NAVAIR_01-1A-509-1.pdf

NAVAIR 01-1A-509-1

TM 1-1500-344-23-1

TO 1-1-689-1

TECHNICAL MANUAL

CLEANING AND CORROSION CONTROL

VOLUME I

CORROSION PROGRAM AND

CORROSION THEORY

01 MARCH 2005

This publication supersedes NAVAIR 01-1A-509/TM 1-1500-344-23, dated 1 May 2001 and NAVAIR 16-1-540/TM 1-1500-343-23/TO 1-1-689, dated 1 Sep 2000.

DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.

DESTRUCTION NOTICE - For unclassified, limited documents, destroy by any method that will prevent disclosure of contents or reconstruction of the document.

PUBLISHED BY DIRECTION OF COMMANDER, NAVAL AIR SYSTEMS COMMAND

0801LP1043459

NATEC ELECTRONIC MANUAL

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LIST OF EFFECTIVE PAGES

Dates of issue for original and changed pages are:

Original ........................ 0 ......................... 01 Mar 2005 Change ....................... x ........................ xx XXX 199X

Insert latest changed pages; dispose of superseded pages in accordance with applicable regulations.

NOTE: On a changed page, the portion of the text affected by the latest change is indicated be a vertical line, or other change symbol in the outer margin of the page. Change in illustrations are indicated by miniature pointing hands. Changes to wiring diagrams are indicated by shaded areas.

Total number of pages in this manual is 52, consisting of the following:

Page *Change Page *Change Page *Change No. No. No. No. No. No.

Change ....................... 0 ......................... 15 Sep 1993 Change ....................... x ........................ xx XXX 199X

A Change X

*Zero in this column indicates an original page.

Title A i-ii

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TPDR-2 Blank 1-1 - 1-3 1-4 Blank 2-1 - 2-4 3-1 - 3-25 3-26 Blank Glossary-1 - Glossary-8 Index-1 - Index-3 Index-4 Blank

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LIST OF ILLUSTRATIONS ......................................... ii LIST OF TABLES ........................................................ ii

LIST OF TECHNICAL PUBLICATIONS

DEFICIANCE REPORTS (TPDR)

INCORPORATED ............................TPDR-1

1 INTRODUCTION

1-1. Overview ......................................... 1-1 1-2. Purpose ........................................... 1-1 1-3. Scope .............................................. 1-1 1-4. Arrangement of Manual .................. 1-1 1-5. Related Publications ....................... 1-2 1-6. Usage and Coflicts .......................... 1-2 1-7 Reporting Errors and Improvement

Recommendations ........................ 1-2 1-8. Manual Change Procedures ........... 1-3 1-9. Requisitioning and Automatic

Distribution ................................... 1-3

2 PREVENTATIVE MAINTENANCE

PROGRAM

2-1. Overview ......................................... 2-1 2-2. Corrosion Prevention Philosophy ... 2-1 2-3. Preventive Maintenance ................ 2-1 2-4. Aircraft Preventive

Maintenance Program .................. 2-1 2-5. Avionics Preventive

Maintenance Program .................. 2-2

2-6. Corrosion Control Program ............. 2-2 2-7. Corrosion-Related Failure

Data Feedback ............................. 2-3 2-8. Safety .............................................. 2-4 2-9. Materials ......................................... 2-4

3 CORROSION THEORY

3-1. Overview ......................................... 3-1 3-2. Purpose ........................................... 3-1 3-3. Scope .............................................. 3-1 3-4. Definition of Corrosion .................... 3-1 3-5. Chemical Definitions ....................... 3-1 3-6. Theory of Corrosion ........................ 3-1 3-7. Development of Corrosion .............. 3-2 3-8. Factors Influencing Corrosion ......... 3-3 3-9. Types of Corrosion .......................... 3-6 3-10. Metals Affected by Corrosion ........ 3-11 3-11. Degradation of Non-Metals ........... 3-16 3-12. Effects of Environment on

Corrosion .................................... 3-18 3-13. Natural Environment ..................... 3-19 3-14. Biological Corrosion ...................... 3-21 3-15. Man-Made Environments .............. 3-23

GLOSSARY ................................................ Glossary-1 ALPHABETICAL INDEX .................................. Index-1

TABLE OF CONTENTS

Chapter Page Chapter Page

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LIST OF TABLES

Table Title Page Table Title Page

1-1. Outline of Manual - All Volumes .................. 1-1 1-2. Outline of Volume I ....................................... 1-2

3-1. Effects of Corrosion on Metals .................... 3-13 3-2. Effects of Deterioration on NonMetals ........ 3-17

Figure Title Page Figure Title Page

LIST OF ILLUSTRATIONS

2-1. Corrosion Prevention Program ..................... 2-1 2-2. Basic Maintenance Functions ....................... 2-3

3-1. Simplified Corrosion Cell ............................... 3-2 3-2. Elimination of Corrosion by Application of an Organic Film to a Metal Surface ....... 3-2 3-3. Effect of Sea Water on

Galvanic Corrosion .................................... 3-2 3-4. Galvanic Series of Metals and

Alloys in Sea Water ................................... 3-4 3-5. Galvanic Corrosion in a Flashlight Battery ... 3-5 3-6. Effect of Area Relationship in

Dissimilar Metal Contacts .......................... 3-5 3-7. Surface Corrosion on Frequency Test Set ... 3-6 3-8. Galvanic Corrosion of Magnesium

Adjacent to a Steel Fastener ..................... 3-6 3-9. Variations in the Cross-Sectional

