General Procedure
for Ultrasonic Examination
Using Phased Array
May 1, 2006
Prepared by:
J. Mark Davis
ASNT UT Level III
Davis NDE, Inc.
for Olympus NDT
DISCLAIMER
Carefully read the following by starting to use the procedure, you are deemed to accept all the terms and
conditions set forth below.
1. The procedure is without warranty of any kind, provided to the customer on an “as is” basis. The entire risk to
the results and performance of the procedure is assumed by the customer and its end users. Olympus
NDT Inc. and Davis NDE, Inc. disclaim all warranties, expressed or implied, including but not limited to the
implied warranties of merchantability, fitness for a particular purpose, title, and noninfringement, with respect
to the procedure.
2. In no event shall Olympus NDT Inc. and Davis NDE, Inc. be liable for any direct, consequential, indirect,
incidental, punitive, special or other damages whatsoever, including without limitation, damages for loss of
business profits, business interruption, loss of business information, and the like, arising out of this agreement
or use of or inability to use the procedure, and any derivative technology thereof, even if Olympus NDT Inc.
has been advised of the possibility of such damages.
This document is the exclusive property of Olympus NDT Inc. No part of this document may be used or reproduced in its entirety or in part without the prior written consent of Olympus NDT Inc.
2
General Procedure for Ultrasonic Examination Using Phased Array
Table of Contents
1.0
Purpose
2.0
Scope
3.0
References
4.0
Ultrasonic Phased Array Examination Equipment
5.0
Phased Array Instrument Linearity
6.0
Phased Array Probe Element Operability Verification
7.0
Phased Array System Calibration
8.0
Surface Preparation
9.0
Examination Coverage and Scanning Technique
10.0
Recording/Evaluation Criteria and Amplitude Determination
11.0
Post Examination Cleaning
12.0
Documentation
Addendum 1
Phased Array Terminology
Addendum 2
Guidelines for Evaluation of Dead Elements within a Phased
Array Probe
Addendum 3
Ultrasonic Signal Flaw Characterization
Addendum 4
Flaw Sizing Using Phased Array
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General Procedure for Ultrasonic Examination Using Phased Array
3
1.0
2.0
3.0
Purpose
1.1
This procedure provides requirements for the manual and encoded ultrasonic examination of
welds and base materials using phased array.
1.2
This procedure may also be used for Performance Demonstrate Qualification (PDQ) of the
OmniScan® Phased Array System for the following:
1.2.1
Detection
1.2.2
Characterization
1.2.3
Flaw Length
1.2.4
Flaw Location: upstream or downstream
1.2.5
Flaw Sizing: ID or opposite side connected crack
Scope
2.1
This procedure establishes the generic phased array ultrasonic examination requirements that
shall be used to examine carbon steel or stainless steel plate and pipe base materials and
weldments.
2.2
This procedure is applicable for components that are between 0.5 in. and 1.0 in. in thickness.
The qualified range shall be .5 to 1.5 times the thickness of the components examined in
accordance with this procedure, (for example, 0.250 in. as the minimum to 1.5 in. as the
maximum allowed to be examined in accordance with this procedure).
2.3
This procedure is designed to demonstrate the Olympus NDT OmniScan Phased Array
System as a qualified UT system in accordance with the ASME Code, when required by the
referencing code section.
2.4
A non-blind test shall be used as a Performance Demonstration for the OmniScan Phased
Array System.
2.5
The Phased Array Scan Plan for each demonstration is outlined the Addendum with specific
requirements for each product form and material type.
References
3.1
American Society of Mechanical Engineers, Boiler and Pressure Vessel Code, Section V,
Article 4, latest Edition and Addenda
3.2
American Society for Nondestructive Testing (ASNT), SNT TC 1A, 2001
3.3
Davis NDE, Inc. Advanced UT Flaw Sizing Handbook
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4
General Procedure for Ultrasonic Examination Using Phased Array
4.0
3.4
Scan Plan Report for Detection and Flaw Characterization Report
3.5
Scan Plan Report for Crack Sizing
Ultrasonic Phased Array Examination Equipment
4.1
The ultrasonic phased array instrument shall be an OmniScan® pulse echo type and shall be
equipped with a calibrated dB gain or attenuation control stepped in increments of 2 dB or
less. The OmniScan contains 16 or 32 independent pulser/receiver channels. The system is
capable of generating and displaying sectorial-scan (also called an S-scan) images, which can
be stored and recalled for subsequent review.
4.2
Examination personnel may use a real-time sectorial-scan image during scanning to assure
that proper data has been collected. Sectorial-scan images contain signal amplitude and
reflector depth information projected for the refracted angle of the ultrasonic beam. The
OmniScan phased array system provides a variety of analysis capabilities including A-scan
display and parameter readout associated with software cursors. Images produced by B-, C-,
and sectorial-scan images are a useful aid in evaluation.
4.3
The OmniScan Phased Array system has on-board focal law generation software that permits
direct modification to ultrasonic beam characteristics. The OmniScan phased array system
requires the use of an external storage device, flash card, or USB memory Stick. A remote
portable PC connected via Ethernet® may be used for this purpose.
4.4
In addition to data storage, the PC will also be used by the data-analysis personnel for
analyzing data subsequent to the completion of data collection. Data-display software
compatible to that residing on the OmniScan Phased Array System will also be used on the
remote PC for data playback. Reference the manufacturer operating manuals for instrumentoperation specifics.
4.5
Any control, which affects the instrument linearity, such as, Reject, shall be in the off or
minimum position for instrument calibration, system calibration, and examination.
4.6
If any control (for example, filters, averaging, pulse duration, etc.) are used in calibration,
then these controls shall not be adjusted afterwards since they may affect the OmniScan
system calibration.
4.7
The Ultrasonic Phased Array System shall be calibrated for linearity in accordance with
Paragraph 5.0.
4.8
Ultragel II, Sonotrace 40, Sonatech, glycerine, or equivalent may be used as couplant when
performing calibrations and examinations. The total chlorine and sulfur content shall be less
than 1000 ppm.
4.9
The same couplant material, including batch number where applicable, used for calibration
shall be used for examinations.
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General Procedure for Ultrasonic Examination Using Phased Array
5
4.9.1
5.0
Ultrasonic transducer configurations are specified by the technique used for
examination. Linear phased Array probe configurations may include from 10 to 128
elements.
4.10
The phased array probe frequency shall be between 2 MHz and 10 MHz depending upon
material type and thickness.
4.11
Phased array wedges should be of a design to accommodate the aforementioned phased array
probes. Nominal refracted-wedge angles shall be 45, 55, 60, or 70 degrees to ensure coverage
of the weld and heat affected zone (HAZ).
4.12
An encoder interfaced with the OmniScan® phased array instrument may be used to track the
phased array probe movement. The encoder shall be calibrated to coordinate its movement
with the OmniScan instrument.
Phased Array Instrument Linearity
5.1
Ultrasonic instrument linearity shall be verified at the beginning and end of each series of
examinations, which is not to exceed 3 months.
5.2
The instrument linearity verification shall be recorded on the Ultrasonic Instrument Linearity
Verification (Form 1).
5.2.1
Screen-Height Linearity
5.2.1.1 Position a search unit on a calibration block to obtain indications from the two
calibration reflectors.
5.2.1.2 Alternatively, a straight-beam search unit may be used on any calibration block
that will provide amplitude differences with sufficient signal separation to
prevent the overlapping of the two signals.
5.2.1.3 Adjust the search unit position to give a 2:1 ratio between the two indications,
with the larger indication set at 80% of full-screen height (FSH) and the
smaller indication at 40% of FSH.
5.2.1.4 Without moving the search unit set the larger indication to 100% of FSH;
record the amplitude of the smaller indication, estimated to the nearest 1% of
FSH.
5.2.1.5 Successively set the larger indication from 100% to 20% of FSH in 10%
increments (or 2 dB steps if a fine control is not available); observe and record
the smaller indication estimated to the nearest 1% of FSH at each setting. The
reading must be 50% of the larger amplitude within ±5% of FSH.
5.2.2
Amplitude-Control Linearity
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6
General Procedure for Ultrasonic Examination Using Phased Array
5.2.2.1 Position a search unit on a calibration block to obtain maximum amplitude
from a calibration reflector.
5.2.2.2 As a minimum, the amplitude control linearity shall be performed to document
linearity at both ends of the gain range being used with the equipment.
5.2.2.3 Without moving the search unit, set the indication to the required percentage of
FSH and increase or decrease the dB as specified on the Ultrasonic Instrument
Linearity Verification (Form 1). The estimated signal shall be recorded to the
nearest 1% of FSH and shall fall within the limits specified on Form 1.
