flaw detection with emat ultrasound

OPTIMESS Engineering GmbH Phone +49 (0) 365 / 4319459 Gewerbepark Keplerstr. 12 Fax +49 (0) 365 / 4319458 D-07549 Gera [email protected] Germany www.optimess.net

EMAT –

Technology

EMAT – Principle

What is an EMAT?

A magnet, a wire, an air gap and a metal surface.

• like an eddy current probe

• Transmission of a sound wave:

A current J in the wire induces an eddy

current I in the metal surface across the

air gap G.

The eddy current I + magnetic field

cause a force F to launch a sound wave

in the metal surface.

• Receiving a sound wave:

A sound wave moves the surface in the

magnetic field to generate an eddy

current that induces a current J in the

wire

EMAT enjoys all the benefits of UT plus other particular advantages

EMAT – Ultrasound inspection

Ultrasound is Generated in the Part Inspected

Dry inspection (no couplant)

- Easy to Automate and Integrate in Production - No Couplant Induced Errors - High Inspection Speeds (up to 60 m/s) - Capable of High and Sub-Zero Temperatures

Insensitive to Surface Conditions

Capable of Inspecting Rough, Dirty (Oily/Wet), Oxidized or Uneven Surfaces

Easier Probe Deployment

- No Signal Variations from Probe to Probe - Small Changes in Probe Angle do not Affect Results (e.g. part curvature)

Unique Wave modes

- Capable of Generating Horizontally Polarized Shear Wave Energy - Highly efficient for guided waves due to frequency selectivity

EMAT can be used on most metals and geometries for all the standard UT

applications

Type of Inspection Material Geometries

• Flaw Detection

• Points (1D)

• Seams (2D)

• Surfaces (2D)

• Volumes (3D)

• Thickness & Distances

• Material Properties

• Stress/Anisotropy

• Nodularity

• R-Value

• Electrical Conductors

• Ferrous:

Carbon Steel, Stainless

Steel, Nickel, Cobalt

• Non-Ferrous:

Aluminum, Copper, Brass,

Uranium and most other

metals

• Discrete and

Continuous Geometries

• Plates (thin and thick)

• Cylinders, Rods

• Tubes (round, square or

others)

• Structural Elements


EMAT can generate the same wave modes as piezoelectric transducers,

plus some unique ones

Boundary Beam

Orientation Wave mode Technique Main application

Bulk

Normal

Longitudinal Piezo

EMAT • Thickness and velocity measurements

• Flaw detection

• Properties measurement Shear horizontal EMAT1

Angle

Shear vertical Piezo

EMAT • Flaw detection

Shear horizontal EMAT • Flaw detection including austenitic

materials

Guided

Suface Rayleigh Piezo

EMAT • Flaw detection (surface)

Volumetric

Lamb Piezo

EMAT

• Flaw detection (including corrosion)

• Velocity and properties measurement

Shear horizontal EMAT • Flaw detection (including corrosion)

• Velocity and properties measurement


Guided waves


What can be a guided wave?

• A surface

• A plate,

• A rod, tube, pipe

• A Rail or other structure

• Unlike bulk waves where boundaries are only

considered during reflection/refraction, boundaries

in guided waves affect the formulation of wave

modes

• In ultrasound, the practical range of guided waves

can vary from centimetres to tens of meters

Guided waves Particle motion Graphical display

Rayleigh or

surface

Elliptical,

penetrating one

wave length

Lamb Asymmetrical or

symmetrical

Shear horizontal

Perpendicular to

wave direction on a

horizontal plane

Guided waves


Shear Horizontal (SH) at 90º degrees and Lamb generate guided waves are uniquely

suited for weld inspection up to 12mm thick

EMAT – Weld inspection

Characteristics:

Only available with EMAT for

practical purposes

The SH/Lamb wave fills up the

volume of the material independent

of thickness

No “rastering” motion or “phased

array” of sensors necessary

Separate transmitter and receiver

permits normalization of the signal

(self-calibration)

Less sensitive to probe positioning

Signal normalization


In practice, the signal that is used for weld interpretation is the ratio between the RT and DT. The receiver is situated

between the transmitter and the weld and first measures the DT which is the amount of ultrasound induced in the material.

In some cases DT signal maybe low due to excessive standoff between the sensor and the material or other material-

related variances. However, variance in the DT will also result in an identical variance in the RT. A reliable measure of the

ultrasound received from the weld is RT with respect to DT which for a given defect will always stay the same, regardless of

the level of ultrasound being induced.

Flaw detection with shear horizontal

Experimental setup for

determination the detection

limits


Defect width - 1 mm Defect height – from 0.5 mm to 2 mm

Evaluation of the

measuring results


Flaw detection with shear horizontal

Transducer design

Basic design of an EMAT transducer for generation of shear

horizontal


Transducer configuration for the inspection of axial welded steel profiles


Flaw detection

For steel and aluminium sheets with a thickness between 0.3 and 3.5 mm


Software / Evaluation


• The top-part of the right-hand part of the screen shows meta-data including the job reference and the

record number of the piece being inspected.

• The lower part of the right-hand part shows the result. This particular part has failed due to a defect

located approximately one third of the way across the blank.

• The left-hand part of the screen shows the strip scans which show 4 result lines and two threshold lines

for each channel. (The orange and blue lines). The highest amplitude lines are the two DT plots, and

the two RT/DT plots are shown lower.

Flaw detection assembly for weld inspection for thin material


Thank you

OPTIMESS Engineering GmbH

Gewerbepark Keplerstraße 10-12

D-07549 Gera

Phone +49 365 4319459

Fax. +49 365 4319458

[email protected]

www.optimess.net

flaw detection with emat ultrasound

Engineering

emat technology

emat principle

sound wave

wave direction

metal surface

formulation of wave

polarized shear wave

surface elliptical