Shape of Corrosion Pits ............................ 3-6 3-10. Pitting of an Aluminum Wing Assembly ........ 3-7 3-11. Cross-Section of 7075-T6 Aluminum Alloy ... 3-7 3-12. Scanning Electron Micrograph of a

Corroding Aluminum Surface .................... 3-7

3-13. Intergranular Corrosion of 7075-T6 Aluminum Adjacent to Steel Fastener ........................................... 3-8

3-14. Extreme Example of Exfoliation at Edge of Sheet ............................................ 3-8

3-15. Exfoliation Adjacent to Fasteners ................. 3-8 3-16. Crevice Corrosion Mechanisms .................... 3-9 3-17. Filiform Corrosion Found Under Paint

Coating on a Magnesium Panel ................ 3-9 3-18. Schematic of the Development of Filiform

Corrosion on an Aluminum Alloy ............... 3-9 3-19. Cracking (Typical of Stress Corrosion or

Corrosion Fatigue) ................................... 3-10 3-20. Fretting Corrosion ....................................... 3-11 3-21. Hot Corrosion on Fasteners ........................ 3-12 3-22. Hot Corrosion on Engine Components ....... 3-12 3-23. Aluminum Surface Corrosion Products ....... 3-13 3-24. Magnesium Corrosion Products .................. 3-13 3-25. Steel Corrosion Products ............................ 3-14 3-26. Color Changes in Titanium Due to

Heating .................................................... 3-14 3-27. Cadmium Plated Surface Conditions .......... 3-15 3-28. Failed Chromium Plate ............................... 3-15 3-29. Corroded Circuit Card ................................. 3-16 3-30. Biological Growth on Helicopter Wall .......... 3-21

3-3. Effects of Moisture and Fungi on Various Materials .................................................. 3-22

3-4. Effects of Airframe Flluid Intrusion .............. 3-24

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NONE

Report Control Number (RCN) Location alskjalkj 0000/00000 Pg x-xx

0000/00000 Pg x-xx alskjalkj 0000/00000 Pg x-xx alskjalkj 0000/00000 Pg x-xx alskjalkj 0000/00000 Pg x-xx alskjalkj 0000/00000 Pg x-xx alskjalkj 0000/00000 Pg x-xx alskjalkj 0000/00000 Pg x-xx alskjalkj 0000/00000 Pg x-xx

Report Control Number (RCN) Location

AIMD NAS PENSACOLA, FL

52814-2000-0022 Pg 9-2 alskjalkj 0000/00000 Pg x-xx alskjalkj 0000/00000 Pg x-xx alskjalkj 0000/00000 Pg x-xx alskjalkj 0000/00000 Pg x-xx alskjalkj 0000/00000 Pg x-xx alskjalkj 0000/00000 Pg x-xx alskjalkj 0000/00000 Pg x-xx

LIST OF TECHNICAL PUBLICATIONS DEFICIENCY REPORTS INCORPORATED

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CHAPTER 1

INTRODUCTION

1-1. OVERVIEW. Prevention and repair of corrosion damage to aircraft and avionic systems continues to be an ever increasing cost and safety burden for military aircraft. Equipment is routinely exposed to changes in temperature and pressure, varying humidity levels, dust, dirt, ultraviolet light, aircraft fluids, and environments that promote corrosion. Increasing environmental and safety restrictions, which limit traditional corrosion control materials, are also a significant factor in the safe and economic operation of aircraft and avionics.

1-1.1. The Cleaning and Corrosion Control manual was established jointly by the Navy, Air Force, and Army as a combined effort to consolidate and coordinate corrosion control best practices for aircraft and avionics.

1-1.2. This volumized set of corrosion manuals combines and replaces the former Aircraft Weapons Systems Cleaning and Corrosion Control (NAVAIR 01- 1A-509/TM 1-1500-344-23) and Avionics Cleaning and Corrosion Prevention/Control (NAVAIR 16-1-540/TO 1-1-689/TM 1-1500-343-23) manuals.

1-2. PURPOSE. The purpose of this manual is to provide information on materials and procedures to prevent, control, and repair corrosion damage to aircraft and avionics on land or at sea.

1-3. SCOPE. The material in this manual contains basic corrosion prevention and corrective maintenance information to be used at Organizational, Intermediate, and Depot levels.

1-4. ARRANGEMENT OF MANUAL.

1-4.1. OVERVIEW OF ALL VOLUMES. The NAVAIR 01-1A-509/TM 1-1500-343-23/TO 1-1-689 series of manuals is arranged as shown in Table 1-1.

1-4.1.1. A complete set of manuals to perform aircraft cleaning and corrosion control functions consists of Volumes I, II, and IV (replaces NAVAIR 01-1A-509/

TM 1-1500-344-23).

1-4.1.2. A complete set of manuals to perform avionics and electronics cleaning and corrosion control functions consists of Volumes I, III, and IV (Navy and Army) or Volumes I, II I , and V (Air Force) (replaces

NAVAIR 16-1-540/TM 1-1500-343-23/TO 1-1-689).

This volume was prepared under the technical cognizance of the Materials Engineering Division, NAVAIR North Island, San Diego, California.

Table 1-1. Outline of Manual - All Volumes

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.tiezingocer

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1-4.2. ARRANGEMENT OF VOLUME I. Volume I consists of three chapters and a glossary, arranged as shown in Table 1-2.

1-5. RELATED PUBLICATIONS. A listing of related publications is provided in Chapter 1 of each volume of this manual, as applicable.

1-6. USAGE AND CONFLICTS.

