MIL-STD-889D Overview

NAVAIR Public Release 2018-631. Distribution Statement A – “Approved for public release; distribution is unlimited"

MIL-STD-889D Overview3-7 AUG 2020

Presented to: ASETS Defense 2020

Presented by: Victor Rodriguez-Santiago

2NAVAIR Public Release 2018-631. Distribution Statement A – “Approved for public release; distribution is unlimited"

Meeting Comms

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Agenda

• Background• Rationale for New Approach• Changes and impact of the updated standard• Future Plans


MIL-STD-889: Dissimilar MetalsPurpose: This standard defines and classifies dissimilar metals and establishes requirements for protecting coupled dissimilar metals against corrosion with attention directed to the anodic member of the couple.

MIL-STD-889D

Current Approach: This approach is to move to galvanic current, rather than potential, in order to determine galvanic compatibility.

MIL-STD-889C

Modernized Revision: Current version was modernized in 2016 to replace obsolete references to other standards

MIL-STD-889B

The last technical revision was done in 1967, based on an AMCOM report (TR-67-11). Was not done in sea water.

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Approach in MIL-STD-889C

• The galvanic series listed previously in MIL-STD-889C was generated from a sodium chloride solution (not artificial sea water)

• Compatibility was determined solely on the difference in potential of the metals This led to discrepancies from what is seen in practice


ComparisonMIL-STD-889DMIL-STD-889C

No clear requirement for galvanic compatibility

Lack of information required for making accurate decisions

Potential for incompatible metals to be paired together

No measure of how quickly the anodic metal will corrode

No standardization for data generation or analysis

Identifies compatibility in multiple environments

Added requirements for galvanic compatibility

Added information to create informed decisions

Accounts for the kinetics (rate) and the potential of corrosion

Can be used to calculate rate of corrosion of the anodic material

Added methodology for generating and analyzing data

Identifies one environment with future additions possible~

NAVAIR Public Release 2020-545. Distribution Statement A – “Approved for public release, distribution is unlimited.”


Wrong Compatibility Decisions are Possible

Al Alloys

StainlessSteels

Titanium

Based in the galvanic series, stainless steels are a better material choice than titanium when coupled to Al7075. However, titanium has almost an order of magnitude lower galvanic current.


Galvanic Potential Doesn’t Tell the Whole Story (it doesn’t tell anything about rate)

3.5 wt.% NaCl


Round Robin for Developing a Test Methodology

• A methodology was established to obtain potentiodynamicpolarization data. This methodology provides a best-practicesapproach in order to generate data across laboratories so that isconsistent and valid.

• Round robin testing, per ASTM E691, was completedencompassing academia, industry, and NAVAIR:

- UVA (Kelly)- OSU (Frankel)- MSU (Swain)- UTRC (Jaworowski)- Corrdesa (Keith, Siva)- Safran- NAVAIR (Safigan, Rodriguez)


Round Robin Results

Combined Al 7075 Combined Steel 1020


Deconvolution Approach: Reactions

• Semi-automated approach published by Yeum and Devereux: – K.S. Yeum and O.F. Devereux, "An Iterative Method for Fitting Complex

Electrode Polarization Curves", Corrosion, Vol. 45, pp. 478-487 (1989).1) Identify curve regions dominated by separate reactions2) Classify those reactions into one of six types3) Provide initial estimates for kinetic parameters4) Operate software to obtain the best fit

Reaction Type Electron Passivation Diffusion Ohmic-drop1 x2 x x3 x x4 x x5 x x x6 x x x


Raw Data 13-8Mo PH13-8Mo PH

Artificial Sea Watern=3


Deconvoluted Components13-8Mo PH

Hydrogen Evolution

Oxygen Reduction

Metal Dissolution

Pitting


Average Deconvoluted Curve for All Data Sets

13-8Mo PHArtificial Sea Watern=3


Galvanic Current/Potential

Can we verify this approach?

Joint sample gives mixed potential curve.

Mixed Potential Approach to Galvanic Current

Galvanic Test (ZRA)24hr


Galvanic Compatibility of Bare Metals

Legend:Galvanic compatibility between two metals of interest is found at the intersection point of the row and column. The anodic member of the couple is listed in the rows and the cathodic member of the couple is listed in the columns. An empty cell at the intersection point indicates that the metal identified as anodic and cathodic should be switched.This table shall not be used to indicate the level of risk associated with the galvanic couple nor shall it be used to determine the level of protection required to protect the metals. The CEA or appropriate design authority shall determine the necessary protection.The corrosion rate was determined for metals in a 1:1 ratio.The number in the cells represent a range at which the anodic material will corrode when coupled with the cathodic material in artificial seawater. Any number above zero indicates galvanic incompatibility. The range of the corrosion rate in mils/year is as follows:Galvanically Compatible:0: <0.009 mil/yearGalvanically Incompatible:1: 0.01-0.09 mil/year2: 0.1-0.9 mil/year3: 1-4.99 mil/year4: 5-9.99 mil/year5: 10-99.99 mil/year6: > 100 mil/year



Galvanic Compatibility of Treated Metals




Galvanic Compatibility of Bare and Treated Metals




Estimated Release Schedule

Dec 2020*

January 2020

March2020

July 2020

August 2020*

Oct2020*

Nov 2020*

* Projected dates



Updates from Informal Review• Added Appendix D which includes the following tables:

Accelerating Factors Table Material Characteristic Table

• Re-categorized materials in Appendix A• Anodized materials to galvanic compatibility table



AcknowledgementsNAVAIR: Anna Safigan, Kip Koonce, Elizabeth Monillas, Andrew Lee, Kaylee Canales, Taylor Wolt, Van Nuyen, Nahid Ilyas, Ian MacIntyre, Zachary Nega, Alex Lilly, Rachel Cusic, Rachel Black, Steven Kopitzke, Margaret Aaron, Jenny Elliott

Round Robin Participants: Rob Kelly, Jerry Frankel, Keith Legg, Siva Palani, Alan Rose, Mark Jaworowski, Greg Swain, SAFRAN, students.

