Challenges Facing KSC in Corrosion Management and the NASA/KSC Corrosion Technology Testbed

Luz Marina Calle

Corrosion Technology Testbed

NASA, Kennedy Space Center, Florida, USA

2005 C3P-NASA International Pollution Prevention Workshop, Lisbon, Portugal

OutlineEffects of corrosionCost of corrosionWhat is corrosionEvaluation of corrosionAtmospheric exposure studiesElectrochemical measurementsEnvironment at KSCChallenges:

Highly corrosive environmentAcidic exhaust from SRBsEnvironmental issues

Materials and Coatings SelectionCorrosion Protective CoatingsCorrosion Resistant Alloys

NASA Corrosion Technology Testbed

Effects of Corrosion

Cost of Corrosion in the US

Cost of Corrosion in the US

$ = Billion 1998 dollarswww.corrosion-doctors.org

What is Corrosion?

Corrosion is the deterioration of a material due to its reaction with its environment (M.G. Fontana).

Corrosion is the destructive attack of a metal by chemical or electrochemical reaction with its environment (H.H. Uhlig).

Metal atoms in nature are present in chemical compounds (i.e. minerals).

What is Corrosion?

The same amount of energy that is needed to extract metals from their minerals is emitted during the chemical reactions that produce corrosion. Most corrosion is electrochemical.Corrosion returns the metal to the minerals or similar compounds from which the metal was extracted.Corrosion has been called extractive metallurgy in reverse

Electrochemical Nature of Metallic Corrosion

Chemical reaction involving the transfer of electrons at the metal surface.

Metal is oxidized (anodic reaction)Fe Fe2+ + 2e-

Something else is reduced (cathodicreaction)

2H+ + 2e- H2

Requirements for Corrosion

1. Anode sites on a metal surface2. Cathode sites on a metal surface3. Electrolyte in contact with anode and

cathode (provides path for ionic conduction)

4. An electrical connection between anode and cathode (allows electrons to flow between anode and cathode)

Evaluation of Corrosion

Field Exposure TestsElectrochemical MethodsAccelerated Exposure

Coupon Exposure Stands

Atmospheric Exposure

Atmospheric exposure provides valuable data but it takes a long time and relies on human visual inspection.

NASA Technical Standard for Protective Coatings requires 18 months of good performance for preliminary approval and continued good performance for 5 years for final approval of a coating system.

Electrochemical Techniques

Corrosion rate measurement by dc methods usually involve applying a small amplitude dc signal, of either voltage or current, to a corroding metal. The resulting current or voltage is measured and a polarization resistance can be calculated.

Corrosion rate is inversely proportional to polarization resistance.

Electrochemical Methods

Corrosion PotentialDirect current methods

Linear polarizationTafel plotsCyclic polarizationPotentiodynamic scanning

Electrochemical ImpedanceSpectroscopy

EIS

EIS is an electrochemical technique in which a small amplitude sinusoidal potential perturbation is applied to the working electrode at a number of discrete frequencies, ω. At each of these frequencies, the resulting current waveform will exhibit a sinusoidal response that is out of phase with the applied potential signal by a certain amount (θ) and has a current amplitude that is inversely proportional to the impedance of the interface.

Z(ω) = V(ω)/I(ω)

EIS Experiments

AC Waveforms for an Applied Voltage and Resulting Current

Time

E

I

θ

Environment at KSC

Introduction

Corrosion studies began at KSC in 1966 during the Gemini/Apollo Programs.

Saturn V

NASA/KSC Beach Corrosion Test Site

LAUNCH COMPLEXES39A 39B

KSC BEACH CORROSION LABORATORY

COUPON EXPOSURE STANDS ATLANTICOCEAN

Introduction

The launch environment at KSC is extremely corrosive:

• Ocean salt spray• Heat• Humidity• Sunlight• Acidic exhaust from

SRBs

Corrosion Rates of Carbon Steel

L o c a ti o nT y p e O f

E n v i r o n m e n t µ m / y rC o r r o si o n

r a te (a ) m i l s/ y r

E s q u im a lt , V a n c o u ve r Is la n d , B C , C a n a d a

R u ra l m a rin e 1 3 0 . 5

P i t t s b u rg h , P A In d u s t r ia l 3 0 1 . 2C le ve la n d , O H In d u s t r ia l 3 8 1 . 5

L im o n B a y , P a n a m a , C Z

T ro p ic a l m a rin e 6 1 2 . 4

E a s t C h ic a g o , IL In d u s t r ia l 8 4 3 . 3B ra z o s R ive r, T X In d u s t r ia l m a rin e 9 4 3 . 7

D a y t o n a B e a c h , F L M a rin e 2 9 5 1 1 . 6P o n t R e y e s , C A M a rin e 5 0 0 1 9 . 7

