general pa procedure for detection and sizing

8/11/2019 General PA Procedure for Detection and Sizing

http://slidepdf.com/reader/full/general-pa-procedure-for-detection-and-sizing 1/46

General Procedurefor Ultrasonic Examination

Using Phased Array

May 1, 2006

Prepared by:

J. Mark DavisASNT UT Level III

Davis NDE, Inc.

for Olympus NDT



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

DISCLAIMER

Carefully read the following by starting to use the procedure, you are deemed to accept all the terms andconditions set forth below.

1. The procedure is without warranty of any kind, provided to the customer on an “as is” basis. The entire risk tothe 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 theimplied warranties of merchantability, fitness for a particular purpose, title, and noninfringement, with respectto 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 agreementor 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.





1.0 Purpose

1.1 This procedure provides requirements for the manual and encoded ultrasonic examination ofwelds and base materials using phased array.

1.2 This procedure may also be used for Performance Demonstrate Qualification (PDQ) of theOmniScan® 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

2.0 Scope

2.1 This procedure establishes the generic phased array ultrasonic examination requirements thatshall be used to examine carbon steel or stainless steel plate and pipe base materials andweldments.

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 inaccordance with this procedure, (for example, 0.250 in. as the minimum to 1.5 in. as themaximum allowed to be examined in accordance with this procedure).

2.3 This procedure is designed to demonstrate the Olympus NDT OmniScan Phased ArraySystem as a qualified UT system in accordance with the ASME Code, when required by thereferencing code section.

2.4 A non-blind test shall be used as a Performance Demonstration for the OmniScan PhasedArray System.

2.5 The Phased Array Scan Plan for each demonstration is outlined the Addendum with specificrequirements for each product form and material type.

3.0 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




General Procedure for Ultrasonic Examination Using Phased Array 5

3.4 Scan Plan Report for Detection and Flaw Characterization Report

3.5 Scan Plan Report for Crack Sizing

4.0 Ultrasonic Phased Array Examination Equipment

4.1 The ultrasonic phased array instrument shall be an OmniScan® pulse echo type and shall beequipped with a calibrated dB gain or attenuation control stepped in increments of 2 dB orless. The OmniScan contains 16 or 32 independent pulser/receiver channels. The system iscapable 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 assurethat proper data has been collected. Sectorial-scan images contain signal amplitude andreflector depth information projected for the refracted angle of the ultrasonic beam. TheOmniScan phased array system provides a variety of analysis capabilities including A-scandisplay 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 permitsdirect modification to ultrasonic beam characteristics. The OmniScan phased array systemrequires 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 foranalyzing data subsequent to the completion of data collection. Data-display softwarecompatible to that residing on the OmniScan Phased Array System will also be used on theremote PC for data playback. Reference the manufacturer operating manuals for instrument-

operation 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 OmniScansystem calibration.

4.7 The Ultrasonic Phased Array System shall be calibrated for linearity in accordance withParagraph 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 lessthan 1000 ppm.

4.9 The same couplant material, including batch number where applicable, used for calibrationshall be used for examinations.





4.9.1 Ultrasonic transducer configurations are specified by the technique used forexamination. Linear phased Array probe configurations may include from 10 to 128elements.

4.10 The phased array probe frequency shall be between 2 MHz and 10 MHz depending uponmaterial 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 coverageof 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 movementwith the OmniScan instrument.

5.0 Phased Array Instrument Linearity

5.1 Ultrasonic instrument linearity shall be verified at the beginning and end of each series ofexaminations, which is not to exceed 3 months.

5.2 The instrument linearity verification shall be recorded on the Ultrasonic Instrument LinearityVerification (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 twocalibration reflectors.

5.2.1.2 Alternatively, a straight-beam search unit may be used on any calibration blockthat 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 thesmaller 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% ofFSH.

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 recordthe smaller indication estimated to the nearest 1% of FSH at each setting. Thereading must be 50% of the larger amplitude within ±5% of FSH.

5.2.2 Amplitude-Control Linearity





5.2.2.1 Position a search unit on a calibration block to obtain maximum amplitudefrom a calibration reflector.

5.2.2.2 As a minimum, the amplitude control linearity shall be performed to documentlinearity 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 ofFSH and increase or decrease the dB as specified on the Ultrasonic InstrumentLinearity Verification (Form 1). The estimated signal shall be recorded to thenearest 1% of FSH and shall fall within the limits specified on Form 1.