6.0
7.0
Phased Array Probe Element-Operability Verification
6.1
The phased array probe shall be checked for element performance whenever the examiner
suspects an element operability problem. Each phased array probe must be checked to
determine each element’s ability to transmit and receive ultrasonic energy.
6.2
This operability verification verifies performance of each transmitter/receiver module, and
cable conductivity for each channel. Any phased array probe that has greater than 25%
defective elements of the useable aperture should be replaced with a new probe. However, if
an effective calibration is performed then the probe may not be considered defective.
6.3
A guideline for verification of element operability is provided in Addendum 2.
Phased Array System Calibration
7.1
Calibration shall be performed from the surface of the calibration block which corresponds to
the component surface to be examined.
7.2
System calibration shall include the complete ultrasonic examination system. Screen distance
calibration shall be at least 1½ “veepaths” (also known as skip) for the minimum angle that
will be used during the examination, unless otherwise specified.
7.3
The system calibration information shall be recorded on the Ultrasonic Data Report Form
used in the OmniScan®. During scanning, only the gain may be adjusted from the calibrated
reference dB. Adjustment of other controls shall require recalibration.
7.4
Focal-Law Verification
7.4.1
The transmission and reception of ultrasonic waves of a given angle of incidence is a
function of time delays calculated by focal laws using the information provided to the
phased array system. Verification that the input information is correct and that the
phased array system is working properly must be checked.
7.4.2
Select the Angle-beam cursor and adjust its position so that it displays A-scan
information for the 45° angle of refraction or the minimum angle that will be used in
the sectorial scan.
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General Procedure for Ultrasonic Examination Using Phased Array
7
7.5
7.4.3
Using the 4 -in. radius on the IIW block, peak the signal shown on the A-scan display.
Note: Although the sectorial scan may indicate higher amplitude responses from other
angles, only use the A-scan response associated with the 45° angle of propagation.
7.4.4
Indicate the beam exit point on the transducer wedge. This beam exit location is only
valid for the 45° angle of propagation.
7.4.5
Using the primary angle of beam refraction exit location, measure the actual angle of
propagation by peaking the response in the A-scan display using the plexiglass insert
on the IIW block. Record the actual angle of propagation as indicated on the IIW
block using the beam exit point location.
7.4.6
If the measured angle of propagation is 45° ±2°, then critical focal-law parameters are
correct.
7.4.7
If the measured angle of propagation is outside the allowable tolerance (45° ±2°), then
all transducer and setup parameters must be reviewed for accuracy. If these parameters
are correct, then check the shear-wave velocity value used for the material. If this is
correct, then small adjustments must be made to the transducer-wedge velocity entry.
If the measured angle is too high, then the wedge velocity must be increased slightly,
and repeated. Similarly, if the measured angle is too low, then the wedge-velocity
parameter must be lowered and repeated until the measured angle is within tolerance.
Time-Base Verification
7.5.1
Position the angle cursor and adjust its position so that it displays A-scan information
for the 45° angle of refraction.
7.5.2
Place the transducer so that reflections from both the 2- and 4-in. radius reflectors on
the IIW block are peaked and observed simultaneously on the A-scan display.
7.5.3
Use the A-scan cursors to measure the distance between the 2- and 4-in. signals. This
result shall be 2 in. ±0.1 in.
7.5.4
If the measured separation between the signals is too large (greater than 2.1 in.),
decrease the shear-velocity parameter under the Part Setup menu. Similarly, if the
measured distance is too short (less than 1.9 in.), increase the velocity value. Repeat
adjustment until an acceptable value is achieved.
7.5.5
With the transducer remaining in the peaked position, measure the metal path of the
4 -in. radius reflector using a cursor in the A-scan display.
7.5.6
The value should measure to be 4 in. ±0.1 in. If this measurement is less than 3.9 in.,
increase the value of the Delay parameter until the measurement is correct. If this
value is greater than 4.1 in., decrease the Delay parameter until the measurement is
correct. The requirements for focal law verification, time base verification and
sensitivity adjustments are listed below. Instrument linearity verification and
ultrasonic beam spread is not required.
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8
General Procedure for Ultrasonic Examination Using Phased Array
7.5.7
7.6
As an alternative, other calibration blocks may be used to perform the time-base or
wedge-delay calibration.
Sensitivity and Wedge-Delay Calibration
7.6.1
The OmniScan® shall be calibrated for wedge delay and sensitivity.
7.6.2
The wedge-delay calibration shall be calibrated for true depth with the angles used in
calibration.
7.6.3
The sensitivity calibration will provide the required gain adjustments for each
refracted angle and sound path used.
7.6.3.1 Select a calibration reflector, which is approximately one-half the thickness of
the component to be examined, or within the zone of material to be examined.
7.6.3.2 Peak up this signal from the calibration reflector and scan the phased array
probe backwards through all the different angles or focal laws.
7.6.3.3 Scan forward over the calibration reflector through all the refracted angles or
focal laws.
7.6.3.4 The OmniScan system will calculate the required gain needed at each focal law
to adjust the amount needed.
7.7
A time-corrected gain (Auto-TCG) calibration shall be used to compensate for attenuation in
the material at the sound paths used during calibration and examination.
7.8
As an alternative, DAC may be used for electronic scans (E-scans) of specific angles; for
example, 45, 60 or 70 degrees.
7.9
The examination system calibration may be stored in the OmniScan System with electronic
memory, on an external chip or data storage device. This calibration may be used at a later
date provided that the system calibration is verified prior to examination.
7.10
A complete Ultrasonic System Calibration shall be performed at least once prior to the
examination.
7.11
Temperature Requirements
The basic calibration block temperature shall be within 25°F of the component temperature.
The surface temperature of the component to be examined shall be taken during each
examination.
7.12
System Calibration Verification
7.12.1 System calibration verification shall include the entire examination system. Sweep
range and TCG calibration shall be verified on the appropriate calibration block or
simulator block, as applicable, under the following conditions:
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General Procedure for Ultrasonic Examination Using Phased Array
9
7.12.1.1 Prior to and within 24 hours of the start of a series of examinations.
7.12.1.2 With any substitution of the same type and length of search-unit cable.
7.12.1.3 With any substitution of power using the same type source, such as a change
of batteries.
7.12.1.4 At least every 12 hours during the examination.
7.12.1.5 At the completion of a series of examinations.
7.12.1.6 Whenever the validity of the calibration is in doubt.
7.12.2 A simulator block (for example, IIW block and miniature DSC) may be used for the
entire exam system-calibration verifications. The simulator block may be of any
material and configuration that will permit verification of the sweep range and TCG
sensitivity.
7.12.3 The initial system calibration shall be made using a basic calibration block. Whenever
possible, the final system calibration verification should be made using the basic
calibration block. If a reference block, such as Rompas, is used to perform system
calibration verification, the location and amplitude of the simulator reflector(s) shall
be documented on the calibration record at the time of the initial calibration. If the
gain controls are adjusted, the dB settings shall be recorded for the reference block.
The reference block shall be identified by type and part number or serial number on
the system calibration record.
7.13
System Calibration Changes
7.13.1 Perform the following if any point on the TCG decreases by 20% or 2 dB of its
amplitude, or any point on the sweep line has moved more than 10% of the sweep
division reading.
7.13.1.1 Void all examinations performed after the last valid calibration verification.
7.13.1.2 Conduct a new system calibration.
7.13.1.3 Repeat voided examinations.
7.13.2 Perform the following if any point on the TCG has increased more than 20% or 2 dB
of its amplitude:
7.13.2.1 Correct the system calibration.
7.13.2.2 Re-examine all indications recorded since the last valid calibration
verification.
7.13.2.3 Enter proper values on the applicable forms.
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10
General Procedure for Ultrasonic Examination Using Phased Array
7.14
Recalibration
7.14.1 Any of the following conditions shall be cause for system recalibration:
8.0
9.0
7.14.1.1
Search unit transducer or wedge change
7.14.1.2
Search unit cable type or length change
7.14.1.3
Ultrasonic instrument change
7.14.1.4
Change in examination personnel
7.14.1.5
Couplant change
7.14.1.6
Change in type of power source
Surface Preparation
8.1
Contact Surfaces - The finished contact surface should be free from weld spatter and any
roughness that could interfere with free movement of the search unit or impair the
transmission of ultrasonic vibrations.
8.2
Weld Surfaces - The weld surface should be free of irregularities that could mask or cause
reflections from defects to go undetected and should merge smoothly into the adjacent base
materials.