1-6.1. Supervisory and maintenance personnel shall use this manual as a guide for all corrosion control and maintenance efforts. Contractors who maintain and repair corrosion for military aircraft and avionics shall also comply with the requirements of this manual.

1-6.2. This manual shall be used in conjunction with and in support of the appropriate Army Technical Manuals (TMs), Technical Bulletins (TBs), Department of the Army Pamphlets (DA PAMs), Navy Maintenance Instruction Manuals (MIMs), Navy Structural Repair Manuals (SRMs), Maintenance Requirement Cards (MRCs), or Air Force Technical Orders (TOs).

1-6.2.1. In the case of a conflict between this manual and other Navy manuals, this manual shall take precedence; however, maintenance activities shall contact the appropriate Cognizant Field Activity (CFA)/ Fleet Support Team (FST) for immediate resolution of the conflict.

1-6.2.2. The Army and Air Force specific systems/ components manuals shall take precedence over this manual.

1-6.3. WORDING. The following definitions are adhered to in preparing this manual.

1-6.3.1. Shall is used when a procedure is mandatory.

1-6.3.2. Should is used when a procedure is recommended but not mandatory.

1-6.3.3. Will indicates future action but does not indicate a mandatory procedure.

1-6.3.4. May is used only when a procedure is optional.

1-6.4. SYMBOLS (WARNINGS, CAUTIONS and NOTES). The following definitions apply to WARNINGS, CAUTIONS and NOTES found throughout the manual.

1-6.4.1. WARNING. An operation or maintenance procedure, practice, condition, or statement, which if not strictly observed, could result in injury to or death of personnel, or long term health hazards to personnel.

1-6.4.2. CAUTION. An operating or maintenance procedure, practice, condition, or statement, which if not strictly observed, could result in damage/destruction of equipment or loss of mission effectiveness.

1-6.4.3. NOTE. An operating procedure, practice, or condition which is essential to emphasize.

1-6.5. SERVICE DESIGNATIONS. Since this is a tri-service manual, not all sections apply to all services.

Information within the text that does not apply to all three services is designated after the paragraph number as follows: (N) NAVY ONLY, (A) ARMY ONLY, or (AF) AIR FORCE ONLY. Large sections that are service specific are included as appendices in the appropriate volume.

1-7. REPORTING ERRORS AND IMPROVEMENT

RECOMMENDATIONS.

1-7.1. GENERAL. All activities using this manual are invited to submit recommended changes, additions, or deletions.

Table 1-2. Outline of Volume I

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1-7.2. SPECIFIC REPORTING REQUIREMENTS.

Recommended changes, additions, or deletions shall be reported as follows:

1-7.2.1. Navy personnel should submit recommended changes to the appropriate technical services facility using the reporting system outlined in OPNAVINST 4790.2.

1-7.2.2. Air Force personnel should refer to TO 00-5-1 to report changes.

1-7.2.3. Army personnel should submit completed DA 2028/2028-2 forms to Commander, U.S. Army Aviation and Missile Command, ATTN: AMSAM-MMC-MA-NP, Redstone Arsenal, AL 35898-5220. Changes may also be submitted electronically via the Army website, https://amcom2028.redstone.army.mil, or via email to:

2028@redstpme/army.mil.

1-8. MANUAL CHANGE PROCEDURES.

1-8.1. RESPONSIBILITY. This manual is a tri-service document, coordinated by the Materials Engineering Division, Naval Air Depot North Island, Code 4.9.7, San Diego, CA. The following activities are responsible for maintaining this document: the Naval Air Systems Command, the Air Force Corrosion Program Office, and the U.S. Army Aviation and Missile Command. As necessary, representatives from these activities shall meet to review proposed engineering and logistical changes to this manual. Changes are approved by all services, except for service-specific information.

1-8.2. PROCEDURES. The Navy is the lead service for publication of this manual; therefore, the following Navy publication change procedures apply:

1-8.2.1. Revisions. Volumes will be updated periodically by the issuance of a revision, which is a complete replacement of all pages with all change information incorporated.

1-8.2.2. Routine Changes. Between revisions, routine changes may be issued in the form of corrected pages to a portion of the existing manual. They consist of replacement change pages for that section of the manual affected by the change.

1-8.2.3. Rapid Action Changes. Changes may be issued as a formal Rapid Action Change (RAC) or an Interim Rapid Action Change (IRAC). IRACs are issued as naval messages to expedite the release of urgent and essential operational and maintenance change information. Army and Air Force program managers are responsible for retransmittal of IRACs to the appropriate service addressees.

1-9. REQUISITIONING AND AUTOMATIC

DISTRIBUTION.

1-9.1. Procedures to be used by Naval activities and other Department of Defense activities requiring NAVAIR technical manuals are defined in NAVAIR 00-25-100.

1-9.2. To automatically receive future changes and revisions to NAVAIR technical manuals, an activity must be established on the Automatic Distribution Requirements List (ADRL) maintained by the Naval Air Technical Data and Engineering Service Command (NATEC). To become established on the ADRL, notify your activity central technical publications librarian. If your activity does not have a library, you may establish your automatic distribution requirements by contacting the Commanding Officer, NATEC, Naval Air Station North Island, P.O. Box 357031, Bldg. 90 Distribution, San Diego, CA 92135-7031. Annual reconfirmation of these requirements is necessary to remain on automatic distribution. Use your NATEC assigned account number whenever referring to automatic distr ibution requirements.

1-9.3. If additional or replacement copies of this manual are required with no attendant changes in the ADRL, they may be ordered by submitting requisitions to the Commanding Officer, Naval Supply Systems Command, Naval Logistics Library, 5801 Tabor Avenue, Philadelphia, PA 19120-5099.