6.0 Phased Array Probe Element-Operability Verification

6.1 The phased array probe shall be checked for element performance whenever the examinersuspects an element operability problem. Each phased array probe must be checked todetermine each element’s ability to transmit and receive ultrasonic energy.

6.2 This operability verification verifies performance of each transmitter/receiver module, andcable 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, ifan 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.

7.0 Phased Array System Calibration

7.1 Calibration shall be performed from the surface of the calibration block which corresponds tothe component surface to be examined.

7.2 System calibration shall include the complete ultrasonic examination system. Screen distancecalibration shall be at least 1½ “veepaths” (also known as skip) for the minimum angle thatwill be used during the examination, unless otherwise specified.

7.3 The system calibration information shall be recorded on the Ultrasonic Data Report Formused in the OmniScan®. During scanning, only the gain may be adjusted from the calibratedreference 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-scaninformation for the 45 ° angle of refraction or the minimum angle that will be used inthe sectorial scan.





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 otherangles, 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 inserton 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 arecorrect.

7.4.7 If the measured angle of propagation is outside the allowable tolerance (45 ° ±2 ° ), thenall transducer and setup parameters must be reviewed for accuracy. If these parametersare correct, then check the shear-wave velocity value used for the material. If this iscorrect, 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.

7.5 Time-Base Verification

7.5.1 Position the angle cursor and adjust its position so that it displays A-scan informationfor the 45 ° angle of refraction.

7.5.2 Place the transducer so that reflections from both the 2- and 4-in. radius reflectors onthe 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. Thisresult 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 themeasured distance is too short (less than 1.9 in.), increase the velocity value. Repeatadjustment until an acceptable value is achieved.

7.5.5 With the transducer remaining in the peaked position, measure the metal path of the4 -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 thisvalue is greater than 4.1 in., decrease the Delay parameter until the measurement iscorrect. The requirements for focal law verification, time base verification andsensitivity adjustments are listed below. Instrument linearity verification andultrasonic beam spread is not required.





7.5.7 As an alternative, other calibration blocks may be used to perform the time-base orwedge-delay calibration.

7.6 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 incalibration.

7.6.3 The sensitivity calibration will provide the required gain adjustments for eachrefracted angle and sound path used.

7.6.3.1 Select a calibration reflector, which is approximately one-half the thickness ofthe 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 orfocal laws.

7.6.3.4 The OmniScan system will calculate the required gain needed at each focal lawto adjust the amount needed.

7.7 A time-corrected gain (Auto-TCG) calibration shall be used to compensate for attenuation inthe 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; forexample, 45, 60 or 70 degrees.

7.9 The examination system calibration may be stored in the OmniScan System with electronicmemory, on an external chip or data storage device. This calibration may be used at a laterdate 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 theexamination.

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 eachexamination.

7.12 System Calibration Verification

7.12.1 System calibration verification shall include the entire examination system. Sweeprange and TCG calibration shall be verified on the appropriate calibration block orsimulator block, as applicable, under the following conditions:





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 changeof 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 theentire exam system-calibration verifications. The simulator block may be of anymaterial and configuration that will permit verification of the sweep range and TCGsensitivity.

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 basiccalibration block. If a reference block, such as Rompas, is used to perform systemcalibration 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 thegain 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 onthe 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 itsamplitude, or any point on the sweep line has moved more than 10% of the sweepdivision 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 calibrationverification.

7.13.2.3 Enter proper values on the applicable forms.





7.14 Recalibration

7.14.1 Any of the following conditions shall be cause for system recalibration:

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

8.0 Surface Preparation

8.1 Contact Surfaces - The finished contact surface should be free from weld spatter and anyroughness that could interfere with free movement of the search unit or impair thetransmission of ultrasonic vibrations.

8.2 Weld Surfaces - The weld surface should be free of irregularities that could mask or causereflections from defects to go undetected and should merge smoothly into the adjacent basematerials.

8.3 Conditions, which do not meet these requirements, shall be recorded as limitations on theUltrasonic Examination Data Report Form.