8.3
Conditions, which do not meet these requirements, shall be recorded as limitations on the
Ultrasonic Examination Data Report Form.
Examination Coverage and Scanning Technique
9.1
The specifics of the examination volume, weld identification, and location shall be identified
in the Scan Plan.
9.2
The examination volume shall cover the weld metal and a quarter from the toe of the weld.
This area includes the heat affected zone or HAZ.
9.3
The Scan Plan shall demonstrate by plotting or with using a computer simulation the
appropriate examination angles for the weld prep bevel angles (for example, 40 to 60 degrees
or 55 to 70 degrees) that will be used during the examination. This Scan Plan shall be
documented to show that the examination volume was examined. This Scan Plan shall be a
part of the final examination report.
9.4
The OmniScan® may use multiple-group settings to establish sector scans and E-scans for the
appropriate angles as identified in paragraph 9.3 to ensure complete coverage of the weld and
heat-affected zone.
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General Procedure for Ultrasonic Examination Using Phased Array
11
9.5
To determine the required examination volume and scan area, profiles may be taken on each
weld at the top-dead-center or L0, the beginning of the area to be scanned, as a minimum.
Profile data will consist of ultrasonic thickness measurements and outside surface contours
using a contour gage. Thickness measurements should be taken at a maximum interval of
approximately 1/4 in. and should cover the material volume to be examined and recorded. The
“t” dimension shall be the nominal wall thickness.
9.6
Scanning shall be performed using a Line-scan technique. This is also called LSAT, (Line
Scanning Analysis Technique ™, Davis NDE, Inc.). Each Line scan shall be parallel to the
weld using a sectorial scan, (S-scan) and/or an electronic scan, (E-scan).
9.7
Appropriate refracted angles as accepted by ASME will define the positions of the arrays, and
hence the angles. These should be detailed in the ultrasonic Scan Plan.
9.8
A minimum of two (2) line scans shall be performed at two (2) different index points from the
center of the weld from both sides of the weld where practical to ensure coverage of the weld
and heat-affected zone (HAZ).
9.9
For thicker materials with a nominal wall thickness great than 1 in., multiple line scans shall
be performed to the degree to cover the required volume of weld and base material.
9.10
Scans shall be parallel to the weld at 90°- and 270°-scan axes and parallel to the weld at 0°and 180°-scan axes.
9.11
Raster scanning will aid in flaw characterization.
9.12
The rate of search unit movement shall be limited to a maximum of 6 inches per second for
vessel welds and 3 inches per second for piping welds unless calibration has been verified at a
higher speed.
9.13
Perform the examination from both sides of the weld, where practical, or from one side as a
minimum. All examination volume limitations shall be documented on the Ultrasonic
Examination Data Report Form.
9.14
The entire examination volume comprising the weld and adjacent base metal shall be
examined with the beam parallel to the weld on either side of the weld in two directions, (for
example, clockwise and counterclockwise). Phased array wedges contoured to the radius of
the pipe or vessel may be used in the examination to ensure proper contact with the pipe or
vessel.
It is recommended that full A-scan data shall be recorded when using encoders.
9.15
10.0
Recording/Evaluation Criteria and Amplitude Determination
10.1
Only personnel certified Level II or III in Ultrasonics shall evaluate the results of ultrasonic
examinations for acceptance.
10.2
All reflectors that exceed 20% of DAC or TCG shall be investigated completely to determine
the type of reflector. Addendum 3 will provide guidance for flaw characterization.
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12
General Procedure for Ultrasonic Examination Using Phased Array
10.3
Indications that exceed 50% of DAC or TCG and determined to be of geometric or
metallurgical origin shall be recorded.
10.3.1 The following steps shall be taken in order to classify an indication to be of geometric
or metallurgical origin:
10.3.1.1
Interpret the area containing the reflector in accordance with the applicable
examination instruction;
10.3.1.2
Plot and verify the indication coordinates. Weld profiles will be performed
to determine the OD contour.
10.3.1.3
Review fabrication or weld prep drawings when accessible.
10.3.2 The position and location of indications shall be recorded in accordance with
Reference 5.1.11.
10.3.3 All recordable indications shall be resolved to determine the shape, identity, and
location of the reflector. Final evaluation and disposition of the indication is the
responsibility of owner/user of the component to be examined.
10.3.4 Amplitude determination - Signal amplitude shall be measured as a percentage of the
calibrated DAC or TCG.
10.3.5 The appropriate Code or Specification shall be used to determine final acceptance of
the weld inspection using the OmniScan®.
11.0
Post Examination Cleaning
The remaining couplant shall be wiped from the surface at the completion of the examination.
12.0
Documentation
12.1
Results of ultrasonic examination shall be reported on the OmniScan Data Report Form used
in the software. All Phased Array examination data for each recordable indication, A-, B-, C-,
and S-scans shall be saved as a report file.
12.2
The examiner shall record the results of the examination on the OmniScan Data Report From.
All recordable indications shall be documented on the examination report. All blocks should
be completed with the appropriate data or “NA.”
12.3
The Ultrasonic Scan Plan, Ultrasonic Calibration, and Ultrasonic Instrument Linearity
Verification (if required) shall be considered part of the examination report.
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General Procedure for Ultrasonic Examination Using Phased Array
13
ULTRASONIC INSTRUMENT LINEARITY VERIFICATION
INSTRUMENT MANUFACTURER
MODEL NUMBER
RECORD NO.
CALIBRATION BLOCK NO.
INITIAL DATE
FINAL DATE
SCREEN HEIGHT
LINEARITY
AMPLITUDE CONTROL LINEARITY
INSTRUMENT WITH FINE dB
CONTROL
FIRST
SIGNAL IN %
SECOND
SIGNAL IN %
*
INDICATION
dB
SET AT % OF
CONTROL
CHANGE
FULL
SCREEN
INDICATION
LIMITS % OF FULL
SCREEN
ACTUAL % OF FULL SCREEN **
HI GAIN SETTING
LOW GAIN
SETTING
INITIAL
FINAL
INITIAL
FINAL
_____dB
_____dB
_____dB
_____dB
100
90
80
70
80
-6 dB
32 TO 48
80
-12 dB
16 TO 24
40
+6 dB
64 TO 96
20
+12 dB
64 TO 96
40
60
50
40
30
20
*READING MUST BE 50% OF FIRST-SIGNAL AMPLITUDE WITHIN ±5% OF FULL-SCREEN HEIGHT.
**FINAL READINGS SHALL BE RECORDED TO THE NEARSEST 1% OF FULL-SCREEN HEIGHT
COMMENTS:
INSPECTOR
CERT LEVEL
DATE
INSPECTOR
CERT LEVEL
DATE
SUPV/LEVEL III REVIEW
DATE
Form 1
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14
General Procedure for Ultrasonic Examination Using Phased Array
Addendum 1
1. Terminology
Angle Compensated Gain: Also called ACG. This is compensation for the variation in signal amplitudes
received from fixed-depth SDHs during S-scan calibration. The compensation is typically performed
electronically at multiple depths. Note that there are technical limits to ACG, (i.e. beyond a certain angular
range, compensation is not possible).
Annular array probes: Phased array probes that have the transducers configured as a set of concentric rings.
They allow the beam to be focused to different depths along an axis. The surface area of the rings is in most
cases constant, which implies a different width for each ring.
Array (phased): A patterned arrangement of transducers. Typical arrangements include linear, annular,
square (2-D) matrix, annular-sectorial, and circular.
Circular array probes: Phased array probes made up of a set of elements arranged in a circle. The elements
can direct the beam either towards the interior, towards the exterior of the circle, or along the axis of
symmetry of the circle (typically using a mirror) to give the beam the required angle of incidence.
Electronic scan: Also termed E-scan. The same focal law is multiplexed across a group of active elements;
electronic raster scanning is performed at a constant angle and along the phased array probe length. This is
equivalent to a conventional ultrasonic probe performing a raster scan; also called electronic scanning.
Focal law: The time delays applied to a specific group of elements in the array that determines the beam
characteristics in both the transmitted and received modes.
Linear array probes: Probes made using a set of elements juxtaposed and aligned along an axis. They
enable a beam to be moved, focused, and deflected along a single plane.
Matrix array probes: These probes have an active area divided into two dimensions in different elements.
This division can, for example, be in the form of a checkerboard, or sectored rings. These probes allow the
ultrasonic beam to be steered in three dimensions.
Sectorial scan: Also termed S-scan or Azimuthal scan. This may refer to either the beam movement or the
data display. As a data display it is a 2-D view of all A-scans from a specific set of elements corrected for
delay and refracted angle. When used to refer to the beam movement it refers to the set of focal laws that
sweeps a defined range of angles using the same focal distance and elements.