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CHAPTER 2

PREVENTIVE MAINTENANCE PROGRAM

2-1. OVERVIEW. Investigations during the past ten years have identified corrosion as a major factor in electronics failure in the field. As much as 30% to 40% of military avionic failures are due to the corrosion process. This is despite steady improvements in reliability of avionic systems fielded to date and outlines the need for an effective preventive maintenance program.

2-2. CORROSION PREVENTION PHILOSOPHY.

Corrosion and environmental conditions are natural phenomena that adversely affect equipment in field service. Although never totally eliminated, the problems these factors cause can be minimized so that they are less severe and better controlled. This can be achieved by understanding equipment failure mechanisms and development/utilization of corrosion control technology.

2-2.1. As a general rule, maintenance personnel should assume corrosion is ongoing, regardless of visible physical evidence. The aim of corrosion prevention is to enable systems to perform satisfactorily for a specified time period. In other words, maintenance efforts should allow equipment to approach its maximum lifetime.

2-2.2. The general workflow diagram, in Figure 2-1, defines procedures followed to implement a corrosion preventive maintenance program. This process is designed to indicate the sequence of events needed to implement and maintain an effective corrosion prevention and control program.

2-3. PREVENTIVE MAINTENANCE. The two most important factors in preventing corrosion, and the only ones which can be controlled by field personnel, are the removal of the electrolyte and the application of protective coatings. Since the extent of corrosion depends on the length of time electrolytes are in contact with metals, aircraft corrosion can be minimized by frequent washing.

If noncorrosive cleaners are used, the more frequently a surface is cleaned in a corrosive environment the less the possibility of corrosive attack. In addition, by maintaining chemical treatments and paint finishes in good condition, corrosion can be minimized. The degradation of non-metallic materials can be minimized by avoiding the use of unauthorized maintenance chemicals and procedures. In addition, when repair or replacement of non-metallic materials is required, only approved materials shall be used. Dedication to proper preventive maintenance practices maximizes equipment reliability.

2-4. AIRCRAFT PREVENTIVE MAINTENANCE

PROGRAM.

2-4.1. The prevention and control of corrosion on aircraft and related equipment is a command responsibility.

Each command must place special emphasis on the importance of the corrosion control program and lend its full support to ensure that corrosion prevention and control receives sufficient priority to be accomplished along with other required maintenance.

Figure 2-1. Corrosion Prevention Program General Workflow Diagram

Train Personnel to Detect, Identify, Clean, Preserve, Treat

& Prevent Corrosion

(Re)Emphasize the Concept of All Hands Responsibility for Corrosion Control

Conduct Required Maintenance Corrosion Inspections

Report Any Material/Design Deficiencies

Treat Corrosion Promptly After Detection Using the Approved

Materials, Equipment & Techniques

Clean, Preserve, & Lubricate Equipment at Prescribed Intervals

Maintain Accurate Maintenance Records

Corrosion Damage Present

NO

YES

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2-4.2. Aluminum and magnesium alloys found in aviation equipment will normally begin to corrode if salt deposits, other corrosive soils, or electrolytes are allowed to remain. In order to prevent corrosion, a constant cycle of cleaning, inspection, operational preservation, and lubrication must be followed. Prompt detection and removal of corrosion will limit the extent of damage to aircraft components. An effective preventive maintenance program requires cleaning, lubrication and preservation, as well as corrosion removal, paint removal, surface treatment, sealing, and painting. A disciplined preventive maintenance program includes:

a. Regularly scheduled aircraft washing as specified by parent service organization directives;

b. Using clean water with low chloride content for aircraft washing and rinsing (chloride content should be less than 400 parts per million, approximately the same limit as that for potable water);

c. Regularly scheduled cleaning or wipe down of all exposed unpainted surfaces, such as landing gear struts and actuating rods of hydraulic cylinders as specified by parent service organization directives, with a compatible fluid or lubricant;

d. Keeping low-point drains open;

e. Inspection, removal, and reapplication of corrosion preventative compounds (CPCs) on a scheduled basis;

f. Earliest detection and repair of damaged protective coatings; and

g. Using padded panel racks to store panels/parts for aircraft and equipment during maintenance and using protective measures to prevent abrasions/ scratches resulting from placement of parts, tools, or tool boxes on wings, fuselage or other aircraft surfaces.

2-5. AVIONICS PREVENTIVE MAINTENANCE

PROGRAM.

2-5.1. PROGRAM REQUIREMENTS. Successful avionic cleaning and corrosion prevention/control efforts depend on a coordinated, comprehensive preventive maintenance program. Everyone involved in maintenance, repair, and operation of avionic systems must be concerned with corrosion, cleaning, inspection, prevention, and treatment. Specifically, avionic corrosion prevention/control is everyone’s responsibility. Each command must place special emphasis on the corrosion control program and lend their full support. This ensures the program receives sufficient priority to be accomplished along with other required maintenance.

The goal of a preventive maintenance program is to halt corrosion before significant decline in equipment performance occurs. As such, it is important to recognize the difference between prevention of corrosion and repair of damage caused by corrosion. A preventive maintenance program at the Organizational/Unit and Intermediate Maintenance Activities should:

a. Reduce the maintenance time spent repairing corrosion damage.

b. Improve avionic system reliability, durability, and service life.

c. Make the military avionics community aware of the extent of the problem.

d. Report any deficiencies with materials and processes associated with corrosion control.

