Projection Radiography application „on stream“application ... · Principle of projection...

Corrosion and Wall Thickness Measurement

U. Zscherpel, O. Alekseychuk, S. Bär, BAM VIII.3P. Rost, BASF AG, DWF/FZ

Imaging NDE 2007, April 2007, Kalpakkam, India1

application „on stream“application „on stream“

contents:- basic principles- software for evaluationand documentation

- corrosion depth evaluation- validation of methods

contents:- basic principles- software for evaluationand documentation

- corrosion depth evaluation- validation of methods

common research projectBASF and BAM, later withAGFA/GE IT, IAEA:computer based radiographicwall thickness measurement

common research projectBASF and BAM, later withAGFA/GE IT, IAEA:computer based radiographicwall thickness measurement

Projection Radiography




Corrosion ErosionCorrosion and Seads

Projection Radiography Examples on Corrosion and Erosion




History: radiographic wall thickness evaluation

BASF drawing from 1954• applied since ca.

1950• nearly no literature

until 1980• growing importance

in chemical industrycaused by on-stream application

• since 1996 projectsBASF und BAM forphysical studies

• standardizationopen (IAEA Draft)




classical set-up:classical set-up: film,imagingplate,orflatpanel

pipeline

radiation source, Ir 192

insulationtypical exposure:typical exposure:

profile line





on-site exposure, Ir 192 radiograph

sourcefilm

Example : distribution station




visual evaluation of wall thickness

error sources:- wrong density range - inaccurate edge detection (unsharpness)- wrong magnification factor

w





Principle of projection radiography

w` measured on film

tangential penetration of pipe wall

pipe

insulation

f - film focus distancer - outer pipe radiusR - outer radius of insulationw‘ - wall thickness projection

on detector plane




overview of measurement equipment (BASF at 2000, before CR):

RT exposure scanner PC

protocol

data basefilm digitisation(16 bit, 300 dpi)

software formeasurement

(algorithms) anddocumentation

screen/film :RCF + F8 (7% of exposuretime of Pb+D7)

Projection Radiography PC based wall thickness measurement




film digitisation flat panelimaging plate

PC based wall thickness measurement

• single program for evalution of all digital images, no size limitation• support for all detectors by external 16 bit LUT tables for lineari-

sation (gray value proportional to radiation intensity)





16 bit software platform

image processing know-how on Windows PC:(ISee!, see http://www.kb.bam.de/~alex/ic.html)- fully 16 bit data depth for evaluation and display- unlimited image sizes, limited only by main memory (>1 GByte)- all detectors (digitized film, imaging plates, flat panel detectors)via external 16 bit Lookup Tables (LUT) linearizable, ASCII text

- fast rekursive moving average filtering for arbitrary sizes of high andlow pass filters, convolution with variable kernels (ASCII text)

- sub-sampling for image display with true averaging- error estimation for measured values and geometric correction- quick documentation of measurements by protocol generation andtransfer to Word- protection of application by individual encrypted license keys

image processing know-how on Windows PC:(ISee!, see http://www.kb.bam.de/~alex/ic.html)- fully 16 bit data depth for evaluation and display- unlimited image sizes, limited only by main memory (>1 GByte)- all detectors (digitized film, imaging plates, flat panel detectors)via external 16 bit Lookup Tables (LUT) linearizable, ASCII text

- fast rekursive moving average filtering for arbitrary sizes of high andlow pass filters, convolution with variable kernels (ASCII text)

- sub-sampling for image display with true averaging- error estimation for measured values and geometric correction- quick documentation of measurements by protocol generation andtransfer to Word- protection of application by individual encrypted license keys

wtScope.exe




tangential wall thicknessalgorithm

wall thickness result

table with mea-surement regions

wall thickness deviation in mea-surement region

input exposureparameters

Projection Radiography PC based wall thickness measurement




synchronous display of positions in profile and image !

position correction by hand, if algorithm fails !




PC generated measurement protocolProjection Radiography




PC based wall thickness measurementProjection Radiography Algorithms : problem: correct detection of wall positions

characteristic points, curve fitting, CT reconstr.inner wall of pipe

outer wall of pipemax.

projectedwall thickness w‘




Limits of Tangential Radiography (TRT):Limits of Tangential Radiography (TRT):

Energy: Lmax100 kV : 10 mm200 kV : 30 mm300 kV : 40 mm400 kV : 50 mmSe-75 : 60 mmIr-192 : 75 mmCo-60 : 120 mm

L max

W

Lmax = 2W sqrt(Da/W –1)

200 kV

300 kV




2003 2004 2005

Algeria Hungary Romania Iran Pakistan Germany Uruguay Syria India Turkey Malaysia Canada

Radiographic Evaluation of Corrosion and Deposits in Pipelines:

Results of an IAEA Co-ordinated Research Programme

Steel pipes up to 20” with NDT film and X-ray, Ir-192, Co-60Steel pipes up to 20” with NDT film and X-ray, Ir-192, Co-60




Fabricated Reference Blocks with Steps and Holes:Fabricated Reference Blocks with Steps and Holes:

Iran

Idea:explore inspection methods with known wall thicknessesIdea:explore inspection methods with known wall thicknesses




Ir 192, DN200:6 11 mm

Co 60, DN300:14 24 mm

algorithm detects edges, visual not seeable in image :

extension ofapplicationrange in com-parison tovisual evalu-ation




2005: Validation of wtScope, CR-Tower and Ir-192 2005: Validation of wtScope, CR-Tower and Ir-192

BAMBASFGE IT




Validation as measurement method according to ISO 17025: Validation as measurement method according to ISO 17025:

Steel pipes 50 – 300 mm dia, empty, water filled, w/o insulation




Two inspection techniques possible :

2. Corrosion assessment from local film density changes (Double Wall Technique, DWT)

Radiographic Corrosion InspectionRadiographic Corrosion Inspection




erosionw-Δw

intensity change, ΔI

detector

pipesource

attenuation law: µeff - effective attenuation coefficientIw = I0 e -µeff w

local corrosion : wall thickness differences in penetration direction (DWT)

relative measurement:relative measurement: 2 step algorithm

1. Calibration:2. Measurement:

µeff = ln ( DREF / DIQI ) / ΔwIQI

Δw = ln ( DREF / DMEAS ) / µeff




1. Calculation of effectiveattenuation coefficient µeff

signal atreference point

signal atmeasurement point

known pipe wall thicknessw at reference point

known hole depth

DWT for localcorrosionDWT for localcorrosion

Result: µeff = f(w)dep. on radiation energy andwall thickness differences

Result: µeff = f(w)dep. on radiation energy andwall thickness differences




Double wall technique 6" and 8", 100 kV, with and without insulation

y = 0,6689x-0,3385

R2 = 0,7316

y = 0,5039x-0,3927

R2 = 0,3817

0,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

0,45

0,50

0 2 4 6 8 10 12 14 16 18

Penetrated steel wall thickness (mm)

Cal

cula

ted

atte

nuat

ion

coef

ficie

nt

(1/m

m)

insulation

decreasing µeff with penetrated wall and insulationdecreasing µeff with penetrated wall and insulation

Iran, UruguayIAEA CRP, filmIAEA CRP, film




Double wall technique, Ir 192

0,00

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0,08

0,09

0,10

0 10 20 30 40 50 60

Penetrated steel wall thickness (mm)

Cal

cula

ted

atte

nuat

ion

coef

ficie

nt

(1/m

m)

Uruguay Iran

Uruguay with Insulation Iran with Insulation

80 % of all measurements: µeff = 0.046 +/- 0.005 mm-180 % of all measurements: µeff = 0.046 +/- 0.005 mm-1

IAEA CRP, filmIAEA CRP, film Ir-192




Double wall technique

0,000

0,005

0,010

0,015

0,020

0,025

0,030

0,035

0,040

0,045

0 10 20 30 40 50 60

Penetrated steel wall thickenss [mm]

Cal

cula

ted

atte

nuat

ion

coef

ficie

nt [1

/mm

]

12" pipe8" pipemean µeff

75 % of all measurements: µeff = 0.028 +/- 0.004 mm-175 % of all measurements: µeff = 0.028 +/- 0.004 mm-1

IAEA CRP, filmIAEA CRP, film Co-60




Computer based evaluationwith wtScope/ISee! software:accuracy 0.5 mm, µeff=0.028/mm

Computer based evaluationwith wtScope/ISee! software:accuracy 0.5 mm, µeff=0.028/mm




Comparison Film / CRComparison Film / CR

DWT with Ir-192:DWT with Ir-192:

reason: scatter sensitivity!reason: scatter sensitivity!0

0,01

0,02

0,03

0,04

0,05

0,06

0 2 4 6 8 10 12 14

pipe wall thickness [mm]

effe

ctiv

e at

tenu

atio

n co

effic

ient

[1/m

m]

CR

Film

Result of wtScopevalidation forCR Tower byBAM / BASF / GE IT

µeff




SummaryProjection Radiography

inspection technique not standardised, written practice necessary !

• program for PC based routine measurements on images from all radiographic detectors, tangential wall thickness measurement and local corrosion, simple documentation

• wall thickness range enlarged compared with visual evaluation in projection radiography

• measurement of corrosion depth (in centre of pipe)• validation as measurement methods acc. to ISO 17025• programs transfered to GE IT for worldwide marketing

(Rhythm Version 2 all methods implemented)• differences in sensitivity to scattered radiation between

film and imaging plates

standard development has to be started soon




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