Research in Fluorescent Research in Fluorescent Penetrant ExaminationPenetrant Examination

Rick Lopez, Lisa Brasche, and David Eisenmann,

Center for Nondestructive EvaluationIowa State University

rlopez@cnde.iastate.edu(515) 294-5903

Funded by the Federal Aviation Administration

Three Rivers Technical Conference, August 6th, 2008

id4483812 pdfMachine by Broadgun Software - a great PDF writer! - a great PDF creator! - http://www.pdfmachine.com http://www.broadgun.com

2

Why Research in Penetrant?� A typical U.S. commercial air carrier has over 30,000 parts

in inventory that require FPI at some point� Over 90% of metal components will be inspected using

FPI at least once during its lifetime

� Uncontained engine failures in the 1990�s led to a review of 6 aircraft overhaul facilities by an FAA team

� Poor quality assurance practices were noted at most facilities

� NTSB and FAA team recommended R&D to determine critical parameters in FPI process

� Research initiated in 1999

3

� Define areas where engineering data is deficient due to:� Change in process or materials� Change in applications� Data not available in the public domain

� Perform studies to provide quantitative assessment of performance

� Indication luminance measurements� Digital recording of UV-A indication� Probability of detection

� Complete study using either lab or shop facilities� Distribute results through use of web

� Support changes to industry specifications as warranted� Utilize results to update/create guidance materials

www.cnde.iastate.edu/faa-casr/fpi/index.html

Goals

Studies and Partners

� ES � 1 � Developer

� ES � 2 � Cleaning of Ti, Ni and Al� ES � 3 � Applied Stress� ES � 4 � Assessment tool for dryness

and cleanliness� ES � 5 � Surface treatments� ES � 6 � Light levels

� ES � 7 � Detectability Studies� ES � 8 � Prewash and Emulsification� ES � 9 � Drying Temperatures

� ES � 10 � Part geometry effects� ES � 11 � Penetrant Application

4

5

Is This All That CASR Does?CASR is a single slice of CNDE, which deals with:� UT, and UT arrays� EC, pulsed EC, and EC arrays� RT� FPI� MPI� MOI� Signal classification� Inspection of composite repairs� Vibrothermography� NDE simulation software� Inspection of aircraft wiring

6

Sample FabricationSample Fabrication

� Materials:� Titanium 6Al-4V � Inconel 718� Aluminum 6061-T6511

� EDM notches used as starter defects

� Three point bending at 0.1 R-ratio gave 2.5:1 aspect ratio

� Lengths from 20 to 180 mils, centered at 80 mils

7

Sample CharacterizationSample Characterization

� White light micrographs captured for each defect

� Indication luminance measurements

� UV-A micrographs captured to establish baseline response

� Removed those that showed high variability

How Was Work PerformedHow Was Work Performed

� Indication luminance measurements made with a Photo Research photometer� UV-A irradiation provided by twin 40W fluorescent bulbs

(3,000 µW/cm2)� Indications captured using a Leica UV-A binocular

microscope and QImaging cooled camera

½-degree spot size

8

9

Field StudiesField Studies� Required access to typical

drying, cleaning and FPI lines used in commercial aviation

� Several partners provided access to their facilities� Chem. cleaning lines for Ti and Ni� Mechanical blasting facilities � FPI lines for sample processing� Inspection booths for image capture

and luminance measurements

Developer Questions

� Do penetrants self-develop?

� Comparison of different penetrant/developer families

� Compare dry powder developer application methods� dust storm cabinet, bulb, spray wand, dip/drag, and

electrostatic

� Compare different developer forms� dry powder, water soluble, water suspendible, and non-

aqueous wet developer (NAWD)

� Effect of white light on detectability?