2-5.2. APPLICABLE GUIDELINES. All activities responsible for the maintenance of military aircraft and avionic systems shall establish a corrosion prevention/ control program. The type of program depends on the conditions or environments to which the aircraft/avionic systems are exposed. Those aircraft and avionic systems exposed to salt-air and tropical environments require the most stringent corrosion prevention and control programs.

2-5.3. MAINTENANCE FUNCTIONS. Experience has shown that all activities have a corrosion problem. This is regardless of whether the equipment is an installed avionic system, ground support equipment, or missile system. Accordingly, corrosion control efforts by all hands is mandatory. This must be a day-to-day requirement to prevent corrosion before it starts.

Figure 2-2 depicts the basic maintenance functions.

2-6. CORROSION CONTROL PROGRAM. All activities responsible for aircraft maintenance shall establish corrosion control programs as required by the parent service organization. This program shall be structured as required by OPNAVINST 4790.2 (Navy), TO 00-20-1 (Air Force), or AR 750-59 (Army) and ensure that personnel receive hazardous material/waste handlers training. The type of program depends upon the environment to which the aircraft may be exposed.

At sea, where conditions are normally the most severe, aircraft are exposed to salt spray, ship stack gases, and

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01 March 2005 aircraft engine exhausts. Land-based aircraft may be exposed to industrial gases, salts, rain, mud, and, near salt water, mists containing sea salts. A comprehensive corrosion control program shall consist of either a Corrosion Control Work Center or a Corrosion Control Team with personnel trained in the prevention, early detection, reporting, and repair of corrosion damage.

Such a program requires a dedicated effort by all maintenance personnel to prevent corrosion before it starts. These efforts will improve the operational readiness of equipment and minimize costly repairs.

2-6.1. TRAINING. Personnel performing maintenance on aircraft shall be trained in basic corrosion control skills as established by the parent service organization.

Personnel shall be fully aware of the reasons for the corrosion control program. Without such training and understanding, further damage or additional problems may result.

2-6.2. TRAINING AND QUALIFICATION REQUIRE-

MENTS. Personnel responsible for corrosion control maintenance and treatment shall receive the following training.

a. Supervisors and corrosion control personnel shall attend basic corrosion control courses established by the parent service organization.

b. Cleaning and repair personnel shall be trained in inspection, identification, cleaning, treatment, preservation, lubrication, hazardous material handling/ hazardous waste disposal, and proper documentation reporting.

c. Supervisors shall ensure maximum use of in-service and on-the-job-training.

2-6.3. MAINTENANCE. An effective corrosion control program shall include thorough cleaning, inspection, preservation, and lubrication, at specified intervals, in accordance with Volumes II and III of this manual.

Check for corrosion damage and integrity of protective finishes during all scheduled and unscheduled maintenance. Early detection and repair of corrosion will limit further damage. When corrosion is discovered, treat corrosion as prescribed in Volumes II and III as soon as possible and use only approved materials, equipment, and techniques. Only affected areas shall be repaired. All maintenance personnel shall report corrosion promptly, in accordance with directives established by the parent service organization.

2-7. CORROSION-RELATED FAILURE DATA

FEEDBACK.

2-7.1. Since corrosion prevention and control for aircraft and avionics is a continuing concern, it is vitally important that corrosion problems are properly reported. Problems can be corrected and improvements made to prevent reoccurrence in future equipment design. Identification of the specific causes and extent of corrosion problems is essential. Improved equipment performance and maintenance assistance (personnel, equipment, materials, and procedures) are dependent on this data.

Establish Maintenance Requirements for Corrosion Control

Establish Requirements to Inspect for Corrosion Damage

Aquire Corrosion Control Equipment & Consumable Supplies

Establish Requirements for Reporting Corrosion Damage

Develop & Maintain Maintenance Instructions Outlining

Corrosion Control Program

Develop Program to Satisfy Specific Inspection, Cleaning, Treatment, Preservation & Lubrication Requirements

Develop Cleaning & Corrosion Training Program

Ensure Proper Training of Personnel in Corrosion Identification & Control

Conduct Required Corrosion Inspections

Ensure Cleaning, Treatment, Preservation, & Lubrication are Completed

Figure 2-2. Basic Maintenance Functions

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2-7.2. MAINTENANCE AND READINESS DATA

COLLECTION. All activities using this manual are required to use the current maintenance data collection system(s) of the parent service organization. This will enable a record of corrosion-related failures to be submitted to the appropriate technical services facility for analysis. Reporting personnel shall identify/report corrosion discrepancies in accordance with OPNAVINST

4709.2 (Navy), TO 00-20-2 (Air Force), or DA PAM 738-750/DA PAM 738-751 (Army).

2-8. SAFETY. Safety is everyone’s business and concern.

2-8.1. RESPONSIBILITY OF SUPERVISORS.

2-8.1.1. Work center supervisors shall receive the following training in accordance with parent service directives:

a. The recognition and elimination of hazards;

b. Occupational safety and health;

c. The safety of the individual;

d. Accident investigation and reporting; and

e. The inspection and maintenance of personal protective equipment (PPE).

2-8.1.2. Supervisors shall ensure that all corrosion control personnel are informed of:

a. Current safety procedures;

b. Characteristics of materials to which they will be exposed; and

c. Required protective clothing to ensure safety of personnel.

2-8.1.3 In addition, supervisors shall ensure that an adequate supply of safety equipment is in a ready-for-issue condition, and that the personnel under their control are given, and use, appropriate protective equipment to prevent accidents, injuries, and occupational illness.