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General Procedure for Ultrasonic Examination Using Phased Array
15
Addendum 2
Guidelines for Evaluation of Dead Elements
within a Phased Array Probe
Scope
This Addendum provides guidelines for the determination of dead elements in a phased array probe, which
may become an ultrasonic inspection issue, and what corrective actions can be taken.
These guidelines are not mandated, as each specific application and each set of focal laws is different. In the
event of any dead element issues not adequately covered by this guideline, we recommend discussing the
specific case with Olympus NDT, or one of the ONDT Training Academy companies.
Definitions
•
•
•
•
Dead element: This refers to a dead ultrasonic channel. There are up to 128 channels in the
OmniScan®, and each beam is formed by multiple channels (typically around 16 channels, though it
may be much fewer).
Cause of dead elements: Dead elements can be caused by either a broken wire in the cable, a defunct
element in the array, or a bad connection. The usual cause of dead elements is a damaged cable. In
practice, it doesn’t matter much whether dead elements are caused by a decaying array or by a broken
cable.
Focal Law: The ASCII file that controls which elements are fired with what time delay, and at what
voltage.
Calibration: A specific (code) calibration scan on an approved calibration block, as per normal.
Assumptions
•
•
•
•
•
•
•
It is assumed that the OmniScan provides an acceptable calibration at the start of the project. (In
practice, there may be one or more isolated dead elements, but these will generally have a negligible
effect).
Future degradation will be in comparison with this initial reference point.
The operator has performed a baseline dead-element check at the start of the project.
The initial calibration is used as a “gold standard” for judging subsequent calibrations for determining
if excessive dead elements are present.
The “gold standard” is used to measure:
♦ Calibration reflector amplitudes as normal incidence
♦ Beam skew changes
♦ Signal-to-noise ratios (S/N)
Subsequent calibration scans will be performed at essentially the same temperature and calibration
conditions as the “gold standard.”
Evaluation of the effect of dead elements is based on a performance criterion, not on the number or
location of the dead elements.
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16
General Procedure for Ultrasonic Examination Using Phased Array
Detecting Dead Elements
Dead elements can be identified with a “one-at-a-time, zero-degree response check.”
Dead Element Acceptance Criteria Guidelines
There are several possible criteria for determining whether the number of dead elements is excessive. These
guidelines are essentially based on essential performance criteria (i.e. the beam amplitude, beam skew or
signal-to-noise ratio). The operator should take remedial measures (suggested later) if any one of these three
criteria is not met.
Blanket requirements, such as “no more than two dead elements per focal law”, or “unacceptable if two dead
elements are adjacent” are overly restrictive, and results in Appendix A show that they do not reasonably
define an acceptable beam, based on performance criteria.
Criterion 1: Calibration amplitude drop >6 dB
If a calibration-scan change of more than 6 dB vs. the “gold standard” is noted on any channel, the cause
may be due to dead-center elements.
R&D has shown that the reduction in signal strength could be due to failed elements from any area of the
array (see Appendix A). Failed elements in the center of the array seem to reduce the overall signal
response, without affecting beam steering, whereas losing elements at the edges of the array leads to both
loss of sensitivity and also change in beam angle.
The operator should perform the usual evaluation of the system (which applies to any change of
ultrasonic behavior):
• Check for poor coupling.
• Check for local disbonding on the wedge face.
• Check for poor wedge-array coupling.
• Determine if the 6 dB drop is a gradual change, or a sudden drop. If this is a gradual change, then
the cause may be a natural decay of the array or similar; in this case it may be possible to increase
the gain provided the beam skew and signal-to-noise ratio criteria are met.
• Check temperature control.
1. If there are “excessive” dead elements (see Appendix A and the criteria used there), then the operator
can:
a. Increase the number of elements if possible, (for example, from 8 to16, or from 16 to 18 or
20), and re-scan; this may not be feasible (see Appendix B).
b. Adjust the Focal Law (angles, position, etc.) so that different Focal Laws are used, and rescan; again, this may not be feasible or code-acceptable.
c. Replace defective equipment (cable, array, or connectors).
2. Document the results.
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General Procedure for Ultrasonic Examination Using Phased Array
17
Criterion 2: Beam skewing
If the beam angle (as measured during normal calibration) changes by more than ±2o from the “gold
standard”, then dead elements are a possible cause.
Besides the usual ultrasonic checks (see above), recommended corrective actions when beam skew changes
by ±2o from the “gold standard” would include:
1. Perform a dead element check.
2. If there are “excessive” dead elements, then the operator can:
a. Increase the number of elements if possible, (for example, from 8 to16, or from 16 to 18 or
20), and re-scan; this may not be feasible.
b. Adjust the Focal Law (angles, position, etc.) so that different focal laws are used, and re-scan;
again, this may not be feasible, or permitted.
c. Replace defective equipment (umbilical, array, connectors).
3. Document the results.
Criterion 3: Signal-to-Noise Ratio
If the signal-to-noise ratio (S/N) is less than a specific value, the channel is essentially non-functional.
Normally, this problem only occurs with high refracted angle channels due to the high beam steering and
acoustic factors, but might occur on other channels due to excessive dead elements, or other problems. The
level of S/N is arbitrary, and is up to the operator or contractor to determine.
If S/N is below the acceptable value, then corrective action should be taken besides the usual checks.
1. Perform a dead element check.
2. If there are “excessive” dead elements, then the operator can:
a. Increase the number of elements if possible, (e.g. from 8 to16, or from 16 to 18 or 20), and rescan; this may not be feasible.
b. Adjust the Focal Law (angles, position etc.) so that different Focal Laws are used, and re-scan.
Again, this may not be feasible, and would normally need the approval of the client or
certifying authority.
c. Replace defective equipment (Probe cable, array, connectors).
3. Document the results.
Summary
•
•
•
•
This document gives guidelines on how to:
– Detect the effects of dead elements.
– Identify what acceptance criteria are recommended.
– Propose some corrective actions.
No definitive criteria for dead elements can be given since the effect of dead elements depends on the
setup, wedge and array, specific focal laws, beam angles, the elements that are dead, etc.
Some preparation for managing dead elements can be undertaken by suitably characterizing the
system beforehand (see Appendix B).
Normally dead elements are not an issue with OmniScan®.
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18
General Procedure for Ultrasonic Examination Using Phased Array
Appendix A: Background on Dead Elements
Normally, industrial arrays are very durable, and can last several years. In comparison with conventional
transducers, arrays have proven very robust since an occasional dead element is not a major consideration.
Simulations of Dead Elements
More recently, dead elements have become a significant issue and cost for some advanced AUT equipment,
primarily in the nuclear and pipeline industries. In collaboration with the Electric Power Research Institute,
ONDT has performed a variety of tests to determine what number of elements causes detrimental
performance for linear and matrix arrays. (See F. Cancre, “Effect of the Number of Damaged Elements on
the Performance of an Array Probe,” 16th World Conference on NDT, Montreal, Canada, August 2004).
Some typical simulation results for a 16-element beam with adjacent dead-center elements are shown in
Figure 1. (The top-left simulation has no dead elements, the bottom-left has one, the center-top has two dead
elements and the bottom-right has five). The beam shape with dead center elements is acceptable until at
least five out of the 16 elements are dead. (This is a significantly higher number of dead elements than the
typical criterion of two adjacent elements.) Note that the beam shape and focal-spot size do not change much,
but that side lobes start appearing with four or five dead elements out of the16.
Figure 1: Simulation of dead-center elements starting with zero dead elements at top left, one
dead element at bottom left, two dead elements at top center, etc.
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General Procedure for Ultrasonic Examination Using Phased Array
19
Similar simulations with dead elements at one end of the array show reasonable performance until four or
five elements are dead. (See Figure 2)
Figure 2: Dead elements at the end of the array, starting with zero at top left.
As with dead-center elements, the major effects appear with four or more dead elements. For dead-edge
elements, the main effect is broadening of the focal spot.
Normal Beam Scans with Dead Elements
The following images show a series of experimental normal beam scans on a calibration block with sidedrilled holes with increasing numbers of dead elements. The actual dead element is shown in the box above
the appropriate scan. In this case, a linear array with eight elements was used.
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20
General Procedure for Ultrasonic Examination Using Phased Array
Figure 3: Normal beam scan with no dead elements.
Figure 4: Normal beam scan with one dead element.
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General Procedure for Ultrasonic Examination Using Phased Array
21
Figure 5: NB scan with two dead elements.
Figure 6: NB scan with three dead elements.
