BASF-DR Techniques for Corrosion Inspection

DR techniques for corrosion inspection

Zscherpel, Alekseychuk, Ewert, BAM VIII.3Rost, BASF AG, DWF/FZ

NDT 2003, BINDT, September 2003, Worcester, U.K.1

application „on stream“application „on stream“

contents:- basic principles- software for evaluation and documentation

- corrosion depth evaluation- „corrosion mapping“

contents:- basic principles- software for evaluation and documentation

- corrosion depth evaluation- „corrosion mapping“

common research projectBASF and BAM :

computer based radiographic wall thickness measurement

common research projectBASF and BAM :

computer based radiographic wall 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




0

1

2

3

4

2 4 6 8 10

f/2r

erro

r [%

]

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fw

rRfr

fw

rRfrRf

rw

exact magnificationcorrection :

practicalapproximation :

program :




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)





overview of measurement equipment at BASF :

RT exposure scanner PC

protocol

data basefilm digitisation(16 bit, 300 dpi)

software for measurement

(algorithms) anddocumentation

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

Projection Radiography PC based wall thickness measurement




16 bit software platform

transfer of image processing know-how to Windows PC(ScanManager 1992 -1995, SUN workstations) :- fully 16 bit data depth for evaluation and display - unlimited image sizes, limited only by main memory (>512 MByte)- 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 „simple“ geometric correction- quick documentation of measurements by protocol generation andtransfer to Word- protection of application by individual encrypted license keys

transfer of image processing know-how to Windows PC(ScanManager 1992 -1995, SUN workstations) :- fully 16 bit data depth for evaluation and display - unlimited image sizes, limited only by main memory (>512 MByte)- 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 „simple“ 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





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‘




Accuracy DN 150 steel test pipe

-0,8

-0,6

-0,4

-0,2

0

0,2

0,4

0,6

0 2 4 6 8 10 12

wall thickness / mm

Abw

eich

ung

/ mm

BASF altBASF neuCTPWT

new wall thickness algorithm with adaptive smoothingfor improved detection of inner wall position :

Accuracy DN 200 steel test pipe

-0,8

-0,6

-0,4

-0,2

0

0,2

0,4

0,6

0 2 4 6 8 10

wall thickness / mm

Abw

eich

ung

/ mm

BASF altBASF neuCTPWT

Comparison of accuracy of PC based algorithms




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




erosionw-Δw

intensity change, ΔI

detector

pipesource

absorption law : µ-effective absorption coefficientIw = I0 e -µw

local corrosion : wall thickness differences inpenetration direction

relative measurement :relative measurement : 2 step algorithm

1. Calibration :2. Measurement :

µeff = ln ( DREF / DIQI ) / ΔwIQI

Δw = ln ( DREF / DMESS ) / µeff




digitized film, step wedge, 160 kV:digitized film, step wedge, 160 kV: imaging plate, pipe (DN 150), Ir :imaging plate, pipe (DN 150), Ir :


linearization of film curve and (log.) imaging plate scanner by external 16 bit LUT [Log(gray value proportional to radiation dose)]




test pipe DN 100 x 5,6 mmpit 1 Ø R3 x 1mm (Tool-Ø / depth)

pit 2 Ø R3 x 2 mm

pit 3 Ø R3 x 3 mm

Measurement of local corrosion1. Calibration (µ-eff estimation)

reference point

measure point

LUT for linearisation

known wall thicknessat reference point

known wall thicknessat measurement point




Measurement of local corrosion

2. depth measurement

reference point

measure point

known wall thicknessat reference point (un-changed)

result : local penetratedwall thickness in mm(error ca. 0.2 mm)

pitting depth: 3mm




Projection Radiography evaluation of corrosion depth ininner third of pipe diameter possible

error < 0,5 mm




simulation

separable investigations on influence of :• wall thickness• radiation source

• scattered radiation

• unsharpness


G.-R.Tillack,C. Bellon




Simulation: visual position of edge in image and profile differ !




problem :

simulation

local corrosionin wall, tangentialprojection

wall thickness on bothsides of pipe 5 mm, only profile form differ !




median filtering indirection of symmetry :

measurement after mapping :

corrosion 5 mm -> complete wall !

corrosion pit

median filterperpenticular(1x49) >2x flaw size

difference imagepseudo colorrepresentation




- 0 mm

+ 10 mm

- 5 mm

real pipe, innercorrosion, insulated

corrosion mappingafter median high pass(gray value prop. penetratedwall thickness, 1x300 points) :




corroded pipewith weld

+ 5 mm

- 0 mm

- 5 mm

corrosion mappingafter median high pass(gray value prop. topenetrated wall thickness1x200 points) :




validation

L

w

application range, limits for pipe inspection

material: steelEwert, Onel BAM VIII.3 wall thickness




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)• 3D simulation tool for case studies on recognibility• Corrosion mapping with median high pass along

symmetry axis of the pipe allows presentation of wall thickness differences relative to the nominal wall thickness of the pipe

standard development will be started in 2004




The END

contact : [email protected]

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BASF-DR Techniques for Corrosion Inspection

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