11

Developer Chamber CharacterizationDeveloper Chamber Characterization

� Dry powder developers qualified using dip/drag� Indication luminance is high with dip/drag, and results

are repeatable, but not realistic for shop floor

� Team evaluated four dust storm cabinets and a spray wand applicator at two field locations

� Penetrant process and chemistry was held constant while samples developed with cracks facing up, sideways, or downward

12

Dust Storm Cabinets: Chamber ADust Storm Cabinets: Chamber A

38" 36"38"

13

Chamber A CharacterizationChamber A Characterization

Applied through linear diffusers at top and bottom of chamber

Linear diffusers

Top of samples after development

Bottom of sample

14

Chamber BChamber B

80"

50" 54"

� Circular diffusers at top and bottom of chamber

� Evacuation in upper, center region of chamber

15

Chamber CChamber C

39 "

36 "44 "

Circular diffuser located in top of chamber

Chamber D Characterization

� Two jets below rollers� Lobster cage for sample

positioning

Example Results

Chamber d

0

10

20

30

40

50

60

0 10 20 30 40 50 60

AVG Brightness

Brig

htne

ss

UP

DOWN

BASELINE

Significant difference in indication luminance vs. application method and crack position

17

18Length (Inches)0.002 0.005 0.020 0.050 0.200

0.0

0.2

0.4

0.6

0.8

1.0

PO

DHit-Miss POD with 95% lower confidence bound

R3.I2.5kuva.0fc

POD results for samples processed using dip/drag, 5,000 UVA, no white light contamination

Developer Application MethodDeveloper Application Method

19Length (Inches)0.002 0.005 0.020 0.050 0.200

0.0

0.2

0.4

0.6

0.8

1.0

PO

DHit-Miss POD with 95% lower confidence bound

R4.I2.DevCh.5kuva.0fc

POD results for dust storm chamber processing, 5,000 UVA, no white light contamination

Developer Application MethodDeveloper Application Method

*

20

Manual Spray ApplicationManual Spray Application

Increasing spray time from 5 to 25 sec offered significant indication luminance improvements

21

� POD was related to indication luminance� Team found that:� Increasing UV-A from 1,000 to 3,000 µW�cm-2 was not a

significant change� Crack orientation within chamber affects POD, with a

0.010� deficit when facing downward � Use of 5,000 µW�cm-2 resulted in a 0.015� POD change� Increasing white light contamination led to over a 0.100�

reduction in 90/95 point POD� A characterization method for chambers is needed

Preliminary ConclusionsPreliminary Conclusions

22

Need for DeveloperNeed for Developer

� Indication luminance of 3 penetrants was evaluated without developer

� Cracks ranged from 13 to 130 mils

� Some large cracks had acceptable luminance

� Most small and large cracks were likely to be missed

No Developer Runs

0

5

10

15

20

25

30

0

0.0

2

0.0

4

0.0

6

0.0

8

0.1

0.1

2

0.1

4

Crack length (in)

Bri

gh

tne

ss

- N

o D

ev

elo

pe

r

R3-P1 R4-P1

R5-P1 R7-P2

R8-P3 R9-P3

R10-P2 R13-P2

PENETRANTS DO NOT SELF DEVELOP � DEVELOPER IS REQUIRED!

Lessons Learned Lessons Learned �� So FarSo Far

� Developer application is critical to overall FPI performance

� Crack orientation matters � Avoid barriers that prevent direct application of the

developer � Ensure chamber configuration or part handling

fixtures (rollers, baskets, etc.) don�t hamper application

� No metal-to-metal contact� May require multiple trips through the chamber to

ensure adequate coverage on all surfaces

24

Drying StudyDrying Study� Samples included shot-

peened and as-machined surfaces

� Penetrants� Level 4 ultrahigh PE� Level 3 surfactant-based WW� Level 2 oil-based WW

� Flash dry� Water bath soak at RT � Flash dry at 150°F

� Oven dry � Water bath soak at RT� Oven dry at 225°F for 30 minutes

25

Drying StudyDrying Study

26

� Evaluate geometry and thermal mass effects on luminance

� Utilized real part with fatigue cracks generated during spin pit test (Rolls Royce plc)� Weighed ~300 lbs � Waspaloy material

