TM-584C
TM-584C
TM-584C
REVISION C
CORROSION CONTROL AND TREATMENT
MANUAL
TM-584C
REVISION C
CORROSION CONTROL AND TREATMENT
MANUAL
This Revision Supersedes All
Previous Editions of This Manual
NOVEMBER 1, 1994
TABLE OF CONTENTS
Section Title Page
I. INTRODUCTION 1-1
1.1 General 1-1
1.2 Responsibility 1-1
1.3 Reference Documentation 1-1
II. CORROSION CONTROL 2-1
2.1 General 2-1
2.2 Preventive Maintenance 2-1
2.3 Surveillance 2-2
2.4 Design Considerations 2-2
2.4.1 Corrosion Control 2-2
III. TYPES OF CORROSION AND THEIR CAUSES 3-1
3.1 General 3-1
3.2 Basic Causes of Corrosion 3-1
3.2.1 Conditions Necessary for Corrosion 3-1
3.2.2 Effect of Material Selection 3-1
3.2.3 Water Intrusion 3-1
3.2.4 Environmental Factors 3-2
3.3 Types of Corrosion 3-2
3.3.1 Concentration Cell Corrosion 3-2
3.3.1.1 Metal Ion Concentration Cells 3-3
3.3.1.2 Oxygen Concentration Cells 3-3
3.3.1.3 Active-Passive Cells 3-3
3.3.2 Galvanic Corrosion 3-3
3.3.2.1 Filiform Corrosion 3-5
3.3.3 Intergranular Corrosion 3-5
3.3.3.1 Exfoliation Corrosion 3-6
3.3.4 Pitting Corrosion 3-6
3.3.5 Uniform Etch Corrosion 3-6
3.3.6 Stress Corrosion Cracking 3-7
3.3.7 Fatigue Corrosion 3-7
3.3.8 Fretting Corrosion 3-8
3.3.9 Crevice Corrosion 3-8
Section Title Page
IV. CORROSION REMOVAL AND TREATMENT 4-1
4.1 General 4-1
4.2 Aluminum and Aluminum Alloys 4-1
4.2.1 General 4-1
4.2.2 Cleaning To Remove Foreign Matter 4-1
4.2.3 Corrosion Removal 4-2
4.2.4 Surface Treatment 4-2
4.2.4.1 Application of Chemical Conversion Coating4-2
4.2.4.2 Application of Paint System 4-3
4.2.5 Contact With Dissimilar Materials 4-3
4.3 Carbon Steel and Low-Alloy Steel 4-3
4.3.1 General 4-3
4.3.2 Cleaning To Remove Foreign Matter 4-4
4.3.3 Paint Stripping (When Required) 4-4
4.3.3.1 Chemical Paint Stripping 4-4
4.3.4 Corrosion Removal 4-4
4.3.4.1 Phosphoric Acid Base (Brush-On Method) 4-4
4.3.4.2 Phosphoric Acid Base (Immersion Method) 4-5
4.3.4.3 Alkaline Corrosion Remover (Immersion Method)
4-5
4.4 Stainless-Steel Alloys 4-6
4.4.1 General 4-6
4.4.2 Cleaning To Remove Foreign Matter 4-6
4.4.3 Corrosion Removal 4-6
4.4.3.1 Mechanical Method 4-6
4.4.3.2 Chemical Method 4-6
4.4.4 Application of Protective Coating 4-8
4.5 Copper and Copper-Base Alloys 4-8
4.6 Plated Surfaces 4-8
4.6.1 General 4-8
4.6.2 Cleaning To Remove Foreign Matter 4-8
4.6.3 Paint Stripping (When Required) 4-8
4.6.4 Corrosion Removal and Treatment of Plated Surfaces
4-8
4.6.4.1 Zinc- and Aluminum-Plated Surfaces 4-8
4.6.4.2 Chromium, Nickel, Copper, and Tin Plate 4-9
V. TREATMENT OF TYPICAL AREAS 5-1
5.1 General 5-1
5.2 Communications, Electronic, and Associated
Electrical
Equipment 5-1
5.2.1 General 5-1
5.2.2 Enclosures Purges for Hazard Protection 5-1
Section Title Page
5.2.3 Enclosures Intermittently Purged for Hazard
Protection 5-2
5.2.4 Enclosures Not Purged for Hazard Protection5-3
5.2.5 Coating of Communications, Electronic, and
Associated
Equipment 5-3
5.2.5.1 Items To Be Treated 5-4
5.2.5.2 Items Not To Be Treated With Conformal Coating
5-5
5.2.6 Electrical Connectors 5-7
5.2.6.1 Potting and Molding 5-7
5.2.6.2 Lubricating Connectors 5-8
5.3 Carbon Steel Structures 5-8
5.3.1 General 5-8
5.3.2 Typical Problem Areas 5-8
5.3.2.1 Sharp Edges 5-8
5.3.2.2 Back-To-Back Structures (Faying Surfaces) 5-8
5.3.2.3 Nuts and Bolts 5-8
5.3.2.4 Tubular Structural Steel 5-8
5.3.2.5 Water Traps 5-9
5.3.2.6 Unistrut Channels 5-9
5.3.2.7 Tube Clamps 5-9
5.3.2.8 Galvanized Steel 5-10
5.4 Stainless-Steel Components 5-10
5.4.1 General 5-10
5.4.2 Stainless-Steel Tubing Assemblies 5-10
5.4.2.1 Application of Protective Coatings 5-10
5.4.3 Stainless-Steel Bellows 5-11
5.4.4 Stainless-Steel Pipe, Flange Bolts, and Nuts5-12
5.5 Aluminum Alloy Pipe and Tubing 5-12
5.5.1 General 5-12
5.5.2 Corrosion Treatment 5-12
5.6 Miscellaneous 5-12
5.6.1 Steel Cabling 5-12
5.6.2 Piano-Type Hinges 5-13
5.6.3 Adjustable Parts 5-13
5.6.4 Bare Metal Piston Surfaces 5-13
APPENDIX A GALVANIC SERIES IN SEA WATER A-1
ABBREVIATIONS AND ACRONYMS
cm centimeter
CP cathodic protection
DOD Department of Defense
gal gallon
GN2 gaseous nitrogen
HF hydrofluoric acid
HNO3 nitric acid
in inch
IVD ion vapor deposition
kg kilogram
KSC John F. Kennedy Space Center
ksi kips per square inch
MIL military
m3 cubic meter
mm millimeter
MPa megapascal
NACE National Association of Corrosion Engineers
NH4HF2 ammonium bifluoride
oz ounce
psi pounds per square inch
SCC stress corrosion cracking
SPEC specification
SSPC Steel Structures Painting Council
STD standard
TM technical manual
UTS ultimate tensile strength
m micrometer
C degree Celsius
F degree Fahrenheit
SECTION I
INTRODUCTION
1.1 GENERAL
This manual provides guidelines for the control of corrosion of
materials in facilities, systems, and equipment at the John F.
Kennedy Space Center (KSC), Florida.
1.2 RESPONSIBILITY
The design agency has a responsibility to deliver hardware and
equipment to the operator without "built-in" corrosion problems.
Cooperation and communication between design, operation, and
maintenance activities are vital to identify existing problems so
design errors are not repeated in new designs. Minor design
changes to existing equipment will often serve to eliminate a
major corrosion problem.
Each organization must develop and implement a corrosion-control
program to satisfy its particular requirements. Responsibility
for maintaining an item must be fixed and controls must be
stringent enough to ensure accomplishment. Scheduled inspection
and preventive maintenance are essential to determine system
status and to provide early correction of weaknesses. Preventive
maintenance reduces the total amount of labor used and the
expense incurred and ensures corrosion will not prevent the
particular system from performing its design function.
Corrosion control and treatment are of vital concern because
corrosion of equipment and primary structures has a great effect
on the operational and structural integrity of systems. Economy
is another basic consideration since severe corrosion will
eventually weaken structural members to the point where
replacement or reinforcement is required in order to sustain
design loads.
1.3 REFERENCE DOCUMENTATION
The following documents are referenced in this manual.
KSC-SPEC-E-0001
Application of Coating, Conformal
(Polyurethane), Printed-Circuit
Assemblies, Specification for
KSC-STD-132 Potting and
Molding Electrical Cable Assembly
Terminations
KSC-STD-C-0001 Standard for
Protective Coating of Carbon Steel,
Stainless Steel, and Aluminum on
Launch Structures, Facilities, and
Ground Support Equipment
KSC-STD-Z-0004 Structural
Steel Building and Other
Structures, the Design of, Standard
for
MIL-STD-889 Dissimilar
Metals
MIL-A-9962 Abrasive
Mats, Non-Woven, Non-Metallic
MIL-C-5541 Chemical
Conversion Coatings on Aluminum and
Aluminum Alloys
MIL-C-10578 Corrosion
Removing and Metal Conditioning
Compound
MIL-C-14460 Corrosion
Removing Compound, Sodium Hydroxide
Base; for Electrolytic or Immersion
Application
MIL-C-16173 Corrosion
Preventive Compound, Solvent
Cutback, Cold-Application
MIL-C-83488 Coating,
Aluminum, Ion Vapor Deposited
MIL-C-87936 Cleaning
Compounds, Aircraft Exterior
Surfaces, Water Dilutable
MIL-G-23549 Grease,
General Purpose
MIL-G-81322 Grease,
Aircraft, General Purpose, Wide
Temperature Range
MIL-L-46000 Lubricant,
Semi-Fluid (Automatic Weapons)
MIL-L-46010 Lubricant,
Solid Film, Heat Cured, Corrosion
Inhibiting
MIL-P-46002
Preservative Oil, Contact and
Volatile Corrosion-Inhibited
MIL-S-8802 Sealing
Compound, Temperature-Resistant,
Integral Fuel Tanks and Fuel Cell
Cavities, High Adhesion
MIL-S-29574 Sealing
Compound, Polythioether, for
Aircraft Structures, Fuel and High
Temperature Resistant, Fast Curing
at Ambient and Low Temperatures
MIL-T-23142 Tape,
Pressure-Sensitive Adhesive, for
Dissimilar Metal Separation
DOD-P-15328 Primer
(Wash) Pretreatment (Formula No.
