CPO Basic Corrosion Course 1
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Transcript of CPO Basic Corrosion Course 1
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CORROSION POLICY AND OVERSIGHT OFFICE OF THE SECRETARY OF DEFENSE
FOR ACQUISITION, TECHNOLOGY, AND LOGISTICS
BASIC CORROSION OVERVIEW:
AN INTRODUCTION This content is provided as a public service by the Department of Defense Corrosion and Policy Oversight Office (DoD CPO). Information presented on this website is considered public information and may be
distributed or copied unless otherwise specified. Use of appropriate byline/photo/image credits is requested.
This work is not Public Domain outside of the United States. The DoD CPO makes no guarantees this material is Public Domain. Therefore, reproduction of this material could violate individual copyrights, licensed to the
U.S. Government. The DoD CPO makes no warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, product, or process disclosed,
or represents that its use would not infringe privately owned rights.
Reference herein to any specific commercial products, process, or service by trade name, trademark manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by
the United States Government. The opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government, and shall not be used for advertising, commercial gain or product
endorsement purposes. The DoD CPO welcomes your comments regarding this website, its contents and this Statement. If you have questions or concerns, please contact the DoD CPO.
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Upon completion of this chapter, you will be able to:
– Define corrosion.
– Describe the economic, environmental, and safety significance
of corrosion.
– Explain why metals corrode.
– Describe the differences between inspection and monitoring.
More information on all of the topics covered today can
be found in your course manual.
Course Objectives
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Introduction
Which of these show corrosion?
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The deterioration of a material, usually a metal, or its
properties because of a reaction with its environment.
Definition of Corrosion
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Total Direct Cost of Corrosion in U.S.
– $276 billion per year
– 3.1% of Gross Domestic Product (GDP)*
It’s easier to control corrosion to a reasonable limit than
to eliminate it completely.
*Source: Corrosion Cost and Preventative Strategies in the United
States, September 2001, Report FHWA-RD-01-156
Importance of Corrosion
Cost of Corrosion (1 of 3)
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Importance of Corrosion
Cost of Corrosion (2 of 3)
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Losses include corrosion of:
– Residential property:
• Water heaters
• Home plumbing
• Exposed metal surfaces like gutters and downspouts
– Industry:
• Deterioration of public infrastructure such as:
– Bridges
– Public buildings
– Water-supply and waste-water disposal systems
Importance of Corrosion
Cost of Corrosion (3 of 3)
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Importance of Corrosion
Corrosion preparation begins in initial design of system
– Prevents frequent breakdowns
– Limits excessive maintenance, repair, and replacement costs
Over time, corrosion maintenance is more costly than
avoidance
Design phase preparation includes:
– Substituting more corrosion-resistant materials
– Changing operating conditions of system
– Applying other corrosion control measures
Excessive Maintenance, Repair, and Replacement
Direct Costs of Corrosion (1 of 8)
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Importance of Corrosion
Lost Production and Downtime
Direct Costs of Corrosion (2 of 8)
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Importance of Corrosion
Product Contamination
Direct Costs of Corrosion (3 of 8)
Corrosion may contaminate – Foods during production and storage
– Drinking water through distribution lines and plumbing-system components
May result in – Unsightly water (red/brown)
– Illnesses and deaths
Pharmaceutical contamination may cause – Product loss during manufacture
– Premature deterioration and loss of potency during storage
Corrosion on interior of a metal food container
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Importance of Corrosion
Loss of Product
Direct Costs of Corrosion (4 of 8)
Losing a product due to leaks can have significant direct
and indirect costs
– Direct costs include value of the product itself, cost of repairs,
associated costs of downtime, including shutdown and startup, and
disposal costs of contaminated products
– Indirect costs often result in other damage many times greater than
the cost to repair or prevent the leak
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Importance of Corrosion
Loss of Efficiency
Direct Costs of Corrosion (5 of 8)
Corrosion Allowance on offshore platform leg in Cook Inlet, Alaska
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Importance of Corrosion
