Advanced Inspection Techniques and Best Practices

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10/7/20

N. Al-Khirdaji, AZTech Sr Consultant

2.4 Advanced Inspection

Techniques and Best Practices

• Guided wave ultrasonic long range inspection

• vance p ase arrays or we nspect on

Advanced Inspection Techniques

• Inspection Techniques with Unique

arac er s cs:

– May Use One or More NDT Technologies

– Typically Computerized

– Inspection Utilizes Electronic Detection and

Processing

– Requires Very Specialized Training

– May Locate and Size or Just Locate



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Advanced Inspection Techniques

• Advance Inspection Techniques for RBI and

– Acoustic Emission

– Ultrasonic Corrosion Mapping

– Ultrasonic Weld Inspection

– EMATS

– Phased Array

– Digital Radiography

– Leak Detection

Limitations of Conventional Inspection

Techniques

• The impetus for the use of long range ultrasonics is that

ultrasonic thickness checks for metal loss due to corrosion or

erosion are highly localized , in that they only measure the

thickness of the area under the transducer itself.

• To survey a large area requires many measurements and access

to much of the surface of the component. Where access is

difficult or costly a detailed survey becomes unattractive

economicall conse uentl limited sam lin onl is carried

out. Similar restrictions apply to other methods of measuring

wall thickness, such as radiography, eddy currents etc..

• Partial inspection of this type is not effective for reliable

overall assessment as the probability of detection of defects in

uninspected areas is zero.



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Guided Wave Ultrasonic Inspection

• Guided waves are a form of ultrasonic waves that

rave roug a oun e es spec men n s case, a

pipe), parallel to the boundaries (inner and outer

wall), while being guided by these same boundaries.

• Due to the nature of the waves and the testing

frequencies used, the technique can be used to scan

location, thereby negating the time-consuming type of

grid scans required by conventional techniques such

as UT and ET.

Guided Wave Ultrasonic Inspection

• The performance of the inspection depends on the

chosen kind, either extensional or torsional .

• Imperfections could arise from non-uniform strength of

excitation of the transducer elements, phase errors

between the signals at the adjacent rings, ovality of the

pipe, or circumferential variation of the wall thickness of

the pipe.• Any such imperfections could lead to the generation of

some of the other, unwanted, modes of the pipe; such

signals would appear as coherent noise, that is to say, they

could not be removed by averaging multiple signals.



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Why use EMATs ?

Because In-Service Inspection is DIRTY

EMATs can tolerate adverse conditions

EMATs can be FAST

High Speed Screening – Global Inspections

Capable of covering Large areas

EMATs can inspect areas not normally

accessibleBuried or Hidden Regions can be reached with Guided Waves

Why use EMATs ?

• Pipeline Direct Assessments

-

• High Temperature Piping

• Vessel Inspection

• Weld Inspections

• Pipe Support Inspection

• re ea er u e nspec ons• Tank Inspections

– Weld location

– Soil to Air inspections



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EMAT Inspection Technology

EMAT Guided WaveFlaw Detection

• General Wall Thinning

• so a e ng

• General Corrosion

• Hydrogen Induced Cracking

• Stress Induced Cracking

•• Chromium Depletion

• Corrosion Under Insulation



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Localized Guided Wave

EMAT

Can bein

PLATES

EMAT

Or

PIPES

Or

CIRCUMFERENTIAL

Measurement Principals

• Time of Flight Velocity

• Transmitted Amplitude Attenuation

• Reflected Amplitude Reflection-

Coefficient

• Minimum Flaw Size proportional to Wave

front• Large Wave Front Long Distance/Lower

Sensitivity

• Small Wave Front Shorter Distance/Higher

Sensitivity



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Volumetric Inspection

example in ½ inch (12mm) plateAmplitude Change vs Pit Volume

Round bottom holes

5mm, 10mm, 20mm, 30m m diameter

R2 = 0.947

80

Change in Transit Time vs Pit Volume

R2

= 0.8478

300

350

10

20

30

40

50

60

70

d A M P

50

100

150

200

250

d T

( n s e c )

0

0.00 3.00 6.00 9.00 12.00 15.00

Pit Volume (cc)

Guided Wave Propagation depends on the shape of the wave guide boundaries.

Fundamentally these are volumetric inspections.