117 for Metals) (Metric)
TT-E-751 Ethyl Acetate,
Technical
TT-R-248 Remover, Paint
and Lacquer, Solvent Type
TT-S-230 Sealing
Compound, Elastomeric Type, Single
Component (for Calking, Sealing,
and Glazing in Buildings and Other
Structures)
TT-T-266 Thinner: Dope
and Lacquer (Cellulose- Nitrate)
National Association of Corrosion Engineers (NACE)
Standard RP0178
Fabrication Details, Surface Finish
Requirements, and Proper Design
Considerations for Tanks and
Vessels To Be Lined for Immersion
Service
Standard RP0189 Standard
Recommended Practice On-Line
Monitoring of Cooling Waters
"Designing for Corrosion Control"
by R. James Landrum
(Application for copies should be addressed to the National
Association of Corrosion Engineers, P.O. Box 218340, Houston, TX
77218-8340.)
Steel Structures Painting Council (SSPC)
SSPC SP-1 Solvent
Cleaning
SSPC SP-2 Hand Tool
Cleaning
SSPC SP-3 Power Tool
Cleaning
SSPC SP-10 Near-White
Blast Cleaning
[Applications for copies should be addressed to the Steel
Structures Painting Council (SSPC), 4516 Henry Street,
Pittsburgh, PA 15213.]
SECTION II
CORROSION CONTROL
2.1 GENERAL
A properly implemented corrosion control program will disclose
corrosion attack in the early stages. Minor maintenance can
correct such corrosion. Preventive maintenance is the most cost-
effective method of controlling corrosion, including problems
caused by poor design.
2.2 PREVENTIVE MAINTENANCE
Preventive maintenance as related to corrosion control includes
the following specific functions:
a. An adequate cleaning program.
b. Detailed scheduled inspection of facilities and systems
for corrosion and failure of protective coating
systems.
c. Prompt treatment of corrosion after it is detected.
d. Touchup of damaged paint areas.
e. Periodic lubrication.
f. Use of supplementary preservative coatings as
necessary.
g. Adequate drainage of moisture entrapment areas by
maintaining drain holes free of obstruction. Holes
should be large enough so they can be protected.
h. Periodic removal of accumulated water and other foreign
matter from fuel containers. Keep fuel containers full
to minimize the accumulation of water and debris.
i. Coat exposed critical surfaces (such as pistons) with
preservative compounds. Surfaces that must remain bare
shall be wiped clean frequently.
j. Protection of equipment against water, dust, etc., by
use of covers or storage in a protected enclosure.
k. Periodic and frequent inspections of areas where
absorbent materials are in contact with metals.
2.3 SURVEILLANCE
Continuing surveillance is required to disclose corrosion attack
in its early stages. Without proper preventive maintenance,
corrosion can seriously damage equipment. All equipment must be
carefully inspected for signs of corrosion during scheduled and
random inspections. These activities should be organized and
properly managed to produce an effective program. Materials that
require special treatment to protect them against corrosion are
those most vulnerable to corrosion attack and require careful
inspection and maintenance.
2.4 DESIGN CONSIDERATIONS
2.4.1 CORROSION CONTROL. The atmosphere at KSC contains a high
salt content that is readily deposited on exposed surfaces.
This, combined with acidic solid rocket booster effluent that is
pH of 1 to 2, substantial rainfall, steady winds, low land
elevation, and generally high humidity and temperature, results
in an ideal environment for extensive metal corrosion. These
conditions induce both electrolytic action and chemical reactions
dependent upon the metals involved and how they are used.
Although corrosion control is primarily the responsibility of the
maintainer of the equipment, the designer is responsible for
providing hardware that will not present unnecessary problems.
The designer must determine where the end item will be located at
KSC. Such locations can vary from the severe conditions present
at a launch complex to partially controlled environments in air-
conditioned rooms to the carefully controlled conditions in a
clean room. The control and treatment of corrosion are of vital
concern because of degradation of the operational and structural
integrity of the equipment and facilities.
The best procedure for corrosion control is to minimize the
potential for corrosive attack while designing the equipment.
Many corrosion problems encountered could be avoided by proper
design. Frequently, minor design changes can eliminate
particularly troublesome corrosion problems. The equipment
operator should advise the designer when such situations exist.
Basic recommendations for eliminating corrosion in the design
phase are summarized as follows:
a. Use corrosion-resistant materials including plastics
and nonmetallics in severe environments where possible.
Galvanized supports should be specified for outside
installations in neutral atmospheres and for inside
installations where corrosive agents are present.
b. Avoid dissimilar metal couples (see MIL-STD-889 for a
definition of dissimilar metal combinations).
Materials classified in different groups are considered
dissimilar or incompatible with one another. The
tendency toward galvanic corrosion is greater between
widely separated groups than between adjacent groups.
Metals from different groups may be placed in contact
where suitable protection against galvanic action is
provided through use of barrier tape protective
coatings or other methods of isolation. The method of
protection required will be dependent on the design and
usage environment.
c. Keep moisture away or provide for its removal.
d. Avoid exposure to corrosive liquids or fumes.
e. Protect surfaces with metallic, inorganic, or organic
coatings as required. Consider use of powder coatings
such as polyester, epoxy, PVC, and similar coatings
applied by the fluidized bed process.
f. Improve the environment by providing seals,
dehumidification, purges, adequate ventilation, vapor
phase inhibitors, and air-conditioning or by
maintaining temperature above the dew point.
g. Protect exposed bearing surfaces with corrosion
inhibiting lubricant. Greases in accordance with MIL-G-
81322 (Mobilgrease 28) and MIL-G-23549 (Royco 49B or
Supermil grease 94532) provide good protection.
h. Apply protective coatings to all buried and submerged
metallic facilities in accordance with KSC-STD-C-0001.
Where applicable, provide cathodic protection to
prolong the effectiveness of the protective coating.
Consult NACE RP0189 for cathodic protection (CP)
requirements.
i. Consult the book Designing for Corrosion Control by R.
James Landrum for more detailed recommendations for
corrosion design criteria. This book is available from
the National Association of Corrosion Engineers, NACE
International, P.O. Box 218340, Houston, TX 77218,
(713) 492-0535, ext. 81, or the KSC Library.
j. Use flameproof inorganic zinc sacrificial protective
coatings to protect carbon steel in accordance with KSC-
STD-C-0001 and comply with NACE inspection requirements
as specified.
k. Use acid-resistant topcoats in the launch environment.
l. Anodize, alodine, or use AR-7 treatment of unpainted
aluminum. Follow KSC-STD-C-0001 for application of
additional protective coatings.
m. Use sealed and treated tubular structural columns in
tension and compression members. The internal surfaces
shall be treated by filling and draining with a
volatile corrosion-inhibiting lubricating oil in
accordance with MIL-P-46002 grade 1, or approved equal.
After treatment, all openings shall be seal welded.
n. Avoid the use of back-to-back structural shapes, such
as boxbeam sections and unistrut. When the exterior
use of unistrut cannot be avoided, selection of
appropriate material shall be considered, such as
stainless steel. In addition, alternate structural
shapes shall be considered such as C- or Z-shaped
channel, especially in highly corrosive areas.
o. Provide large drainage holes so the edges can be
painted.
p. Seal faying surfaces of bolted and skip-welded joints
with caulking. Use TT-S-230 for caulking.
q. Consider the plating of steel surfaces in accordance
with KSC-STD-C-0001 or MIL-C-83488, Class 1. Avoid the
use of cadmium plating due to possible health and
outgassing concerns. Bare, cadmium-plated surfaces in
exterior applications are prohibited.
r. Avoid the use of alloys susceptible to stress-corrosion
cracking in accordance with KSC-STD-Z-0004.
s. Consider system compatibility, environment, and
location in relation to hypergolic or cryogenic systems
and their vapors.
t. Use galvanized or other corrosion-resistant bolts or
rivets, if possible. Avoid lap joints with skip welds
wherever possible. Use butt welds or seal welds, if
possible. NACE Standard RP0178 should be used in metal
tank and vessel design.
SECTION III
TYPES OF CORROSION AND THEIR CAUSES
3.1 GENERAL
Corrosion can be defined as the deterioration of material by
reaction to its environment. The corrosion occurs because of the
natural tendency for most metals to return to their natural
state; e.g., iron in the presence of moist air will revert to its
natural state, iron oxide. Metals can be corroded by the direct
reaction of the metal to a chemical; e.g., zinc will react with
dilute sulfuric acid, and magnesium will react with alcohols.
3.2 BASIC CAUSES OF CORROSION
3.2.1 CONDITIONS NECESSARY FOR CORROSION. For the purpose of
this manual, electrochemical corrosion is the most important
classification of corrosion. Four conditions must exist before
electrochemical corrosion can proceed: (1) there must be
something that corrodes (the metal anode), (2) there must be a
cathode, (3) there must be continuous conductive liquid path
(electrolyte, usually condensate and salt or other
contaminations), and (4) there must be a conductor to carry the
flow of electrons from the anode to the cathode. This conductor
is usually in the form of metal-to-metal contact such as in
bolted or riveted joints.
The elimination of any one of the four conditions will stop
corrosion. An unbroken (perfect) coating on the surface of the
metal will prevent the electrolyte from connecting the cathode
and anode so the current cannot flow. Therefore, no corrosion
will occur as long as the coating is unbroken.
3.2.2 EFFECT OF MATERIAL SELECTION. One of the fundamental
factors in corrosion is the nature of the material. Materials
are usually selected primarily for structural efficiency, and
corrosion resistance is often a secondary consideration in
design. The use of corrosion-resistant alloys is not a cure-all
for corrosion prevention. Corrosion-resistant metals are by
nature passive (more noble) and can cause severe galvanic
corrosion of active (less noble) materials. A common occurrence
is to replace a corroded part with a corrosion-resistant alloy
only to find that the corrosion has shifted to another location
and increased in severity.