� Complicated geometry� Shot peened surface

Drying StudyDrying Study

27

Drying: Preliminary ConclusionsDrying: Preliminary Conclusions

For the parameters chosen:� No significant difference between drying methods

(250F air, 225F air, or 150F flash)� Dust chamber application for disk showed similar

luminance debits to those noted for lcf samples� Results were analyzed as function of penetrant method,

drying parameter, and surface finish� Surface finish was strongest factor, shot-peened surfaces

gave lower detectability

� Expected differences found between penetrant levels, L4 best, but difference between L3/L2 not strong

28

Developer ComparisonDeveloper Comparison

The objectives of this work:

� Analyze the amount of time that fluorescent penetrant indications required to reach peak luminance

� Determine the best developer option for a given set of parameters

� Evaluate whether specifications are adequate

*29

BackgroundBackground

� Standards allow several developer forms, including:

� Dry powder (Form a)

� Water soluble (Form b)

� Water suspendible (Form c)

� Non-aqueous wet developer (Form d)

� Past studies showed choice played a strong role in indication luminance and appearance

� Standards mandate minimum and maximum development times, and they differ slightly based upon developer choice

*

* 30

BackgroundBackground

This work monitored indication luminance while varying:Developer Type

� Dry powder brand� Water soluble� Water suspendible� NAWD (acetone or isopropanol)

Developer Application Method� Dip/Drag for dry powder� Dipping for water soluble or suspendible� Spraying of NAWD

Other Factors

*

ChemistryChemistryChemistry

�PE level 4 penetrant�Hydrophilic emulsifier (19.6%, remainder DI water)�Dry powder developer (3 brand names)

�NAWD (isopropanol-based)�NAWD (acetone-based)�Water soluble developer in DI water

(recommended conc.)�Water suspendible developer in DI water

(recommended conc.)

31

� 20 minute penetrant dwell� 90 second pre-wash� 120 second emulsification� 90 second post-wash

(water soluble or suspendible)� developer dip application � photometric luminance during 6 minute dry with heat gun, and

through 90 minutes� UV-A micrograph

(dry powder or NAWD)� 10 minute dry @ 155°F� developer application� UV-A micrograph� photometric luminance through 90 minutes� UV-A micrograph

32

ProcedureProcedureIn

spec

tion

Proc

ess

Variation depending upon experimental run

33

Dip / Drag

Surface Appearance After Developer Application at ISU

ProcedureProcedure

34

Water Soluble

Dipped Once per End

Surface Appearance After Developer Application at ISU

Constant Agitation

ProcedureProcedure

35

Water Suspendible

Dipped Once per End

Surface Appearance After Developer Application at ISU

Constant Agitation

ProcedureProcedure

36

NAWD

Surface Appearance After Developer Application at ISU

ProcedureProcedure

37

ResultsResultsComparison of Dry Powder to Other Options�Manual processing has inherent scatter�Data from relevant runs allowed for calculation of

average and standard deviation for each powder�Resultant plots used for comparison

Example DP-II data from

several runs

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0 2 4 6 8 10

Brightness (ft-L)

Time Elapsed (min)

DP-II (30 min)DP-II (60 min)DP-II (10 min)DP-II (30 min)AVERAGE

38

ResultsResults

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.900

1.000

0 2 4 6 8 10

Brightness (ft-L)

Time Elapsed (min)

DP-I (ave)

DP-II (ave)

DP-III (ave)

Average of all dry

powders with +/-2óerror bars

Average and Standard Deviation

39

ResultsResults

Comparison of Developer Options

�Developer forms a, b, c, and d were compared

�While all other factors held constant, indication appearance and luminance varied widely with choice of developer

�Luminance could be increased by 1,211% (0.040�crack), or 2,192% (0.069� crack) solely with choice of developer

0.00

0.50

1.00

1.50

2.00

2.50

0 10 20 30 40 50 60 70 80 90

Brightness, ft-L

Time Elapsed, minutes

Lum

ina

nce,

ft-

L

40

Results: 0.040Results: 0.040�� CrackCrackWater Soluble

Dry Powder III

Isopropanol NAWD

Dry Powder IAcetone NAWD

Dry Powder II Water Suspendible

*

41

0.00

0.50

1.00

1.50

2.00

2.50

0 10 20 30 40 50 60 70 80 90

Brightness, ft-L

Time Elapsed, minutes

Developer Form Max Luminance (ft-L) Time Until Max (min)