Good Linear Correlation to VOLUME of round bottom holes

0

0.00 3.00 6.00 9.00 12.00 15.00

Pit Volume (cc)

EMATs Efficiently GenerateGuided Waves in Pipes

Transmitter Receiver

• The Guided Wave travels around the

circumference of a pipe.

• 100% Coverage is achieved from one location



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Circumferential Guided Wave

• High Speed; Volumetric Inspection

• Performed in Pitch Catch,

• High Resolution Detection

– through transmission mode

• Attenuation Measures obstruction of beam

– i.e.. Pitting

• Velocity Measures thinning – i.e.. general corrosion

Geometry Affects Guided Wave Travel

Pits Scatter

Sound Attenuatio

n

Wave

Propagation

Thinning Speeds Up the Transit Time Change

ave



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EMAT Guided Wave

Sample Amplitude “A”-Scan Presentation

EMAT Guided WaveSample E-Scan Presentation

• 10%

• 20%

• 30%

•

• 50%



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EMAT Screening ToolsCan Be Designed for Client Specific Applications

High Speed Multi

Big Bore Circumferential Encoded

Guided Wave Crawler

Size Encoded

Crawler

EMAT Guided Wave Inspection

Systems

• Multiple Unit Designs

applications

• Lightweight and

portable

• Battery powered

versions



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Guided Waves

Can Provide Global Inspections• Piping, Tanks, Vessels, and Heater Tubes

•

• Repeatability

• Can be used In-service or During outages

• No Couplant needed

• High Speed Scanning

• Rough Surfaces

• Thick Coatings

• Numerous Scan Presentations• Portable Systems for easy access

EMAT Guided Wave Inspections

• Anything Inspectable fromma

• High Speed Screening Tool

• Remote Detection Capabilities

•• Relative Sizing Capable

• Absolute Sizing Capabilities in Limitedand Special Cases



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These Claims are Possible

because of Guided Waves

EMATs have superior control of Guided Waves

The EMAT specifies both WAVE LENGTH and

FREQUENCY to precisely define the wave

mode.

Inspection Methods - Surface

•

– Intelligent pigging,

• MFL, UT, RFT,

– Remote Visual

Inspection.

– Guided WaveUltrasonic Testing.



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Guided Wave Ultrasonic

• What is Guided Wave Ultrasonic Testing?

–

waves.

– Sensitive to ID and OD wall losses.

– Up to 48” diameter.

Guided Wave Ultrasonic



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Guided

WaveUltrasonic

Guided Wave Signals

(a) A typical weld is completely symmetric and shows up as only a

black curve.

(b) A typical corrosion patch is non-symmetric and is identified by the

presence of a red curve.



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Guided Wave Ultrasonics

• Advantages:

– ,

– Non-intrusive, on-line and off-line,

– Up to 4,000 feet per day,

– Use on lined, coated, insulated or buried pipe,

– Portable,

– Repeatable results.

Guided Wave Ultrasonics

• Disadvantages:

– .

• Concrete lining,

• Coatings,

• Wrapping.

– Placement on pipe critical.

– pe con gura on cr ca . – Not quantitative data; sorting tool only.

– Follow-up with direct inspection required.



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Guided Wave UT Inspection

• The benefits of this inspection include:

– o arge sec ons o p p ng can e nspec e rap y

– Minimal insulation removal

– Localized damage can be identified

– Previously inaccessible areas can be inspected especially

where consequences and likelihood of failure are high

– Point of contact corrosion areas can be ra idl ins ected

for piping systems resting on supports, eliminating the need

to “lift” pipes. The environmental impact and potential for further damaging suspect pipes during live “lifting” is

eliminated

Guided Wave Transducer System

Guided Ultrasonics solid transducer system is used for pipes up

to



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Guided Wave Transducer System

Flexible, pneumatically clamped transducer system for larger

diameter pipe ( > NPS 8)

Guided Wave UT Inspection



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Typical Ranges Obtained in Different

Conditions with Standard Transducers

Application

Typical Range in

each direction

(m)

Ideal conditions 80+

Typical 30 year old pipe with little internal or

external corrosion40

T ical 30 ear old i e with some eneral corrosion 20

Typical pipe wrapped in factory applied foam 15

Heavily generally corroded pipe 5Bitumen coated pipe 5*

* The range in bitumen coated pipe is strongly dependent on the bitumen condition

(source: Guided Ultrasonics Ltd training manual)

Applicability Guided Wave

Inspection Method• The method is essentially a screening tool since it gives only a

ualitative measure of the wall loss of an defect. Its value is

that it gives 100% coverage of the pipe, and so enables

detailed inspection to be deployed only at areas identified as

problematic.

