Vibration Induced Failure Avoidance

and Management Around Vendor

Packages

Brisbane April 2014

Why The Concern?

• FIV (flow induced vibration) failures have lead to fatalities,

fires and lost production – many of these around vendor

packages

• Vibration related failures in 2000 – 2010 represented on

average deferment costs of A$1.5M per incident

• Vibration typically not addressed comprehensively during

project phase

Vibration Mechanisms

• Steady State – Flow induced turbulence (FIT):

– Mechanical excitation

– High frequency acoustic excitation (HFAE):

– Pulsation

• reciprocating machinery or rotating stall

• flow induced excitation

– Cavitation and Flashing

• Transient Issues – Fast acting valves

Vibration Mechanisms

Assessment Process – Energy Inst. Guidelines

• Approach relevant

to all stages of

project life.

• Should be

addressed at

FEED

• Particularly

important for

process or plant

changes (MoC)

Assessment Approach (Energy Inst. Guidelines)

• Identify main lines

and key process

conditions

• Identify rotating

and reciprocating

pumps

• Locate deadlegs

• Locate RVs

FIV Screening - Technical Approach

Main Pipework Assessment

34 Lines

3 Lines

Typical Outcome

for LNG Train

Screening Survey Outputs

Small Bore Connection Assessment

Small Bore Connection Bracing

Examples of Good and the Less Good

Case Study 1: Compressor Pipework

Background:

• Project to increase throughput as

consequence of new “tie-in”

• Increased duty planned for

compressor

• Increased plant capacity >100%

of design

Objective to understand integrity

impact

Suction

Line

Discharge

Line

Recycle

Line

Dead Leg A

Dead Leg B

Actual Configuration

Flow FlowVortices

Side Branch

d

L

0

20

40

60

80

100

120

140

0 50000 100000 150000 200000 250000 300000 350000 400000 450000 500000

Flow Rate (kg/hr)

Natu

ral

Fre

qu

en

cy (

Hz)

f5/4

f3/4

f1/4

Quarter Wave

Acoustic Frequencies

Vortex Shedding

Frequencies

1,3

2,1

1,1

Quarter Wave

Acoustic Frequencies

Vortex Shedding

Frequencies

Solution: modified

location of valve

Analysis of Deadlegs

Case Study 2: RV Piping

Valves closed – no flow

Flow Valve closed – no flow

Main Pipe OD is 48”

Situation: New flare tie-ins as part

of plant expansion

Design

Marginal

Correction

Danger

Perception Level0.01

0.1

1

10

1 10 100 1000

Frequency (Hz)

Vib

rati

on

al

Am

pli

tud

e (

mm

) -

Pe

ak

to

Pe

ak

Wachel and Bates Criteria

Vibration of Flare Take-offs Observed

Detailed Analysis: Vortex Shedding Frequency

• Spectral densities of flow kinetic energy and pressure traces at the RV take-off mouths’ are used to estimate dominant vortex shedding frequencies at each mouth. Examples are shown below.

Dominant shedding

frequency is 10.5 Hz

for this 18 inch take-off

Flow

Root Cause of Vibration

Field data and analysis indicate that the root cause of vibrations is due to

“lock-in” of RV take-off mouth vortex shedding frequency and RV take-off

piping (standing wave) acoustic resonant frequency.

• Piping vibration frequencies (measured): 6.25 Hz, 12.5 Hz

• RV piping first acoustic resonant frequency range (computed): 6.0 Hz – 10.5 Hz

• RV take-off mouth vortex shedding frequency range (computed): 6.0 Hz – 30.0 Hz

Vortex Shedding Frequency

• Closely spaced 18 inch take-offs show high energy content at a frequency of 6.4 Hz

• Shedding frequency can easily “lock-in” to a first acoustic resonant frequency (e.g. f1 ~ 6.0 Hz) , at which point pulsations and energy content will start to amplify.

Flow

Analysis Summary

• Vortex shedding frequencies and first acoustic natural frequencies of RV piping are too close!

• Based on flow & acoustic analyses a response curve (for the 18 inch take-offs) which predicts the onset of pulsations can be constructed:

First acoustic resonance

frequency range of 18 inch RV

piping

Principal shedding Strouhal curves (blue,

red, green), are identified from CFD analysis.

First mode (red) is associated with highest

pulsation amplification potential.

Onset of significant pulsation happens when

flow ~ 8 m/s (slightly above 10,000 tons

/day).

True onset of pulsation occurs at ~ 5 m/s,

but is most likely very weak (blue curve is a

high mode of shedding)

“Lock-out” may occur for flow > 18 m/s. Not

practical solution to avoid pulsations.

Vibration Mitigation Solutions

• Move the relief valves closer to the take-off points. This will have the effect of increasing the acoustic resonant frequencies of the RV piping.

• Modify the RV take-off mouths to minimize / weaken vortex shedding. Example: Forge entrance pieces to provide a 45-deg funnel into the RV piping. Minimize flow-tripping weld protrusions when welding the piece in place. Some simulation work is recommended to ensure that a design would work.

• Install orifice plates just upstream of the take-off points. The plates will suppress vortex shedding and increase the acoustic resonant frequencies of the RV piping. The plates would have to be carefully designed to retain original relief capacity.

Vibration mitigation is achieved by de-tuning the vortex shedding frequency

and the RV piping first acoustic resonant frequency. Candidate action

items are:

Detailed Analysis – Potential Approaches

Conclusions

• Address vibration Issues holistically at the plant level and ensure

provision is in place for projects – Energy Inst. Guidelines

• Ensure vibration management process is in place for new and existing

assets to allow impact of plant or process changes on integrity to be

quantified

• Ensure vibration management processes are in place around “grey

area” equipment where responsibilities are potentially not well defined or

coordinated

• Ensure flow induced vibration is considered as part of MoC process.

• Ensure awareness of FIV issues amongst integrity stakeholders