The Conversion from Film to Digital RadiographyThe Conversion … · 2017. 1. 8. · EN ISO 19232-1 Step hlholes EN 462-1 EN ISO 19232-1 Step plates (USA) ASME, ASTM Duplex wire for

The Conversion from Film to Digital RadiographyThe Conversion from Film to Digital RadiographyThe Conversion from Film to Digital Radiography The Conversion from Film to Digital Radiography and and

the New Standard EN ISO 17636the New Standard EN ISO 17636--2:20132:2013the New Standard EN ISO 17636the New Standard EN ISO 17636--2:2013 2:2013 for Radiographic Weld Inspectionfor Radiographic Weld Inspection

by Uwe Ewert, Uwe Zscherpel www.bam.de [email protected]

11

ISO 17636: Radiographic Weld InspectionRadiographic Weld InspectionEwert Stockholm - April 20138.38.3 Radiological Radiological

MethodsMethods

Introduction- The proof of minimum image quality in radiography is the basis for

technical safety and contractual agreements in industry.- Film replacement by digital radiography requires a different practice p y g g p y q p

compared to film radiography to guaranty the same image quality.

- EN ISO 17636 replaced EN 1435 in 2013!- EN ISO 17636-2 defines the required practice to replace film by Digital

Radiology (DR) for weld inspection. EN ISO 17636 1 is equivalent to EN 1435 with minor changes- EN ISO 17636-1 is equivalent to EN 1435 with minor changes.

- New requirements exist for digital detector selection on basis of the detector unsharpness.

- The parameters “Signal to noise ratio” (SNR) and “Basic Spatial Resolution” (SRb) have to be understood and controlled for optimization of image quality in DR.p g q y

- Minimum SNRN Values or Grey Values (CR only) substitute requirements for the opt. density limits in film radiography.N t i id fl t d t t d tt

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MethodsMethods

- New exposure geometries consider flat detectors and cassettes.

Film Replacement Techniques in EN ISO 17636-2

ImagingPl t

Scannerfor Imaging Plates g gPlates

Computed Radiography

CR: Mobile Orex ScannerCR: Mobile Orex Scanner

Radiographywith

C

Digital Detector Arrays(DDA)

Flat PanelDetector

Hard CopyGrayscalePrinterAgfa

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MethodsMethods

DDA: Amorphous Selenium Flat Panel, Agfa-NDT

Motivation for Film Replacement by C t d R di h d DDA‘Computed Radiography and DDA‘s

• Shorter test and interpretation time

• New application areas due to higher inspection quality and wall Film (D4)thickness range

• No chemicals and dangerous

( )

• No chemicals and dangerous waste

• Less consumablesFlachdetektor (Hamamatsu)

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MethodsMethods

( )

Fuji IX25SNRnorm~ 265

DDA TechnologyTechnology provides better image Best (slowest) NDT filmquality than film !

Images high pass filtered for better presentation

PerkinElmer 1620

presentation

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MethodsMethods

SNRnorm~ 1500

DDA exposure Images after zoom, high paas filter

Basic Requirements for Radiography

B i t d d i t f fil d di it l di l i i

g yin all National and International Standards

Basic standard requirements for film and digital radiology in comparison:

E d i i ti l D it E d i i SNRFilm Digital Detector (CR)

• Exceed minimum optical Density Exceed minimum SNRN• Do not exceed film system class or calibrated minimum grey value

FFD SDD

• Select right FFD Select right SDD and

detector type with right SRb• Prove minimum Image Quality (IQI visibility)

• Wires or, Use same IQIs to prove quality• Step holes or Use optional duplex wire IQI• Plate holes (USA)

SNR – Signal to noise ratioIQI I Q lit I di t

FFD – Film Focus DistanceSDD S D t t Di t

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MethodsMethods

IQI – Image Quality IndicatorSDD – Source Detector Distance

Basics of Digital Radiographyandand

Image Quality Parameter

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MethodsMethods

Influence of Image Noise on Detail Visibility in Digital RadiographyDetail Visibility in Digital Radiography

Inte

nsity Contrast

Signal(base material)

Inte

nsity Contrast

Signal(base material)

Length

(base material)

Length

(base material)

Notch visible!