• Therefore inspectors do not waste time doing detailed

scanning of areas that the screening test have shown to be

defect-free.

• The main application area of the technology is the rapid

screening of long lengths of pipe.



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Inspection Method• The application of the technique to the detection of

where the feature density on the pipe system is low

(i.e. infrequent welds, tees, bends etc) and the

attenuation is low (no heavy general corrosion, no

highly attenuating coating), is relatively

strai htforward and the si nals obtained can be

interpreted by experienced NDT


Inspection Method• It is particularly cost effective in difficult to access locations

such as:

– Sleeved road crossings

– Insulated pipes

– Wall penetrations

– Pipe racks

– Under supports

– Cases where rope access or scaffolding would be needed

for conventional inspection



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Time-of-Flight Diffraction (TOFD)

•inspection technique.

• The TOFD technique is a fully computerizedsystem able to scan, store, and evaluate indicationsin terms of height, length, and position with agrade of accuracy superior to other ultrasonic

.

• It is based on diffraction of ultrasonic waves ontips of discontinuities, instead of geometricalreflection on the interface of the discontinuities.

TOFD Principles

• The basic configuration for TOFD (Time Of g rac on ec n que cons s s o a separa e

ultrasonic transmitter and receiver.

• After emission of a compressional wave from atransmitter, the first signal to arrive at the receiver is lateral wave through upper surface.

• In the absence of defects the second si nal to arrive at the receiver is the backwall echo.

• The diffracted signal generated at the upper tip of a defect will arrive before the signal generated atthe lower tip of a defect.



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TOFD PrincipleOn both sides of the weld an ultrasonic probe is positioned. One acts as an

emitter of ultrasound, the other as a receiver.

The longitudinal sound beam can encounter obstacles on its path, which cause

reflected and diffracted signals.

When the probes are moved parallel along the weld, the resultant waveforms are

digitized, stored on hard disk and displayed on the video-screen as a grey scale

image

The image build up is in effect a through sectional view of the weld examined

and can be used for accurate sizing and monitoring of indications.

Features of TOFD

– High Probability of Flaw Detection

– g ccuracy o aw ocat on easurement

– High Accuracy of Flaw Sizing in Length

– Weld Integrity to be observed on CRT in Real

Time as probes scan

– All inspection Data to be Digitised and Stored so

that the Data can be Recalled and Processed for In-Service Inspection



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Time of Flight Diffraction (TOFD)

TOFD Principle



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A-Scan to Grey Level Plot

TOFD System



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Cost of TOFD vs. Radiography

What is a Phased Array?

• An array transducer is simply one that contains a number

,

refers to how those elements are sequentially pulsed.

• A phased array system is normally based around a

specialized ultrasonic transducer that contains many

individual elements (typically from 16 to 256) that can be

pulsed separately in a programmed pattern.

• These transducers may be used with various types of wedges, in a contact mode, or in immersion testing. Their

shape may be square, rectangular, or round, and test

frequencies are typically in the range from 1 to 10 MHz



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What is a Phased Array?

• Phased array systems pulse and receive from multiple

elements of an arra . These elements are ulsed in such a wa

as to cause multiple beam components to combine with each

other and form a single wave front traveling in the desired

direction. Similarly, the receiver function combines the input

from multiple elements into a single presentation.

• Because phasing technology permits electronic beam shaping

and steerin it is ossible to enerate a vast number of

different ultrasonic beam profiles from a single probe

assembly, and this beam steering can be dynamically programmed to create electronic scans.

Advantages of Phased Array Testing as

Compared with Conventional UT

The benefits of phased array technology over conventional UT

,

scan beams with a single transducer assembly.

Beam steering, commonly referred to sectorial scanning, can be

used for mapping components at appropriate angles. This can

greatly simplify the inspection of components with complex

geometry.



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Compared with Conventional UT• The small footprint of the transducer and the ability to

inspection of such components in situations where there

is limited access for mechanical scanning.