Water Soluble 2.37 34.2

Isopropanol NAWD 2.27 34.1

Dry Powder I 1.2 59.6

Acetone NAWD 0.9 47.6

Dry Powder II 0.38 33.2

Water Suspendible 0.33 89.8

Dry Powder III 0.2 67.5

Results: 0.040Results: 0.040�� CrackCrack

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

0 10 20 30 40 50 60 70 80 90

Brightness, ft-L

Time Elapsed, minutes

Lum

ina

nce,

ft-

L

42

Results: 0.069Results: 0.069�� CrackCrack

Water SuspendibleDry Powder II

Acetone NAWD

Dry Powder IWater Soluble

Isopropanol NAWD

Dry Powder III

*

43

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

0 10 20 30 40 50 60 70 80 90

Brightness, ft-L

Time Elapsed, minutes

Developer Form Max Luminance (ft-L) Time Until Max (min)

Isopropanol NAWD 14.7 29.9

Dry Powder I 8.94 81.2

Water Soluble 8.90 64

Acetone NAWD 3.0 51.1

Dry Powder II 2.9 43.7

Dry Powder III 2.7 86.2

Water Suspendible 0.6 88.4

Results: 0.069Results: 0.069�� CrackCrack

44

ResultsResultsComparison of Developer Options� 90-minute development isn�t realistic�Maximum luminance and initial rate of increase related�Rates of luminance increase ranked on following slide

Average of both cracks

Average of both cracks noted

during initial 9 minutes

45

ResultsResultsDeveloper Initial Rate of Luminance Increase

Water Soluble 0.321 ft-L/min

Isopropanol NAWD 0.259 ft-L/min

Dry Powder I 0.137 ft-L/min

Acetone NAWD 0.055 ft-L/min

Dry Powder II 0.023 ft-L/min

Dry Powder III 0.016 ft-L/min

Water Suspendible 0.016 ft-L/min

� Increase in indication luminance over first 9 minutes

�Agreed with past studies on these two defects, but overall trend varied slightly when average of 10 cracks considered

46

Final Indication AppearanceFinal Indication Appearance

Isopropanol NAWD 700 ms

0.040� lcf crack, 90 minute development, 40X original magnification

Water Soluble 826 ms

(Brightest)

Dry Powder I 1.4 sec

Dry Powder II 7 sec

Dry Powder III 21.8 sec (Dimmest)

Acetone NAWD 700 ms

Water Suspendible 500 ms

*

47

Isopropanol NAWD 243 ms

(Brightest)

0.069� lcf crack, 90 minute development, 40X original magnification

Water Soluble 188 ms

Dry Powder I 214 ms

Dry Powder II 606 ms

Dry Powder III 1.54 sec

Acetone NAWD 475 ms

Water Suspendible 500 ms

(Dimmest)

Final Indication AppearanceFinal Indication Appearance

48

ConclusionsConclusions� Maximum indication luminance varied with developer form:

over 2,000% difference between choices� Time until maximum luminance varied, and was 3 � 9 times

longer than minimum: 9 � 49% increase after 10 minutes

� NAWD development is limited to 60 minutes, but max luminance wasn�t realized until 32 minutes (isopropanol) and 50 minutes (acetone), and increased 17 � 21% after 10 minutes

� Indication appearance varied with developer type:� Isopropanol-NAWD quickly formed bright, wide indications

� Acetone-NAWD and water suspendible formed dimmer and more intermittent indications

� While luminance varied, water soluble and dry powder generally formed sharply-defined indications