Contrast/Noise is highSignal/Noise is high

Notch not visible!

Contrast/Noise is lowSignal/Noise is low

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MethodsMethods

Signal/Noise is high Signal/Noise is low

8

Noise Sources in Radiographic Images

Typical noise sources in digital radiography:yp g g p y1. EXPOSURE CONDITIONS: Photon noise, depending on exposure dose

(e.g. mAs or GBqmin). This is the main factor! SNR increases with higher exposure dose.

2. Limitation for the maximum achievable SNR:

1 DETECTOR: Structural noise of DDAs and Imaging Plates also1. DETECTOR: Structural noise of DDAs and Imaging Plates also called fixed pattern noise (due to variations in pixel to pixel response and inhomogeneities in the phosphor layer).

2. OBJECT:1. Crystalline structure of material (e.g. nickel based steel, mottling)

2 Surface roughness of test object2. Surface roughness of test object

See new training course of DGZfP and IAEA!

99


MethodsMethods 9

g

Essential Parameters for Calculation of Just Visible IQI 1 T Hole Diameter

The essential parameters are: µeff, SNR and SRb?

New (magic) FormulaDepends on Hardware: effective pixel sizeMagnificationFocal spot size, source size{

SRPTdimageb

visible

p{SNR - Signal to noise ratio µeff – specific contrast,

effective attenuation coefficientSNReff

visible

}M t i l

SRb – effective pixel size in the image,basic spatial resolution of image

{}Material, keV, Source typeScattered radiationScreens and filters

Exposure timeTube current, ActivityDetector efficiencyS t D t t Di t

PT 2,8 for 1T-holes ; slightly dependent on

{}Screens and filters Source-to-Detector Distance

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MethodsMethods

, ; g y pviewing conditions and operator

10

EN ISO 17636:2013Radiographic Weld InspectionRadiographic Weld Inspection

Part 1: Non-destructive testing of welds -- Radiographic testing -- Part 1: X- and

t h i with filmgamma-ray techniques with film

Part 2:Non-destructive testing of welds -- Radiographic testing -- Part 2: X- and gamma-ray techniques with digital detectors

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MethodsMethods

EN ISO 17636-2 Radiographic testing of welds with digital detectorsRadiographic testing of welds with digital detectors.

Most important parameters that are regulated by this standard:

I. Minimum value for wire type or step-hole type Image Quality Indicators (IQI’s) in function of test technique (similar to ASME)

II. Maximum image/detector unsharpness requirements (using a duplex wire gauge)

III. Choice of tube voltage or gamma source in function of object composition, penetrated thickness and detector

IV. Exposure geometry

V. Minimum normalized Signal-to-Noise ratio (SNRN) requirementsg ( N) q

VI. Metal screens, type & thickness

VII. New compensation principles

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MethodsMethods

p p p

EN ISO 17636: Image Quality Indicators (IQI)

WiresEN 462-1EN ISO 19232-1

St h lStep holesEN 462-1EN ISO 19232-1

Step plates (USA)ASME, ASTM,

Duplex wire for part 2EN 462-5EN 462-5EN ISO 19232-5

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MethodsMethods

EN ISO 17636-1 and -2, Annex B: Minimum Requirements for Wire Type or Step-Hole Type IQIsRequirements for Wire Type or Step Hole Type IQIs

IQI values takenfrom EN1435from EN1435

New Exceptions for Gamma• Same requirements for wire q

type and step hole IQI’s as in EN 1435 and ISO 19232-3

• New exceptions for i t f d bl llisotopes for double wall inspections

– 10 mm < w 25 mm : 1 wire or step-hole valuewire or step hole value less for Ir192

– 5 mm < w 12 mm: 1 wire or step-hole value less for Se75less for Se75

EN ISO 19232-314

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MethodsMethods

EN ISO 19232-3

Selection of X-Ray Tube Voltage and Influence of µeff

Compensation principle I:Image Quality = f (µeff ▪ SNR)

Di l ti f

Image Quality f (µeff SNR)

Diagram on selection of maximum tube voltage

applies for film only (ISOapplies for film only (ISO 17636-1)

Selection of maximum tube voltage for application of digital detectors:application of digital detectors:- CR, Class B: reduce kV by 20%

Well calibrated DDAs: increase kV

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MethodsMethods

- Well calibrated DDAs: increase kV

Requirements for Techniques and Opt. DensityEN ISO 17636 1EN ISO 17636-1

Part 1 and 2

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MethodsMethods

Equivalent to opt. Density of Part 1: SNRN – Requirements in Part 2

• Concept for SNRNConcept for SNRNrequirement was taken from EN14784-1.EN14784 1.