3.2.3 WATER INTRUSION. Water intrusion is the principal cause
of corrosion problems encountered in the field use of equipment.
Water can enter an enclosure by free entry, capillary action, or
condensation. With these three modes of water entry acting and
with the subsequent confinement of water, it is almost certain
that any enclosure will be susceptible to water intrusion. As a
general rule, assume that water enters any unit except the
hermetically sealed or pressurized designs. Sump-like areas,
enclosures, or sealed members wherein water can accumulate should
be provided with drain holes at their lowest point or wherever
water may collect. The size of the drain holes should be large
enough to permit proper application of a protective coating.
Typical drainhole size should be 12 millimeters (mm) [0.5-inch
(in)] minimum. Where drain holes are not practical, provide
dehumidification or purge with dry air or nitrogen.
3.2.4 ENVIRONMENTAL FACTORS. At normal atmospheric temperatures
the moisture in the air is enough to start corrosive action.
Oxygen is essential for corrosion to occur in water at ambient
temperatures. Other factors that affect the tendency of a metal
to corrode are: (1) acidity or alkalinity of the conductive
medium (pH factor), (2) stability of the corrosion products, (3)
biological organisms (particularly anaerobic bacteria), (4)
variation in composition of the corrosive medium, and (5)
temperature. The corrosion problem at KSC is complex. The
presence of salts and acids on metal surfaces greatly increases
the electrical conductivity of any moisture present and
accelerates corrosion. Moisture tends to collect on dirt
particles. The maintenance of clean surfaces on passive metals
or alloys and alloys plated with more noble metals can be of even
greater importance than for plain carbon steel. If small
corrosion areas develop, the combination of small active anodes
in relation to large passive cathodes causes severe pitting.
This principle also applies to metals that have been passivated
by chemical treatments as well as for metals that develop
passivation due to environmental conditions (e.g., stainless
steel and aluminum). Alloys that owe their corrosion resistance
to passivity are susceptible to accelerated corrosion within
crevices. This phenomenon is caused by the formation of an
oxygen cell resulting from a lower oxygen concentration in the
crevice. For these reasons, cleanliness must be maintained and
corrosion-preventive measures, such as painting as dictated by
service conditions, must be observed even on corrosion-resistant
materials. Corrosive attack begins on the surface of a metal
exposed to a corrosive environment. If allowed to progress, the
corrosion works down into the core of the material. Because
corrosion never originates in the core, there will always be
evidence on the surface when an attack is in progress. The most
common visible manifestations of corrosion are pitting on
stainless steel or aluminum, rust on carbon steel, and
intergranular exfoliation on aluminum.
3.3 TYPES OF CORROSION
3.3.1 CONCENTRATION CELL CORROSION. Concentration cell
corrosion occurs when two or more areas of a metal surface are in
contact with different concentrations of the same solution.
There are three general types of concentration cell corrosion:
(1) metal ion concentration cells, (2) oxygen concentration
cells, and (3) active-passive cells.
3.3.1.1 Metal Ion Concentration Cells. In the presence of
water, a high concentration of metal ions will exist under faying
surfaces and a low concentration of metal ions will exist
adjacent to the crevice created by the faying surfaces. An
electrical potential will exist between the two points. The area
of the metal in contact with the low concentration of metal ions
will be cathodic and will be protected, and the area of metal in
contact with the high metal ion concentration will be anodic and
corroded. This condition can be eliminated by sealing the faying
surfaces in a manner to exclude moisture. Proper protective
coating application with inorganic zinc primers is also effective
in reducing faying surface corrosion.
3.3.1.2 Oxygen Concentration Cells. A water solution in contact
with the metal surface will normally contain dissolved oxygen.
An oxygen cell can develop at any point where the oxygen in the
air is not allowed to diffuse uniformly into the solution,
thereby creating a difference in oxygen concentration between two
points. Typical locations of oxygen concentration cells are
under either metallic or nonmetallic deposits (dirt) on the metal
surface and under faying surfaces such as riveted lap joints.
Oxygen cells can also develop under gaskets, wood, rubber,
plastic tape, and other materials in contact with the metal
surface. Corrosion will occur at the area of low-oxygen
concentration (anode). The severity of corrosion due to these
conditions can be minimized by sealing, maintaining surfaces
clean, and avoiding the use of material that permits wicking of
moisture between faying surfaces.
3.3.1.3 Active-Passive Cells. Metals that depend on a tightly
adhering passive film (usually an oxide) for corrosion
protection; e.g., austenitic corrosion-resistant steel, can be
corroded by active-passive cells. The corrosive action usually
starts as an oxygen concentration cell; e.g., salt deposits on
the metal surface in the presence of water containing oxygen can
create the oxygen cell. If the passive film is broken beneath
the salt deposit, the active metal beneath the film will be
exposed to corrosive attack. An electrical potential will
develop between the large area of the cathode (passive film) and
the small area of the anode (active metal). Rapid pitting of the
active metal will result. This type of corrosion can be avoided
by frequent cleaning and by application of protective coatings.
3.3.2 GALVANIC CORROSION. Galvanic corrosion is an
electrochemical action of two dissimilar metals in the presence
of an electrolyte and an electron conductive path. It occurs
when dissimilar metals are in contact. It is recognizable by the
presence of a buildup of corrosion at the joint between the
dissimilar metals. For example, when aluminum alloys or
magnesium alloys are in contact with steel (carbon steel or
stainless steel), galvanic corrosion can occur.
Appendix A represents a galvanic series in sea water. If
electrical contact is made between any two of these materials in
the presence of an electrolyte, current must flow between them.
The farther apart the metals in appendix A are, the greater will
be the galvanic corrosion effect or rate. Metals or alloys at
the upper end are noble while those at the lower end are active.
The more active metal is the anode or the one that will corrode.
The galvanic series of metals and alloys are to be used only for
general information and must be augmented by experience and a
knowledge gained of the behavior of dissimilar metal combinations
in field service. When the use of plated steel bolts is
necessary on aluminum flanges, the bolts should be separated from
the flange by nonmetallic sleeves and backup washers to prevent
conditions favorable to galvanic corrosion. When dissimilar
metals must be used, always protect both components. A break in
the protective coating on the anodic surface will result in
severe pitting if the cathodic surface is not protected. This is
because of the concentration of current upon the relatively small
anodic area exposed when the cathode is uncoated. When
practical, bolts, rivets, and other fasteners should be made of
the same material as the main structure. When this is not
practical, they should be selected from materials higher in the
listing of appendix A so as to distribute the anodic attack over
the larger of the two coupled metals. When the anode is large
with respect to the cathode, two advantages are realized: (1)
because the anode is being dissolved by the electrolyte, uniform
corrosion takes place over a relatively large area at a
relatively slower rate, thus increasing the service life of the
anode, and (2) the small cathode areas tend to become polarized,
thereby slowing or stopping the reaction. For more information
concerning corrosion control of dissimilar metals, consult MIL-
STD-889.
To summarize, the following recommended practices should be
observed to keep galvanic corrosion to a minimum.
a. Avoid the use of widely dissimilar metals in direct
contact.
b. When dissimilar metals must come into contact, they
should be separated by using nonconductive barrier
materials, a paint coating, or by plating.
c. The anode should be as large as feasible in relation to
the cathode.
d. Coat both the anode and the cathode with the same
material.
e. When possible, install fasteners that have been dipped
in epoxy mastic coatings in accordance with KSC-STD-C-
0001.
f. Seal threaded inserts with epoxy mastic coatings prior
to insertion into castings.
g. Avoid the use of lock or toothed washers over plated or
anodized surfaces.
h. Use only dry-film lubricants that are graphite free
[MIL-L-46010 (MR) is graphite free].
3.3.2.1 Filiform Corrosion. Filiform corrosion is a unique type
of galvanic corrosion occurring under painted surfaces or plated
surfaces that do not exhibit good adhesion and under gaskets. It
appears as a radial "worm-like" corrosion path emanating from a
central core of corrosion. This type of corrosion occurs under
painted or plated surfaces when moisture permeates the coating.
Lacquers and "quick-dry" paints are most susceptible to the
problem; their use should be avoided unless absence of an adverse
effect has been proven by field experience. Where a coating is
required, it should exhibit low water vapor transmission
characteristics and excellent adhesion. Zinc-rich coatings
should also be considered for coating carbon steel because of
their cathodic protection quality.
3.3.3 INTERGRANULAR CORROSION. Intergranular corrosion is an
attack on the grain boundaries of a metal or alloy. A highly
magnified cross section of any commercial alloy will show its
granular structure. This structure consists of quantities of
individual grains, and each of these tiny grains has a clearly
defined boundary that chemically differs from the metal within
the grain center. Frequently, the grain boundaries are anodic to
the main body of the grain, and when the grain boundaries are in
this condition and in contact with an electrolyte, a rapid
selective corrosion of the grain boundaries occurs. One example
of this type of corrosion is in unstabilized 300-series stainless
steels sensitized by welding or brazing and subsequently
subjected to a severe corrosion environment. Another example of
intergranular or grain boundary corrosion is that which occurs
when aluminum alloys are in contact with steel in the presence of
an electrolyte. The aluminum alloy grain boundaries are anodic
to both the aluminum alloy grain and the steel. In the later
case, intergranular corrosion of the aluminum alloy occurs. Some
austenitic steels are unstable when heated in the temperature
range of 470 to 915 degrees Celsius ( C) [800 to 1600 degrees
Fahrenheit ( F)], after which they become susceptible to
corrosion attack at their grain boundaries. The cause of
intergranular corrosion has been the subject of much study.
Decreased corrosion resistance in austenitic stainless steels is
due to depletion of chromium in the area near the grain
boundaries, caused by the precipitation of chromium carbide.
