MAGNETIC FLUX LEAKAGE - A COMPARATIVE ASSESSMENT OF … · the magnetic flux leakage technique is...

MENDT- 7 PAGE 1 SEPTEMBER 29, 2015

MENDT 7- BAHRAIN

09-2015

MAGNETIC FLUX LEAKAGE - A COMPARATIVE

ASSESSMENT OF THE ADVANTAGES AND

DISADVANTAGES OF THIS TUBE INSPECTION

TECHNIQUE

INTRODUCTION

•

SEPTEMBER 29, 2015MENDT- 7 PAGE 2

• CONTEXT

• MAGNETIC FLUX LEAKAGE PROBE DESIGN

• Overview

• Principle of Operating

• EQUIPMENT PARAMETERS

• Evaluation Equipment

• Calibration

• MFL Panel layout

• RESULTS COMPARISON

• Volumetric- Grooving & FBH

• Fin Fan- Internal Grooving Resolution

• External Resolution- Pitting Detectability

• Elongated Grooving

• RESULTS TABLE

• EQUIPMENT COMPARISON

• CONCLUSIONS

CONTEXTFERROUS TUBING IN BOTH FIN FAN COOLERS AND HEAT EXCHANGERS CAN

SUFFER FROM SEVERAL FORMS OF DAMAGE;

• Pitting Corrosion

• General Corrosion

• Cracking

• Erosion

THE MAGNETIC FLUX LEAKAGE TECHNIQUE IS GENERALLY USED FOR THE INSPECTION OF FIN FAN

COOLERS AND A PREFERRED METHOD WHEN INSPECTING HEAT EXCHANGER TUBING WHERE SMALLER

VOLUMETRIC PITTING IS REQUIRED TO BE DETECTED AS COMPARED TO RFT TECHNIQUE.

MAGNETIC FLUX LEAKAGE IS A TUBE INSPECTION TECHNIQUE WHICH OUT OF ALL THE MAIN

TECHNIQUES SUFFERS FROM A REPUTATION AS BEING A VOLUMETRIC (NO PHASE) METHOD OF

DETECTING VARIOUS DAMAGE MECHANISM.

PULLING SPEED HAS A IMPORTANT EFFECT ON THE QUALITY OF THE DATA AND SUBSEQUENT ANALYSIS

NEW METHODS IN THE MARKET ARE BEING INTRODUCED WHICH OVER TIME SHOULD START TO REPLACE THE MFL TECHNIQUE- ALTHOUGH THIS WILL TAKE TIME. MANY CLIENTS REQUIRE A FIRST HAND EXPERIENCE PRIOR TO CHANGING.

IN-SERVICE INSPECTIONS ESPECIALLY ON FIN FAN TUBES HAVE A DIFFICULT HISTORY FOR CORRECT INSPECTION AND ANALYSIS


Magnetic field generated by the

magnet and affected by a defect

MFL THEORY


MFL Theory (Olympus + Eddyfi) Probes

Permanent Magnets saturate the tube

Absolute and Differential coils detect the Flux

leakage from a tube anomaly

Trail coil detects any residual flux at internal only

anomalies

Probes are sold with hardened Steel wear guides

Olympus: Drift Adaptor externally located between

MS5800 unit and Probe for Absolute Channel

Eddyfi: Uses magnetic sensor within probe to allow

for Absolute drift

Lead pickup coils, absolute/differential Sturdy probe cable

Trail pickup coils, differential

Axially oriented saturating magnetic field

Neodymium-iron-boron permanent magnet set

DINSEARCH THEORY


Electromagnetic Theory (Dinsearch)-

Probes Electromagnetic principle using 110 or

220V mains power

Tube wall is magnetized

Sensors detect the changes in the level of

magnetization (flux) within the tube wall

Probes are continuously air Cooled during

operation

Probes have interchangeable Sheaths to

cater for variations of tube internal

diameters.

Probes can be automated in both the

push and pull directions

EVALUATION EQUIPMENT

Carbon steel tubing both

25mm and 19mm diameters were

used (most common sizes

used in the industry)

Both circumferential and longitudinal

flaws were machined

Externally Pits (flat bottom holes) were machined

Series of machined flaws with equivalent

volume, different depths vs width

for signal comparison

Machined flaws at decreasing

distances apart were machined for resolution

evaluation

Actual fin fan sample was internally machined

SEPTEMBER 29, 2015MENDT-7 PAGE 6

CALIBRATION

SEPTEMBER 29, 2015ASSET LIFECYCLE INTEGRITY PARTNER PAGE 7

Depth Curves Calibration Points Comments

OD Grooves out by

~5 to ~10% of actual

calibration point

machining

Hole at 1.00V

Flat bottom holes

out by between ~5

to ~10% of actual

calibration point

machining

Absolute Channel

Differential Channel

PANEL LAYOUT

SEPTEMBER 29, 2015ASSET LIFECYCLE INTEGRITY PARTNER PAGE 8

EDDYFI MS5800

Absolute AbsoluteDifferential DifferentialTrail Trail

MS5800 External grooves Volumetric 25.4mm Tube

Eddyfi External grooves Volumetric 25.4mm Tube

Tube Details- Circumferential Volumetric Grooving & FBH

75mm 75m

m 75m

m

External Pits (Flat Bottom Holes)

