Download pdf - ACOUSTICALLY INDUCED AND FLOW INDUCED VIBRATION

Welcome to PowerPointLITTLE-KNOWN FAILURE MODES NOW ADDRESSED IN AS/NZS 2885.1:2018
Prepared by: S. J. Monaghan Lead Vibration Engineer, Enscope (A Quanta Services Company), Brisbane, Australia E. L. Metcalfe Principal Consultant, Metcalfe Engineering, Melbourne, Australia R. J. Swindell Vibration Engineering Lead, Vibration Dynamics and Noise, Wood PLC, Southampton, UK
Presented by:
S. J. Monaghan APGA Annual Convention & Exhibition in Adelaide, South Australia on 15 October 2019
PRESENTATION OVERVIEW
Introduction to the Concepts AIV & FIV on an Operating Pipeline AIV & FIV Changes in AS/NZS 2885.1
Basic vibration introduction
How AIV & FIV was identified & rectified
To avoid a repeat – changes to AS 2885.1:2012
What the changes are
Avoidance by design
BASIC VIBRATION INTRODUCTION
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1. Pipework as a dynamic system
The mass of the pipe is dependent on: diameter & wall thickness material (density) and lagging isolated masses (valves, flanges) fluid mass inside (and for submerged pipes, outside) the pipe
The higher the mass, the lower the natural frequency of the pipe
The stiffness of the pipe is dependent on: diameter & wall thickness material (Young’s Modulus) presence of ‘stiff’ components (valves) pipe supports and how they act dynamically
The higher the stiffness, the higher the natural frequencies of the pipe
Mass
= Stiffness
The relevant bypass piping 1. High-pressure steel gas transmission pipelines
2. Varying length, diameter and design pressure
3. Typically include: • Isolation valves or Main Line Valves (MLVs) • Manual depressurising capability • Manual repressurising capability
Main Line Valves (MLVs) MLVs typically full-bore ball valves with soft seats for assurance of a positive seal
This means that once closed, the MLV cannot then be simply re-opened without risk of damaging the seats Therefore, bypass piping is necessary to enable pressure equalisation
PIPELINE BYPASS SYSTEMS & UNUSUAL OPERATIONS
The purpose of bypass piping 1. For unusual operations:
• Section 4.5 of AS/NZS 2885.1:2018 lists: • initial fill & pressurisation • depressurisation • purging & repressurisation
2. The pressure let-down device is typically: • Plug valve for repressurisation; • Restriction orifice for depressurisation.
Bypass Piping No flow during normal pipeline operations
To remote
Acoustic Induced Vibration
1. Intense noise generated by choked velocity across a pressure let-down device
2. Broad band, high frequency (typically >500 Hz) in the downstream pipe
3. Generates pipe wall flexure (shell flexural modes) and high stress at weld discontinuities such as weldolets / re-pads
Example: 24” sch STD, 10m span
High frequency Shell flexural modes
AIV & FIV DURING UNUSUAL OPERATIONS
Flow Induced Vibration – Primarily: Flow Induced Turbulence
1. Energy generated by the gas and transferred to the piping.
2. Broad band excitation of the low frequency (typically < 100 Hz) structural modes of the piping.
3. Turbulent gas force is generated by flow through valves, expansions and elbows.
Example: 24” sch STD, 10m span
Low frequency ‘Beam’ bending modes
AIV & FIV DURING UNUSUAL OPERATIONS
Subsets of Flow Induced Vibration – Flow Induced Pulsation (FIP) and Jet Impingement Induced Vibration (JIV)
1. Gas velocity main determinant for generating tonal (discrete frequency) response
2. Severe problems when acoustic resonant response coincides with structural resonance
FIP: Excitation of local deadleg sidebranch acoustic resonance JIV: High Mach number flow from a side-branch into a header
AIV, FIV & LOW TEMP DURING UNUSUAL OPERATIONS
Low temperature (Joule-Thomson) cooling
2. Static stress due to contraction / expansion
3. Piping flexibility required to minimise static stress
• But! Stiffness for suitable vibration response
4. Coincident vibration during low temp excursions
• Fatigue predictions to BS 7608:2014 + A1:2015
requires demonstrated fracture toughness
The failure chain
The result
Modal stress plot
“The damage of a structural part by the initiation and gradual propagation of a crack or cracks caused by repeated applications of stress.”
(source: BS 7608)
WHY HASN’T AUSTRALIA SEEN THIS PROBLEM BEFORE?
That’s the vibration introduction… but before we answer this question:
WHY is AIV & FIV only NOW a problem in Australia?
Quick recap:
FIV: Flow discontinuity
Gas turbulence (force)
Low frequency piping vibration
Some Generalisations about Design of Onshore Pipeline Systems
Parameter International Pipelines Australian Pipelines Length Varying, few exceeding several hundred km. Many long-distance pipelines connecting sources
Diameter Many large diameter pipelines Mostly smaller, larger becoming more common
MLV Spacing Typically 20 miles (~30 km) per ASME B31.8 In rural areas restricted only by scraper pig wear, up to 200 km or more
Piping Class Mainly Class 600, with a few at Class 900 Older pipelines Class 600, now Class 900 common
Bypass Piping Specification
Commonly ASME B31.3 or equivalent Typically ASME B31.3 or AS4041, but not always
Bypass Piping Diameter
Various, not often exceeding DN300 (12”) Various, not often exceeding DN300 (12”)
Vent Systems Commonly local to the MLV Older pipelines local, but more common now to have remote vents
• Frequency of events causing AIV & FIV is low
• Minimal investigation of historical pipeline piping failures , and therefore failures not attributed to AIV or FIV
What’s changed?