2-8.2. RESPONSIBILITY OF PERSONNEL. Mainte-nance personnel shall use appropriate equipment while exposed to hazardous conditions, and shall report to the supervisor any protective equipment that is bro-ken, damaged, defective, or inadequate. No one shall use protective equipment that is not in a satisfactory and serviceable condition. Personnel shall comply with occupational safety and health requirements, including medical examinations, respirator training and fit testing, and use of protection for eyes, ears, head, skin, and feet.

2-8.3. MATERIALS HANDLING. Many of the materials and procedures outlined in this manual are potentially hazardous to personnel and potentially damaging to aircraft, especially with improper use. When using any chemicals, such as paint removers, detergents, conversion coatings, and solvents, follow the correct procedures with appropriate protective gear to prevent personnel injury and aircraft damage. Read the appropriate warnings and cautions in this manual prior to use of any hazardous materials. Misuse of certain materials can damage parts or cause corrosion which may lead to catastrophic failure. Refer to DoD 6050.5- LR, Hazardous Materials Information System, or the appropriate parent service organization documents for the handling, storage, and disposal of hazardous materials. Refer to local directives and policies pertaining to hazardous waste management. When in doubt, contact the local safety office, industrial hygienist, bioenvironmental engineer, or regional medical center.

2-9. MATERIALS.

2-9.1. Consumable materials and equipment listed in Volumes IV and V shall be used for corrosion control.

These materials and equipment have been approved only after extensive testing to prove their ability to perform properly and effectively without damaging any of the metallic or nonmetallic materials used in aircraft.

2-9.2. Only those materials listed in this manual shall be used for cleaning or corrosion control of aircraft components. When several methods or materials are listed, the preferred one is listed first, with alternates following. Materials listed in other manuals shall be used only when required procedures are not covered by this manual. When approved materials are not available, substitutions shall only be made by the appropriate Aircraft Controlling Custodians (ACC) or System Program Manager (SPM).

2-9.3. Materials or processes considered to be an improvement over existing ones, after local laboratory analysis and evaluation, shall be forwarded to the Aircraft Controlling Custodians (ACC) or System Program Manager (SPM) for submission to the parent service organization for further evaluation.

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CHAPTER 3

CORROSION THEORY

3-1. OVERVIEW.

3-1.1. Maintenance of military aircraft and avionic equipment requires knowledge of why metals corrode and materials degrade. The theory lies in the definition and description of mechanisms that cause equipment to fail in field service. Corrosion is the chemical or electrochemical deterioration of a material. This deterioration is complex in nature because of the various types of corrosion, the frequent simultaneous presence of several types of corrosion, and the design characteristics and maintenance/environmental factors that make aircraft and avionic systems susceptible to corrosion.

3-1.2. Corrosion can cause complete failure of equipment or undesirable changes in electrical characteristics. It is a process that is active on a 24 hour basis. Equipment does not necessarily have to be installed, operated, or resident in a particularly harsh environment. Some form of corrosion will take place even in near ideal environments. All personnel should recognize that corrosion is the natural continuing process of materials returning to their normal state. Inadequate corrosion prevention and control will ultimately affect equipment life cycles, downtime, and overall system reliability.

3-2. PURPOSE. The purpose of this chapter is to provide maintenance personnel with the background knowledge necessary to understand the causes of corrosion.

3-3. SCOPE. This chapter is an introduction to corrosion theory: the causes of corrosion and the factors which influence its development. The theory of corrosion and the factors influencing corrosion of aircraft metals are described. The types of corrosion and how to recognize them are discussed.

3-4. DEFINITION OF CORROSION. Corrosion is the electrochemical deterioration of a material or its properties due to its chemical reaction with the surrounding environment. This reaction occurs because of the tendency of metals to return to their naturally occurring state, usually oxide or sulfide ores. For example, iron in the presence of moisture and air will return to its natural state, iron oxide or rust. Aluminum and magnesium form corrosion products that are white oxides or hydroxides. When a water solution containing soluble salts is present, corrosion of many alloys can occur easily at ambient temperatures. This type of corrosion can be effectively treated by maintenance personnel as discussed in this manual. Corrosion can also occur in the absence of water but only at high temperatures, such as those found in gas turbine engines. However, the most common type of corrosion (and the one that can be most effectively treated by maintenance personnel) is electrochemical corrosion.

3-5. CHEMICAL DEFINITIONS.

3-5.1. ATOM. The smallest unit of an element, made up of a positively charged nucleus surrounded by a system of negatively charged electrons. There are over 100 elements, including metals (such as aluminum, magnesium, gold, platinum, iron, nickel, titanium, cadmium, chromium, copper, silver, lead, beryllium, zinc), and non-metals (such as carbon, boron, sulfur, chlorine, hydrogen, oxygen, nitrogen, and helium).

3-5.2. ELECTRON. A negatively charged subatomic particle. An electric current occurs when electrons are forced to move through metal conductors. Electrons flow through liquid solutions only in the presence of ions.

3-5.3. ION. An atom or group of atoms or molecules which has acquired a net electric charge by gaining (negative ion) or losing (positive ion) electrons. When ions are forced to move through liquid solutions, an electric current can occur. Ions cannot move through metal conductors.

3-5.4. ELECTROLYTE. A liquid (usually water) solution containing ions. Sea water is an electrolyte: an aqueous (water-based) solution whose major components are sodium and chloride ions. Electrochemistry is the branch of science concerned with chemical reactions at surfaces in contact with electrolytes.

3-6. THEORY OF CORROSION. All metals will corrode to some extent in a natural environment. When a metal corrodes, the atoms lose electrons and become positively charged. In solution, the positively charged metal ions can combine with negatively charged ions to form corrosion products, such as metallic chlorides, oxides, hydroxides, and sulfides.