Developer Form Comparison

0

3

Fo

rm A

dip

/dra

g

Fo

rm A

du

st c

lou

d c

ha

mb

er

- Mix

ed

orie

nta

tion

Fo

rm A

du

st c

lou

d c

ha

mb

er

- U

p

Fo

rm A

du

st c

lou

d -

S o

r D

For

m A

- M

S -

mix

ed

Fo

rm A

- M

S U

p

For

m A

- b

ulb

- U

p

Fo

rm A

- b

ulb

- s

ide

way

s

For

m B

- R

ec

Co

nc

Fo

rm B

- L

o C

on

c

Fo

rm C

- R

ec

Co

nc

Fo

rm C

- L

o C

on

c

Fo

rm D

Developer Application Method

Nor

ma

lize

d b

righ

tne

ss

Dip/dr

ag

10-s

ampl

e D

ata

Set

Dust S

torm

-Up

NAWD

Wate

r Solu

ble

Dust S

torm

-Side

/Dow

n

Wate

r Sus

pend

ible

49

50

Electrostatic ApplicationElectrostatic Application� Dust storm cabinet application varied strongly between

cabinets, and with defect position � Electrostatic application has the potential for rapidly and

evenly coating multiple sides simultaneously� Many variables to control, and some are out of

operator�s control� Indication luminance was monitored while varying

applied thickness and other parameters

51

Spray Time / Coating ThicknessSpray Time / Coating Thickness

Average indication luminance versus

spray time

Optimum Spray Time

� To establish an ideal spray time 6 samples were chosen� These blocks were re-processed several times while

varying the spray time� Results suggested that 3.5 � 4.0 seconds (1.2 - 1.7 mils)

was ideal in a fume hood setup with direct spray

Effect of Position

� Four samples chosen that produced similar indication luminance

� Stacked such that crack is facing front, back, top or bottom

� Processed parts in rotation-each sample saw each position

� Sprayed for 3 seconds at 12� stand-off

Found that coating thickness and luminance were greatest on front and top surfaces of cluster using this setup.

52

� 3 sec spray at 24� with no airflow

� Decreased indication luminance due to increased spray distance

� More even distribution coating thickness around all sides

Effect of Position

vs.

Effect of Position

Performance: Electrostatic vs. Dip/DragSUSPENDED RUN -- % DIP/DRAG AVERAGE ACHIEVED

02-057 02-058 02-066 02-090 AVERAGE STD DEV

Front 119.13% 40.66% 28.99% 55.09% 60.97% 0.402195

Top 90.58% 12.79% 38.61% 28.75% 42.68% 0.336582

Back 27.16% 18.41% 30.31% 40.41% 29.07% 0.090781

Bottom 135.51% 20.04% 31.82% 15.85% 50.80% 0.568758

SUSPENDED RUN -- % DIP/DRAG AVERAGE ACHIEVED

0%

10%

20%

30%

40%

50%

60%

70%

Front Top Back Bottom

Position

% D

ip/D

rag

Ave

rag

e A

chie

ved

45.88%

Indication luminance for suspended cycle averaged 46% of the baseline value when results were analyzed by sample and position

55

� Concentration and contact time are mandated for immersion and spray application of hydrophilic emulsifiers� With complex parts with recesses, ensuring coverage

and process timing can be challenging

EmulsificationEmulsification

56

Four maximum emulsifier concentration ranges are listed in AMS 2647B

5% = 5% max10% = 7-10% concentration20% = 17-20% concentration30% = 27-30% concentration

Three representative Level IV sensitivity hydrophilic PE penetrant families were chosen:

PL-10 = 10% maxPM-20 = 20% max (baseline material)PH-30 = 30% max

EmulsificationEmulsification

57

Monitored the change in FPI indication luminance while varying:

1. ConcentrationLower than recommendedWithin the recommended rangeAbove the specified range

2. Application MethodImmersionSpray

3. AgitationNo agitationPeriodic agitationConstant agitation

4. DurationShort emulsifier timeMaximum emulsification time allowableTwice the maximum emulsification time Example Indication

EmulsificationEmulsification

58

How Was It PerformedHow Was It Performed

Emulsification MethodsImmersion using a 5-gallon tub�Varied concentration�Varied emulsification time�Varied agitation rate