This condition can be eliminated by the use of stabilized
stainless steel, such as columbium, tantalum, or titanium
stabilized stainless steels (types 321 and 347), or by the use of
low-carbon stainless steels. Molybdenum additions as in type 316
stainless steels decrease the sensitivity to and the severity of
the intergranular attack.
Intergranular corrosion can be prevented by adopting one or more
of the following methods:
a. Select an alloy type that is resistant to intergranular
corrosion.
b. Avoid heat treatments or service exposure that makes a
material susceptible. Normally this occurs with
austenitic stainless steels when they are held for some
time in the sensitizing temperature range of 470 to 915
C (800 to 1600 F).
c. Apply a protective coating.
3.3.3.1 Exfoliation Corrosion. Exfoliation is a form of
intergranular corrosion. It manifests itself by lifting up the
surface grains of a metal by the force of expanding corrosion
products occurring at the grain boundaries just below the
surface. It is visible evidence of intergranular corrosion and
most often seen on extruded sections where grain thickness is
less than in rolled forms.
3.3.4 PITTING CORROSION. The most common effect of corrosion on
aluminum and magnesium alloys is called pitting. It is
noticeable first as a white or gray powdery deposit, similar to
dust, which blotches the surface. When the deposit is cleaned
away, tiny pits or holes can be seen in the surface. Passive
metals such as stainless steel resist corrosive media and can
perform well over long periods of time. However, if corrosion
does occur, it forms at random in pits. Pitting may be a serious
type of corrosion because it tends to penetrate rapidly into the
metal section. Pits begin by a breakdown of passivity at nuclei
on the metal surface. The breakdown is followed by formation of
an electrolytic cell, the anode of which is a minute area of
active metal and the cathode of which is a considerable area of
passive metal. The large potential difference characteristic of
this "passive-active cell" (0.5 to 0.6 volt for 18-8 stainless
steel) accounts for a considerable flow of current with attendant
rapid corrosion at the small anode. The corrosion-resistant
passive metal surrounding the anode and the activating (passivity-
destroying) property of the corrosion products within the pit
account for the tendency of corrosion to penetrate the metal
rather than spread along the surface. Pitting is most likely to
occur in the presence of chloride ions, combined with such
depolarizers as oxygen or oxidizing salts. Methods that can be
used to control pitting include maintaining surfaces clean,
application of a protective coating, and use of inhibitors or
cathodic protection for immersion service.
3.3.5 UNIFORM ETCH CORROSION. The surface effect produced by
most direct chemical attacks (e.g., as by an acid) is a uniform
etching of the metal. On a polished surface, this type of
corrosion is first seen as a general dulling of the surface and,
if allowed to continue, the surface becomes rough and possibly
frosted in appearance. The discoloration or general dulling of
metal created by its exposure to elevated temperatures is not to
be considered as uniform etch corrosion. The use of chemical-
resistant protective coatings or more resistant materials will
control these problems.
3.3.6 STRESS CORROSION CRACKING. Stress corrosion cracking
(SCC) is caused by the simultaneous effects of tensile stress and
corrosion. Stress may be internally or externally applied.
Internal stresses are produced by nonuniform deformation during
cold working, by unequal cooling from high temperatures, and by
internal structural rearrangement involving volume changes.
Stresses induced when a piece is deformed, those induced by press
and shrink fits, and those in rivets and bolts are internal
stresses. Concealed stress is more important than design stress,
especially because stress corrosion is difficult to recognize
before it has overcome the design safety factor. The magnitude
of the stress varies from point to point within the metal.
Stresses in the neighborhood of the yield strength are generally
necessary to promote SCC, but failures have occurred at lower
stresses. A few guides in avoiding the problem are:
a. Use metal alloys at no greater than 75 percent of their
yield strength and use exotic materials only where they
are actually required.
b. Avoid assemblies where high-tensile loads are
concentrated in a small area.
c. Place surfaces under compressive stresses where
feasible, by shotpeening, sandblasting, etc.
d. Remove stress risers from counter bores, grooves, etc.
e. Metals shall be selected from alloys that are highly
resistant to SCC as specified in KSC-STD-Z-0004.
3.3.7 FATIGUE CORROSION. Fatigue corrosion is a special case of
stress corrosion caused by the combined effects of cyclic stress
and corrosion. No metal is immune from some reduction of its
resistance to cyclic stressing if the metal is in a corrosive
environment. Damage from fatigue corrosion is greater than the
sum of the damage from both cyclic stresses and corrosion.
Fatigue corrosion failure occurs in two stages. During the first
stage, the combined action of corrosion and cyclic stresses
damages the metal by pitting and crack formation to such a degree
that fracture by cyclic stressing will ultimately occur, even if
the corrosive environment is completely removed. The second
stage is essentially a fatigue stage in which failure proceeds by
propagation of the crack and is controlled primarily by stress
concentration effects and the physical properties of the metal.
Fracture of a metal part due to fatigue corrosion generally
occurs at a stress far below the fatigue limit in laboratory air,
even though the amount of corrosion is extremely small. For this
reason, protection of all parts subject to alternating stress is
particularly important wherever practical, even in environments
that are only mildly corrosive.
3.3.8 FRETTING CORROSION. The rapid corrosion that occurs at
the interface between contacting, highly loaded metal surfaces
when subjected to slight vibratory motions is known as fretting
corrosion. This type of corrosion is most common in bearing
surfaces in machinery, such as connecting rods, splined shafts,
and bearing supports, and often causes a fatigue failure. It can
occur in structural members such as trusses where highly loaded
bolts are used and some relative motion occurs between the bolted
members. Fretting corrosion is greatly retarded when the
contacting surfaces can be well lubricated as in machinery-
bearing surfaces so as to exclude direct contact with air.
3.3.9 CREVICE CORROSION. Crevice or contact corrosion is the
corrosion produced at the region of contact of metals with metals
or metals with nonmetals. It may occur at washers, under
barnacles, at sand grains, under applied protective films, and at
pockets formed by threaded joints. Whether or not stainless
steels are free of pit nuclei, they are always susceptible to
this kind of corrosion because a nucleus is not necessary.
Crevice corrosion may begin through the action of an oxygen
concentration cell and continue to form pitting. Contact or
crevice corrosion occurs when surfaces of metals are used in
contact with each other or with other materials and the surfaces
are wetted by the corrosive medium or when a crack or crevice is
permitted to exist in a stainless-steel part exposed to corrosive
media. Cleanliness, the proper use of sealants, and protective
coatings are effective means of controlling this problem.
SECTION IV
CORROSION REMOVAL AND TREATMENT
4.1 GENERAL
This section describes typical corrosion removal and treatment
for various materials. To provide optimum protection from
corrosion, the proper coating systems must be selected for a
specific application. The selection of the proper coating system
depends on the material to be coated, service conditions,
required service life, and surface preparation possible. Consult
KSC-STD-C-0001 for recommended coating systems for aluminum.
4.2 ALUMINUM AND ALUMINUM ALLOYS
4.2.1 GENERAL. Aluminum alloys as a class are normally very
resistant to outdoor exposure conditions. However, they are
anodic to most common alloys in many aqueous solutions. Thus,
galvanic attack is likely to occur on aluminum items in contact
with dissimilar metals.
A common type of corrosion attack of aluminum alloys is pitting
and crevice corrosion. Under certain conditions, these alloys
are susceptible to intergranular corrosion, exfoliation, and
stress-corrosion cracking.
Corrosion on aluminum alloys can be removed by first cleaning oil
and dirt from affected surfaces and then removing the corrosion
by mechanical methods or by use of a corrosion-removing chemical
treatment. After cleaning and corrosion removal, the item should
be protected against further corrosion by application of a
suitable paint system. Acceptable procedures are described
below.
4.2.2 CLEANING TO REMOVE FOREIGN MATTER. Remove foreign matter
with a cleaner in accordance with MIL-C-87936, type I.
Aluminum alloys shall be cleaned using a cleaning compound
conforming to MIL-C-87936, type I. The following mixing
concentrations are suggested:
a. Light soil (dirt, dust, mud, salt): 1 part compound, 9
parts water
b. Moderate soils (hydraulic fluid, lube oils, light
preservatives): 1 part compound, 4 parts water
c. Heavy soils (carbonized oil, grease, aged
preservatives, exhaust deposits): 1 part compound, 1
part water
Apply the solution by spraying or with a mop, sponge, or brush.
Allow to remain on the affected surface for several minutes while
agitating with a brush. Rinse thoroughly with water. Do not
allow compound to dry before rinsing with running water since
poor cleaning may result.
4.2.3 CORROSION REMOVAL. Remove corrosion by mechanical method
such as wire brushing or abrasive blasting as appropriate.
Failure to adequately clean all residues will permit corrosion to
continue. Light corrosion may be removed from thin members, such
as ducts and tubing, with a nonwoven, nonmetallic abrasive mat in
accordance with MIL-A-9962, or number 400 aluminum oxide or
silicon carbide grit abrasive paper or cloth. Do not use steel
wool. Stainless-steel brushes having bristles not exceeding 0.25
mm (0.010 inch) in diameter may be used provided surfaces are
finally polished with number 400-grit abrasive paper followed by
600-grit abrasive paper. Dry abrasive blasting with fine
abrasives in accordance with KSC-STD-C-0001 is also an acceptable
method of removing corrosion products when surfaces will
subsequently be painted and where dimensional tolerances are not
critical. All abrasive residues should be thoroughly removed
using high-pressure clean air or running water. Never use carbon
steel wool or wire brushes since particles from these materials
may become imbedded in the aluminum surface causing galvanic
corrosion problems.
Chemical corrosion removal compounds, such as Pasajell 102 or
105V, or approved equal, may be used in accordance with the
manufacturer's printed instructions. Care must be taken when
using these materials to prevent exposure of adjacent surfaces.
4.2.4 SURFACE TREATMENT. Corrosion protection may be provided
by application of a chemical conversion coating or a protective
paint system. Where possible, the protective paint system should
be used since it affords greater corrosion protection than the
chemical conversion coating.