• Minimum values are tabulated in function of radiation energyof radiation energy and object thickness, similar to table 2 of EN14784-2.

• Front lead screens are reduced toare reduced to maximum values only except for high energy.

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MethodsMethods

gy

Higher SNRN requirements than in EN14784-2

Influence of SNRN on Image QualityD d E TiDependence on Exposure Time:

Normalized at constant contrast

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MethodsMethods

Contrast Sensitivity LimitationEPS equivalent penetrameter sensitivity in % of tickness

4

EPS vs.SNR method with 3/4" Fe

EPS - equivalent penetrameter sensitivity in % of tickness

Contrast Sensitivity (EPS) vs. Grey Value for CR%

3

3,5

tivity

in %

s (E

PS) Above a certain exposure level the

contrast sensitivity changes only marginally

1 5

2

2,5

qrt(SN

R)EPS

Measured EPS, UR 1, DynamIx HR

Measured EPS, ST VI, HD‐CR 35

st S

ensi

thi

ckne

ss

0,5

1

1,5

PT/sq E

Calc. EPS from SNR, ST VI, HD‐CR 35

Calc. EPS from SNR, UR 1, DynamIx HRCon

tras

of T

h

0

0 10000 20000 30000 40000 50000 60000 70000

Pixel value SNRµSR

tPTEPS

imageb

'Min Grey Values Grey ValuePixel value SNRµt efftestplate

PT’ is about 2 for visibility of the 2 T hole of IQIs corr. to ASTM E 1025 EPS by ASTM E 746 with 200 kV, t = 19 mm Fe plate and µeff = 0.05 mm-1

Min. Grey Values(Working range)

Grey Value

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MethodsMethods

EPS by ASTM E 746 with 200 kV, t 19 mm Fe plate and µeff 0.05 mm

Exposure Chart for CR on basis of Grey Values, not part of ISO 17636-2

100,0

Exposure chart 7.5MV‐Betatron

.65m

A]

2.5MV7.5MV

10,0

B [m

in @

0.

7.5MeV‐Betatron

IP = STVIGV = 17000

SNRmin=100

1,0

B GV = 17000Filter = Cu 4mm/noScreen = Fe 0.8/ 0.8 mmSDD = 1000 mmMaterial = Fe

,

0 20 40 60 80 100 120 140 160 180 200

t [mm]

Exposure chart for IP ST VI, Dürr scanner CR35NDT and its setting.

Measure the exposure time and mA for different tube voltages which are required to achieve a reference grey value GVreference!

Make a plot as shown

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MethodsMethods

Make a plot as shown

Selection of Detector Before TestingMaximum Acceptable Image Unsharpness (or SRb) of Detectorp g p ( b)

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MethodsMethods

Measurement of Unsharpness and Basic Spatial Resolution

Duplex wire IQIEN 462-5EN ISO 19232-5 ASTM E 2002ASTM E 2002

• Determination of the basic spatial resolution in each production radiograph is not required but recommended.SNR l ffi i l

• SNRN controls sufficiently the image quality at a given pixel size.

• The detector unsharpness QI,

90 k

V,

l foc

us

• The detector unsharpnessudetector shall be controlled by reference exposures

ex W

ire IQ

DD

, sm

all

totalb uSR 21

Dup

le1m

SD

2222


MethodsMethods

totalb 2

Compensation Principle (II)

Compensation of high detector unsharpness by increased SNR

This is required if no detector is available with sufficient inherent unsharpness!

