Effective PA UT Inspection Techniques for Austenitic Welds · 2017-02-17 · 2 Introduction • PA UT examination of austenitic welds, has been qualified and applied for ISI in nuclear

Effective PA UT Inspection Techniques for Austenitic Welds

NDTMA 2017 Las Vegas, February 15, 2017

1 1 © Zetec Inc. – All right reserved

Guy MAES, Johan BERLANGER, Frédéric LAPRISE (Zetec, Quebec, Canada)

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Introduction

•  PA UT examination of austenitic welds, has been qualified and applied for ISI in nuclear power plants since more than 10 years

•  Due to more stringent regulations on the use of RT for weld inspections in many countries all over the world, other industries show increased interest in PA UT as an alternative volumetric inspection technique, even for austenitic welds

•  Most of the elements of a “successful” inspection solution are known to UT experts, but he implementation is still perceived as complex and expensive, and often requires high-end equipment and software, or multiple software packages

© Zetec Inc. – All right reserved NDTMA 2017 - Las Vegas, February 15, 2017

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Overview

•  Inspection Challenge

•  PA UT of Austenitic Welds – Good Practice

•  Hardware and Software Innovation

•  Effective Inspection Techniques for Austenitic Welds

•  Conclusions


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Inspection Challenges

Propagation issues caused by anisotropic coarse-grain structure of stainless steel and austenitic welds can result in very challenging conditions for PA UT :


•  High, and variable attenuation of sound beam

•  High noise level, caused by reflection on individual grains

•  Low-pass filtering effect of the material

•  Beam skewing and distortion

•  Local variations of material structure

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PA UT on Austenitic Welds – Good Practice

•  Examination procedures for austenitic steel welds typically use low-frequency dual 2D matrix arrays (from 1.5 MHz to 3.5 MHz), with exchangeable wedge assemblies

•  Shear waves can be used for examination of fine grain base material, but longitudinal waves will provide better inspection capability for propagation through coarse-grain austenitic weld material


•  The dual (T/R) configuration offers the following benefits: –  absence of near-surface “dead-zone” –  elimination of “ghost echoes” caused by internal reflections

in the wedge, allows reduction of stand-off distance –  better sensitivity and SNR due to the “convolution” of

Transmitter and Receiver beams.

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PA UT on Austenitic Welds – Good Practice 2D matrix array technology allows for :

–  adequate beam steering for full coverage of the examination volume –  optimized focusing at various depths


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2D matrix array technology allows for simultaneous variation of refracted angle and skew angle, to improve detection capability on mis-oriented flaws.

Beam 45°LW, no skew

Beam 45°LW, 15° skew

•  Reliable ultrasonic examination of austenitic welds requires careful design of inspection techniques, and the use of state-of-the art probes

•  Probe frequency, wave mode (LW and/or SW), active aperture and beam focusing are to be selected while taking into account base material(s), weld type and material, weld thickness and component geometry

•  Acoustic beam simulation is an essential tool to design probe and wedge assemblies, and to perform preliminary assessment of inspection capability

•  Experimental validation of detection and sizing capability on representative test specimen(s) is highly recommended

•  Encoded examinations, with offline data analysis are to be preferred for the challenging inspection configurations

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Hardware & Software Innovation

•  Zetec’s recently launched high-power portable PA UT unit allows to set up and deploy inspections with 2D matrix array probes

•  The embedded software allows to generate and optimize focal laws, and includes on-board tools for interpretation and reporting of inspection results

•  No transfer, data conversion or additional software package required


•  Most of the elements of this “good practice” are known to UT experts •  In past years, the implementation of effective inspection techniques for

austenitic welds required high-end equipment and software, or multiple software packages

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DM Welds – Background

•  Dissimilar Metal (DM) welds typically join 2 or more different materials, and very often involve Inconel Alloys

•  DM welds can be particularly challenging because of multiple acoustic interfaces, and complex geometry (nozzles, tapers, …)

•  PWSCC type cracking was encountered in multiple PWR nuclear plants all over the world, and led to development of formal PDI qualification program


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DM Welds – Circumferential Flaws

•  PDI qualified technique for detection and sizing of circumferential flaws in DM welds : ID cracks

•  1.5 MHz dual 2D matrix array probes, and multiple wedge assemblies (adapted to component diameter)