4.2.4.1 Application of Chemical Conversion Coating. In areas
where corrosion protection is required and a paint system would
be objectionable, apply by brush or dipping a chemical conversion
coating in accordance with MIL-C-5541. Most materials in
accordance with MIL-C-5541 leave a stain. Where a bright metal
finish is required, one can specify a clear coating to that
specification. Surfaces to be treated must be clean and dry
before the conversion coat is applied.
The conversion coating is a toxic chemical and requires that
personnel wear rubber gloves when applying the coating. If acid
accidently contacts the skin or eyes, flush immediately with
clear water. Do not permit MIL-C-5541 materials to contact paint
thinner, acetone, or other combustible materials. Fire may
result. The solution should be mixed in a stainless steel,
rubber, or plastic container (not in lead, copper alloy, or
glass). Mix in accordance with the manufacturer's instructions.
Apply to clean and dry surfaces using a fiber bristle brush or a
clean soft cloth. Keep the surface wet with the solution until a
coating is formed (1 to 5 minutes depending on the metal surface
condition). Do not permit the MIL-C-5541 material to dry because
the residue is difficult to flush off, and poor paint adhesion
may result if paint is subsequently applied. Misapplication
resulting in over conversion will require complete removal and
reapplication to produce adequate protection with this material.
4.2.4.2 Application of Paint System. All painting of aluminum
in the various zones of exposure shall be performed in accordance
with the applicable paragraphs in KSC-STD-C-0001.
4.2.5 CONTACT WITH DISSIMILAR MATERIALS. Aluminum alloy parts
in contact with or fastened to steel members or other dissimilar
materials shall be kept from direct contact with the steel or
other dissimilar material as follows:
Aluminum surfaces to be placed in contact with steel shall be
given a pretreatment in accordance with DOD-P-15328 (wash primer)
or MIL-C-5541 (chromate conversion coating) followed by an
inhibited polyamide epoxy primer in accordance with KSC-STD-C-
0001. An alternate approach would be to apply the pretreatment
as above and assemble components with MIL-S-29574, type II,
sealing compound. Where severe corrosion conditions are
expected, additional protection can be obtained by applying
sealing compound in addition to using the inhibited epoxy primer.
Primer should be allowed to cure 24 hours prior to assembly of
components. Steel surfaces should be coated with a zinc-rich
primer in accordance with KSC-STD-C-0001.
Aluminum in contact with wood, concrete, or masonry construction
should be given a heavy coat of coal-tar epoxy or epoxy mastic in
accordance with KSC-STD-C-0001 before installation. Aluminum
surfaces to be imbedded in concrete shall be coated with coal-tar
epoxy or epoxy mastic, or shall be wrapped with plastic tape in
accordance with MIL-T-23142 applied in such a manner as to
provide adequate protection at the overlap.
4.3 CARBON STEEL AND LOW-ALLOY STEEL
4.3.1 GENERAL. Ferrous alloys are commonly used construction
materials. If the metal is not protected, it will corrode
readily in the marine acidic environment at KSC. KSC-STD-C-0001
defines detailed requirements for protecting carbon steel. It
defines basic requirements for surface preparation and acceptable
protective coatings.
4.3.2 CLEANING TO REMOVE FOREIGN MATTER. If the corroded area
is soiled by foreign materials such as grease or dirt, the
surfaces must be cleaned before stripping paint or removing
corrosion. Surfaces may be cleaned in accordance with SSPC SP-1.
4.3.3 PAINT STRIPPING (WHEN REQUIRED). Residual paint or primer
may be removed by mechanical or chemical treatment after cleaning
surfaces.
4.3.3.1 Chemical Paint Stripping. Readily accessible areas may
be stripped with thickened stripper in accordance with TT-R-248.
Less accessible areas may be stripped with ethyl acetate in
accordance with TT-E-751 and lacquer thinner in accordance with
TT-T-266.
4.3.4 CORROSION REMOVAL. Abrasive blasting is the preferred
method of removing corrosion; other mechanical methods (SSPC SP-2
or SSPC SP-3) that may be used are grinding, chipping, sanding,
or wire brushing. Chemical corrosion removal may be used when
there is no danger of the chemical becoming entrapped. The
chemical method should be used on complex shapes and machined
surfaces. Chemical rust removers are of two types: acid or
alkaline. The acid type can be used in removing rust and black
oxide by immersion or brush application. This phosphoric-acid-
type remover must not be used on high-strength steel heat treated
above 1.24 gigapascals (GPa) [180,000 pounds per square inch
(psi)] tensile strength because of possible stress corrosion or
hydrogen embrittlement problems. The alkaline type (sodium
hydroxide base) is suitable for use by immersion only. It is
preferred for use on machined surfaces where a dimensional change
would be objectionable.
4.3.4.1 Phosphoric Acid Base (Brush-On Method).
a. Remove foreign matter by a method described previously
(SSPC SP-1).
b. Remove heavy corrosion products by an appropriate
mechanical method.
c. Add one part of MIL-C-10578, type III, solution to one
part of water by volume. Always add the acid to water.
d. Apply the solution to the corroded surface with a
brush. Allow the solution to remain on the surface for
2 to 20 minutes, depending on the severity of the
rusting.
e. If available, rinse thoroughly with hot water;
otherwise, cold water may be used.
f. Dry the part quickly and thoroughly and immediately
apply a protective coating or corrosion preventive.
4.3.4.2 Phosphoric Acid Base (Immersion Method).
a. Remove foreign matter by a method described previously
(SSPC SP-1).
b. Remove heavy corrosion products by an appropriate
mechanical method.
c. Add one part of MIL-C-10578, type III, solution to one
part of water by volume. Always add the acid to water.
d. Immerse parts while agitating for sufficient duration
to remove the rust. The solution may be warmed to 60
C (140 F) to accelerate corrosion removal.
e. If available, rinse thoroughly with hot water;
otherwise, cold water is acceptable.
f. Dry the part quickly and thoroughly and immediately
apply protective coating or corrosion preventive.
4.3.4.3 Alkaline Corrosion Remover (Immersion Method).
a. Remove grease and loose corrosion products.
b. Prepare rust remover by mixing the chemical (MIL-C-
14460) in accordance with the manufacturers'
instructions.
c. Immerse for sufficient time to remove the rust. The
solution may be heated up to the boiling point to
increase the rate of corrosion removal.
d. Rinse in water, preferably hot.
e. Dry the part thoroughly and immediately apply the
protective coating or corrosion-preventive compound.
4.4 STAINLESS-STEEL ALLOYS
4.4.1 GENERAL. Stainless steels owe their inherent corrosion
resistance to a condition known as passivity, which is a result
of the presence of their oxide films called "passive films."
Under favorable conditions, such films are protective; however,
unfavorable conditions deficient in oxygen will destroy the films
and leave the surface in an "active" state with corrosion
resistance comparable to carbon steel. The presence of
hygroscopic salt deposits, dirt, dust, and other foreign matter
all serve to destroy passivity. Underground exposure of bare
stainless steel will result in unacceptable corrosion damage.
Consult KSC-STD-C-0001 for coating systems for underground
exposure. Under circumstances where localized corrosion occurs,
rapid penetration (pitting corrosion) at the point of initiation
can occur because an active-passive electrolytic cell is formed
between the large cathodic (passive) area and the small anodic
area under attack. Attack is particularly severe in the presence
of halide salts. Localized attack will also occur in crevices,
such as under sleeves on tube fittings.
Superior resistance to pitting is attainable with type 904L
unified numbering system (UNS) N08904 stainless steel over other
commonly used steels. However, this is only a matter of degree
and localized attack can still occur. Maintaining clean surfaces
will greatly reduce the opportunity for corrosion, regardless of
which alloy is employed.
4.4.2 CLEANING TO REMOVE FOREIGN MATTER. Where foreign
materials are present on a corroded surface, they must be removed
before stripping paint or removing corrosion products. Surfaces
should be cleaned in accordance with SSPC SP-1.
4.4.3 CORROSION REMOVAL.
4.4.3.1 Mechanical Method. When paint is present, it must be
removed prior to corrosion removal by mechanical or chemical
means as appropriate. Abrasive blasting shall be used only when
a final protective coating will be applied. When mechanical
corrosion and paint removal methods other than abrasive blasting
are used and a fine finish is required, the treated area shall be
polished as a final operation, first with 400-grit emery cloth
and then with 500-grit cloth. When a very fine finish is
required, 600-grit emery cloth shall be used.
4.4.3.2 Chemical Method. Chemical corrosion-removal methods can
be used when no danger exists that the chemical being used will
become entrapped in recesses and when there is no danger that
adjacent materials will be attacked. After cleaning in
accordance with 4.4.2, surfaces shall be treated with MIL-C-
10578, Type I, II, or III.
Type I (wash off) shall be used when treatment can be by
immersion and when a protective coating is to be applied.
Stainless-steel brushes or stainless-steel wool may be used to
assist in removing corrosion products. The solution should be
permitted to remain on long enough to remove rust (2 to 10
minutes) and to lightly etch the surface to promote paint
adhesion.
Type II (wipe off) shall be used when treatment is done in the
field. The solution may be applied by brush, rag, sponge, or
stainless-steel wire brush or stainless- steel wool. The
compound should be permitted to remain on the metal surface for
approximately 2 to 5 minutes. Residue should be removed with
damp rags followed with dry rags.
4.4.3.2.1 Scale Conditioning. Scale conditioners may be used as
necessary to facilitate oxide scale removal by acid cleaning.
The use of scale conditioners shall not cause pitting,
intergranular attack, or reduction of mechanical properties below
the minimum values as specified in the applicable material
specification for the alloy, gage, and heat-treat condition.
4.4.3.2.2 Acid Cleaning. When acid cleaning is used to remove
heat-treat scale, flux, corrosive media, stains, and other
contaminants, it shall be within the limits specified herein.
Acid cleaning shall not result in intergranular attack that would
be detrimental to the fabrication or use of the material or part.