3-6.1. Four conditions (illustrated in Figure 3-1) must exist before metal corrosion can occur.

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a. A metal which has a tendency to corrode must be present (the corroding metal is called the anode);

b. A dissimilar conductive material (the cathode), which has less tendency to corrode than the anode, must be present (a dissimilar metal may be a different metal, a protected part of the same metal, or conductive plastic);

c. A conductive liquid (electrolyte) must connect the anode and cathode (so that ions can carry electric current between them); and

d. Electrical contact between the anode and cathode (usually in the form of metal-to-metal contact) must exist so that electrons can move between the anode and the cathode.

3-6.2. The elimination of any one of the four conditions will slow or stop corrosion. For example, a paint film on a metal surface will prevent the electrolyte from connecting the anode and cathode, thereby stopping the electric current (see Figure 3-2). A change in the electrolyte can also affect the rate of corrosion. Two connected dissimilar metal parts placed in distilled water corrode very slowly due to a lack of ions in solution to conduct the electric current; in sea water the corrosion reaction is accelerated by a factor of 1000 or more (see Figure 3-3).

3-7. DEVELOPMENT OF CORROSION. All corrosive attack begins on the surface of the metal. If allowed to progress, corrosion can penetrate into the metal. If

Figure 3-1. Simplified Corrosion Cell

Electron Flow

Electrolyte (Fresh or Sea Water, Acids, Gases)

Anodic Area

Metal

Cathodic Area

Figure 3-3. Effect of Sea Water on Galvanic Corrosion corrosion begins on an inside surface of a component (for example, the inner wall of a metal tube), it may go undetected until perforation occurs.

3-7.1. When corrosion products form, they often precipitate onto the corroding surface as a powdery deposit. This film of corrosion products may reduce the rate of corrosion, if the film acts like a barrier to electrolytes. Some metals (such as stainless steel and titanium), under the right conditions, produce corrosion products that are so tightly bound to the corroding metal that they form an invisible oxide film (called a passive film) which prevents further corrosion. However, when the film of corrosion products is loose and porous (such as those of aluminum and magnesium), an electrolyte can easily penetrate and continue the corrosion process, producing more extensive damage than surface appearance would indicate.

Figure 3-2. Elimination of Corrosion by Application of an Organic Film to a Metal Surface

Anodic Area

Metal

Cathodic Area

Unbroken Paint Film

No Contact Between

Electrolyte & Anode & Cathode

Electrolyte (Continuous Liquid Path)

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3-7.2. Paint coatings can mask the initial stages of corrosion. Since corrosion products occupy more volume than the original metal, the paint surfaces may become blistered, flaked, chipped, or appear lumpy.

3-8. FACTORS INFLUENCING CORROSION. Factors which influence metal corrosion and the rate of corrosion are outlined below.

3-8.1. TYPE OF MATERIAL. The best time to prevent corrosion is at the design stage. Proper material selection is critical for the protection of equipment against harmful environmental effects. Most pure metals are not suitable for aircraft construction and are used only in combination with other metals, and sometimes non-metals, to form alloys. The metals most commonly used in aircraft construction are aluminum, steel, titanium, and magnesium. Cadmium, nickel, chromium, and silver are sometimes used as protective platings. Metals have a wide range of corrosion resistance. The most active metals (those which tend to lose electrons easily), such as magnesium and aluminum, corrode easily and are listed at the top of Figure 3-4. The most noble metals (those which do not lose electrons easily), such as gold and silver, do not corrode easily and are listed at the bottom of Figure 3-4.

3-8.2. HEAT TREATMENT AND GRAIN DIRECTION.

Most alloys are made up entirely of small crystalline regions called grains. When heat treated during manufacturing or repair, heavy sections of metals do not cool uniformly and, as a result, tend to vary in chemical composition from one part of the metal to another. This can cause corrosion if one area is more active than another. Alloys which are fabricated by rolling, extruding, forging, or pressing have properties which depend highly on direction (parallel to grain elongation vs. cross grain). Corrosion can occur on surfaces of those regions which are less resistant and also at grain boundaries, resulting in the formation of pits and intergranular corrosion. For example, exposed end grains corrode much more easily than flattened elongated surfaces in sheet stock. This explains why exfoliation occurs at the edge of aircraft skin sections or next to countersunk fasteners.

3-8.3. DISSIMILAR METALS. When two dissimilar metals make electrical contact in the presence of an electrolyte, the rate at which corrosion occurs depends on the difference in their activities, that is, their positions in Figure 3-4. The greater the difference in activity, the faster corrosion occurs. For example, magnesium would corrode very quickly when coupled with gold in a humid atmosphere. But aluminum would corrode very slowly, if at all, in contact with cadmium. A flashlight battery is an example of galvanic corrosion put to practical use. In Figure 3-5, the zinc battery casing steadily corrodes, supplying a steady flow of electrons, but only when the switch is closed. When the switch is open, there is no corrosion because electrons are not able to leave the zinc anode.

3-8.4. ANODE AND CATHODE SURFACE AREA.

The rate of corrosion also depends on the size of the parts in contact. If the surface area of the corroding metal (the anode) is smaller than the surface area of the less active metal (the cathode), corrosion will be rapid and severe. But, when the corroding metal is larger than the less active metal, corrosion will be slow and superficial. For example, an aluminum fastener in contact with a relatively inert monel structure may corrode severely, while a monel bracket secured to a large aluminum member would result in a relatively superficial attack on the aluminum sheet (see Figure 3-6).