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Inspection Technique : •  Electronic linear scanning at 45°, 60° and 70°LW (and 45°, 60°SW) •  Multiple scan lines “along” the weld for full coverage of the examination

volume (inner 1/3 of wall thickness) •  Encoded scanning, motorized or manually driven

© Zetec Inc. – All right reserved

70°LW 45°LW 60°LW

NDTMA 2017 - Las Vegas, February 15, 2017

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PA UT data (merged 45°LW) from circumferential ID cracks in DM weld (12” NPS, T = 1.2”)

Excellent SNR, tip diffraction signals for through-wall sizing NDTMA 2017 - Las Vegas, February 15, 2017

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DM Welds – Axial Flaws

•  PDI qualified technique for detection and sizing of axial flaws (also applicable on other austenitic welds in ground-flush condition)

•  1.5 MHz dual 2D matrix array probes, 5 x 3 or 8 x 4 configuration •  Discrete refracted angles between 25° and 65°LW (depending on OD, T) •  Multiple skew angles to increase coverage and reduce # scan lines


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DM Welds – Axial Flaws


PA UT data (merged 25°LW) from axial ID cracks in DM weld (T = 1.2”)

Excellent SNR, and accurate flaw positioning in cylindrical geometry


•  PDI qualification covers (single-sided) detection of circumferential and axial ID cracks, length sizing (RMSE < 0.75ʺ) and depth sizing (RMSE < 0.125ʺ)

•  Since the initial qualification (late 2005) this solution has been adopted by NDE vendors and utilities worldwide: USA, Finland, Korea, Taiwan, …

•  In collaboration with EPRI/PDI and several NDE vendors, improvements were introduced from lessons learned during site deployment

•  At least 5 NDE vendors in the USA have been deploying the procedure(and its derivatives) regularly, and successfully !

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DM Welds

16 16 © Zetec Inc. – All right reserved NDTMA 2017 - Las Vegas, February 15, 2017

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SS Welds with Cap – Circumferential Flaws


•  Manufacturing inspection of SS and CRA welds “in Lieu of RT” requires coverage of complete wall thickness of weld volume and HAZ

•  In carbon steel welds, SW beams are used to insonify examination volume “after skip”; this technique is not reliable here because of : –  poor propagation in SS weld volume –  poor reflection (skip) on clad ID surface


•  Alternative solution : dual 2D matrix array •  Refracted angles from 30° to 85°LW, for full

coverage

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•  1.5 MHz (8 x 4) or 2.25 MHz (10 x 3) dual 2D matrix array probes can be used, depending on material thickness and attenuation

•  Optimum focusing mode can be selected : “half path” or “projection” •  User interface allows for generation of “skewed beams” if required


304 SS weld specimen (T = 1.0”), cap in place, with realistic defects 19 19



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PA UT data (merged 30° to 85°LW) from 304 SS weld (T = 1.0”) all flaws detected from one side with 2.25 MHz dual 10x3 matrix array (TRL)

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SS Welds with Cap – Axial Flaws


•  Detection and sizing of axial cracks (e.g. IGSCC) with weld cap in place •  1.5 MHz or 2.25 MHz matrix array probe, in pulse-echo mode •  Flaws at the near-side of the weld are detected through base material ! •  Ideally, 4 probe orientations should be used, i.e. CW and CCW from both sides


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•  Refracted angles between 40° and 65°SW •  Multiple skew angles, between 25° and 50° relative to scan axis orientation,

more than 50 acoustic beams fired at each probe position •  Optimized footprint of wedge, to minimize probe stand-off •  Full coverage of examination volume through two-line inspection sequence


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Merged PA UT data from axial ID crack in SS pipe weld (T = 1.0”)

Excellent SNR, and accurate positioning in cylindrical geometry


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Conclusions

•  Examination techniques based on 2D matrix array probes provide very good inspection capability on both circumferential and axial flaws in stainless steel and dissimilar metal welds

•  Standardized dual 2D matrix array configurations, operating in TRL mode, can

effectively cover the complete examination volume for stainless steel welds with weld cap in place, and allow to detect both planar and volumetric flaws

•  Inspections with 2D matrix array probes can be efficiently set up, deployed and

interpreted using only a portable phased array unit and its on-board software, without the need of any additional software package


Documents

Effective PA UT Inspection Techniques for Austenitic Welds · 2017-02-17 · 2 Introduction • PA UT examination of austenitic welds, has been qualified and applied for ISI in nuclear