Intergranular attack shall be considered detrimental when it
completely surrounds the surface grains and is in an
interconnected pattern along with the surface, either continuous
or semi-continuous. Evidence of grain boundary attack, exhibited
in localized areas, which does not completely surround the grains
and is not in an interconnected pattern, shall not be considered
detrimental. Acid cleaning shall not result in pitting or
smutting, which will not be readily removed by subsequent
processing, nor shall it reduce the mechanical properties below
the minimum values as specified in the applicable material
specification for the gage, alloy, and heat-treat condition.
Acid cleaning shall be accomplished in the following bath:
a. Nitric acid (HNO3) (42 Baum‚): 225 to 375 kilograms
per cubic meter (kg/m3) [30 to 50 ounces per gallon
(oz/gal) weight]
b. Hydrofluoric acid (HF) (ammonium bifluoride, NH4HF2
may be used in lieu of HF): 9 to 52 kg/m3 (1.2 to 7.0
oz/gal) (weight)
c. Temperature: room 60 C (140 F)
d. Metal content, HF ratio (replenish bath when the metal
concentration exceeds 1 part of metal to 1.8 parts of
HF): 1:1.8
4.4.4 APPLICATION OF PROTECTIVE COATING. Stainless-steel
components should be painted in accordance with the requirements
in KSC-STD-C-0001. When severe corrosive conditions are
anticipated in zones 4 and 5, protective coatings should be
applied. A protective coating should be selected that is
compatible with the corrosive environment.
4.5 COPPER AND COPPER-BASE ALLOYS
Protective coatings are normally not required for copper and
copper-base alloys because of their inherent corrosion
resistance. The green tarnish commonly noted on copper alloys
does not normally affect its performance characteristics. The
green patina actually provides corrosion protection to the base
metal. However, copper-based materials should be protective
coated in highly acidic conditions such as the Shuttle launch
zone.
4.6 PLATED SURFACES
4.6.1 GENERAL. Metal parts are usually plated to increase
corrosion resistance (for appearance) or to develop special
surface properties such as abrasion or wear resistance. Some
coatings are anodic to the underlying surface while others are
cathodic. Coatings that are anodic to the base metal corrode
preferentially thereby protecting the underlying metal. Examples
of such plated coatings are zinc and cadmium on steel. Cadmium
plating is no longer recommended and should be totally avoided
due to both environmental and technical concerns. Use zinc
plating in accordance with KSC-STD-C-0001 (galvanizing) or ion
vapor deposition (IVD) aluminum in accordance with MIL-C-83488,
Class 1 where possible. Cathodic coatings include tin, copper,
chromium, silver, gold, and nickel on steel. These cathodic
coatings accelerate the corrosion of the underlying material if a
break in the film develops and an electrolyte is present.
4.6.2 CLEANING TO REMOVE FOREIGN MATTER. If the corroded area
is soiled by foreign materials such as grease or dirt, the
surfaces must be cleaned before stripping paint or removing
corrosion. Surfaces may be cleaned with an alkaline water base
cleaner in accordance with MIL-C-87936.
4.6.3 PAINT STRIPPING (WHEN REQUIRED). Residual paint or primer
may be removed by mechanical or chemical treatment after cleaning
surfaces.
4.6.4 CORROSION REMOVAL AND TREATMENT OF PLATED SURFACES.
4.6.4.1 Zinc- and Aluminum-Plated Surfaces. If requirements do
not permit application of a final protective finish to the
affected surfaces, special care shall be taken to avoid
unnecessary removal of the plating. This is particularly true
for zinc- and aluminum-plated surfaces since they are very soft
and, hence, are easily removed by abrasive methods.
Corrosion products may be removed with fine abrasive paper,
followed by treatment with phosphoric acid base rust remover in
accordance with MIL-C-10578. The solution should contact the
affected surfaces only long enough to remove the corrosion. Type
I should be used when the surfaces can be rinsed off with water,
preferably hot, after application. Type II should be used when
rinsing is not possible. Apply by brush, rag, or sponge. Allow
the compound to remain on the metal surface about 30 seconds.
Wipe off residue first with damp rags and then with dry rags.
4.6.4.2 Chromium, Nickel, Copper, and Tin Plate. Treat in
accordance with 4.6.4.1 when a protective coating can be applied.
Where a coating cannot be applied, surfaces should be protected
when possible by coating with a thin film of preservative
compound such as Cortec VCI-368 available from Cortec
Corporation, 4119 White Bear Parkway, St. Paul, MN 55110 [(612)
429-1100]. Where no protection can be provided, surfaces should
be cleaned frequently to remove foreign matter.
SECTION V
TREATMENT OF TYPICAL AREAS
5.1 GENERAL
This section describes the safeguards, treatments, and methods of
corrosion protection for specific items used at KSC.
5.2 COMMUNICATIONS, ELECTRONIC, AND ASSOCIATED ELECTRICAL
EQUIPMENT
5.2.1 GENERAL. Moisture normally enters components or
enclosures as rain or condensate. Condensate can enter a system
even though the system is rainproof. Condensate enters
nonairtight components in the form of moist air. During the
daily temperature cycle, the ambient temperature rises to a peak
and causes an expansion of air inside the components and thereby
drives part of the air from the enclosures. As the temperature
falls, the air within the components cools and contracts, which
causes air from the atmosphere to be drawn into the enclosures.
If this air is moist and if the temperature of the components
drops to the dew point during the temperature cycle, a film of
moisture is deposited on the inside of the components. If the
enclosure is sealed enough to be waterproof, evaporation of the
deposited moisture cannot occur when the temperature rises during
the daily cycle. Moisture will therefore accumulate as a result
of many temperature cycles. Experience has shown that serious
problems, such as corrosion, fungus growth, changes in electrical
characteristics, and shorting, can occur as a result of the
accumulated moisture.
Preventive procedures for controlling moisture problems include
hermetically sealing, application of a conformal coating,
pressurizing with dry gas, ventilation of enclosed areas, use of
desiccants, use of volatile corrosion inhibitors, potting of
electrical connectors, heating to prevent cycling to the dew
point, providing static and dynamic dehumidification systems, and
providing adequate drain holes to prevent moisture accumulation.
Each problem must be inspected to determine the most practical
preventive procedure to follow. However, certain procedures and
preventive measures are common to most moisture problems and can
be readily performed. This includes potting, sealing, and
fungusproofing using a conformal coating.
5.2.2 ENCLOSURES PURGED FOR HAZARD PROTECTION. Electronic
equipment will usually deteriorate rapidly if subjected to
conditions of high humidity. Because of requirements for purging
of electronic equipment during hazardous periods (when gaseous
hydrogen may be present), such equipment must be provided with
airtight seals. Since it is practically impossible to make an
enclosure completely airtight, moisture can accumulate within the
equipment due to "breathing" during periods when the purge is not
in operation. Under these conditions, moisture can enter the
enclosures more readily than it can escape. Because of wide
temperature variations and frequent high humidity, moisture can
accumulate to the point where it becomes discernible as standing
water. This standing water and 100-percent relative humidity
within the enclosure tend to accelerate the corrosion and
deterioration of many materials. If this moisture can be
reduced, the reactions resulting in deterioration are reduced.
When lowered below a limiting amount, the reactions cease.
5.2.3 ENCLOSURES INTERMITTENTLY PURGED FOR HAZARD PROTECTION.
Equipment that is purged with gaseous nitrogen (GN2) or dry air
during hazardous periods when hydrogen may be present is suitably
protected during this period of time. During periods when the
purge is not operating, the equipment should be protected from
corrosion by employing one or more of the following steps, as
determined to be the most appropriate:
a. Purge continuously with dry air or GN2 rather than just
during hazardous periods. Purging during nonhazardous
periods may be intermittent on a daily basis to
conserve purge gas. That is, for periods when the
ambient temperature is increasing or is remaining
constant, no purge would be required. The purge would
be activated when the ambient temperature is decreasing
to avoid drawing in moist air.
b. Provide static pressurization.
c. Install strip heaters to maintain the temperature
within the equipment always higher than the external
temperature.
d. Replace unsuitable materials of construction with
materials more resistant to corrosion and use
protective coatings and potting wherever practical.
e. Install controllable vents and drains.
f. Relocate portable equipment to a controlled atmosphere
for storage when possible.
g. Provide static or dynamic dehumidification systems.
h. Provide sufficient amount of desiccants within the
equipment enclosure during periods of nonpurging.
i. Attach a breather cartridge containing desiccant to
each fitting otherwise used for purging or venting.
j. Install volatile corrosion-inhibitor cartridges on
interior to protect metallic surfaces.
5.2.4 ENCLOSURES NOT PURGED FOR HAZARD PROTECTION. Equipment
not required to be purged for hazard protection should be
protected by application of one or more of the following
corrective measures as required:
a. Purge continuously or intermittently on a daily basis
with dry air or GN2.
b. Static pressurization with dry air or GN2.
c. Replace corroded components with more corrosion-
resistant materials, apply protective coatings, and pot
electrical connectors when possible.
d. Install dynamic or static dehumidification systems.
e. Move equipment to a controlled environment for storage
when possible.
f. Install vents and drains.
g. Protect during bad weather or inactive periods by use
of covers that allow free ventilation.
h. Provide sufficient amount of desiccants within the
equipment enclosure during periods of nonpurging.
i. Attach a breather cartridge containing desiccant to
each fitting otherwise used for purging or venting.
j. Install volatile corrosion-inhibitor cartridges on
interiors to protect metallic surfaces.
5.2.5 COATING OF COMMUNICATIONS, ELECTRONIC, AND ASSOCIATED
EQUIPMENT. An effective method of preventing corrosion of
external surfaces of electrical components is by treatment with
moisture- and fungus-resistant conformal coating in accordance
with KSC-SPEC-E-0001. Coating materials to this specification
has been proven by experience to be effective in minimizing
corrosion and preventing fungus growth.
