic and pressure ratio greater than 3. Downstream line size less than 200 mm (8 in) swaged up or "teed" to a 200 mm (8 in) or larger line: downstream line velocity greater than 50% sonic and pressure ratio greater than 3. Branch connections having a run size 400 mm (16 in) and greater: mass flow rate greater than 91,000 kg/hr (200,000 lb/hr) and sonic velocity at the branch to run intersection point.

All pressure let-down systems meeting any one of the criteria listed above will be studied further in AIV LOF (Likelihood of Failure) calculation process as discussed in section 2.2 below. A preliminary spreadsheet to facilitate the 1 st stage screening is attached in Appendix 1.. Table 1 Example of 1st Stage Screening

Pressure reducing devices HCV 0130 FCV 0610 RO 0420 PSV 0402

Downstream pipe ND (mm) DN DN DN DN

80 80 80 80

Line Velocity

< 200 (mm)

Mach

> 50% sonic

YES YES YES YES

0.07 0.004 0.05 1.00

NO NO NO YES

2.2 AIV Second (2nd) Screening (EI Guideline)

Pressure Ratio Calculated pressure ratio 2.65 1.02 15.62 16.20

>3

Detailed AIV needed?

NO NO YES YES

NO NO NO YES

The further screening requires the calculation of the acoustic sound power (PWL) acting on the main line due to the sound generated by the pressure reducing device where PWL values < 155 dB are considered as safe from AIV problems. The LOF is calculated as detailed below:

PWL=10 log 10

[( ) ( ) ] P1−P2 P1

3.6

W2

Te Mw

1.2

+126.1+ SFF

[2.0]

Where

PWL = sound power level (dB) generated by the pressure reducing device P1 = pressure upstream of pressure reducing device (kPa absolute) P2 = pressure downstream of pressure reducing device (kPa absolute) W = mass flow rate (kg/s) Te = upstream temperature (K) Mw = molecular weight of gas (g/mol) SFF = a correction factor to account for sonic flow. If sonic conditions exist, then SFF = 6; otherwise SFF = 0 Note: 1.

If the source is a valve, check whether a low noise trim is fitted. If yes, the PWL (source) should be reduced in line with data supplied by the valve manufacturer. When using this method, the source power level (PWL) supplied by the valve manufacturer MUST NOT be used.

If PWL < 155 dB, then LOF = 0.29 If PWL > 155 dB, then go to next welded discontinuity (for e.g. SBC, welded tee, welded support) and calculate the PWL in the main line at the discontinuity, accounting for attenuation using equation 2.1.

PWLdiscontinuity =PWLsource −60

Ldis D∫ ¿ ¿

[2.1]

Where

Ldis = distance between source and the welded discontinuity (m) Dint = internal diameter of the main line (mm)

If there is any additional source of excitation, recalculate the PWL at discontinuity, considering all sources using formula 2.2.

PWLdiscontinuity ,total =10 log 10 [10 Where

PWL1discontinuity = PWL at discontinuity due to source 1 PWL2discontinuity = PWL at discontinuity due to source 2

PWL1discontinuity 10

+ 10

PWL2discontinuity 10

+. … ..] [2.2]

This process should be repeated at subsequent welded discontinuities until PWLdiscontinuity ,total LOF ≥0.5

Action The main line shall be redesigned, resupported or a detailed analysis of the main line shall be conducted, and vibration monitoring of the main line shall be undertaken.

Technical Module Note 1 TM-09 TM-07/TM-08

Corrective actions shall be examined and applied as necessary.

TM-10

Small bore connections on the main line shall be assessed.

TM-03

A visual survey shall be undertaken to check for poor construction and/or geometry and/or support for the mainline and/or potential vibration transmission to neighbouring pipework. The main line should be redesigned, resupported or a detailed analysis of the main line shall be conducted, and vibration monitoring of the main line should be undertaken. Corrective actions should be examined and applied as necessary. Small bore connections on the main line shall be

TM-05 TM-06 TM-09 TM-07/TM-08

TM-10

assessed. A visual survey shall be undertaken to check for poor construction and/or geometry and/or support for the mainline and/or potential vibration transmission to neighbouring pipework. Small bore connections on the main line should be assessed.

0.5> LOF ≥ 0.3

LOF LOF ≥ 0.4

LOF