3-8.5. PRESENCE OF ELECTROLYTES. Electrically conducting solutions are easily formed on metallic surfaces when condensation, salt spray, rain, or rinse water accumulate. Dirt, salt, acidic stack gases, and engine exhaust gases can dissolve on wet surfaces, increasing the electrical conductivity of the electrolyte, thereby increasing the rate of corrosion.

3-8.6. ELECTROLYTE CONCENTRATION. In the same way that metals can corrode when exposed to different concentrations of oxygen in an electrolyte, corrosion will also occur if the concentration of the electrolyte on the surface varies from one location to another. This corrosive situation is known as a concentration cell.

3-8.7. AVAILABILITY OF OXYGEN. When some of the electrolyte on a metal surface is partially confined (such as between faying surfaces or in a deep crevice), metal in this confined area corrodes more rapidly than other metal surfaces of the same part outside this area. This type of corrosion is called an oxygen concentration cell or differential aeration cell. Corrosion occurs more rapidly than would be expected because the reduced oxygen content of the confined electrolyte causes the adjacent metal to become anodic to the metal surfaces exposed to the air.

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ANODIC - High Corrosion Potential

CATHODIC - Low Corrosion Potential

Lithium Magnesium Alloys

Zinc (plate) Beryllium

Cadmium (plate) Uranium (depleted)

Aluminum Alloys Indium

Tin (plate) Stainless Steel 430 (active)

Lead 1010 Steel

Cast Iron Stainless Steel 410 (active)

Copper (plate) Nickel (plate)

AM 350 (active) Chromium (plate)

Stainless Steels 350, 310, 301, 304 (active) Stainless Steels 430, 410 (passive)

Stainless Steel 13-8, 17-7PH (active) Brass, yellow, Naval

Stainless Steel 316L (active) Bronze 220

Copper 110 Stainless Steel 347 (active)

Copper-Nickel 715 Stainless Steel 202 (active)

Monel 400 Stainless Steel 201 (active)

Stainless Steels 321, 316 (active) Stainless Steels 309, 13-8, 17-7 PH (passive)

Stainless Steels 304, 301, 321 (passive) Stainless Steels 201, 316L (passive)

Stainless Steel 286 (active) AM355 (active)

Stainless Steel 202 (passive) Carpenter 20 (passive)

AM355 (passive) Titanium Alloys

AM350 (passive) Silver

Palladium Gold

Rhodium Platinum

Carbon/Graphite

Figure 3-4 . Galvanic Series of Metals and Alloys in Sea Water

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3-8.8. TEMPERATURE. Higher temperature environments tend to produce more rapid corrosion due to accelerated chemical reactions and, in humid environments, higher concentration of water vapor in the air. In addition, nightly drops in temperature can cause greater amounts of condensation, leading to increased corrosion rates.

3-8.9. BIOLOGICAL ORGANISMS. Bacterias, molds, fungi, and other living organisms (some microscopic) can grow on damp surfaces. Once they are well established, the area tends to remain damp, increasing the possibility of corrosion. Their presence can cause the areas they occupy to have different oxygen and electrolyte concentrations. In addition, acidic wastes are secreted, which cause corrosion.

3-8.10. MECHANICAL STRESS. Many alloys used in aircraft construction are sensitive to a form of corrosion known as stress corrosion cracking. Manufacturing processes such as machining, forming, welding, or heat treatment can leave residual mechanical stresses in aircraft parts. The addition of in-service stresses to residual stresses can cause corrosion to proceed more rapidly than would be expected in normal service.

3-8.11. LENGTH OF EXPOSURE. As time passes, metals naturally tend to corrode. In some cases, the corrosion process occurs at the same rate, no matter how long the metal has been exposed to the environment.

In other cases, corrosion can decrease with time, due to the barrier formed by corrosion products, or increase with time if a barrier to corrosion is being broken down.

Relatively Little Corrosive Attack

Heavy Corrosive Attack

Aluminum Sheet (Large Anode)

Monel Sheet (Large Cathode)

Aluminum Rivet (Small Anode)

Monel Rivet (Small Cathode)

Figure 3-6. Effect of Area Relationship in Dissimilar Metal Contacts

Figure 3-5. Galvanic Corrosion in a Flashlight Battery e e e e e e e e

Electrolyte

Electrolyte

Zinc Anode

Carbon Cathode

Direction of Current Flow

Metal Ions Go Into Solution From the Anode

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3-9. TYPES OF CORROSION. Corrosion is catalogued and typed in many ways. Occasionally, different names are used for the same type of corrosion.

The common types of corrosion are described below.

3-9.1. UNIFORM SURFACE CORROSION. Uniform surface corrosion is probably the most common type of corrosion. It results from a direct chemical attack on a metal surface that proceeds uniformly over the entire exposed surface (see Figure 3-7). The metal gradually becomes thinner and eventually fails. On a polished surface, this type of corrosion is first seen as a general dulling or etching of the surface and, if the attack is allowed to continue, the surface becomes rough and possibly frosted in appearance. An example is the etching of metals by acids. The discoloration or general dulling of metal created by exposure to elevated temperatures is not considered to be uniform surface corrosion. Coating/sealing the exposed surface will protect it from this type of attack. Also, corrosive elements may be removed through air movement and drain holes.

3-9.2. GALVANIC CORROSION. Galvanic corrosion occurs when different metals are in contact with each other and an electrolyte, such as sea water. It is usually recognizable by the presence of a buildup of corrosion deposits at the joint between the metals. For example, aluminum skin panels and stainless steel doublers, riveted together in an aircraft wing, form a galvanic couple if moisture and contamination are present.

Fig…