Accidents
Direct Costs of Corrosion (6 of 8)
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Adding extra material to a system for corrosion control
can increase cost for construction and maintenance
– Protective coatings
– Cathodic protection systems
– Equipment for injection of corrosion inhibitors
Importance of Corrosion
Increased Capital Costs
Direct Costs of Corrosion (7 of 8)
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An oil containment boom deployed by the U.S. Navy
surrounds New Harbor Island, Louisiana
Importance of Corrosion
Photographer unknown http://en.wikipedia.org/wiki/File:Oil_containment_boom.jpg
Fines
Direct Costs of Corrosion (8 of 8)
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Point Pleasant Bridge over the Ohio River following
structural collapse on December 15, 1967 due to
corrosion
Importance of Corrosion
Accidents Indirect Costs of Corrosion (1 of 4)
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Importance of Corrosion
Accidents
Indirect Costs of Corrosion (2 of 4)
Natchitoches, Louisiana, 1965
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Importance of Corrosion
Accidents
Indirect Costs of Corrosion (3 of 4)
Parking Garage Collapse, St. Paul, MN
Caused by Corrosion of Reinforcing Steel, St. Paul,
Minnesota
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Importance of Corrosion
Appearance
Indirect Costs of Corrosion (3 of 4)
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Importance of Corrosion
Environmental Cost
Indirect Costs of Corrosion (4 of 4)
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Better direct assessment efforts
Better designs
Importance of Corrosion
Changes in Engineering Practice
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pH Scale with Common Items
pH and Corrosion
0 7 14
Acid Neutral Base
Concentrated Hydrochloric Acid
pH=0
Diluted Hydrochloric Acid
pH=2.0
Vinegar
pH=3.0
Beer
pH=4.5
Pure Water
pH=7
Sodium Bicarbonate
pH=8.5
Household Ammonia
pH=11.0
Sound Concrete
pH=12.8
Concentrated Sodium
Hydroxide Solution
pH=14.0
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Describes changes in potential due to passage of
electrical current
Limits amount of current associated with corrosion
Slows corrosion
pH and Corrosion
Polarization
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Passive films are chemicals that form on metal surfaces
due to reactions with their environment
– May be protective, but typically are not on carbon steel
– Provide increased corrosion protection on corrosion-resistant
alloys (CRAs)
– Many cannot be seen
pH and Corrosion
Passivation
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Is a surface film that deposits
on metal surfaces from liquid
water and may also provide
corrosion protection
Also describes reaction
products of metals with high-
temperature environments
pH and Corrosion
Passivation: Scale
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Atmospheric Corrosion
What are the four classifications of atmospheric
corrosion?
Industrial
Marine
Rural
Indoor
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Combined Effects
Atmospheric Corrosion
Above-ground Storage Tank
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Atmospheric Corrosion
Industrial
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High concentrations of wind-
borne salt may be carried many
kilometers (miles) inland
Hygroscopic materials absorb
water and release water only
during conditions of very low
relative humidity
Atmospheric Corrosion
Marine
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Few strong chemicals
Potential for stress corrosion
cracking from:
– Dusts – fertilizers
– Gases – ammonia (NH3)
Atmospheric Corrosion
Rural
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Can be controlled when air is kept above dew point
Is generally less corrosive
Electronics processing and control rooms often use
positive pressures to limit ingress of outside, moist, and
contaminated air
Vapor-phase corrosion inhibitors prevent corrosion
during shipping and storage in warehouses that are
protected from rain but are not heated
Atmospheric Corrosion
Indoor
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Condensed water necessary for metallic corrosion at low
temperatures
Hydrocarbon-wetted metal surfaces prevent or limit
corrosion
Water
Overview
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Effects of Mineral Deposits (1 of 3)
Water
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Water
Effects of Mineral Deposits (2 of 3)
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Water
Effects of Mineral Deposits (3 of 3)
Leaks on bottom of 3% AFFF mixture lines
Fluid velocities affect corrosion rates
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High temperatures generally increase all chemical
reactions, including corrosion reactions
High temperatures lower solubility of dissolved gases
Pressure alters boiling points. Pressure vessels and
downhole environments often have liquid water up to
250°C (400+°F).