K u re B e a c h , N C (8 0 ft . fro m o c e a n )

M a rin e 5 3 3 2 1

G a le t a P o in t B e a c h , P a n a m a C Z

M a rin e 6 8 6 2 7

K e n n e d y S p a c e C e n t e r, F L (b e a c h )

M a rin e 1 0 7 0 4 2

(a) Two-year average

Corrosion Rate Change

Space Shuttle Launch

SRB Exhaust

In 1981 the Space Shuttle introduced acidic deposition products

Solid Rocket Booster Fuel Reaction

NH4ClO4(s) + Al(s) ⎯⎯⎯⎯⎯⎯ →⎯ 32 , OFebinder Al2O3(s) +HCl(g) + H2O(g) + NOx(g)

Materials and Coatings Selection

HistoryA 1969 Study determined that inorganic zinc-rich primers (ZRPs) outperformed organic zinc in the KSC seacoast environment and that, in general, top-coats were detrimental to the long-term performance of the inorganic ZRPs. Some of the panels exposed at the Beach Site for this study are still in perfect condition.

ZRP Panels After 8 Years of Atmospheric Exposure

Untopcoated ZRP Epoxy and urethane coated ZRP

History

In 1981 the Space Shuttle introduced acidic deposition problems to the ZRP coatings.Studies conducted to identify coating systems to improve the chemical resistance of zinc primers10 topcoat systems were approved for use in the Space Shuttle launch environment.

History

The coating systems selected were all solvent-basedClean Air legislation and environmental regulations began to restrict the use of solvents in paintsA 1995 Study determined that total inorganic coating systems provided excellent protection in launch environments

Silicone Ablative CoatingsLaunch structures receive severe damage during launch due to high heatNew primerless silicone technology developed between KSC, DuPont, and Dow CorningAblative material installed in 1994 on entire 95’ level

Protective Coating Research

EIS evaluation of inorganic ZRPs.Conductive polymer coatings.Polysiloxane coatings.Silicone coatings for blast and heat protection of launch structures.Molybdate conversion coatings as possible replacement of chromium conversion coatings.

Development of Molybdate Conversion Coatings for Aluminum

Investigated the corrosion protection properties of six formulations of environmentally friendly molybdate conversion coatings as possible replacements for chromate conversion coatings on aluminum alloy 2024-T3.Used EIS as well as Scanning Electron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), and Energy Dispersive Spectroscopy (EDS).

The acidic chloride environment is aggressive to most metals and causes severe pitting in some of the common stainless steel alloys.

304L is susceptible to pitting corrosion that can cause cracking and rupture of both high-pressure gas and fluid systems.

The failures can be life catastrophic.

Micrograph (100x magnification) of Pit from KSC’s Launch Pad 304L Tubing

Tubing Split Caused by Pitting

Electrochemical Investigation of the Corrosion Behavior of Metal Alloys in

the STS Launch EnvironmentElectrochemical characterization of the corrosion behavior of 24 alloys using DC techniques and EIS.Correlation between electrochemical data and atmospheric exposure data at the Beach Corrosion Test Site.

Cyclic Polarization for 304L - 3.55% NaCl

E(m

V)

log(I)(log(A))

-100

-200

-300

-400

-500

0

100

200

300

-3-4-5-6-7-8-9-10 -2

Alloys

Alloy Class

304L Low carbon austenitic stainless steel

AL6XN Superaustenitic stainless steel

254SMO Austenitic stainless steel

Alloy Composition

Alloy Fe Ni Cr Mo Mn C N Si P S Cu

304L 71.567 8.200 18.33 0.500 1.470 0.023 0.030 0.380 0.030 0.0002 0.460

AL6XN 48.11 23.88 20.470 6.260 0.300 0.020 0.330 0.40 0.021 0.0003 0.200

254SMO 55.162 17.900 20.000 6.050 0.490 0.012 0.196 0.350 0.019 0.001 0.680

Racks at KSC’s Beach Corrosion Test Site

Atmospheric Exposure

304L

S31603

S31703

Tubing after one year of natural seacoast atmospheric exposure (no acid rinse)

S30403 304L AL6XN

254SMO

Electrochemistry

Corrosion potentialLinear polarizationCyclic polarizationElectrochemical Impedance Spectroscopy (EIS)Electrolyte conditions:3.55% NaCl3.55% NaCl–0.1N HCl3.55% NaCl–1.0N HCl

Electrochemical Cell

Corrosion Potential

(a) neutral 3.55% NaCl

(b) 3.55% NaCl-0.1N HCl

(c) 3.55% NaCl-1.0N HCl

(a) (b)

(c)

-150

-100

-50

0

50

0 50 100 150 200 250 300 350 400 450

Time / hrs

OC

P / m

V

304L (0N HCl) 254SMO (0N) AL6XN (0N)