Note that one dead element out of eight has little effect; even two dead elements (25%) are marginally
acceptable, though three dead out of eight shows significant tails.
The essential results for linear arrays are shown in Table 1
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22
General Procedure for Ultrasonic Examination Using Phased Array
Table 1: Effect of dead elements on signal amplitudes
(8-and 16-element linear arrays)
16 elements virtual
probe
8 elements Virtual
Probe
Linear Array on Pipe, Angle Beam, Notch
Theoretical
Loss in dB
Minimum
loss in dB
Maximum
Loss in dB
Worst
Configuration
Theoretical
Loss in dB
Minimum
loss in dB
Maximum
Loss in dB
Worst
Configuration
Dead Elements
3
4
1
2
2.3
5.0
8.2
1.1
0.3
1.5
2.2
2.9
8.2
8
1.3
6, 7, 8
1.1
2.3
3.6
0,7
0,2
1,9
1.8
3.1
16
1, 3
5.0
5
6
6.5
8.2
4.8
5.6
7.4
7.4
8, 9, 10 or
6, 7, 8, 9, 6, 7, 8, 9,
7, 8, 9
6, 7, 8, 9
10
10, 11
Implications of dead element research
Dead element simulations and experiments show that up to 25% of the elements in a whole array can be dead
before the beam is significantly affected. The location of the elements is important. All dead elements in the
center of the array will cause signal amplitude to decline significantly, while dead elements at the edge will
cause beam skewing.
More important, the impact of dead elements will depend on the specific focal law, and potentially on
the customer specifications and requirements. Therefore, it is not possible to produce specific criteria
for dead elements for all OmniScan inspections; however, it is possible to generate guidelines, tests,
and actions, which is the purpose of this document.
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General Procedure for Ultrasonic Examination Using Phased Array
23
Appendix B: Sample Approach for Managing Dead Elements
Before Inspection
1. Perform dead element check.
2. Perform “gold standard” calibration. Record.
3. Measure actual beam angle at a specific nominal angle; such as, the natural refracted angle. (For
example, with a N45S wedge, the natural refracted angle is 45o; use this angle as a reference).
4. Note the S/N (signal-to-noise ratio) on a selected channel, such as, the natural refracted angle from a
standard reflector.
5. Monitor the calibration, beam angle and S/N as appropriate.
During Inspection
1. Perform dead element checks if required.
2. Perform regular calibrations, noting any gain changes, change in beam angle, and S/N.
3. If significant discrepancies are noted, follow procedures in main text.
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24
General Procedure for Ultrasonic Examination Using Phased Array
Addendum 3
Ultrasonic Signal Flaw Characterization
General Information
1.
Any reflector which causes an indication in excess of 20% DAC, at reference sensitivity,
shall be investigated to the extent necessary to provide accurate characterization, identity, and
location. All such indications shall be evaluated in terms of the applicable acceptance criteria
of the referencing code Section.
2.
During examination, the sweep range may be adjusted for indication discrimination and
characterization. Final recording of indications shall be done utilizing the sweep and DAC
settings established during calibration.
Indication Classification
1.
Flaw Indications - All indications produced by reflectors within the volume to be examined,
regardless of amplitude, that cannot be clearly attributed to the geometry of the weld
configuration (counter bore, root, metallurgical responses, etc.) shall be considered as flaw
indications.
2.
Geometric or Metallurgical Indications - All indications produced by reflectors within the
volume to be examined that can be attributed to the geometry of the weld configuration
(counter bore, root, acoustic interface, weld noise, etc.) shall be considered as geometric or
metallurgical indications.
The identity, maximum amplitude, location, and extent of reflector causing a geometric
indication shall be recorded. The following steps shall be taken to classify an indication as
geometric:
•
Interpret the area containing the reflector in accordance with the Flaw Indications or
the Geometric or Metallurgical Indications criteria, listed below in this section.
•
Plot and verify the reflector coordinates. Prepare a cross-section sketch showing the
reflector position and surface discontinuities such as root and weld crown.
•
Review radiographs, fabrication or weld preparation drawings, as-built drawings, or
any other means available to accurately identify the reflector.
Ultrasonic Indication Discrimination
1.
Flaw Indications - All suspected flaw indications shall be investigated and evaluated taking
into account the following indication characteristics. These characteristics should not be
considered as mandatory criteria for classifying indications as flaws, but are listed as
significant points of interest for the examiner to consider during evaluation of suspect areas.
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General Procedure for Ultrasonic Examination Using Phased Array
25
2.
The indication has a good signal-to-noise ratio, such as SN 2:1, with defined start and end
points. This characteristic can be supported by observing signal-to-noise ratio variations along
the length of the component.
3.
The indication plots to a location susceptible to cracking. This characteristic can be supported
by obtaining localized thickness and surface contour recordings at the location of the
indication(s).
4.
The indication can be detected with multiple search-unit angles, and a higher angle provides
comparable or greater signal response. This characteristic can be supported with an adequate
reference reflector (inside-surface notch or equivalent).
5.
The indication provides substantial and unique echo-dynamic travel. This characteristic can be
supported by observing other areas along the length of the sample and with an adequate
reference reflector (inside-surface notch or equivalent).
6.
Several areas of unique or multiple amplitude peaks are observed throughout the indication
length. This characteristic can be supported by observing other areas along the length of the
sample and by scanning laterally along the indication length.
7.
The indication maintains or provides an increase in signal amplitude when the beam is skewed
away from normal. This characteristic can be supported by observing other areas along the
length of the sample.
8.
Inconsistent time base positions are observed throughout the indication length as the search
unit is moved parallel along the length of the reflector. This characteristic can be supported by
scanning laterally along the indication length.
9.
The indication shows evidence of flaw tip diffracted signals
10.
Circumferential indications provide axial components while performing tangential scans.
11.
For circumferential flaws, the indication(s) can be confirmed from the opposite side of the
weld. This characteristic may require a reduced search-unit frequency.
12.
For axial flaws, the indication(s) can be confirmed from the opposite direction. This
characteristic is dependent upon flaw orientation and may not always be available.
13.
The indication is in close proximity to, or initiates from, a geometrical reflector and distinct
signal separation and amplitude fluctuation can be observed. This characteristic may require
an increase in signal-resolution capability in order to make this evaluation. Examples include
reducing screen size and slower scan speeds.
14.
For components where access is limited to a single side of the component, document the
reason for the limitation.
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26
General Procedure for Ultrasonic Examination Using Phased Array
15.
Because of the uncertainties associated with the flaw orientation and the actual thickness of
the component on the inaccessible side of the weld, an accurate inside-surface connection on
the far side of the weld may not be obtainable.
16.
For suspect far-side flaw indications, several search unit angles should be evaluated to
optimize the response.
Geometric or Metallurgical Indications
1.
All suspected geometric or metallurgical indications shall be investigated and evaluated taking
into account the following indication characteristics. These characteristics should not be
considered as mandatory criteria for classifying indications, but are listed as significant points
of interest for the examiner to consider during the evaluation of suspect areas.
2.
The indication appears at or near the centerline of the weld or other documented geometrical
condition (i.e. counter bore) and can be seen continuously or intermittently along the length of
the weld at consistent amplitude and sweep positions. This characteristic can be supported by
obtaining localized thickness and surface contour recordings at the location of the
indication(s).
3.
The indication provides additional responses, which occur from the same scan position, but at
different sweep positions (multiples) along the length of the weld. This may be a sign of
mode-converted shear-wave signals from counter bore or similar geometric reflectors. This
characteristic may require an increase in time-base size in order to observe these responses.
4.
The indication can be seen across the entire length of the scan, either continuously or
intermittently, at consistent amplitude and sweep positions. This characteristic can be
supported by scanning laterally along the indication length.
5.
When examining with a higher-angle search unit, the amplitude response is lower or not
detected. This characteristic should consider localized thickness and contour information to
ensure that the search-unit angles provide comparable examination volume coverage and
sound penetration. This characteristic can additionally be supported with an adequate
reference reflector (Inside surface notch or equivalent).
6.
The indication provides minimal echo-dynamic travel (walk). This characteristic can be
supported by observing other areas along the length of the sample and with an adequate
reference reflector (inside-surface notch or equivalent).
7.
The indication provides a rapid and consistent drop in signal amplitude when the beam is
skewed away from normal in either direction.
8.
The indication provides a clean, single-signal response with minimal to no signal faceting. No
discernible tip signals are observable. This characteristic can be supported by optimizing the
signal presentation on an adequate reference reflector (inside-surface notch or equivalent).
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General Procedure for Ultrasonic Examination Using Phased Array
27
9.
