ut inspection of welding joins: issues and contribution of ... · pdf filecontext: weld...

UT inspection of welding joins: issues and contribution

of CIVA simulation tools

GENERAL CONTEXT: ISSUES AND PROBLEMS OF WELD INSPECTION BY ULTRASONIC METHODS

67th IIW Annual Assembly and International Conference | Pierre CALMON | 2

CONTEXT: NDT OF WELDING JOINS

• Kind of defects commonly observed – Hot tearing (solidification cracking)

– Cold cracking (residual stresses, hydrogen embrittlement…)

– Blowholes, voids, gas inclusions, …

– Corrosion or fatigue cracks

Several classes of NDT :

• Penetrant (PT)

• Radiographic (RT)

• Electromagnetic (ET)

• Ultrasonic (UT)

67th IIW Annual Assembly and International Conference | 13th-18th July, 2014, Seoul, Korea | Pierre CALMON | 3

CONTEXT: WELD INSPECTION BY ULTRASONIC METHODS

• UT drawbacks in welding structures – Textured polycrystalline material: heterogeneous and anisotropic

properties

Beam splitting and beam deviation

Anisotropic damping depending on grain geometry and grain texture


Difficult analysis of inspection results in welded areas

L

T

TIME

US field acquisition above base metal

L

T Skewing Splitting Attenuation Structural noise

US field acquisition above the weld bead

CIVA modelling tools: improved diagnosis and inspection techniques by simulating numerical experiments

CONTEXT: WELD INSPECTION SIMULATION

• How to describe the weld structure? – Assuming a common stiffness matrix in a local coordinate system

defined by axis orientation of the grain: 3 kinds of description are proposed


Piecewise description

Mapping description

Parametric description

Orientation of grains defined on a regular grid

Large domains with respect to wavelength considering the same

orientation for a set of grains

Grain orientation defined as a function of

coordinates in the weld


• Piecewise description of grain orientation – Definition of large homogeneous domain with a unique

crystallographic orientation

• Derived from

– post-processing of macrographic images gathering, with a tolerance threshold, the grains according to their orientation around a common average axis

• Advantages and drawbacks

– easy to implement description

– unrealistic artefacts and wave mode conversions due to fictive interfaces

– excessive approximation or difficulties to divide any welds in domains with similar orientation


Piecewise description


• Mapping description of grain orientation – The grain orientation is given on a regular grid with a spatial sampling

depending on the process to define these orientations

• Derived from

– post-processing of macrographic images extracting orientation from gradient-based operators (OrientationJ, ImageJ's plugin for directional analysis in images)

– simulation tools modelling the grain structure formation during solidification

» MINA (Modelling anIsotropy from Notebook of Arc Welding) - LCND/EDF

» CAFE module - ESI Group


– accurate description

– requires a smoothing procedure for ray-based models


Mapping description


• Parametric description of grain orientation – Empiric laws deduced from observation

• Derived from

– Analytical formulation of grain orientation

e.g. Ogilvy’s law for V-shaped weld


– easy-to-use description accounting for anisotropy effects

– Too simplistic characterization without any local variability


Parametric description

Grain orientation defined as a function of

coordinates in the weld

θ =

− 𝒂𝒓𝒄𝒕𝒂𝒏 𝑻(𝑫 + 𝒛 ∗ 𝒕𝒂𝒏 α)

𝒚η 𝒑𝒐𝒖𝒓 𝒚 ≥ 𝟎;

𝒂𝒓𝒄𝒕𝒂𝒏𝑻(𝑫 + 𝒛 ∗ 𝒕𝒂𝒏 α)

(−𝒚)η𝒑𝒐𝒖𝒓 𝒚 < 𝟎.