9.0 Examination Coverage and Scanning Technique

9.1 The specifics of the examination volume, weld identification, and location shall be identifiedin 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 theappropriate examination angles for the weld prep bevel angles (for example, 40 to 60 degreesor 55 to 70 degrees) that will be used during the examination. This Scan Plan shall bedocumented 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 theappropriate angles as identified in paragraph 9.3 to ensure complete coverage of the weld andheat-affected zone.





9.5 To determine the required examination volume and scan area, profiles may be taken on eachweld at the top-dead-center or L 0, the beginning of the area to be scanned, as a minimum.Profile data will consist of ultrasonic thickness measurements and outside surface contoursusing a contour gage. Thickness measurements should be taken at a maximum interval ofapproximately 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 theweld 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, andhence 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 thecenter of the weld from both sides of the weld where practical to ensure coverage of the weldand 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 forvessel 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 UltrasonicExamination Data Report Form.

9.14 The entire examination volume comprising the weld and adjacent base metal shall beexamined with the beam parallel to the weld on either side of the weld in two directions, (forexample, clockwise and counterclockwise). Phased array wedges contoured to the radius ofthe pipe or vessel may be used in the examination to ensure proper contact with the pipe orvessel.

9.15 It is recommended that full A-scan data shall be recorded when using encoders.

10.0 Recording/Evaluation Criteria and Amplitude Determination

10.1 Only personnel certified Level II or III in Ultrasonics shall evaluate the results of ultrasonicexaminations for acceptance.

10.2 All reflectors that exceed 20% of DAC or TCG shall be investigated completely to determinethe type of reflector. Addendum 3 will provide guidance for flaw characterization.





10.3 Indications that exceed 50% of DAC or TCG and determined to be of geometric ormetallurgical origin shall be recorded.

10.3.1 The following steps shall be taken in order to classify an indication to be of geometricor metallurgical origin:

10.3.1.1 Interpret the area containing the reflector in accordance with the applicableexamination instruction;

10.3.1.2 Plot and verify the indication coordinates. Weld profiles will be performedto 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 withReference 5.1.11.

10.3.3 All recordable indications shall be resolved to determine the shape, identity, andlocation of the reflector. Final evaluation and disposition of the indication is theresponsibility of owner/user of the component to be examined.

10.3.4 Amplitude determination - Signal amplitude shall be measured as a percentage of thecalibrated DAC or TCG.

10.3.5 The appropriate Code or Specification shall be used to determine final acceptance ofthe 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 usedin 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 LinearityVerification (if required) shall be considered part of the examination report.





ULTRASONIC INSTRUMENT LINEARITY VERIFICATION

INSTRUMENT MANUFACTURER MODEL NUMBER RECORD NO.

CALIBRATION BLOCK NO. INITIAL DATE FINAL DATE

SCREEN HEIGHTLINEARITY AMPLITUDE CONTROL LINEARITY

ACTUAL % OF FULL SCREEN **INSTRUMENT WITH FINE dBCONTROL

HI GAIN SETTING LOW GAINSETTING

INITIAL FINAL INITIAL FINALFIRSTSIGNAL IN %

SECONDSIGNAL IN %

*

INDICATION

SET AT % OF

FULLSCREEN

dB

CONTROLCHANGE

INDICATIONLIMITS % OF FULL

SCREEN

_____dB _____dB _____dB _____dB

100

90

80 40

80 -6 dB 32 TO 48

70

60

80 -12 dB 16 TO 24

50

40

40 +6 dB 64 TO 96

30

20

20 +12 dB 64 TO 96

*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 HEIGHTCOMMENTS:

INSPECTOR CERT LEVEL DATE SUPV/LEVEL III REVIEW DATE

INSPECTOR CERT LEVEL DATE

Form 1





Addendum 1

1. Terminology

Angle Compensated Gain: Also called ACG. This is compensation for the variation in signal amplitudesreceived from fixed-depth SDHs during S-scan calibration. The compensation is typically performedelectronically at multiple depths. Note that there are technical limits to ACG, (i.e. beyond a certain angularrange, 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 mostcases 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 elementscan direct the beam either towards the interior, towards the exterior of the circle, or along the axis ofsymmetry 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 isequivalent 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 beamcharacteristics in both the transmitted and received modes.