3. Non-ideal geometry
• One step-out, may be perfectly fine
• Two or three coupled step-outs, potential problem
• Four step-outs, likely problem and AIV/FIV failure
Design step-outs
Failure pre-conditions
Australian pipeline designers have unwittingly been edging closer to AIV / FIV failure
HOW AIV & FIV WAS IDENTIFIED ON AN OPERATING PIPELINE
To remove
Objective: Achieving a safe rectification without a full pipeline shutdown
Main Line Valve (M
• Downstream small bore connection welds at risk
Shell mode response – high stress at branch weld
Discovered using a screening guideline
Main Line Valve (M
• When flowing through small bore bypass
• Girth welds of secondary bypass at risk
Gas turbulence – exciting piping bending modes
Discovered via field measurements of:
- Strain - Vibration - Temperature
Main Line Valve (M
(JIV)
• Branch weld and girth welds at risk
Exciting acoustic cross-modes – high stress at branch weld
Discovered via field measurements of:
- Strain - Vibration
Main Line Valve (M
• Branch weld of secondary bypass at risk
Flow past deadleg – excites acoustic resonance resulting in
shaking of the piping
(JIV)
Main Line Valve (M
Main Line Valve (M
(JIV)
• Flow through large bore
Gas turbulence – exciting piping bending modes
HOW AIV & FIV WAS MITIGATED
Main Line Valve (M
• Process modelling (HYSYS)
• Fatigue life calculations
Rectification works implemented
• Valve interlocks
This amount of effort must be avoided in the future
TO AVOID A REPEAT – CHANGES TO AS 2885.1:2012 Main Line Valve
(M
LV)
The authors noted that over recent years:
• Designers unwittingly edged closer to AIV/FIV failure
• Occurred as AIV/FIV failure not previously recognised
Particular failure modes identified by the authors on an operating pipeline were: • A significant risk to piping integrity and process safety
• A consequence of concurrent step-outs in pipeline design
• Not currently well understood in Australian pipeline design
Demonstrating a duty of care to the industry, the authors:
• Contacted and provided input via the ME-038 Committee
• Assisted with wording now appearing in AS/NZS 2885.1:2018
AS/NZS 2885.1:2018 – WHAT’S CHANGED? Main Line Valve
(M
LV)
• Relied heavily on experience and competence
Updated Guidance • AIV and FIV recognised as explicit loads requiring piping fatigue assessment
• Low temperature, AIV and FIV:
• Individually and cumulatively create piping stress (static and dynamic)
• Now required by the Standard to be considered
• Existing clauses and guidance (intended to prevent poor design) strengthened
• Designers are encouraged to seek expert advice where appropriate
AS/NZS 2885.1:2018 – SPECIFIC CHANGES Main Line Valve
(M
LV)
• AIV & FIV recognised as a design condition
Section 4 Pipeline System Design • Isolation Plan and Isolation Valves:
• Consideration of AIV and FIV when designing pipeline segments
• Spacing between valves
• Design of bypass piping
(M
LV)
Extract from AS/NZS 2885.1:2018 of FIGURE 4.1: PIPELINE SYSTEM SCHEMATIC
Section 5.9 PIPELINE ASSEMBLIES: Clause 5.9.1 General: Part (ii)
(M
LV)
• Where high mass flow / significant pressure drop conditions exist
• AIV & FIV may exist
• Fatigue failures may occur
(M
LV)
Appendix J FATIGUE
• Section J1(c) introduces rapid fatigue due to AIV or FIV as a source of fatigue loading
• Section J3 relates solely to AIV and FIV
• Defines AIV and FIV
• Considers instrumented field testing during commissioning
AS/NZS 2885.1:2018 – HOW TO IMPLEMENT THE CHANGES Main Line Valve
(M
LV)
Stored volume and MAOP
Apply Energy Institute guidelines
---prudent but not essential to retrospectively apply to existing assets---
AS/NZS 2885.1:2018 – AVOIDANCE OF AIV & FIV BY DESIGN Main Line Valve
(M
LV)
coincident with vibration
• Move low temp
• Promotes AIV and/or FIV?
damping
Avoidance by design far simpler than avoidance by procedure (eg Critical Operating Procedure)
SUMMARY AND RECOMMENDATIONS
Lessons learned in the pipeline industry should be openly shared
• Three simple take-aways relating to AIV and FIV as now duly recognised pipeline design conditions:
AIV failure at a reinforcement pad weld
1. AS/NZS 2885.1:2018 should not be interpreted without suitable background knowledge. If you are not certain, get some expert technical assistance.
2. Never be reluctant to ask a more experienced Engineer or the ME-038 Committee for advice before changing an established design practice.
3. Innovative design step-outs must only be done with caution, and probably only one step-out at a time.
QUESTIONS?
AIV, FIV & Low Temp during Unusual Operations
Why AIV & FIV Is a Problem for Pipeliners
Why AIV & FIV Is a Problem for Pipeliners
Why Hasn’t Australia Seen this Problem Before?
How AIV & FIV was Identified on an OPERATING Pipeline
How AIV & FIV was MITIGATED
To Avoid a Repeat – Changes to AS 2885.1:2012
AS/NZS 2885.1:2018 – What’s Changed?
AS/NZS 2885.1:2018 – Specific Changes
AS/NZS 2885.1:2018 – AVOIDANCE OF AIV & FIV By DESIGN
Summary and Recommendations