• Sectorial scanning is also typically used for weld

inspection. The ability to test welds with multiple

angles from a single probe greatly increases the

probability of detection of anomalies.

• Electronic focusing permits optimizing the beam shapeand size at the expected defect location, as well as

further optimizing probability of detection.


Compared with Conventional UT

• The ability to focus at multiple depths also improves

inspections.

• Focusing can significantly improve signal-to-noise

ratio in challenging applications, and electronic

scanning across many groups of elements allows for

- .



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Phased Array Testing

Waves that combine in phase reinforce

each other, while waves that combine

out-of-phase will cancel each other.

Phased Array Inspection Technique

E-scans inspect a weld at two separate angles



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Phased Array AUT Technology

The upper left corner in this figure illustrates the coverage options of

the technologies. The single element probe in the upper left corner

shows the limited region in the single beam available. In the upper

right, a TOFD pair is used in transmit-receive mode and the entire weld

volume is covered in a single pass.

The lower left illustrates

the phased array S-scan

created by sweeping from

from a single range of

elements (only 16 of the64 elements available are

used for this

configuration).

Pressure Vessel Inspection using

Phased Arrays



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Encoded Arrays for Semi-Automatic

Inspections

CHIME(Creeping Head-wave Inspection Method)

The new technique (AEA Technology) offers

lar e area sin le ass screenin which ins ects

the full volume between the probes (may be

separated by up to 1 m).

It can be used on both pipes and plate, and is

suitable for inaccessible geometries such as

clamps, saddles and pipe supports.

This eliminates the need for expensive shutdown

yet provides full information to indicate areas of corrosion and aid the prediction of plant lifetime.



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CHIME(Creeping Head-wave Inspection Method)

• The system employs a combination of ultrasonic- ,

Creeping Head-wave Inspection Method .

• Creeping and head waves are generated using a piezoelectric transducer mounted on an angled shoe.

• The unique way in which the waves propagate provides complete isonification of plate or pipe with

tt e attenuat on, a ow ng t e transm tt ng anreceiving probes to be well separated (up to 1 m).

• Defects due to corrosion or cracking affect the signalmagnitude and arrival time of the signal peaks.

2.5 On-Line Monitoring



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On-line Stress/strain Monitoring

Acoustic Emission Binary Localizer

A new Acoustic Emission s stem for on-lineStructural integrity monitoring of critical plantcomponents has been applied successfully for over one year.

AEBIL (Acoustic Emission Binary Localizer) isdesigned to identify and locate concentrated AE

scattered AE events, a typical condition

encountered in on-line monitoring of operating plant components.

Stress/strain Microprobe

• A portable in-situ Stress-Strain Microprobe (SSM)

- - -

behavior of several metallic materials, welds, and their

heat-affected-zones (HAZs) in various metallurgical

and damage conditions.

• The microprobe system utilizes an electro-

mechanicall -driven indenter hi h-resolution

penetration transducer and load cell, a personal

computer (PC), a 16-bit data acquisition /control unit,

and software.



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Stress/strain Microprobe

• The automated ball indentation (ABI)

ec n que o e sys em s ase on

strain-controlled multiple indentations (at a

single penetration location).

• The technique permits measurement of yield

stren th stress-strain curve stren th

coefficient, and strain-hardening-exponent

(uniform ductility).

ACFM Technique - 1• The Alternating Current Field Measurement (ACFM)

techni ue is a non contactin electroma netic

technique for the detection of surface breaking

defects in conducting materials.

• The technique provides reliable detection and sizing

of cracks in metallic components and can be used

over paint, coatings and process related residue.

• The significant advantage over magnetic particle

inspection is that surface preparation is eliminated or

significantly reduced.



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ACFM Technique - 2

–The ACFM probe induces a

uniform electric current into the

material to be inspected which

then produces a magnetic field

which will be disturbed and flow

around the edges of a defect if

present.

–Small detectors (sensors) are

built into probes which are used to

detect these magnetic field

disturbances.

ACFM Technique - 3

Two components of the magnetic field are measured,the Bx to estimate crack de th and Bz to estimatecrack length). These measurements together withsoftware algorithms are used to determine theaccurate length and depth of the defect.

Typical Bx and Bz traces

as the probe passes over a

crack

Characteristic ACFM

Butterfly plot

Advanced Inspection Techniques and Best Practices

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