Degree of ionization of water depends on temperature,
and this alters the pH at which water is neutral
Water
Effects of Temperature
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Microbially-influenced corrosion
(MIC) and bacteria that can
produce MIC can be classified
as:
– Planktonic bacteria that
freely float or "swim" in a
body of water
– Sessile bacteria that are
attached to surfaces and
become motionless
Water
Microbially-influenced Corrosion
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Air-soil interface is most corrosive location for buried
soils
Underground corrosion varies with soil types
Soil moisture and access to air determine the amount of
corrosion
Soils
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Materials are chosen for a number of reasons, and
corrosion-resistance is often less important than
strength, formability, cost, etc.
Almost all metals used in engineering applications are
alloys
– Stronger than pure metals
Metallurgy Fundamentals
Overview
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Tensile and yield strength
Hardness
Ductility
Toughness
Fracture
Creep
Properties
What are some of the mechanical properties to
consider when selecting a metal?
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Overload (ductile) fracture
Brittle fracture
Creep
Fatigue
Properties
What are the four (4) forms of fracture for many
metals?
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Materials Specifications
Order materials based on standardized materials
specifications
– API specifications for oil-country-tubular goods
– Unified Numbering System (UNS)
– ASTM Specifications
– ASME Specifications
Metallurgy Fundamentals
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General
Pitting SCC
Crevice
Erosion
Intergranular
Embrittlement Fatigue
Frequency of Forms of Corrosion
Forms of Corrosion
Most Structures and Equipment Experience Multiple Forms of Corrosion
http://corrosion-doctors.org/Localized/Introduction.htm
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Claiborne Avenue Bridge from Lower 9th Side Photo by
Infrogmation © CC-BY-2.5
General Attack
Introduction
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Proceeds more or less uniformly over exposed surface
without significant attack in a single area
Also called
– General corrosion
– Uniform corrosion
Most common form, but little engineering significance
– Structures become unsightly before they are structurally
compromised
General Attack
Definition
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Stray current corrosion (electrolysis)
Differential cells due to:
– Differential aeration
– Temperature differences
– Changes in soil types
Stress areas
Sharp areas
Different microstructures (e.g. in welds)
Galvanic Corrosion
Galvanic Coupling of Two or More Metals (1 of 2)
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Galvanic corrosion of galvanized piping in connection
with bronze valve
Galvanic Corrosion
Galvanic Coupling of Two or More Metals (2 of 2)
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Galvanic Corrosion
Environmental Effects on Galvanic Corrosion
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Design
Materials selection
Electrical isolations
Barrier coatings
Cathodic protection
Modification of environment
Galvanic Corrosion
What are some ways you can control galvanic
corrosion?
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Localized attack on a metal
surface at locations where overall
metal surface is relatively
uncorroded and is often covered
with passive films or scales
– Results in cavities or holes
Most common way of removing
deposits by mechanical removal
using pipeline pigs or similar
devices
Pitting Corrosion
Definition
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Material selection
Modification of environment
Protective coatings
Electrochemical techniques
Design
Pitting Corrosion
What are some ways to control pitting corrosion?
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Major difference between crevice corrosion and pitting
corrosion is scale of corrosion initiation site
Electrochemical mechanisms of crevice corrosion:
– Oxygen-concentration cell corrosion
– Metal ion-concentration cell corrosion
Crevice Corrosion
Definition
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Materials selection
Design
Cathodic protection
Crevice Corrosion
What are the three principal options for controlling
crevice corrosion?
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Filiform corrosion underneath transparent protective
coating
Filiform Corrosion
Filiform corrosion on skin of aircraft (Courtesy Kingston Technical Software)
Definition
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Corrosion, particularly on painted surfaces, can be
prevented by:
– Properly cleaning and preparing metallic surface
– Applying coating only to thoroughly-cleaned and dried surface
Filiform Corrosion
Control
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Can lead to catastrophic failure
Inspectors must find cracks before they reach critical
flaw size
Environmental Cracking
Definition
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Tensile stress
Alloy composition and structure
Corrosion environment
Corrosion potential
Temperature
Environmental Cracking
Control
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All metals and many other materials can degrade due to
corrosion fatigue
Corrosion fatigue
Definition
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Cracked fuselage on Aloha Airlines Flight 243 in 1988,
photo from
http://www.airdisaster.com/photos/aloha243/6.shtml
(photographer unknown)
Corrosion Fatigue
Collapsed Alexander Kielland semi-submersible platform in the North Sea, 1980
Examples
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Use conventional methods of corrosion control
– More corrosion-resistant alloys
– Corrosion inhibitors
– Cathodic protection
Corrosion Fatigue
Control
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Intergranular corrosion:
– Can happen in many different alloy systems including carbon
steels
– Is an attack on, or adjacent to, grain boundaries of metal or alloy
Can occur:
– In heat-affected zones of welds, where local segregation
concentrates some alloy constituents
– When through-section grain boundaries are exposed in wrought
metals (plate, extrusions, etc.)