MIL-STD Logistics: Steven Spadafora.

MIL-STD-889 Working Group: AF, Army, Navy, MDA


Questions?

Backup


Proposed Approach for Technical Revision

• Aim: Update MIL-STD-889C based on current density rather than ΔE, and to update the materials list.

• Proposed Methods:• Method 0: Replace galvanic series with a similar table based on current

density for equal areas, but using alloys rather than the generic materials in the current standard. Include simple ways of adjusting for relative areas and finishes. Galvanic current would be obtained from polarization data, and curve crossing.

• Task: Define methodology to acquire polarization data in bulk electrolyte using flat cell -- this methodology will be based on a Best Practices Document for generating polarization curves.

• Method 1: Define galvanic acceleration factors – corrosion testing such as weight loss.

• Method 2: Define computational method using curve crossing.• Method 3: Define methodology for full FEA approach.

Phas

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Oth

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Galvanic Current of Several Couples

*Conversion coatings and anodization treatments will be attacked in a localized manner. All galvanic current will be concentrated in a small area.

Decr

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ng C

urre

nt

0.01 mil/yr for Al


Deconvolution Approach: Parameters

I is the current resulting from the reactionI0 is a reaction-dependent constant called the exchange currentE is the electrode potentialE0 is the equilibrium potential (constant for a given reaction) also Ecorrβ is the reaction’s Tafel constant (constant for a given reaction, with units of

volts/decade


MIL-STD-889 POA&M


Al 7075 Analysis


Steel 1020 Analysis


Galvanic Analysis*


Round Robin Statistics: Al7075

Inter-lab statistics: indicator of how one laboratory’s cell average, for a particular material, compares with the average of the other laboratories (n = 7).

Intra-lab statistics: an indicator of how one laboratory’s within-laboratory variability, under repeatability conditions (n = 3), on a particular material, compares with all of the laboratories combined (n = 7).


Round Robin Statistics: Al7075


Deconvolution Approach


Galvanic Current

A/cm2

2024 Bare

2024 Anodized

Type II Sealed*

2024 Anodized

Type II Unsealed*

2024 Anodized Type IIbSealed*

2024 Anodized Type IIb

Unsealed*2024 Cr3*

2024 Cr6*

A286 Bare 1.48e-5 4.33e-7 7.01e-6 5.50e-8 1.52e-5 1.27e-5 1.33e-513-8MO

Bare2.18e-5 3.61e-7 8.39e-6 3.83e-8 2.18e-5 1.82e-5 1.82e-5

13-8MO Passivated

1.14e-5 3.17e-7 5.41e-6 3.83e-8 1.14e-5 9.07e-6 9.30e-6

Ti64 Bare 5.36e-8 1.30e-8 9.45e-8 8.22e-10 5.09e-8 3.12e-8 3.64e-8

*Conversion coatings and anodization treatments will be attacked in a localized manner. All galvanic current will be concentrated in a small area.


Fully Deconvoluted Curve

13-8Mo PH


Raw and Deconvoluted

13-8Mo PH


A286 Raw and Deconvoluted

A286• Scattered data sets can be averaged and

represented in one curve using individual fit parameters.


Mixed Potentials with Data Variation

Passivation helps with the self corrosion and anodic behavior but…..

…it does not hinder cathodic behavior.


Effect of Conversion Coating

Conversion coatings do not offer a galvanic benefit but can cause severe localized damage when breached. The same applies to anodization.


Best Practices Document• Best Practices document has been finalized

and it is Distribution A.

Item Notes

Equipment Flat cell.

Reference electrode SCE, Ag/AgCl, or other suitable electrode.

Electrolyte Artificial sea water per ASTM D1141 (2013) without heavy metals, 25 +3° C, pH 8.2, vigorously aerated prior to testing, then quiescent condition (naturally aerated; no bubbling)

Working electrode Specimen to be tested. Stationary. Abraded with appropriate P800 or ANSI 400 grinding paper, cleaned with acetone then ethanol, and surface treated appropriately (if required).

OCP stabilization The surface should be stabilized in the electrolyte, but not for a time that causes the surface condition to change significantly (e.g. crevice or pitting):

MORE Noble (OCP > -200 mV vs SCE):

LESS Noble (OCP < -200 mV vs SCE):

24 hours in electrolyte prior to polarization measurement

4 hours in electrolyte prior to polarization measurement

Polarization curve • Anodic polarization: OCP to +0.7 V vs OCP, or when the anodic current density reaches a maximum of 10 mA/cm2

• Cathodic polarization: OCP to -1.4 V vs REF, or when the cathodic current density reaches a maximum of 10 mA/cm2

Note: Cathodic and anodic curves shall be obtained on separate specimens prepared according to section 3.1.

Sweep rate 0.2 mV/s for entire potential range

IR correction The reference electrode should be placed >2x diameter of Luggin tip from the working electrode.

Documents

MIL-STD-889D Overview