• Usual modelling tools for NDT applications – Finite Element Method (FEM) or Finite Difference Method (FDM)

• Industrial FEM codes: ABAQUS, ANSYS, COMSOL…

• FDM academic codes: EFIT, SimSonic, ACEL-NDT,…

• ATHENA FEM code (EDF R&D) specifically dedicated to NDT inspections in welds using fictitious domain method for defects of complex geometry

– Ray-based method with paraxial approximation

• Dynamic Ray Tracing (model used in CIVA)

• Gaussian Beam

• Gaussian Wave Packet


FE calculation zone

Probe

Defect

Weld

MODELLING OF WELD INSPECTION WITH THE CIVA SOFTWARE


MODELLING OF WELD INSPECTION IN CIVA

• Beam simulation with piecewise description of weld in CIVA – DRT method manages only piecewise homogeneous descriptions in the

current CIVA version • Propagation: in each homogeneous domain ray tracing is a straight line in a constant

direction of energy

• Reflexion/Refraction: Snell’s law is applied on the interface between 2 homogeneous domains

– Good agreement with other FE codes if some conditions are met:

• domains characteristic lengths >> wavelength

• small contrast of impedance between adjacent domains


12.7 mm L0 contact probe 2.25 MHz

32

mm

λ ≈ 2,5mm

FEM Athena (EDF) Chassignole PhD Thesis


• Illustration of ray model limits for a piecewise description – Comparison for 2 different descriptions

– Comparison of the results with hybrid Finite Element Code (CIVA/ATHENA)


3λ

Weld #1 respecting the ray theory validity condition

Side drilled hole (located at the same depth)

λ

Weld #2 not respecting the ray theory validity condition

Contrast of impedance equivalent in the two

descriptions

Finite Element Box

Incident field computed with CIVA


• Illustration of ray model limits for a piecewise description – Side-drilled hole echo simulations for weld #1 (dimensions around 3λ)

Good agreement between FE model and the DRT model

– Side-drilled hole echo simulations for weld #2 (dimensions around λ)

Discrepancies between FE model and the DRT model (amplitude and position)


3λ Hybrid Code Athena/CIVA

Scanning position

DRT model in CIVA

Scanning position

0.2dB

- CIVA - Athena

Time

λ Hybrid Code Athena/CIVA

Scanning position

DRT model in CIVA

Scanning position

6.3dB

- CIVA - Athena

Time


• From a piecewise description of weld to a equivalent material with smoothly inhomogeneous properties – Drawbacks of the piecewise description

• Interfaces generate unrealistic artefacts and wave mode conversions

• Penalizing description for the ray model: simulation variations with respect to domain geometry definitions

• Inapplicable or too approximate description for a lot of weld types

– Advantages of a equivalent smoothly inhomogeneous material

• Can be deduced directly from parametric description or from mapping description with smoothing filtering process

• Well-adapted and generic approach for a lot of weld types

• Modelling an average behavior of the coherent wave front used for the inspection


Extension of DRT model for smoothly inhomogeneous anisotropic material in next CIVA version


• DRT model in smoothly inhomogeneous anisotropic material – Evaluation of ray-paths and travel time

• Deduced from Eikonal equation

Differential equation to solve, called axial ray system, defining the ray trajectory

– Computation of ray amplitude

• Deduced from the Transport equation in a ray tube (energy conservation) assuming paraxial approximation

Another differential equation to solve, called paraxial ray system, defining the evolution of the ray tube associated to the axial ray trajectory


Polarization vector

Energy velocity vector position of the ray

slowness of the ray

with 𝑎𝑖𝑗𝑘𝑙 = 𝜌−1𝑐𝑖𝑗𝑘𝑙

V. Cerveny, Seismic Ray Theory, Cambridge University Press, 2001 A. Gardahaut et al., QNDE, 2013

𝑑𝛿𝑥𝑖𝑑𝑇

= 𝐴𝑖𝑗𝛿𝑥𝑗 + 𝐵𝑖𝑗𝛿𝑝𝑗

𝑑𝛿𝑝𝑖𝑑𝑇

= 𝐶𝑖𝑗𝛿𝑥𝑗 + 𝐷𝑖𝑗𝛿𝑝𝑗


• DRT model in smoothly inhomogeneous anisotropic material – Higher computation cost than for straight line ray tracing (piecewise

description)

• Iterative time step procedures to solve differential equations

Euler or RK4 schemes performed with adaptive step

• Examples of ray tracing in the CIVA scene


L45 case T45 case

NUMERICAL VALIDATION: COMPARISON WITH FE CALCULATION

• Comparison with FE calculation (ATHENA code) – First validation with a closed-form description of grain orientation

• the assumption of smoothly inhomogeneous media is observed


Very good agreement between the two simulated results

Hybrid Finite Element Code Dynamic Ray Tracing

-- Hybrid Finite Element Code

-- Dynamic Ray Tracing

FE method DRT method Parametric description

J.A. Ogilvy, NDT International, 1985.