– In many different alloy systems
Intergranular Corrosion
Description
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Copper-based Alloys
Performance of Alloys
Dezincification of a chrome-plated scuba tank valve
Dealloying
Selective phase attack of nickel-aluminum bronze
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Cast Irons
Performance of Alloys
Dealloying in cast irons involves dissolution of iron-rich
phases leaving porous matrix of graphite and iron
corrosion products
Dealloying
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Happens when small oscillations in metal-to-metal
contact abrade protective films on metal surfaces and
produce accelerated corrosion
– Sometimes considered a form of erosion corrosion
Fretting Corrosion
Description
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Fretting Corrosion
Examples:
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Deterioration of metal at
temperatures where direct
chemical reactions between
metal and environment cause
material to degrade
Usually associated with
formation of thick oxide or
sulfide scales
High Temperature Corrosion
Definition
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Protective Coatings
Corrosion Inhibitors and Chemical/Physical Treatment of
Water
Cathodic Protection
Anodic Protection
Corrosion Control
What are the most common methods of corrosion
control?
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Corrosion Control Expenditures by Type
Organic Coatings
Metallic Coatings
Metals and Alloys
Inhibitors
Anodic/Cathodic Protection
Polymers
Services & Others
Corrosion Control
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Protective Coatings
Role of Paint, Protective Coatings, and Linings on Storage Tank
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Cost Breakdown
Surface Preparation
Permits and Scaffolding
Materials
Inspection and OtherCosts
Protective Coatings
Applying Protective Coating to Existing Structure
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Serve as barriers keeping aggressive environments
away from their substrates
– Corrosion inhibitors can be added to coating which, when
wetted, are released into corrosion-causing moisture to limit
corrosion
– Galvanic metallic coatings (like zinc) can be applied to
substrates
– Some systems combine more than one of three methods
Protective Coatings
Coating Systems
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Protective Coatings
Barrier Coatings
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Protective Coatings
Inhibitive Coatings
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Protective Coatings
Sacrificial (Galvanic) Coatings
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Abrasive Blasting
Surface Preparation
Abrasive blasting to prepare a pipeline for recoating in
field
Protective Coatings
Anchor pattern of pipeline ready for field recoating
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Protective Coatings
Waterjetting
Surface Preparation
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Pickling
Surface Preparation
Inexpensive cleaning procedure
Followed by thorough rinsing and drying
One of cleanest and most active surfaces for further
processing
Involves sheet, plate, coil stock, and other forms of
metal, but is rarely used in field
Protective Coatings
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Protective Coatings
Geometric and Access Considerations
Surface Preparation
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1. Poor surface preparation and cleanliness
2. Poor coating application
3. Poor or inadequate inspection
4. Poor specifications (both construction and coating)
5. Poor component design
6. Murphy’s Law
Protective Coatings
What are the primary reasons for coating failures in
order of importance?
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Normal ageing phenomena include:
– Blistering
– Checking, alligatoring, or cracking
– Chalking and discoloration
– Lifting or undercutting paint film
Protective Coatings
Coating Degradation (1 of 3)
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Protective Coatings
Coating Degradation (2 of 3)
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Protective Coatings
Coating Degradation (3 of 3)
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Air-soil interface is most
corrosive location on many
buried pipelines
Loose soil does not provide
effective electrolyte for
cathodic protection
Pipeline coatings are often
damaged by soil motion and
abrasion
Protective Coatings
Wraps and Linings
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Rubber lining being glued onto interior of large-diameter pipe
Protective Coatings
Debonded liner caused by rapid pressure release in fluid piping system
Wraps and Linings
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Used to limit corrosion rates
Can be:
– Anodic to their substrate (zinc, aluminum, or cadmium on steel)
– Cathodic (chrome plating, precious metals, etc.)