1) 3.142 x r0.77²(Ø1.2mm) x 0.95mm Depth= 1.76 Volume

2) 3.142 x r1²(Ø2.0mm) x 0.57mm Depth= 1.76 Volume


4) 3.142 x r1.47²(Ø4.3) x 0.26mm Depth= 1.76 Volume

150m

m

75mm 75mm 75mm 150m

m

25.4mm External Pits (Machined Grooves)

Area = L x W x D

1) Length x 2mm Width x 1.4mm Depth





Variation in Signal height for all

volumetrically same indications

RESULTS COMPARISON

Olympus MS 5800 19mm External Volumetric indications

Eddyfi 19mm External Volumetric indications

Tube Details- Volumetric Grooving & FBH

75mm 75m

m 75m

m

External Pits (Flat Bottom Holes)


2) 3.142 x r1²(Ø2.0mm) x 0.57mm Depth= 1.76 Volume


4) 3.142 x r1.47²(Ø4.3) x 0.26mm Depth= 1.76 Volume

150m

m

75mm 75mm 75mm

External Pits (Machined Grooves)

Area = L x W x D





150m

m


Signal drop in groove

height for #4 indication

Olympus Fin Fan Internal Grooving Eddyfi Fin Fan Internal Grooving Tube Details ID Grooving (Resolution)

30

m

25

mm 20

mm 15

mm 10

mm

Notes:

Flat bottom Hole depth to be 50% of Nominal wall thickness

ID grooves to be machined to the internal bore

Groove Width 3mm wide

Internal Grooves-

Fin Fan Sample 5mm

60

mm


Signal morphology difference between MS5800

and Eddyfi machines

Signal resolution limited below 15mm indication

separation

MS5800 External Pits Machined 25.4mm & 19.05mm Resolution

Eddyfi External Pits Machined 25.4mm & 19.05mm Resolution

External Pits Resolution & Detectability

50m

m

25m

15m

10m

m 5mm

Notes:

Flat bottom hole depth 50% of Nominal wall thickness

Hole Diameter to be 5mm for 1” Tube and 3mm Diameter for 19mm Tube.

100

mm


External Pitting partially defined for both

Systems, indicating minimum external

detectability has been defined

Below 25mm pits are not clearly defined

MS5800 External Flat Bottom Holes Volumetric + Rectangular Slots 19mm

Eddyfi External Flat Bottom Holes Volumetric + Rectangular Slots 19mm

External Elongated Grooving (Elongated Corrosion)

75mm 75mm 75mm

Area = L x W x D

1) 10mm Length x 3mm Width x 1.5mm Depth= 45mm Volume

2) 12mm Length x 3mm Width x 1.25 Depth = 45mm Volume

3) 15mm Length x 3mm Width x 1.0mm Depth = 45mm Volume

4) 20mm Length x 3mm Width x 0.75mm Depth = 45mm Volume

100m

m


RESULTS TABLE

SEPTEMBER 29, 2015MENDT-7 PAGE 14

Flaw MS5800 Eddyfi

Circumferential flaws Very Sensitive, Fair signal

morphology

Very Sensitive, Good

signal Morphology

Longitudinal flaws Not reliable Not reliable

Internal pitting Very Sensitive, Fair signal

Morphology

Very Sensitive, Good

signal Morphology

External pitting Smaller pitting not

reliably Detectable

Smaller pitting not

reliably Detectable

Flaw Resolution Fair, Down to 15mm

Separation

Fair, Down to 15mm

Separation

EQUIPMENT COMPARISON


FEATURE MS5800 EDDYFI DINSEARCH

Differentiate Internal/

External

Yes Via Trail Channel Yes Via Trail Channel No

Adaption for Absolute

channel drifting

External Adaptor No Required Not required

Land-marking Yes (Manual) Yes (Automated) No

Changeable Sheaths No No Yes

Trail Channel Slewing No Yes NA

Multiple Depth Curves No Yes No

Average Speed Calculator No Yes (mm/s) No

CONCLUSIONSEDDYFI AND OLYMPUS RESULTS ARE COMPARABLE FOR DETECTABILITY OF

BOTH INTERNAL AND EXTERNAL FLAWS

EQUIVALENT FLAW VOLUME DOES NOT DIRECTLY RESULT IN EQUIVALENT

SIGNAL MORPHOLOGY (SHAPE)

INTERNAL FLAWS BOTH CIRCUMFERENTIAL AND LOW VOLUME PITTING ARE

READILY DETECTABLE

LONGITUDINAL (ELONGATED) FLAWS ARE NOT EASILY DETECTABLE

EXTERNAL PITTING IS NOT EASILY DETECTED AND CLASSIFIED

FLAWS CLOSER THAN 15MM APART ARE NOT EASILY RESOLVED

ENHANCED SIGNAL MORPHOLOGY (SHAPE) WAS EVIDENT WITH EDDYFI

MACHINE


THANK YOU FOR LISTENING-ANY QUESTIONS


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