The signal responses are consistent from each side of the weld for axial scans, or from each
direction, clockwise (CW) or counter-clockwise (CCW) for circumferential scans.
Indication Positioning
1.
Due to geometrical configuration, (tapers, radius, etc.) indication positioning may require
detailed evaluation. The following information is provided to assist in proper indication
positioning.
2.
Perform detailed thickness and surface contour recordings at the location of the indication(s).
Attempt to identify any position offset of the weld root in relationship to the weld centerline.
3.
Evaluate the flaw-signal amplitude responses from each side of the weld, if possible. Observe
if the signal response appears reduced due to weld-volume sound attenuation from one side or
another.
4.
Evaluate the ultrasonic responses from each side of the weld in both flawed and unflawed
regions. Attempt to identify standard benchmark responses (for example, weld root, weld
noise, counter bore, etc.) and flaw-indication responses. Take notice of the ultrasonic and
surface distance dimensions from these responses.
5.
Coordinate and plot this information on a cross sectional drawing of the weld.
Length Sizing
1.
Length sizing shall be performed utilizing information obtained on the same side of the weld
as the indications. If component geometry provides limitations (for example, longitudinal
weld obstructions, welded attachments, etc.) or the flaw orientation provides improved and
satisfactory UT responses, then length-sizing data from opposite-side examinations may be
used to provide additional information to the same-side data.
2.
If the indication is detectable with multiple PA probe angles, the primary search unit should
generally be used for final-length determination. If geometric conditions or examination
limitations prohibit adequate length-sizing data with the primary search unit, additional angles
shall be used. If multiple angles are evaluated, the angle that provides the most conservative
dimension (greatest length) should be used.
3.
If an extreme length discrepancy exists between search unit angles, the examiner shall attempt
to identify the cause of discrepancy (for example, scan limitation, surface condition, beam
spread, geometrical effects, etc.) and may use the length -sizing measurement of a less
conservative search unit.
4.
Length sizing shall be performed in accordance with the technique below. Multiple searchunit angles should be evaluated in order to properly discriminate flaw responses from
surrounding metallurgical and geometrical conditions.
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28
General Procedure for Ultrasonic Examination Using Phased Array
5.
Optimize the signal response from the flaw indication.
6.
Scan the indication area with specific focus on the flaw-signal responses, (for example, signal
shape, walk, orientation, effect of skew, etc). Adjust the system gain as needed to optimize
flaw responses.
7.
Scan an adjacent unflawed area in close proximity to the flaw area with specific focus on the
surrounding geometrical responses (weld material noise, root, counter bore, etc.).
8.
Maximize the signal response from the flaw indication. Adjust the system gain until this
response is 80% FSH.
9.
Scan along the length of the flaw in each direction until the signal response has been reduced
to 40% FSH (6 dB drop).
10.
Axial Flaws – The length-sizing techniques identified above provide an accurate dimension
for axial flaws detected with the circumferential scan
11.
Circumferential Flaws - The length-sizing techniques identified above provide an outside
diameter length dimension which is longer than the actual inside-diameter length dimension
due to curvature of the piping material. To calculate the actual flaw length at the inside
surface, the following formula shall be used:
⎛ ID ⎞
IDFlawLeng th = ODFlawLeng th⎜
⎟
⎝ OD ⎠
Flaw Signal Characterization
All suspected flaw indications should be evaluated taking into account the following typical
indication characteristics. These characteristics should not be considered as mandatory criteria for
reporting indications as flaws, but are listed as significant signal indicators during the phased array
examination.
1.
Inside-Surface Connected Crack (ID Crack) or Outside-Surface Connected Crack (OD
Crack)
•
•
•
•
•
Unique, significant, and sharp amplitude response with defined start and stop positions
Unique and significant signal travel or “walk”
Multiple points of reflection (flaw base, flaw tip, faceting, etc.)
Similar response from opposite scan direction
Correctly plots to expected ID or OD crack location from both directions (correct
sound path, surface distance, and flaw positioning from both directions).
2. Embedded Center-Line Cracking (CL Crack)
•
Unique, significant, and sharp amplitude response with defined start and stop positions
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General Procedure for Ultrasonic Examination Using Phased Array
29
•
•
•
•
Unique and significant signal travel or echo-dynamic walk
Similar response from opposite direction (comparable amplitude, surface position,
signal responses from each scan direction)
Does not connect to either the inside or outside surfaces.
Correctly plots to centerline area of weld volume from both directions (similar and
correct sound path, surface distance, and flaw positioning from both directions).
3. Lack of Root Penetration (LOP)
•
•
•
•
•
Unique and significant amplitude response with defined start and stop positions
Unique and significant signal travel or “walk”
Similar response from opposite scan direction
Correctly plots near the centerline of weld from both directions (comparable and
correct sound path, surface distance, and signal response from both directions).
Through wall dimension supported by component design.
4. Lack of Side Wall Fusion (LOF)
•
•
•
•
•
Unique and significant amplitude response with defined start and stop positions
Unique and significant signal travel or “walk”
Indication may provide unique upper and lower tip responses from favorable angles
and scan directions.
Response from opposite scan direction may be significantly reduced in amplitude or
observable from a much different sound path and surface distance position.
Correctly plots near the fusion line of weld.
5. Porosity
•
•
•
Multiple less significant signal responses or signal clusters varying randomly in
amplitude and position
Plots correctly to weld volume.
Start and stop positions “blend in” with background responses.
6. Slag Inclusion
•
•
•
Unique signal responses which plot correctly to weld volume
Amplitude responses dependant upon the size, shape, and orientation of inclusion
Typically detectable using several examination angles from both sides of the weld.
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30
General Procedure for Ultrasonic Examination Using Phased Array
Addendum 4
Flaw Sizing Using Phased Array
1.0
PROCEDURE
1.1
The following procedure addresses the Phased Array (PA) instrument, PA probe, and sizing
evaluation techniques to determine the depth of an inside diameter (ID) connected crack.
1.2
This procedure provides guidelines and techniques for ultrasonic sizing of planar cracks like
cracks which originate at the opposite side of the scanning surface or the inside diameter (ID).
1.3
This procedure is applicable to carbon steel and stainless-steel materials with thicknesses from
0.375 in. to 1.5 in.
1.4
The Crack-Sizing Procedure outlines the requirements for Phased Array methods using
refracted longitudinal-wave and shear-wave techniques.
1.5 Other techniques may be used when an appropriate sizing calibration block is used.
1.6 Special longitudinal and/or shear-wave search units, and special ultrasonic sizing calibration
blocks are used for the sizing examinations.
1.7
2.0
These sizing techniques are applicable to manual phased array examinations only.
REFERENCES
2.1 American Society for Nondestructive Testing (ASNT), SNT-TC-1A, 2001.
2.2 American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,
Section V, Latest Edition and Addenda
3.3 ASTM Crack Sizing Standard ASTM E-2192
3.4 Davis NDE, Inc. Advanced Flaw Sizing Handbook
3.0
PERSONNEL REQUIREMENTS
3.1
Personnel performing the sizing examination should be, as a minimum, certified to UT Level
II or III in accordance with their employer’s written practice.
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General Procedure for Ultrasonic Examination Using Phased Array
31
3.2
4.0
Personnel, performing crack sizing examinations, shall have attended an Advanced Ultrasonic
Sizing Training Program or Phased Array for Crack Sizing Training in the methods and
techniques outlined in this procedure.
EQUIPMENT
4.1 Couplant
4.1.1
4.2
Any couplant material may be used.
Calibration and Reference Blocks
4.2.1
Special Crack Sizing Calibration Blocks shall be used to establish specific depth
calibrations for the sizing methods identified in this procedure.
4.2.2 Sizing calibration blocks shall contain notches and/or side-drilled hole (SDH)
reflectors at specific known depths for calibration of the applicable sizing method. The
sizing calibration blocks shall be fabricated from the carbon-steel materials.
5.0
4.2.3
Normally, a flat plate with notches from 20% to 80% through-wall in 20% steps is
used to calibrate the screen range in depth. Other block thicknesses in the range of the
material being examined may be used.
4.2.4
Special blocks may be used for the calibration of specific sizing methods. Also, blocks
with side-drilled holes may be used, as appropriate.
4.2.5
Reference blocks (i.e. IIW, DSC, Rompas, etc.) may be used for establishing linear
screen ranges and determining refracted-angle and exit-point information. Calibration
blocks should be made of carbon-steel material.
CALIBRATION
5.1
The temperature of the calibration block material shall be within 25°F of the component to be
examined.