Protective Coatings
Metallic Coatings
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Applied only to enclosed systems
Economics often dictates that mechanical treatment is
first approach with limitations
Surface waters are classified by their salt contents
– Fresh water
– Seawater
– Brines
– Brackish waters
Water Treatment
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Chemical Water Treatment
Corrosion inhibitors are chemicals that, when added to
water, reduce corrosion rates as much as 95%
Passivating inhibitors may also be used in protective
coating formulations
Most commercial corrosion inhibitor packages are
complex blends of many different chemicals
Chemicals can be damaging to elastometric seals and
similar polymeric components of a system
Corrosion control is only one reason for water treatment
Water Treatment
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Overview
Electrical means of corrosion control
– Protected structure becomes cathode in electrochemical cell
Pipelines are most common structures to be cathodically
protected
Cathodic protection substantially reduces oxidation
current (corrosion) on structure being protected
Cathodic protection does not stop corrosion—it reduces
corrosion rate, hopefully to negligible, or at least
acceptable, rate
Cathodic Protection
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Inspection
– Process used to determine condition of system at time of
inspection
Monitoring
– Process used either periodically or continuously as a tool for
assessing need for corrosion control or effectiveness of
corrosion control methods
Inspection, Monitoring, and Testing
What is the difference between inspection and
monitoring?
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Goals
Determine if structures exposed
to environment conform to safe
parameters of original design
Establish whether corrosion
has consumed “corrosion
allowance”
Are conducted in organized and
systematic manner
May be “Scheduled” or
“Unscheduled”
Inspection
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Types
Scheduled Inspections
– Planned in advance
– Conducted during scheduled plant downtimes
Unscheduled Inspections
– Occur because of a failure, usually
– Result in expensive shutdowns
– Determine what needs to be done to resume safe operations
Inspection
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Visual (VI)
Radiographic (RT)
Ultrasonic (UT)
Eddy-current (ET)
Liquid penetrant testing (PT)
Magnetic particle (MT)
Positive material identification (PMI)
Thermographic
Inspection
What are some common inspection techniques?
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Visual (1 of 2)
Techniques
Oldest, simplest, and least expensive nondestructive
test methods
Inspectors examine objects visually by:
– Using magnifying glass
– Probing discreetly with penknife
– Viewing inaccessible areas with boroscopes and remote
television cameras
Inspection
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Visual (2 of 2)
Techniques
Benefits:
– Ability to:
• Scan large areas quickly
• Identify pit depths and pitting rates
• Use video techniques in areas where personnel access is denied
Limitations:
– Must shutdown during internal inspection
– Borescopes and cameras only work during operation if process
is transparent
– Only identify surface defects
Inspection
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Radiography (1 of 4)
Techniques
Uses penetrating radiation from x-ray tube or radioactive
source to detect surface and subsurface flaws
Measures amounts and absorptive characteristics of
materials between radiation source and detector
– Useful for detecting voids, inclusions, and pit depths
– Less effective in locating cracks unless the orientation of the
crack is known
Inspection
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Radiography (2 of 4)
Techniques
Schematic of film radiography of a metal with a corrosion
pit, an internal crack, and internal porosity defects.
Inspection
Radiograph showing erosion corrosion at a piping elbow.