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MethodsMethods

Compensation Principle IICompensation Principle II

Interesting for detectors with higher unsharpness

Compensate missing spatial resolution by increased single

Interesting for detectors with higher unsharpness

wire sensitivity:• A lower spatial resolution i.e. a lower double wire value (D)

may be compensated by a higher single wire sensitivity i emay be compensated by a higher single wire sensitivity i.e. higher single wire value (W).

• Max. two (or three) single/double wire values may be exchanged.

Required:NotOK

OK: OK OKby agreement

D12W14

D13W13

D11W15

D10W16

D9W17Duplex wire score

Single wire score

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MethodsMethods

Proof of Compensation Principle (II) Test sample BAM 58 mm steel

Detection of fine flaws with subpixel resolution

highpass highpass filtered

13 14 15 16 17 18 19 Wire O3 5 6 8 9

13 14 15 16 17 18 19C1 film:wire ~16 visible

DDA ( ifi ti 1)

Wire O EN 462-1

W13 200µmW14 160µm

200µm pixel size!

100µm contrast resolution DDA (magnification = 1):W19 = 50µm contrast resolution

W15 130µmW16 100µmW17 80µmW18 63µmclass B

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MethodsMethods

200µm pixel size!W18 63µmW19 50µm

class B

Minimum Distance fmin

Class B Class A

3/1tba

df

Class A: a = 7,5Class B: a = 15 td

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MethodsMethods

Conclusions• Digital radiography with CR and DDAs is on the way to substitute film radiography, similar to

digital photography.• Image quality depends on the essential parameters for digital radiography:

• This are: (specific) contrast µeff, SNR and basic spatial resolution SRb. • SNR and contrast sensitivity improve with exposure time, but above a detector specific

value the contrast sensitivity does not change significantly anymore. • The new practice for Computed Radiography (CR) and Digital Radiography with DDA’s is

proposed in one standard document for weld inspection: EN ISO 17636-2.• Wire and step hole value requirements are taken from EN 1435 for EN ISO 17636 part p q p

1 and 2.• SNRN or grey value (CR only) are used as equivalent value for film system class

selection and opt. density limits.• Usage of duplex wire for system qualification and system selection is mandatory.• Usage of flat cassettes and DDAs for curved objects with a new formula for calculation

of SDD is accepted.• New revised unsharpness tables enable correct hardware selection.• New compensation principles are described in the standard practice.

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MethodsMethods

EN 13068 Radioscopy

New Standards on Digital Industrial RadiologyEN 13068 Radioscopy

EN 14096, ISO 14096 Film Digitisation

EN 14784 CR (2005) Part 1: Classification of Systems, Part 2: General ( )Goes to ISO, revision required

y ,principles, becomes ISO 16371

ISO 10893-7 (2010) Steel tubes – NDT of welds with DDA and (CR)

New ISO/DIS 17636-2 NDT of welds: CR and DDA to substitute EN 1435

prEN 16407 (2012): corrosion and wall thickness

Practice with film, CR and DDA for double wall and tangential techniquecorrosion and wall thickness tangential technique

ASME (BPVC,S.V, Article 2) Radiography (film, CR, DDA and more)

ASTM CR (2005) Classification (E 2446-05), Long term stability (E2445-Revision required 05), Guide (E 2007-10), Practice (E 2033-06)

ASTM DDA (2010) Characterisation (E 2597-07), Guide (E 2736-10), Practice (E 2698-10), Long Term Stability (E 2737-10)act ce ( 698 0), o g e Stab ty ( 3 0)

ASTM DICONDE (2010)(data format)

Standard Practice for Digital Imaging and Communication Nondestructive Evaluation (DICONDE)(E 2663 08 E 2699 10 E 2669 10 E 2738 10 E 2767 10 )

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MethodsMethods

(E 2663-08, E 2699-10, E 2669-10, E 2738-10, E 2767-10 )

ASTM E 2422-05, E 2660-10, E 2669-10

Digital reference image catalogues, light alloy, titanium and steel castings

[email protected]@bam.de

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MethodsMethods

Documents

The Conversion from Film to Digital RadiographyThe Conversion … · 2017. 1. 8. · EN ISO 19232-1 Step hlholes EN 462-1 EN ISO 19232-1 Step plates (USA) ASME, ASTM Duplex wire for