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ACOUSTIC EMISSION GLOBAL INSPECTION TECHNIQUE

DAVID PADFIELD

What is Acoustic Emission Monitoring?

• The process of detecting sound produced by

discontinuities (cracking) within a structure when the

structure has stress applied to it or when it is leaking or

corroding.

• The sound is used to determine the structure’s condition.

• Applied to monitoring corrosion in aircraft, storage

tanks, pipelines, ships and bridges made from steel or

aluminium.

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AE Standards ASME - American Society of Mechanical Engineers • Acoustic Emission Examination of Fiber-Reinforced Plastic Vessels, Article 11, Subsection A,

Section V, Boiler and Pressure Vessel Code • Acoustic Emission Examination of Metallic Vessels During Pressure Testing, Article 12,

Subsection A, Section V, Boiler and Pressure Vessel Code • Continuous Acoustic Emission Monitoring, Article 13 Section V

ASTM - American Society for Testing and Materials • E569-97 Standard Practice for Acoustic Emission Monitoring of Structures During Controlled

Stimulation • E650-97 Standard Guide for Mounting Piezoelectric Acoustic Emission Sensors • E749-96 Standard Practice for Acoustic Emission Monitoring During Continuous Welding • E750-98 Standard Practice for Characterizing Acoustic Emission Instrumentation • E976-00 Standard Guide for Determining the Reproducibility of Acoustic Emission Sensor

Response • E1067-96 Standard Practice for Acoustic Emission Examination of Fiberglass Reinforced Plastic

Resin (FRP) Tanks/Vessels • E1106-86(1997) Standard Method for Primary Calibration of Acoustic Emission Sensors • E1118-95 Standard Practice for Acoustic Emission Examination of Reinforced Thermosetting

Resin Pipe (RTRP) • E1139-97 Standard Practice for Continuous Monitoring of Acoustic Emission from Metal Pressure

Boundaries • E1211-97 Standard Practice for Leak Detection and Location Using Surface-Mounted Acoustic

Emission Sensors • E1316-00 Standard Terminology for Nondestructive Examinations • E1419-00 Standard Test Method for Examination of Seamless, Gas-Filled, Pressure Vessels

Using Acoustic Emission • E1781-98 Standard Practice for Secondary Calibration of Acoustic Emission Sensors • E1932-97 Standard Guide for Acoustic Emission Examination of Small Parts • E1930-97 Standard Test Method for Examination of Liquid Filled Atmospheric and Low Pressure

Metal Storage Tanks Using Acoustic Emission • E2075-00 Standard Practice for Verifying the Consistency of AE-Sensor Response Using an

Acrylic Rod • E2076-00 Standard Test Method for Examination of Fiberglass Reinforced Plastic Fan Blades

Using Acoustic Emission

AE Standards ASNT - American Society for Nondestructive Testing • ANSI/ASNT CP-189, ASNT Standard for Qualification and Certification of

Nondestructive Testing Personnel. • CARP Recommended Practice for Acoustic Emission Testing of Pressurized Highway

Tankers Made of Fiberglass reinforced with Balsa Cores. • Recommended Practice No. SNT-TC-1A.

Association of American Railroads • Procedure for Acoustic Emission Evaluation of Tank Cars and IM-101 tanks, Issue 1,

and Annex Z thereto, “ Test Methods to Meet FRA Request for Draft Sill Inspection program, docket T79.20-90 (BRW) ,” Preliminary 2

Compressed Gas Association • C-1, Methods for Acoustic Emission Requalification of Seamless Steel Compressed

Gas Tubes.

European Committee for Standardization • DIN EN 14584, Non-Destructive Testing – Acoustic Emission – Examination of

Metallic Pressure Equipment during Proof Testing; Planar Location of AE Sources. • EN 1330-9, Non-Destructive Testing – Terminology – Part 9, Terms Used in Acoustic

Emission Testing. • EN 13477-1, Non-Destructive Testing – Acoustic Emission – Equipment

Characterization – Part 1, Equipment Description. • EN 13477-2, Non-Destructive Testing – Acoustic Emission – Equipment

Characterization – Part 2, Verification of Operating Characteristics. • EN 13554, Non-Destructive Testing – Acoustic Emission – General Principles.

Institute of Electrical and Electronics Engineers • IEEE C57.127, Trial-Use guide for the Detection of Acoustic Emission from Partial

Discharges in Oil-Immersed Power Transformers.

AE Standards International Organization for Standardization • ISO 12713, Non-Destructive Testing - Acoustic Emission Inspection

– Primary Calibration of Transducers. • ISO 12714, Non-Destructive Testing - Acoustic Emission Inspection

– Secondary Calibration of Acoustic Emission Sensors. • ISO 12716, Non-Destructive Testing - Acoustic Emission Inspection

– Vocabulary • ISO/DIS 16148, gas Cylinders – Refillable Seamless Steel gas

Cylinders – Acoustic Emission Examination (AEE) for Periodic Inspection.