CAUTION
Coating should not be applied indiscriminately
to electrical equipment. It should be applied in
accordance with engineering drawings or as
directed
by the electrical manufacturer.
5.2.5.1 Items To Be Treated. The coating should be applied
thoroughly and completely to all moisture and fungus susceptible
surfaces such as circuit elements (resistors, capacitors, coils,
etc.), surfaces supporting circuit elements, interconnecting
wiring, and connections. To determine if the coating has been
applied previously, surfaces may be examined with an ultraviolet
lamp. Since these thin KSC conformal coatings contain a
fluorescent dye, void areas or defects in the coating can be
readily detected when inspected under ultraviolet or "black
light."
5.2.5.1.1 Preparation for Treatment. Equipment to be treated
shall be exposed so the coating may be applied effectively over
the surfaces to be treated. On assemblies, the cases, cans,
covers, shields, etc., shall be removed in order to expose the
surfaces fully. Where practical, untreated cables and cords
shall be bent back, and untreated terminal boards shall be
loosened to expose the underside.
5.2.5.1.2 Cleaning Before Treatment. All surfaces to be treated
shall be cleaned free from dirt, oil, grease, or other foreign
matter that would interfere with the adhesion of the coating.
All visible deposits of solder flux shall be cleaned off by
scraping, chipping, wiping, or by use of a suitable solvent.
Solvents may be used only on readily accessible surfaces that
must be dried immediately by wiping clean. Solvents that will
soften enamels or cause swelling of insulation, such as ketones,
esters, and aromatic hydrocarbons, shall not be used.
5.2.5.1.3 Drying Before Treatment. Coating shall be applied
only on dry surfaces. Equipment should be dried when obviously
wet or damp or when humidity is very high. Drying shall be
accomplished at a temperature safely below that which may damage
the equipment and at a rate which will not cause shrinking,
cracking, warping, or other deterioration. If there are waxed
parts in the equipment, drying temperature shall not exceed 60 C
(140 F). When possible, the coating shall be applied while the
temperature of the equipment is at least 5 C (9 F) above the
room temperature. Time at 60 C (140 F) should not be longer
than 3 hours.
5.2.5.1.4 Methods of Treatment. Coating may be applied by
spraying, brushing, dipping, or any combination thereof.
a. Spraying. When spraying is used to apply the coating,
a pressure pot spray gun with a tip regulated to give a
wet spray shall be used; for small compact equipment, a
pencil spray tip regulated to give a narrow wet spray
shall be used. The coating shall be applied in a wet
coat. A dry spray that forms spray dust shall not be
used. Surfaces shall be sprayed from as many
directions and angles as necessary to ensure complete
coverage with a wet coat. All parts requiring coverage
not accessible to the overall spray shall be coated
with a brush.
b. Brushing. Brushing shall be used when application by
spraying or dipping would require extensive protection
of surfaces not to be coated.
c. Dipping. Dipping may be used where that method is
advantageous.
5.2.5.1.5 Repairs to Damaged Conformal Coating. If the coating
is broken during adjustment, handling, or replacement of parts,
such breaks shall be recoated. Re-soldering of wire connections
shall be done only after cleaning the ends of wire and terminals
to remove the old coating. After re-soldering, connections shall
be recoated.
5.2.5.1.6 Inspection. To determine completeness of coverage,
treated equipment can be examined for fluorescence under an
ultraviolet lamp having a filtered emission of approximately 360
nanometers; coated areas will glow.
5.2.5.2 Items Not To Be Treated With Conformal Coating. Coating
should not be applied to any surface or part where the treatment
will interfere with the operation or performance of the
equipment. Such surfaces or parts shall be protected against the
application. The following are examples of items and materials
that shall be protected.
a. Cable, wire braids, and jackets flexed in operation and
cable with plastic insulation where treatment would
reduce the insulation resistance below or increase the
loss factor above the acceptable values.
b. Components and materials such as:
(1) Capacitors, variable, (air-, ceramic-, or
mica-dielectric).
(2) Resistors (when wattage dissipation would be
undesirably affected and when coating may become
carbonized).
(3) Wirewound resistors.
(4) Ceramic insulators subject to over 600 volts
operating voltage where danger of flashover
exists.
(5) Painted, lacquered, or coated surfaces,
unless otherwise specified.
(6) Rotating parts such as dynamotors,
generators, motors, etc. However, their
associated electronic components, such as filter
units, etc., shall be treated.
(7) Waveguides (working surfaces).
(8) Electron tubes.
(9) Tube clamps.
(10) Miniature tube shields.
(11) Plug-in relays.
(12) Pressure-contact grounds.
(13) Coaxial test points or receptacles.
(14) Windows, lenses, etc.
(15) Transparent plastic parts.
(16) Plastic materials of the following types that
might be sensitive to the cleaning solvent or
coating: polyethylene, polystyrene, acrylic,
silicone, fluorosilicon, or fluorocarbon, vinyl,
or alkyd.
(17) Materials used for their specific arc-
resistant properties and classified as "arc
resistant" in applicable material specifications,
such as mounting boards of a type material where
treatment would reduce the insulation resistance
below (or increase the loss factor above) the
acceptable values and decrease the arc-resistant
value of the board.
c. Organic materials that have otherwise been protected,
such as bottoms of plastic skids (cotton fabric-
phenolic resin), canvas, duck, cork, felt (wool or
hair), fiber, leather, rope, wood, natural or synthetic
rubber, etc., except that the materials need not be
protected from treatment provided the operation and
performance of the equipment are not adversely
affected.
d. Electrical contacts, contact portions, or mating
surfaces of binding posts, connectors, fuses, jacks,
keys, plugs, relays sockets (including tube sockets),
switches, and test points.
e. Mechanical parts such as:
(1) Bearing surfaces (including bearing surfaces
of gaskets and sliding surfaces).
(2) Gear teeth and gear trains or assemblies.
(3) Pivots and pivot portion of hinges, locks,
etc.
(4) Screw threads and screw adjustments (those
moved in the process of operation or adjustment).
(5) Springs.
f. Surfaces that rub together for electrical or magnetic
contact, such as those in bearings, contact fingers,
potentiometers, shafts, shields, and variable
autotransformers.
g. Surfaces whose operating temperatures exceed 130 C
(266 F) or whose operating temperatures will cause
carbonization or smoking.
h. The exterior or visible outside portion of indicating
instruments (do not open or treat inside).
5.2.5.2.1 Methods of Protection From Coating. Items that are
not to be coated may be protected by the use of any suitable
method or device, such as masking tapes, maskants, metals,
cardboard, Teflon jigs, fixtures, or spray masks. Tapes should
be tested before use since some are adversely affected by the
cleaning or coating solvent.
5.2.6 ELECTRICAL CONNECTORS.
5.2.6.1 Potting and Molding. Electrical connectors shall be
potted and/or molded to their associated cable where possible in
accordance with KSC-STD-132.
5.2.6.2 Lubricating Connectors. A suitable lubricant should be
used to effect a good mating of connectors and to prevent
chaffing and scraping of coated surfaces. The lubricant shall
not affect the electrical characteristics of the circuits nor
attack any components of the connectors.
5.3 CARBON STEEL STRUCTURES
5.3.1 GENERAL. KSC-STD-C-0001 defines the detailed requirements
for surface preparation and coating of carbon steel.
Inorganic zinc-rich coating applied over abrasively blasted steel
is the basic coating for corrosion protection of carbon steel at
KSC. Surfaces that exhibit localized breakdown shall be promptly
cleaned and touched-up in accordance with KSC-STD-C-0001.
5.3.2 TYPICAL PROBLEM AREAS.
5.3.2.1 Sharp Edges. Sharp edges of metal structures will often
be deficient of proper coating thickness. Sharp edges should be
rounded when possible in accordance with the National Association
of Corrosion Engineers (NACE), although this may not be practical
in many instances. In these cases, extra care must be taken to
ensure adequate film build on edges. A stripe coat or brush coat
of primer prior to spray application will assist in obtaining
adequate coverage.
5.3.2.2 Back-To-Back Structures (Faying Surfaces). Such
structures are inaccessible for proper coating application and
should be avoided. To preclude moisture entry, such faying
surfaces should be seal welded.
5.3.2.3 Nuts and Bolts. Premature coating failure and corrosion
on nuts and bolt heads are common. These failures can be reduced
by conscientious surface preparation prior to application of a
protective coating. A brush coat of primer prior to spray
application will ensure adequate coverage.
Bolts that pass through dissimilar metals or have a history of
exhibiting general corrosion or stress corrosion cracking or
galling shall be coated before installation with compound Cortec
VCI-368. Bolts and nuts should be specified as hot-dipped
galvanized where possible.
5.3.2.4 Tubular Structural Steel. Water can enter a tubular
structural member that appears to be watertight by "breathing"
through minute defects. This water, if not detected and removed,
can cause serious degradation. Tapping with a hammer and
observing the ring has been proven to be an effective means of
determining if water is present. A more positive method is by
use of ultrasonic inspection.
Where water is detected, it should be removed and the extent of
corrosion damage should be determined. If corrosion is
significant, internal surfaces should be treated by filling and
draining with a volatile corrosion-inhibited lubricating oil in
accordance with MIL-L-46000, grade 1. After treatment, all
openings should be completely sealed.
5.3.2.5 Water Traps. Proper drainage shall be provided in sump
or low areas by providing drain holes. Where such drain holes
cannot be provided, consideration should be given to filling the
pocket, if small, with sealing compound in accordance with MIL-S-
8802.
5.3.2.6 Unistrut Channels. Use of unistrut channels should be
avoided in exterior locations. When the exterior use of unistrut
cannot be avoided, selection of appropriate material shall be
utilized, such as stainless steel or fiberglass. Where corrosion
is noted, the member shall be mechanically cleaned to remove
corrosion products followed by application of a zinc-rich coating
in accordance with KSC-STD-C-0001. Corroded unistrut should be
examined for extent of damage. If the affected surface is
inaccessible, the part should be replaced with appropriate
material if corrosion is advanced.