Linear array probes: Probes made using a set of elements juxtaposed and aligned along an axis. Theyenable 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 theultrasonic 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 thedata display. As a data display it is a 2-D view of all A-scans from a specific set of elements corrected fordelay and refracted angle. When used to refer to the beam movement it refers to the set of focal laws thatsweeps a defined range of angles using the same focal distance and elements.





Addendum 2

Guidelines for Evaluation of Dead Elementswithin a Phased Array Probe

Scope

This Addendum provides guidelines for the determination of dead elements in a phased array probe, whichmay 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 theevent of any dead element issues not adequately covered by this guideline, we recommend discussing thespecific 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 theOmniScan®, and each beam is formed by multiple channels (typically around 16 channels, though itmay be much fewer).

• Cause of dead elements: Dead elements can be caused by either a broken wire in the cable, a defunctelement 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 brokencable.

• Focal Law: The ASCII file that controls which elements are fired with what time delay, and at whatvoltage.

• 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 negligibleeffect).

• 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 calibrationconditions as the “gold standard.”

• Evaluation of the effect of dead elements is based on a performance criterion, not on the number orlocation of the dead elements.





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. Theseguidelines are essentially based on essential performance criteria (i.e. the beam amplitude, beam skew orsignal-to-noise ratio). The operator should take remedial measures (suggested later) if any one of these threecriteria is not met.

Blanket requirements, such as “no more than two dead elements per focal law”, or “unacceptable if two deadelements are adjacent” are overly restrictive, and results in Appendix A show that they do not reasonablydefine 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 causemay 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 thearray (see Appendix A). Failed elements in the center of the array seem to reduce the overall signalresponse, without affecting beam steering, whereas losing elements at the edges of the array leads to bothloss of sensitivity and also change in beam angle.

The operator should perform the usual evaluation of the system (which applies to any change ofultrasonic 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 increasethe 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 operatorcan:

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 re-scan; again, this may not be feasible or code-acceptable.

c. Replace defective equipment (cable, array, or connectors).

2. Document the results.





Criterion 2: Beam skewing

If the beam angle (as measured during normal calibration) changes by more than ±2 o from the “goldstandard”, then dead elements are a possible cause.

Besides the usual ultrasonic checks (see above), recommended corrective actions when beam skew changes by ±2 o 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 or20), 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 andacoustic factors, but might occur on other channels due to excessive dead elements, or other problems. Thelevel 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 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, and would normally need the approval of the client orcertifying 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 thesetup, 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 thesystem beforehand (see Appendix B).

• Normally dead elements are not an issue with OmniScan®.





Appendix A: Background on Dead Elements

Normally, industrial arrays are very durable, and can last several years. In comparison with conventionaltransducers, arrays have proven very robust since an occasional dead element is not a major consideration.

Simulations of Dead ElementsMore 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 onthe Performance of an Array Probe,” 16 th World Conference on NDT, Montreal, Canada, August 2004).

Some typical simulation results for a 16-element beam with adjacent dead-center elements are shown inFigure 1. (The top-left simulation has no dead elements, the bottom-left has one, the center-top has two deadelements and the bottom-right has five). The beam shape with dead center elements is acceptable until atleast five out of the 16 elements are dead. (This is a significantly higher number of dead elements than thetypical 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, onedead element at bottom left, two dead elements at top center, etc.





Similar simulations with dead elements at one end of the array show reasonable performance until four orfive 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-edgeelements, 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 side-drilled holes with increasing numbers of dead elements. The actual dead element is shown in the box abovethe appropriate scan. In this case, a linear array with eight elements was used.





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 marginallyacceptable, though three dead out of eight shows significant tails.

The essential results for linear arrays are shown in Table 1





Table 1: Effect of dead elements on signal amplitudes(8-and 16-element linear arrays)

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 thecenter of the array will cause signal amplitude to decline significantly, while dead elements at the edge willcause beam skewing.

More important, the impact of dead elements will depend on the specific focal law, and potentially onthe customer specifications and requirements. Therefore, it is not possible to produce specific criteriafor dead elements for all OmniScan inspections; however, it is possible to generate guidelines, tests,and actions, which is the purpose of this document.