NUMERICAL VALIDATION: COMPARISON WITH FE CALCULATION

• Comparison with FE calculation (ATHENA code) – Validation with a mapping description of the weld

• assumption of smoothly inhomogeneous media assumed following a spline interpolation on the grid


Mapping description

2x2 mm mapping of grain orientation macrography of the weld

Image processing

interpolation

Differences below 1.5 dB between the two models

FE method DRT method



Mapping description


NUMERICAL VALIDATION: COMPARISON WITH FE CALCULATION • Comparison with FE calculation (ATHENA code)

– Validation with a mapping description of the weld

EXPERIMENTAL COMPARISONS

• Characteristics of the inspected welded mock-up – Specific mock-up with calibrated flaws (SDH and notches)

– SMAW weld realized in vertical position

• disorientation of the fiber axis along the welding direction (about 18°)

(XZ) inspection plane is not a plane of symmetry (3D case)

SDH1/SDH2 1.5 mm N1/N2/N3 10 mm height N3 located into the weld


MOSAICS Project


• Properties used for simulation – Anisotropic elastic properties obtained with characterization process

• Anisotropic damping properties (2D description only)

(N. Alaoui Ismaili et al., QNDE, 2013)

MOSAICS Project



• Comparison with L45 inspection at 2MHz – Experimental CScan

IP1

IP2

IP3

SDH1 echoes SDH2 echoes

N1 echoes N2 echoes

N3 echoes

Analysis of comparisons in these 3 inspections planes

MOSAICS Project



• Study of SDH echoes:


very good agreement of direct echoes before and after passing through the welding joint

SDH2 :-11.5dB

SDH2 :-11 dB

SDH1 : ref.

SDH1 : ref.

DRT model in CIVA Experimental data

Exp

erim

ent

DR

T m

od

el

MOSAICS Project


• Study of N1 and N2 echoes:


N1 : corner LL


Exp

erim

ent

DR

T m

od

el

N1 : corner LLT

N1 : corner TT N2 : corner LL

N1 : corner LL N1 : corner LLT

N1 : corner TT

N2 : corner LL

simulated mixed corner echo (LLT) of N1 notch overestimated with respect to other corner echoes

good agreement especially for the LL corner echoes

MOSAICS Project


Exp

erim

ent

DR

T m

od

el

N3 : corner LL N3 : corner LLT

N3 : corner LL


• Study of N3 echoes located into the weld:


worse result: - 4 dB discrepancy for the LL echo - mixed corner echo not simulated

weld seam description not enough precise with regards to UT in this area

MOSAICS Project

CONCLUSION AND PERSPECTIVES


CONCLUSIONS

• Evolution of modelling in CIVA to perform NDT in welds – using a ray-based approximation on a smoothly inhomogeneous

anisotropic medium

– GUI tools introduced in CIVA to manage such description (parametric or mapping descriptions)

– Manage 3D configurations in terms of probe, defect and material with a more realistic descriptions of welding joint

• Validations: – Numerical validation: P-wave field successfully compared with FE code

with a closed-form expression and a mapping description provided from a macrograph image processing

– Comparisons with experimental acquisitions:

• good agreement when flaws located outside the weld in the base metal

• discrepancies observed when the notch is located at the weld bead


PERSPECTIVES

• Weld description: – facilitate the procedures for defining the properties of welds

• Mechanical properties and grain properties in weld

Analysis automated tools of macrography

Import of descriptions provided by numerical simulation of welding process

• Geometry of weld

Set of predefined geometric description of weld


PERSPECTIVES

• Ray based modelling in CIVA: – qT modes modelling in progress for inhomogeneous anisotropic

medium

– handle with 3D anisotropy of the wave attenuation

– improve the computation time and the numerical precision

– investigate the sensitivity of the model according to the descriptions of welds obtained by macrography or simulation codes

– Model more accurately the interaction of the ultrasonic wave with the polycrystalline structure of welds;

• determine the anisotropic behavior of the attenuation and wave velocity according to the wavefront direction


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