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32
General Procedure for Ultrasonic Examination Using Phased Array
5.2
System Calibration
5.2.1
System calibration shall include the complete ultrasonic phased array system. Any
changes in the phased array probe, aperture, focus, PA wedge, etc., shall be cause for
recalibration.
5.2.2
The phased array crack-sizing techniques used in accordance with this procedure are
as follows:
5.2.2.1 The ID Creeping-Wave (IDCR) Method, or 30-70-70 mode-conversion
technique is used as a precursor to determine approximate depth of the crack,
such as, shallow (inner 1/3 t), midwall (middle 1/3 t), or deep (outer 1/3 t)
(Technique 1).
5.2.2.2 The Tip-Diffraction Method is used for shallow cracks, which are shallow to
midwall from 10% to 50% in depth (Technique 2).
5.2.2.3 The Focused Refracted Longitudinal-Wave and Focused Shear-Wave Methods
are used for cracks that are very deep, (greater than 40% or 50 %), and
penetrate to the outside surface (Technique 3).
5.3 Calibration for screen range may be accomplished by either direct sound path or actual depth.
Specific calibrations may be performed as outlined in the Appendices for the appropriate sizing
technique.
5.4 Other Phased Array Sizing Techniques or variations of the aforementioned techniques may be
used in accordance with this procedure.
5.5 The crack sizing technique and Phased Array Probe shall be selected from the appropriate
techniques, based upon the zone of investigation.
5.6 Whenever practical, the through wall depth should be verified by more than one sizing technique.
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General Procedure for Ultrasonic Examination Using Phased Array
33
6.0
EXAMINATION
6.1 Scanning Requirements
7.0
6.1.1
The area shall be investigated with the appropriate sizing technique. The sizing
examination shall be preformed along the length of the crack to determine the
maximum crack depth. The deepest crack depth or through-wall height dimension
(not remaining ligament), shall be recorded on the OmniScan Data Reporting Form.
6.1.2
Weld-crown configuration may restrict search unit movement for proper crack sizing
using the specific technique. Select the appropriate crack-sizing technique to
accommodate this limitation.
SIZING EVALUATION AND RECORDING CRITERIA
7.1
Sizing Application
7.1.1
The Sizing Flow Chart (Figure 7) may be used to categorize the suspected crack into
the appropriate zone or material volume.
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34
General Procedure for Ultrasonic Examination Using Phased Array
Ultrasonic Sizing Flow Chart
Signal Presentation
Suspect Area
Sizing Method
__
___
Suspect
Very Deep
Crack
___
Focused
Refracted
L-Wave or
S-Wave
Outside
Diameter
____________
=>
Outer 1/3 t
Zone
__
Calibrated
ID
Creeping
Wave
Method
___
Suspect
Midwall
to
Deep Wall
Crack
___
Focused
Refracted
L-Wave or
S-Wave
=>
____________
Middle 1/3 t
Zone
__
__
Suspect
Shallow
to Midwall
___
___
>15%-20%
Crack
Suspect
Shallow
___
___
Crack
<10%-15%
Tip
Diffraction
=>
____________
Inner 1/3 t
Zone
Tip
Diffraction
=>
______
Inside
Diameter
Figure 7: ID Creeping-Wave Flow Chart
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General Procedure for Ultrasonic Examination Using Phased Array
35
7.1.2
Each Phased Array sizing technique has certain advantages, disadvantages, and
limitations. No one sizing technique is best for sizing cracks of any through-wall
depths in all material types or thicknesses.
7.1.3
7.2
It is important to understand the use and application of each sizing technique and the
associated wave physics so that accurate crack-depth sizing is achieved.
Recording
7.2.1
Clearly document the depth of each crack on the designated OmniScan Data Report
Form. The maximum through-wall depth along the length of the crack in decimals
inches, millimeters or as a percentage through wall from the ID shall be recorded for
each of the cracks to be sized.
Appendixes
The following appendixes will provide the phased array techniques and calibration
requirements for each of the advanced ultrasonic Crack-Sizing methods.
Technique 1
ID Creeping-Wave Method
Technique 2
Tip Diffraction Method
• Time-of-Flight (TOF) Method
• Delta Time-of-Flight (∆ TOF) Method
Technique 3
Focused Refracted Longitudinal-Wave (HALT) Method
•
Time-of-Flight (TOF) Method
Focused Refracted Shear-Wave (HAST) Method
•
Time of Flight (TOF) Method
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36
General Procedure for Ultrasonic Examination Using Phased Array
TECHNIQUE 1
The ID Creeping Wave (IDCR) Method
1.0
Technique Description
1.1
The ID Creeping-Wave technique uses a phased array probe which transmits a nominal 70degree refracted longitudinal wave, a 30-degree direct shear wave (CE-1 or 30-70-70), and a
31.5-degree indirect shear wave (CE-2 or ID Creeping Wave).
1.2 This technique is effective for estimation of crack depths from 10% to 90% through wall. The
ID Creeping Wave (IDCR) is used as a precursor sizing technique to provide a qualitative or
nonquantitative sizing-depth measurement.
Courtesy of Mr. Peter Trelinski
Figure 8: Schematic illustration of IDCR technique.
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General Procedure for Ultrasonic Examination Using Phased Array
37
2.0
Calibration
2.1
Using a phased array probe with a wedge designed to produce a nominal refracted
longitudinal wave of about 70 degrees, perform a wedge-delay calibration for a focal depth to
cover the outer-third thickness.
2.2
Calibrate the PA probe using a sound-path or half-path focus for a 55 to 70-degree angle Sscan. Using the horizontal display of the sound-path or half-path focus, the S-scan imaging
will greatly enhance the identification of the 55 to 70-degree L-waves, the CE-1 signal and the
CE-2 signal. Also, the L-wave will detect and display the top of the notch and the base of the
notch.
2.3
Using a calibration block of similar thickness as the component to be examined with ID
notches from 20% to 80% depths, adjust the CE-1 and CE-2 signals to be displayed on the
phased array A-scan display.
2.4
Adjust the amplitude of CE–1 for the 40% deep notch to approximately 80% full-screen
height (FSH). Record this as the scanning and evaluation gain (dB) setting.
2.5
For each of the notches, record the presence of the 70L, CE-1, and CE-2 signals. Then, record
the echo-dynamics (ED) movement of CE-1, in DA for each of the notch depths.
2.6
Sweep the refracted L-wave angle to present the optimum signal from the tip of the notch. In
other words, use an approximate 55-degree L-wave for the shallow notches and the 70-degree
L-wave for the deeper notches. The advantage of a Phased Array System using the multiple
angles in a Sector scan (S-Scan) allows the operator to find the best angle of refracted for
the tip-diffracted signal.
2.7
3.0
Calibration blocks or reference blocks of other dimensions and designs may be used as long as
they provide equivalent information as described in paragraphs 2.1, 2.2, and 2.3.
Scanning/Evaluation
3.1
Move the IDCR search unit over the area of interest and observe the OmniScan display to
identify the 55L to 70L, CE-1, and CE-2 signals.
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38
General Procedure for Ultrasonic Examination Using Phased Array
3.2
The absence of a CE -2 signal may indicate the suspected crack is actually a metallurgical or
geometric reflection, such as, a counterbore or mismatch.
3.3
When the CE-1 signal is peaked, measure and record the echo-dynamic movement. Using the
(Um-r) reading display in the OmniScan will aid in measuring the echo-dynamic movement
for the CE-1 signal.
3.4
Record the echo-dynamics movement of the CE-1 signal. Record the peaked-amplitude signal
for the 55L to 70L in screen divisions. Compare the absence or presence, the amplitude, echo
dynamics, and the peaked L-wave signals to those signals obtained from the calibration block
examination using the IDCR technique.
3.5
In general, the following may be observed:
a) The presence of a CE-2 signal and the absence of a CE-1 signal is a good indication that the
crack is shallow (for example, less than 10% or 15 % through wall).
b) When a CE-1 signal is observed in conjunction with the CE-2 signal, then the crack is
estimated to be shallow to midwall (for example, greater than 15 % to 20 % through wall).
Again, observe the echo dynamics of the CE-1 signal.
c) When a broad echo-dynamic CE-1 signal is observed, a 70L-signal will generally be
detected to the left of the CE-1 signal. This should indicate a midwall to deep crack. Sweep
the 55L to 70L wave-refracted angle to optimize the L-wave signal response.
Note: These nominal crack-depth estimation values are indicative of the phased array probe
design and frequency, calibration block thickness, and material type.