1 2 3 4 5 6TheoreticalLoss in dB 2.3 5.0 8.2Minimumloss in dB 1.1 0.3 1.5MaximumLoss in dB 2.2 2.9 8.2WorstConfiguration 8 1.3 6, 7, 8TheoreticalLoss in dB 1.1 2.3 3.6 5.0 6.5 8.2

Minimumloss in dB 0,7 0,2 1,9MaximumLoss in dB 1.8 3.1 4.8 5.6 7.4 7.4WorstConfiguration 16 1, 3

8, 9, 10 or7, 8, 9 6, 7, 8, 9

6, 7, 8, 9,10

6, 7, 8, 9,10, 11

1 6 e

l e m e n

t s v

i r t u a

l

p r o

b e

Linear Array on Pipe, Angle Beam, Notch

Dead Elements

8 e

l e m e n

t s V i r t u a

l

P r o

b e





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 45 o; 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.





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, andlocation. All such indications shall be evaluated in terms of the applicable acceptance criteriaof the referencing code Section.

2. During examination, the sweep range may be adjusted for indication discrimination andcharacterization. Final recording of indications shall be done utilizing the sweep and DACsettings 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 weldconfiguration (counter bore, root, metallurgical responses, etc.) shall be considered as flawindications.

2. Geometric or Metallurgical Indications - All indications produced by reflectors within thevolume 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 ormetallurgical indications.

The identity, maximum amplitude, location, and extent of reflector causing a geometricindication shall be recorded. The following steps shall be taken to classify an indication asgeometric:

• Interpret the area containing the reflector in accordance with the Flaw Indications orthe Geometric or Metallurgical Indications criteria, listed below in this section.

• Plot and verify the reflector coordinates. Prepare a cross-section sketch showing thereflector 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 takinginto account the following indication characteristics. These characteristics should not beconsidered as mandatory criteria for classifying indications as flaws, but are listed assignificant points of interest for the examiner to consider during evaluation of suspect areas.





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 alongthe 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 theindication(s).

4. The indication can be detected with multiple search-unit angles, and a higher angle providescomparable or greater signal response . This characteristic can be supported with an adequatereference reflector (inside-surface notch or equivalent).

5. The indication provides substantial and unique echo-dynamic travel. This characteristic can besupported by observing other areas along the length of the sample and with an adequatereference reflector (inside-surface notch or equivalent).

6. Several areas of unique or multiple amplitude peaks are observed throughout the indicationlength. This characteristic can be supported by observing other areas along the length of thesample and by scanning laterally along the indication length.

7. The indication maintains or provides an increase in signal amplitude when the beam is skewedaway from normal. This characteristic can be supported by observing other areas along thelength of the sample.

8. Inconsistent time base positions are observed throughout the indication length as the searchunit is moved parallel along the length of the reflector. This characteristic can be supported byscanning 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 theweld. This characteristic may require a reduced search-unit frequency.

12. For axial flaws, the indication(s) can be confirmed from the opposite direction. Thischaracteristic 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 distinctsignal separation and amplitude fluctuation can be observed. This characteristic may requirean increase in signal-resolution capability in order to make this evaluation. Examples includereducing screen size and slower scan speeds.

14. For components where access is limited to a single side of the component, document thereason for the limitation.





15. Because of the uncertainties associated with the flaw orientation and the actual thickness ofthe component on the inaccessible side of the weld, an accurate inside-surface connection onthe 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 takinginto account the following indication characteristics. These characteristics should not beconsidered as mandatory criteria for classifying indications, but are listed as significant pointsof 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 geometricalcondition (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 byobtaining localized thickness and surface contour recordings at the location of theindication(s).

3. The indication provides additional responses, which occur from the same scan position, but atdifferent sweep positions (multiples) along the length of the weld. This may be a sign ofmode-converted shear-wave signals from counter bore or similar geometric reflectors. Thischaracteristic 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 orintermittently, at consistent amplitude and sweep positions. This characteristic can besupported by scanning laterally along the indication length .

5. When examining with a higher-angle search unit, the amplitude response is lower or notdetected. This characteristic should consider localized thickness and contour information toensure that the search-unit angles provide comparable examination volume coverage andsound penetration. This characteristic can additionally be supported with an adequatereference reflector (Inside surface notch or equivalent).

6. The indication provides minimal echo-dynamic travel (walk). This characteristic can besupported by observing other areas along the length of the sample and with an adequatereference reflector (inside-surface notch or equivalent).