Japanese Institute for Standardization • JIS Z 2342, Methods for Acoustic Testing of Pressure Vessels

during Pressure Tests and Classification of Test Results.

Japanese Society for Nondestructive Inspection • NDIS 2106-79, Evaluation of performance Characteristics of

Acoustic Emission Testing Equipment. • NDIS 2109-91, Methods for Absolute calibration of Acoustic

Emission Transducers by Reciprocity Technique. • NDIS 2412-80, Acoustic Emission Testing of Spherical Pressure

Vessels of High Tensile Strength Steel and Classification of Test Results.

Acoustic Emission (AE)

Transient elastic waves generated by the rapid release of energy from localised sources within a material

(extract from ASTM E610.82)

Primarily “Clustering”

Am

pli

tud

e

Threshold

Duration

Rise

time

Decay

time

AE Counts = 7

Time

An AE hit

Energy

Parameters measured include:

AE event counts

Amplitude

Duration

Rise time

Decay time

Energy

• Sensors – 20kHz to 500kHz

• Preamplifier

• Band pass filters tuned to sensors

10 - 1000kHz

• Location of acoustic signals

• “Clever” Software that can be

taught.

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Sensor Preamplifier Filter

DiSP AE

Card Computer

AE Equipment

AE Testing – Tank Set Up

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Sensors

Tank Bottom Sensor Positioning

• Sensors mounted 0.5 m to 2 m

above knuckle, usually 1m and 2m

• 3 to 24 sensors used depending on

size

• Cables from sensors are run back

to AE computer

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Primary sensors

Guard sensors

Example of Bad Tank

INDUSTRIAL CORROSION

Tank Bottoms - AE Test Procedure

• Tank conditioned – Isolate tank for 6-12 hours

– Large crude tanks 24 hrs, Small tanks 6 hrs

– Valves closed, heaters off, agitators switched off, ultrasonic depth gauges off, fluid flow in attached pipes stopped.

– Insulated tanks require 300 mm square holes removed to mount sensors

• Sensors mounted tank wall around the circumference

• Tank monitored for a pre-determined time – 1hr min

• Data processed to eliminate unwanted noise

• Data evaluated and sources located

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AE Testing – Experimental

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2 Mild steel specimens

Pipe & Flat bar immersed in 3%

Salt (NaCl) solution

Test initially for 120 hours

Monitoring paused for 4 weeks

then monitored for 17 hours

Dewatering then monitoring for

20 hours

AE Corrosion Monitoring – Results

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Bar

Pipe

First 120 hours

AE Corrosion Monitoring – Dry Results

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Bar

Pipe

After removal of corroding solution specimens were

allowed to dry and were monitored over a 17 hour period.

AE Corrosion Monitoring – Results

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Wet Results

Duration maximum about 10,000 μsec

Dry Results

Higher amplitude signals

Correlation plots Duration (microS) vs Amplitude (dB)

Acoustic Emission of FRP

• Storage tanks

• Pipelines

• Structures

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FRP Vessels

• Slow fill

• High Amplitude Events

indicate damage

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FRP Vessels

• Corrosion of FRP

• Disbonding of fibres

from matrix

• Lamination growth

• Gross fibre breakage

from damage

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AE Application to Fibre Composites

• Kaiser Effect – Need to exceed previously applied

load to get more AE.

• When testing FRP load

is applied twice if

significant AE detected

• 2nd load to see if first time to load or failure

occurring

Pressure Vessel Monitoring

• Done to established Standards (ASME) (AS3788)

and Evaluation Criteria.

• Sensors mounted on vessel and system calibrated

Sensors • Number of sensors

determined by the size of

the vessel to be tested.

• Tested to ISO / ASTM

Standards

• Sensors mounted on

ends of cylinders so AE

source can be detected

and located

• 2 sensors per cylinder

• Connected to AE

Monitoring equipment by

co-axial cable up to 100m

long.

Sensor Mounting on Gas Storage Cylinders

Sensors

Pressure

Time

Normal operating pressure

100%

95%

90%

85%

Possible pipe or vessel fill or pressurisation sequence

On new tanks/vessels best done in conjunction with hydrotest

AE Event and cluster location on cylinder 1

Test Results

Clusters

Located AE

Events

Permanent Monitoring – HRH Piping • An array of sensors placed either in areas of interest, or

intermittently along a susceptible pipeline would enable short or long-term monitoring.

• 20m pipe monitored with multiple sensors, gives location, intensity, time of activity, etc

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Is it the Answer? Pros

• Global (whole structures)

• Permanent Installation

• Detects & Locates

• Relatively quick

• Easy for the Asset operator

• Prioritises

• Cost saving. • Safety

• Environmental

• Standards recognition

• Permanent record

Cons

• Limited quantification

• External stress required

• Complimentary method

• Requires Skilled personnel

• Some equipment Isolation

• Background noise

• Attenuation