4.0
Limitations
4.1
The IDCR Wave Method is a qualitative sizing technique which allows the examiner to
classify ID connected cracks as shallow, midwall, or deep. Finite crack depth analysis is best
obtained by one of the other crack-sizing methods; for example, Tip Diffraction, Focused
Refracted Longitudinal or Focused Shear Waves.
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General Procedure for Ultrasonic Examination Using Phased Array
39
TECHNIQUE 2
Tip Diffraction Method
1.0
Description
1.1 The Tip-Diffraction Method is based upon the diffracted sound energy from the tip of a crack.
A linear phased array probe of 5 MHz to 10 MHz producing 45-degree to 60-degree shear wave
is used to measure the time-of-flight (TOF) or sound-path distance (SP) from the crack-tip
signal. This TOF or SP measurement is used to determine the depth or through-wall height of
the ID-connected crack. Generally, a 3 MHz to 5 MHz phased array probe, which produces
shear waves, is used for sensitivity and resolution. Refracted Longitudinal waves may be used
in lieu of shear wave for coarse grain materials.
1.2
The Tip-Diffraction Method is most effective for sizing ID-connected cracks, which are
approximately 5% to 40% deep.
1.3
The half-veepath technique is generally used for the Tip Diffraction method; however, the full
veepath is applicable for qualitative sizing of deep cracks.
1.4
The two basic Tip Diffraction Techniques are:
1. Time of Flight (TOF), or PATT (Pulse Arrival Time Technique), or AATT (Absolute
Arrival Time Technique)
Courtesy of Mr. Peter Trelinski
Figure 9: Schematic illustration of Tip Diffraction technique number 1.
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40
General Procedure for Ultrasonic Examination Using Phased Array
2. Delta Time of Flight (∆ TOF), or SPOT (Satellite Pulse Observation Sizing Technique, or
RATT (Relative Arrival Time Technique)
Courtesy of Mr. Peter Trelinski
Figure10: Schematic illustration of Tip Diffraction technique number 2.
Note: The changes in acronyms (from PATT to AATT, or SPOT to RATT) are primarily due to
changes in authorship of the techniques. The wave physics and the calibration are essentially the
same for each basic technique, either TOF or ∆ TOF.
2.0
Calibration
2.1
Using a phased array probe with a wedge designed to produce a nominal refracted
longitudinal wave or shear wave of about 40 to 60 degrees, perform a wedge delay with a
focal depth of approximately the lower 1/3 to 1/2 thickness.
2.2
Obtain a calibration block of known thickness and similar material specification as the
component to be examined (0.375 in. or 1 in. thick) with the required ID notches, for example,
20%, 40%, 60%, and 80%.
2.3
Time-of-Flight (TOF), PATT/AATT Technique
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General Procedure for Ultrasonic Examination Using Phased Array
41
2.3.1
2.3.2
As a ranging technique, adjust the ID signal from the edge of the calibration block
using the delay or zero-offset control to 5 horizontal screen divisions. Adjust the OD
signal from the edge of the calibration block using the range or sweep control to 10
horizontal screen divisions.
Position the search to obtain the base or corner trap signal from the 80% ID notch.
Move the search unit forward to obtain the 80% notch tip signal. Using the delay or
zero-offset control; adjust the peaked tip signal to 1 horizontal screen division.
2.3.3
Position the search unit to obtain the base signal from the 20% ID notch. Move the
search unit forward to obtain the peaked 20% notch-tip signal. Using the range or
sweep control, adjust the notch-tip signal to 4 horizontal screen divisions.
2.3.4
Position the search unit to obtain signals from the 40% and 60% notches to verify their
respective positions at 3 divisions for the 40% and at 2 divisions for the 60% notches.
2.4 Delta Time of Flight (∆ TOF), SPOT/RATT Technique
2.4.1
With the PATT/AATT calibration complete, record the separation in screen divisions
of the notch tip and the base signal for each of the applicable ID notches, for example,
20%, 40%, and 60%. Due to search-unit beam-spread limitations, the notch-tip signal
and the base signal may not be readily detectable at the same time for the deeper, (60%
to 80% notches. As such, only record the separation for the applicable notch depths.
2.4.2
The SPOT/RATT technique does not require peaking of the signals.
Note: In lieu of the aforementioned calibration techniques, other screen ranges, using appropriate
reference blocks, (for example, Rompas, DSC, and IIW Blocks) are acceptable for the required
zone of examination. This will vary with technique, material type and thickness, search unit
frequency and size, and more specifically the area of interest.
3.0
Scanning/Evaluation
3.1
Position the search unit to obtain the maximum amplitude from the crack-base signal at the ID
of the component for the one half-veepath technique.
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42
General Procedure for Ultrasonic Examination Using Phased Array
5.0
3.2
For the TOF or PATT/AATT technique, move the search unit forward from the crack-base
signal to obtain the maximum amplitude (peaked) and record the depth of the crack from the
calibrated CRT screen.
3.4
When using the full-veepath technique for very deep cracks, the crack-tip signal may not be
readily discernible due to near surface effects.
3.5
Scanning sensitivity shall be established at a level that maintains a noise level of 10% to 15%
of FSH during scanning.
3.6
For the ∆TOF or SPOT/RATT technique, record the separation in screen divisions for the
crack-tip signal and the crack-base signal. Compare this sizing estimate result with the
TOF/PATT/AATT-sizing estimate.
Limitations
5.1
Crack-tip signals from very shallow cracks, 0.05 in. or less from the inside surface (ID) may
be difficult to size due to resolution of the phased array probe. In other words, the resolving
capabilities of the search unit may limit the separation of the crack-tip signal and the crackbase signal.
5.2
As such, varying the frequency, damping, and aperture of the search unit may improve the
sizing accuracy for very shallow cracks or cracks in very thin material, such as, less than
0.3 in.
5.3
When using the half-veepath technique, crack-tip signals from very deep cracks, may be lost
in the near field noise. The examiner must consider near field effects when examining very
deep cracks. Generally, the full-veepath technique is used as a qualitative sizing estimate only.
5.4
When using longitudinal waves, they shall be limited to use with the half-veepath technique
only.
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General Procedure for Ultrasonic Examination Using Phased Array
43
TECHNIQUE 3
Focused Refracted Longitudinal (HALT) Wave and Focused Shear Wave (HAST) Methods
1.0
2.0
Description
1.1
This sizing technique uses a focused phased array probe of 60 degrees to 70 degrees refracted
longitudinal wave or shear wave to detect, locate, and measure the time of flight or sound path
of the crack-tip signal.
1.2
The technique is effective for sizing cracks in the outer-half thickness of material, and is an
effective method for determining if a crack has propagated near the OD surface of the
component.
1.3
As an alternate technique, the refracted L-wave used in the ID Creeping-Wave method may be
used in lieu of an additional L-wave as defined in Technique 3.
Calibration
2.1
Using a phased array probe with a wedge designed to produce a nominal refracted
longitudinal wave of 60 degrees or 70 degrees, perform a wedge-delay calibration for a focal
depth of approximately the outer-half thickness.
2.2
The OmniScan presentation shall be adjusted to represent actual depth or remaining ligament
from the outside surface of material.
2.3
The depth calibration is performed by using a calibration block with holes or notches that
provide a calibrated screen range to cover the outer-half thickness.
2.4
For example, a calibration depth of .5 in. would be required for a 1- in. thick component.
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44
General Procedure for Ultrasonic Examination Using Phased Array
Courtesy of Mr. Peter Trelinski
Figure 11: Schematic illustration of calibration block showing side-drilled
holes with 1/10 in. depth increments
3.0
2.5
The desired search unit should be selected based upon refracted angle, frequency, and focal
depth.
2.6
Other calibration methods using sound-path or depth calibration may be used.
Scanning/Evaluation
3.1
Move the search unit over the area to be examined perpendicular to the suspected crack axis
and observe the signals from the crack indication.
3.2
If a response is obtained, record the first signal (closest in time) at its peaked amplitude.
3.3
Peak the signal and look for a good signal-to-noise response from the crack tip.
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General Procedure for Ultrasonic Examination Using Phased Array
45
4.0
Limitations
4.1
With the refracted longitudinal-wave search unit, an associated shear wave is present, which
may produce confusing signals or other mode-converted signals. The shear-wave and modeconverted signal are not used in this evaluation.
4.2
Focal depth is a very important consideration for accurate crack sizing. This is controlled by
the focusing within the OmniScan® unit.
4.3
Sizing in the less intense area of the beam spread may produce inaccuracies in crack-depth
estimates.
4.4
Generally, the useful focal range is from .5 to 1.5 times the actual focal depth of a refracted LWave or Shear-wave transducer.
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46
General Procedure for Ultrasonic Examination Using Phased Array