5.3.2.7 Tube Clamps. Carbon steel clamps for interior
applications are normally furnished either zinc-plated or
painted. Stainless-steel clamps shall be used for all exterior
applications. Corrosion at the interface between the stainless-
steel tubing and the clamp can occur due to dissimilar metal and
crevice corrosion. The corrosion of the clamp can hasten the
corrosion of the stainless-steel tubing due to the presence of
carbon steel corrosion products. Corrosion at the interface
between tubing and clamps can be controlled by application of
protective coatings. Protection should be provided by coating
clamps with a thick coating 200 to 500 micrometers (8 to 20 mils)
of epoxy or nylon applied by the fluidized bed process. Exterior
exposed stainless-steel clamps shall also be coated by the
fluidized bed process or alternatively may be coated with 75
micrometers (3 mils) minimum of Aerocoat AR-7 coating.
Fasteners shall be coated with Aerocoat AR-7 by dipping prior to
assembly. Following assembly, additional coating shall be
applied to exposed surfaces of the fastener as required to repair
damage to the coating incurred during assembly. If the tubing
that is clamped is not coated with a protective coating,
supplementary corrosion protection should be provided by locally
coating the contact surfaces between the tubing and the clamps
with the Aerocoat AR-7 coating or approved nonconductive tape
material.
5.3.2.8 Galvanized Steel. Galvanized steel shall be coated in
accordance with KSC-STD-C-0001 unless localized breakdown occurs.
Where corrosion is noted, surfaces shall be treated and coated in
accordance with KSC-STD-C-0001 with an inorganic zinc-rich
coating.
5.4 STAINLESS-STEEL COMPONENTS
5.4.1 GENERAL. Stainless steel, although considered very
corrosion resistant, is susceptible to localized corrosion (e.g.,
pitting, crevice corrosion, etc.) when exposed to a marine
environment. A mistake frequently made is to conclude that the
corrosion noted on stainless-steel tubing and bellows is only
superficial. This conclusion is improperly reached when removal
of external corrosion products leave the surface in a condition
that appears almost like new except for what appears to be a very
tiny pit. A cross section taken through such a typical pit
frequently discloses a void considerably greater in diameter than
the surface pit diameter. Thus, external appearance normally
cannot be used to estimate pit depth. Failure to arrest the
apparent superficial corrosion will result in ultimate
penetration of thin wall members.
5.4.2 STAINLESS-STEEL TUBING ASSEMBLIES. Bare tubing assemblies
exposed to the elements shall periodically be cleaned of
superficial grime, oil, grease, and salt deposits using water
followed by rinsing with a solvent such as methyl ethyl ketone.
Frequency of cleaning shall be a minimum of once every 6 months.
Should corrosion be noted, prompt action shall be taken to
protect the material surfaces as described below.
5.4.2.1 Application of Protective Coatings. Tubing assemblies
shall be treated as follows:
a. Accumulated dirt and oil shall be removed by rinsing
with water followed by rinsing with methyl ethyl
ketone.
b. Remove corrosion products by mechanical means, such as
power tool cleaning in accordance with SSPC SP-3 or
hand-tool cleaning in accordance with SSPC SP-2.
c. Clean surfaces with methyl ethyl ketone using clean
rags.
d. Apply by spraying, brushing, or dipping 75 micrometers
(3 mils) minimum of the coating Aerocoat AR-7
manufactured by B.F. Goodrich Aerospace and Defense
Products, Vendor Code 03481. Application of this
material shall be in accordance with KSC-STD-C-0001.
This material may be obtained from KSC Supply under
Federal stock number 8030-00-485-3656.
5.4.2.1.1 Tubing Assemblies That Will Be Abrasive Blasted. When
tubing assemblies are in close proximity to carbon steel
structural members that are to be abrasive blasted and coated
with inorganic zinc-rich primer, the tubing assemblies shall be
similarly treated. The following procedure shall be used:
a. Using clean rags, accumulated dirt and oil shall be
removed with water followed by wiping with methyl ethyl
ketone.
b. Abrasive blast clean surfaces to be coated in
accordance with SSPC SP-10.
c. Apply a zinc-rich coating in accordance with KSC-STD-C-
0001 in accordance with the manufacturer's
recommendations to a dry-film thickness of 100 to 150
micrometers (4 to 6 mils).
5.4.2.1.2 Welded and Brazed Joints. Welded and brazed joints
shall be given the same surface preparation and coated with the
same coating as used on tubing.
5.4.2.1.3 Flared Tube Fittings.
5.4.2.1.3.1 Permanent Installations. Fittings exposed to the
weather and not in enclosures shall be completely coated when
associated tubing is coated. Coating material and surface
preparation shall be the same as that used on the tubing. To
prevent line contamination, fittings should not be coated until
after assembly. Sufficient coating shall be applied to bridge
all crevices to preclude moisture entry. When disassembly of a
coated fitting is required and cleanliness of the line must be
maintained, appropriate methods shall be employed to locally
remove the coating as required prior to disassembly. Mechanical
methods will be required to remove the zinc-rich primer. The
Aerocoat AR-7 coating can be removed with methyl ethyl ketone
solvent using clean rags.
5.4.2.1.3.2 Fittings Within Enclosures. Normally, coating of
fittings within enclosures is not required. Where corrosion
protection is required and the methods described above cannot be
utilized, the metal surfaces should be cleaned frequently to
remove surface contaminants.
5.4.3 STAINLESS-STEEL BELLOWS. Stainless-steel bellows that
require protection from corrosion shall be treated in accordance
with the method described for tubing in 5.4.2.1. Corroded
stainless-steel bellows that require replacement shall be
fabricated from an extremely corrosion-resistant material such as
Hastelloy C-22.
5.4.4 STAINLESS-STEEL PIPE, FLANGE BOLTS, AND NUTS. Where
supplementary corrosion protection of stainless-steel pipe,
flange bolts, and nuts is required, they shall be coated with an
inorganic zinc-rich coating in accordance with KSC-STD-C-0001.
Where only protection of flange bolts and nuts is required, they
shall be coated with 75 micrometers (3 mils) minimum of Aerocoat
AR-7 coating. Surface preparation and treatment should be as
described in 5.4.2.1 for stainless-steel tubing.
5.5 ALUMINUM ALLOY PIPE AND TUBING
5.5.1 GENERAL. Aluminum pipe and tubing that is exposed to the
natural environment (humidity extremes, rain, salt-laden air,
acid fallout from boosters, etc.) shall be protected with an
exterior paint system.
5.5.2 CORROSION TREATMENT.
a. Clean and condition tubing or pipe by an appropriate
method outlined in section 4.
b. Apply chemical conversion coating in accordance with
MIL-C-5541 as a preparation for painting.
c. Alternately apply one coat of wash primer in accordance
with DOD-P-15328 followed by one coat of epoxy primer
and one coat of polyurethane enamel in accordance with
KSC-STD-C-0001. Where tolerances preclude paint
coatings, a chemical conversion coating in accordance
with MIL-C-5541 should be applied.
d. Apply 75 to 125 micrometers (3 to 5 mils) Aerocoat AR-7
in the launch environment in accordance with KSC-STD-C-
0001.
5.6 MISCELLANEOUS
5.6.1 STEEL CABLING. If the surface of the cable is corroded,
cable tension should be relieved and the interior of the cable
visually examined. If internal corrosion is noted, the cable
should be replaced. If internal corrosion is not detected, loose
external rust should be removed with clean, dry rags or a fiber
brush. Do not use metallic wools to clean cables since metal
particles may become imbedded, thus creating other corrosion
problems. Solvents also should not be used as they will remove
the internal cable lubrication, thereby allowing cable strands to
abrade and further corrode. In questionable cases, a prooftest
should be performed.
After thorough cleaning, apply grease in accordance with MIL-G-
81322. Do not apply the grease too thick as it will interfere
with the operation of cables at fairleads, pulleys, or grooved
ballcrank areas.
5.6.2 PIANO-TYPE HINGES. This type of hinge is found on access
doors. Frequently, the hinge assembly is made of dissimilar
materials. Corrosion of this item can be controlled only by
frequent lubrication and periodic actuation. Water displacing
penetrating preservative in accordance with MIL-C-16173, grade 3,
or Cortec VCI-368 is recommended. The hinge should be actuated
during application of the preservative to ensure adequate
penetration to all surfaces.
5.6.3 ADJUSTABLE PARTS. Threads of adjustable parts, such as
tie-rod ends, turnbuckles, etc., shall be protected before and
after assembly with corrosion preventative compound in accordance
with MIL-C-16173, grade 4, or Cortec VCI-368.
5.6.4 BARE METAL PISTON SURFACES. Bare metal piston surfaces
that require supplementary corrosion protection shall be coated
with a thin film of preservative compound in accordance with MIL-
C-16173, grade 2. When operational requirements preclude use of
the preservative compound, surfaces should be cleaned frequently
to remove foreign matter.
APPENDIX A
GALVANIC SERIES IN SEA WATER
Noble Platinum
(least active) Gold
Graphite
Silver
18-8-3 Stainless steel, type 316 (passive)
18-8 Stainless steel, type 304 (passive)
Titanium
13 percent chromium stainless steel, type 410
(passive)
67NI-33Cu alloy
75NI-16Cr-7Fe alloy (passive)
Nickel (passive)
Silver solder
M-Bronze
G-Bronze
70-30 cupro-nickel
Silicon bronze
Copper
Red brass
Aluminum bronze
Admiralty brass
Yellow brass
76NI-16Cr-7Fe alloy (active)
Nickel (active)
Naval brass
Manganese bronze
Muntz metal
Tin
Lead
18-8-3 Stainless steel, type 316 (active)
18-8 Stainless steel, type 304 (active)
13 percent chromium stainless steel, type 410
(active)
Cast iron
Wrought iron
Mild steel
Aluminum 2024
Cadmium
Alclad
Aluminum 6053
Galvanized steel
Zinc
Anodic Magnesium alloys
(most active) Magnesium