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Development of Automated

Electromagnetic Techniques forInspecting Inner Cracks of LPG Tanks

Yung-How Wu,

Feng-Ju Hsieh, Mu-Chung Peng, Hsing-Jeng Yang

Materials Research Laboratories, Taiwan

Email:700606@mrl.itri.org.tw

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Objective

To integrate an automated

ElectroMagnetic Array based systemfor inspecting inner surface crackson LPG Tank.

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Background

LPG tanks were frequently subjected to SCC oninner surface during service and must beinspected from inside regularly.

Conventional ISI by MT or PT is toilsome andcostly.

Extremely hot in summer

Scaffolding & Coating removal ACFM has been used to detect surface breaking

cracks without removing coating on components.

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Electromagnetic Array

Techniques

ACPD EMA or ACFM

V2/V1 = (2d + ) / d =/2((V2/V1) 1)

V1

Span =

V2

dSurface

current Surface crack

Currentperturbation

Surface current

Crack tip

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Crack Detection and Sizing

EMA System Data Display

SDDPUSolo

Probe for AutomationHandheld Probe

Crack

CP Abs Corr.Display

Abs CP

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Samples with Artificial Cracks

Notches Cracks41210

150

Plate-1

A group

B groupC group

Defect(mm)

Block TypeDepth

Lengt

h

Positn

Weld-6 Toe Crack ~2mm 12 30

Weld-9 CenterlineCrack ~2mm 13 380.25102

0.25202

0.25402

Notch/A

WidthLengthDepthType/Positn

Defect(mm)

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Characteristic Defect Signals

A single defect was detected by three successive channels.

Defect could be clearly identified by various displays.

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Signals in Various Conditions

1_Plate1_Plate2

0

1

2

3

4

5

6

0 1 2 3 4 5 6 7

(mm)

(mm)

Weakest response at 380

Amplitude decreased exponentially

with Lift-Off

Measuring error could be

controlled down to 25%

0

2

4

68

0 20 38 50 90

o

1

5

15

10mmx1mm

0

5

10

0 10 20 30

(Max/Min)

1

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Automated Inspection System EMA System

Lizard solo 64 channels SDDPU

Scanner Control Console PC + TFT monitor

Motor control module Motion control &

monitoring package

CCD camera and 2-axis

stage Scanner

With 4 magnetic rollers

Carrying 32-channel

probe

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Automated Inspection Method Weld and Plate regions were

Inspected individually Weld: along the weldment

Plate: as shown

Scanner was moved to the top

position and then scan

automatically on each path.

Scanning route was

monitored by CCD cameraand full coverage was assured.

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Field Trials

Scanning is controlled andmonitored through CCD cameraby inspector operating below theLPG tank.

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Inspection Process

Scan a Line

Yes

No

CCD Camera

or

EMA

EMA

EMA

Control Console

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Conclusions

Laboratory and preliminary field trials provedthe method satisfactory in detecting real

cracks down to 10mm in length and 1mm in

depth in both regions. However, minor

improvement on the scanner manipulation is

required before practical application.