-250

-200

-150

-100

-50

0

50

100

150

0 50 100 150 200 250 300 350 400 450

Time / hrs

OC

P / m

V

304L (0.1N) 254SMO (0.1N) AL6XN (0.1N)

-400

-350

-300

-250

-200

-150

-100

-50

0

50

100

150

0 50 100 150 200 250 300 350 400 450

Time / hrs

OC

P / m

V

304L (1N) 254SMO (1N) AL6XN (1N)

Neutral 3.55% NaCl

254SMO AL6XN

304L

3.55% NaCl-0.1N HCl

254SMO

304L

AL6XN

3.55% NaCl-1.0N HCl

254SMOAL6XN

304L

Surface Morphology

(a) (b) (c)

A

B

SEM images of 304L SS in 3.55% NaCl–1.0N HCl: (a) 22X image of the sample showing the exposed area A and unexposed area B, (b) 1000X image of A, and (c) 1000X image of B.

NASA Corrosion Technology Testbed

http://corrosion.ksc.nasa.gov

The Corrosion Technology Testbed is a capability outfitted with state-of-the-art equipment and facilities to develop new corrosion control technologies and to

investigate, evaluate, and determine material behavior in many different corrosive

environments.

StaffStaff present at the KSC facilities include scientists, engineers, and technicians with degrees and expertise in the following areas:

Discipline PhD MS BSPhysical Chemists 2 0 0Chemical Engineers 1 0 0Corrosion Engineers 0 1 2Analytical Chemists 2 0 0Material Scientists 1 0 1

Corrosion Technology Testbed

Electrochemistry laboratoryAccelerated corrosion equipmentCoatings application laboratoryAtmospheric exposure siteSeawater immersion systemSurface analysis

Seawater Immersion System

Two immersion tanks with a continuous once-through, filtered supply of seawater is used to evaluate test coupons, component hardware, or full scale test articles. Temperature, salinity, dissolved oxygen, conductivity and pH are closely monitored.Can be utilized for the evaluation of protective coatings, metal alloys, reinforced concrete, composites and other materials in a seawater environment. Specialized tests can be designed to study impingement-corrosion, erosion-corrosion, cavitation and other velocityeffects.

Accelerated Corrosion Laboratory

Salt fog testing to study the ability of a material to resist corrosion.

Capabilities include traditional salt spray techniques, as well as advanced cyclic and acidic methods.

Surface AnalysisSurface Analysis

State of the art electron microscopes and experienced staff study corrosion mechanisms through surface chemistry, depth profiling, and composition mapping. Techniques available for surface analysis include:

TEM (Transmission Electron Microscopy)

SEM (Scanning Electron Microscopy)

XPS (X-Ray Photoelectron Spectroscopy)

AES (Auger Electron Spectroscopy)

Rutherford Backscattering Spectroscopy

SIMS (Secondary Ion Mass Spectrometry)

Representative ProjectsNon-chrome Conversion Coating Evaluation (Navy)Airplane Wing Study (Air Force)Seawater Immersion Studies of Welds for Military Applications (Navy)Launch Site Coating Development and Evaluation (Air Force)Single Coat/Rapid Cure Marine Tank Lining Evaluation (Navy)Antifouling Coating Test and Evaluation (Navy) Chloride Rinse Agent Investigation (Army)Smart Coating Development (NASA)Corrosion Resistant Tubing for Shuttle Launch Sites (NASA)Support Equipment Paint Replacement Project (NASA)Electrochemical Evaluation of Coatings for Solid Rocket Motors (Thiokol)VAB/LCC Roof (Reinforced Concrete) Corrosion Study (NASA)Refractory Concrete Study (NASA)Urethane Replacement Study (NASA)Depainting/Surface Preparation Study (NASA)Polysiloxane Coating Development (NASA)Cryogenic Storage Corrosion Study (NASA)Galvanic Coatings for Protection of Steel in Concrete (NASA)Outdoor Video Camera Corrosion Study (NASA)Corrosion of Food Processing Equipment (Industry)

Project HighlightsPerformance of Chemical Rinse Agents on Aircraft Alloys Exposed to a Seacoast Environment

Four chloride rinse agents (CRAs) were evaluated for use on military aircraft, missiles, and various components.

Chromate Coating Replacements for Military Aircraft

The effectiveness of replacements to currently used chromate conversion coatings is being investigated.

The coating system matrix utilizes:Four aluminum substratesNine pretreatmentsFive primersTwo topcoats

Contact InformationLuz Marina Calle, Ph.D.

E-mail: Luz.M.Calle@nasa.govPhone: 1-321-867-3278

Joseph CurranE-mail: Joseph.Curran-1@ksc.nasa.gov

Phone: 1-321-867-7558

http://corrosion.ksc.nasa.gov