Spray emulsification using a Hudson Bak-Pak®

�Constant concentration�Varied emulsification time Spray emulsification

59

How Was It PerformedHow Was It PerformedSpray emulsification using a Hudson Bak-Pak® Sprayer

� 5% maximum concentration

� 60, 120, or 240 second spray

� flat fan spray nozzle

� ~80° spray angle

� regulated to 20 psi

� Approximately 1,200 mL/minute

� 12� stand-off distance

� 1 spray pass every 2 seconds

Backpack sprayer for emulsification

Spray emulsification

60

Immersion using a 5-gallon tubConcentration�PL-10 material

5%, 10%, 15%, 20%�PM-20 material

15%, 20%, 25%�PH-30 material

20%, 25%, 30%, 35%Time�60, 120, and 240 seconds

Agitation�none, 15 second intervals, and constant

Emulsifier immersion

How Was It PerformedHow Was It Performed

61

Regression model showed no significant changes in luminance at the concentrations used

Emulsifier Concentration0.0 0.1 0.2 0.3 0.4 0.5

4

6

8

10

12

14

16

Bri

gh

tne

ss

PL-10UVA=2980, CT=120, AF=15

Emulsifier Concentration0.0 0.1 0.2 0.3 0.4 0.5

12

14

16

18

20

22

24

26

28

Bri

gh

tne

ss

PM-20UVA=2980, CT=120, AF=15

Emulsifier Concentration0.0 0.1 0.2 0.3 0.4 0.5

4

6

8

10

12

14

16

Bri

gh

tne

ss

PH-30UVA=2980, CT=120, AF=15

Emulsifier ConcentrationEmulsifier Concentration

62

Contact TimeContact Time

Regression model showed that luminance decreased with increasing contact time

Contact Time (sec) 0 200 400 600 800 1000 1200

0

2

4

6

8

10

12

14

16

Bri

gh

tne

ss

PL-10UVA=2980, EC=0.05, AF=15

Contact Time (sec) 0 200 400 600 800 1000 1200

10

15

20

25

30

Bri

gh

tne

ss

PM-20UVA=2980, EC=0.05, AF=15

Contact Time (sec) 0 200 400 600 800 1000 1200

4

6

8

10

12

14

16

Bri

gh

tne

ss

PH-30UVA=2980, EC=0.05, AF=15

63

Emulsification ConclusionsEmulsification Conclusions� Concentration had minimal impact on luminance when

held at +/- 5% of recommended � Indication luminance most affected by extended contact

time � No agitation led to reduced luminance for all three

penetrants, stronger effect in PM20 than others� Constant agitation essentially same as 15 sec agitation

64

65

� Chemical cleaning to remove soot, coke, and varnish from Ti 6-4 reduced detectability after some processes (see DOT/FAA AR-03/73)

� Renewed effort utilized commercial cleaners, acids, and molten salt bath to remove contaminants� Molten salt bath widened cracks (etched), but

resulted in unacceptable changes to the surface despite a cautious approach

� Carbon cleaner � scale conditioner � nitric acid process removed scale, but were not fully cleaned

� Alkaline de-ruster process failed to clean the bars, and may have contributed to loss of an indication

Titanium Pre-Cleaning

66

Titanium Pre-Cleaning

� Follow-on work fabricated new samples to determine how best to remove soot and oxidation

� Most (7 of 9) 60-mil cracks were undetectable after 96 hours at 975F (forced air)

� No cracks were missed when samples treated at 800F for 96 hours

67

� Neither alkaline cleaning, nor hot sulfuric acid soak recovered 975F indications � cleaning procedures did not adversely affect non-heat-treated samples

� For 800F samples a 30-minute hot DI water soak seemed to dissolve residual alkaline and increase indication luminance

� Preliminary results showed that hot water soak after alkaline cleaning aided detectability

� Currently studying soak time

Titanium Pre-Cleaning

68

Questions?Questions?

Website provides background info and published technical results

Links to FAA Reports available

www.cnde.iastate.edu/faa-casr/fpi/index.html