7. The indication provides a rapid and consistent drop in signal amplitude when the beam isskewed away from normal in either direction.

8. The indication provides a clean, single-signal response with minimal to no signal faceting. Nodiscernible tip signals are observable. This characteristic can be supported by optimizing thesignal presentation on an adequate reference reflector (inside-surface notch or equivalent).





5. Optimize the signal response from the flaw indication.

6. Scan the indication area with specific focus on the flaw-signal responses, (for example, signalshape, walk, orientation, effect of skew, etc). Adjust the system gain as needed to optimizeflaw responses.

7. Scan an adjacent unflawed area in close proximity to the flaw area with specific focus on thesurrounding geometrical responses (weld material noise, root, counter bore, etc.).

8. Maximize the signal response from the flaw indication. Adjust the system gain until thisresponse is 80% FSH.

9. Scan along the length of the flaw in each direction until the signal response has been reducedto 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 scan11. Circumferential Flaws - The length-sizing techniques identified above provide an outside

diameter length dimension which is longer than the actual inside-diameter length dimensiondue to curvature of the piping material. To calculate the actual flaw length at the insidesurface, the following formula shall be used:

Flaw Signal Characterization

All suspected flaw indications should be evaluated taking into account the following typicalindication characteristics. These characteristics should not be considered as mandatory criteria forreporting indications as flaws, but are listed as significant signal indicators during the phased arrayexamination.

1. Inside-Surface Connected Crack (ID Crack) or Outside-Surface Connected Crack (ODCrack)

• 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

=OD ID

thODFlawLeng th IDFlawLeng





• 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.





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 These sizing techniques are applicable to manual phased array examinations only.

2.0 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 Handbook3.0 PERSONNEL REQUIREMENTS

3.1 Personnel performing the sizing examination should be, as a minimum, certified to UT LevelII or III in accordance with their employer’s written practice.





3.2 Personnel, performing crack sizing examinations, shall have attended an Advanced UltrasonicSizing Training Program or Phased Array for Crack Sizing Training in the methods andtechniques outlined in this procedure.

4.0 EQUIPMENT

4.1 Couplant

4.1.1 Any couplant material may be used.

4.2 Calibration and Reference Blocks

4.2.1 Special Crack Sizing Calibration Blocks shall be used to establish specific depthcalibrations 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.

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.

5.0 CALIBRATION

5.1 The temperature of the calibration block material shall be within 25°F of the component to be

examined.





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.





6.0 EXAMINATION

6.1 Scanning Requirements

6.1.1 The area shall be investigated with the appropriate sizing technique. The sizingexamination 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.

7.0 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.





Ultrasonic Sizing Flow Chart Signal Presentation Suspect Area Sizing Method

__ ___

SuspectVery Deep

Crack ___

FocusedRefracted

L-Wave orS-Wave

=>

Outside

Diameter ____________

Outer 1/3 t Zone

__ ___

SuspectMidwall

toDeep Wall

Crack

___

Focused

RefractedL-Wave orS-Wave

=> ____________

Middle 1/3 t Zone

CalibratedID

CreepingWave

Method

__ ___

SuspectShallow

to Midwall

>15%-20%Crack

___

Tip

Diffraction => ____________

__ ___

SuspectShallowCrack

<10%-15% ___

Tip

Diffraction =>

Inner 1/3 t Zone

______ Inside

Diameter

Figure 7: ID Creeping-Wave Flow Chart





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 It is important to understand the use and application of each sizing technique and theassociated wave physics so that accurate crack-depth sizing is achieved.

7.2 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





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 S-

scan. 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 IDnotches 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 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.

3.0 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.





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 movementfor 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 bedetected 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.





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.





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





2.3.1 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.

2.3.2 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 theirrespective 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.


3.1 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.





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 bereadily 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.

5.0 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 crack-

base signal.

5.2 As such, varying the frequency, damping, and aperture of the search unit may improve thesizing 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 techniqueonly.





Courtesy of Mr. Peter Trelinski

Figure 11: Schematic illustration of calibration block showing side-drilledholes with 1/10 in. depth increments

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.


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.



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 mode-

converted 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 L-

Wave or Shear-wave transducer.

general pa procedure for detection and sizing

Documents