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Radiography (3 of 4)
Techniques
Benefits:
– Can use either electronic cameras instead of film
– Creates permanent image record
– Requires minimal surface preparation since coatings and thin
surface deposits are transparent
– Works on most materials
– Shows fabrication errors, weld defects, and weight-loss
corrosion
Inspection
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Radiography (4 of 4)
Techniques
Limitations:
– Allows inspection of local areas only
– Does not provide depth of defect information with 2D images
– Requires access to both sides of inspected equipment
– Requires radiation safety measures
– Needs free access for radiation source
– Misses crack-like defects if not oriented favorably
– Expensive
Inspection
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Ultrasonic (1 of 3)
Techniques
Sound waves detecting different patterns in the part
Inspection
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Ultrasonic (2 of 3)
Techniques
Benefits:
– Requires direct access to only one side of inspected material
– Provides accurate measurement of thickness and flaw depth
– Can penetrate thick materials
– Permits estimation of maximum allowable pressures based on
measurements and ANSI/ASME B31G, API 653, API 510,
API/ASME 579 and similar codes
Inspection
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Ultrasonic (3 of 3)
Techniques
Limitations:
– Requires extensive training and
experience
– Has limited use on thin materials
– May not be suitable for on-line
inspection of hot equipment due
to temperature limitations
Inspection
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Eddy Current Inspection (ET) (1 of 2)
Techniques
Works on any electrically conductive
material
Allows inspectors to analyze signals
from cracks, bulges, corrosion pits
to correlate flaws
Inspection
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Eddy Current Inspection (ET) (2 of 2)
Techniques
Benefits:
– Relatively simple and rapid method
– Makes surface defects easier to be seen
– Works on all nonporous materials
Limitations:
– Requires extensive training
– Is limited to conductive materials
– Has limited penetration depth
Inspection
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Techniques
Used to locate crack-like surface
defects on a variety of non-porous
materials (metals, polymers, and
concrete)
Also called dye penetrant inspection
(DPI)
Inspection
Liquid Penetrant Inspection (PT) (1 of 2)
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Liquid Penetrant Inspection (PT) (2 of 2)
Techniques
Benefits:
– Is relatively simple and rapid
– Makes surface defects easier to be seen
– Works on all nonporous materials
Limitations:
– Requires skilled inspectors
– Is limited to surface defects
– Requires direct access to surface being inspected
– Requires chemical cleaning and disposal
– Permits paint and other coatings to mask defects
Inspection
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Magnetic Particle Inspection (MT) (1 of 2)
Techniques
Two principle advantages over dye
penetrant inspection:
– Detect near-surface flaws (e.g. hydrogen
blisters or weld defects) that would be
missed by penetrant inspection
– Sometimes detect smaller flaws than would
be detected with penetrant inspection
Inspection
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Magnetic Particle Inspection (MT) (2 of 2)
Techniques
Benefits:
– Relatively simple and rapid method
– May detect fine cracks missed by visual and dye penetrant
inspection
– May reveal shallow subsurface flaws
Limitations:
– Requires extensive training of inspectors
– Allows ferromagnetic material inspection only
– Requires clean, smooth surfaces
– May have reduced sensitivity from paint or coatings
Inspection
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Positive Metal Identification
(PMI) (1 of 2)
Techniques
Uses portable X-ray
fluorescence spectrometers to
identify and confirm
composition of corrosion-
resistant alloys
Analyzes surface in seconds
and compares it with preloaded
spectrum providing nearest
match
Inspection
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Positive Metal Identification (PMI) (2 of 2)
Techniques
Benefits:
– Identifies alloys quickly and accurately
Limitations:
– Cannot differentiate between carbon steels
– Will not detect other light elements
– May get false results from surface contamination
– Requires direct access to cleaned surface for analysis
– Has a high initial equipment cost
Inspection
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Thermographic (1 of 2)
Techniques
Uses infrared cameras to
detect temperature differences
in equipment.
Used as a remote inspection
technique to determine fluid
levels in storage tanks and for
a variety of other purposes
Inspection
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Thermographic (2 of 2)
Techniques
Benefits:
– Is a nonintrusive remote technique
– Can detect temperature changes as low as 5°F (3°C)
– Allows identification of hot or cold spots due to fouling,
maldistribution of flow, settling of sediment or other debris, and
loss of internal refractory lining
Limitations:
– Cannot determine corrosion or wall thinning
Inspection
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Overview
Allows operators to determine if corrosive conditions and
corrosion rates are changing
– Can be used to determine if environments are becoming more or
less corrosive
Determines effectiveness of corrosion control methods
such as chemical inhibitor injection
Inspection
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This course covered:
– The definition of corrosion.
– The economic, environmental, and safety significance of
corrosion.
– Why metals corrode.
– The differences between inspection and monitoring.
Review