CPO Basic Corrosion Course 1

CORROSION POLICY AND OVERSIGHT

OFFICE OF THE SECRETARY OF DEFENSE

FOR ACQUISITION, TECHNOLOGY, AND LOGISTICS

BASIC CORROSION OVERVIEW:

AN INTRODUCTION

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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.

Introduction

 The deterioration of a material, usually a metal, or its properties because of a reaction with its environment.

 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

Importance of Corrosion

 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

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

Importance of Corrosion

Lost Production and Downtime

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

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

Importance of Corrosion

Loss of Efficiency

Direct Costs of Corrosion (5 of 8)

Importance of Corrosion

Accidents

 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

 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

 Point Pleasant Bridge over the Ohio River following structural collapse on December 15, 1967 due to corrosion

Importance of Corrosion

Accidents

Importance of Corrosion

Accidents

Indirect Costs of Corrosion (2 of 4)

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

Importance of Corrosion

Appearance

Importance of Corrosion

Environmental Cost

 Better direct assessment efforts  Better designs

Importance of Corrosion

 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

 Describes changes in potential due to passage of electrical current

 Limits amount of current associated with corrosion  Slows corrosion

pH and Corrosion

 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

 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

Atmospheric Corrosion

What are the four classifications of atmospheric corrosion?

 Industrial  Marine  Rural  Indoor

 Combined Effects

Atmospheric Corrosion

Atmospheric Corrosion

 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

 Few strong chemicals

 Potential for stress corrosion cracking from:

– Dusts – fertilizers

– Gases – ammonia (NH3)

Atmospheric Corrosion

 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

 Condensed water necessary for metallic corrosion at low temperatures

 Hydrocarbon-wetted metal surfaces prevent or limit corrosion

Water

 Effects of Mineral Deposits (1 of 3)

Water

Water

Effects of Mineral Deposits (3 of 3)

Leaks on bottom of 3% AFFF mixture lines

 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

 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

 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

 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

 Tensile and yield strength  Hardness  Ductility  Toughness  Fracture  Creep

Properties

What are some of the mechanical properties to consider when selecting a metal?

 Overload (ductile) fracture  Brittle fracture

 Creep  Fatigue

Properties

What are the four (4) forms of fracture for many metals?

Materials Specifications

 Order materials based on standardized materials specifications

– API specifications for oil-country-tubular goods – Unified Numbering System (UNS)

– ASTM Specifications – ASME Specifications

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

 Claiborne Avenue Bridge from Lower 9th _{Side Photo by}

Infrogmation © CC-BY-2.5

General Attack

 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

 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 corrosion of galvanized piping in connection with bronze valve

Galvanic Corrosion

Galvanic Corrosion

 Design  Materials selection  Electrical isolations  Barrier coatings  Cathodic protection  Modification of environment

Galvanic Corrosion

What are some ways you can control galvanic corrosion?

 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

 Material selection  Modification of environment  Protective coatings  Electrochemical techniques  Design

Pitting Corrosion

 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

 Materials selection  Design

 Cathodic protection

Crevice Corrosion

What are the three principal options for controlling crevice corrosion?

 Filiform corrosion underneath transparent protective coating

Filiform Corrosion

 Filiform corrosion on skin of aircraft

(Courtesy Kingston Technical Software)

 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

 Can lead to catastrophic failure

 Inspectors must find cracks before they reach critical flaw size

Environmental Cracking

 Tensile stress

 Alloy composition and structure  Corrosion environment

 Corrosion potential  Temperature

Environmental Cracking

 All metals and many other materials can degrade due to corrosion fatigue

Corrosion fatigue

 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

 Use conventional methods of corrosion control

– More corrosion-resistant alloys – Corrosion inhibitors

– Cathodic protection

Corrosion Fatigue

 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

Copper-based Alloys

Performance of Alloys

 Dezincification of a chrome-plated scuba tank valve

Dealloying

 Selective phase attack of nickel-aluminum bronze

Cast Irons

Performance of Alloys

 Dealloying in cast irons involves dissolution of iron-rich phases leaving porous matrix of graphite and iron

corrosion products

 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

Fretting Corrosion

 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

 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?

Corrosion Control Expenditures by Type

Organic Coatings Metallic Coatings Metals and Alloys Inhibitors

Anodic/Cathodic Protection Polymers

Services & Others

Protective Coatings

Cost Breakdown

Surface Preparation

Permits and Scaffolding

Materials

Inspection and Other Costs

Protective Coatings

 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

Protective Coatings

Protective Coatings

Protective Coatings

Abrasive Blasting

Surface Preparation

 Abrasive blasting to prepare a pipeline for recoating in field

Protective Coatings

 Anchor pattern of pipeline ready for field recoating

Protective Coatings

Waterjetting

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

Geometric and Access Considerations

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?

 Normal ageing phenomena include:

– Blistering

– Checking, alligatoring, or cracking – Chalking and discoloration

– Lifting or undercutting paint film

Protective Coatings

Protective Coatings

Protective Coatings

 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

 Rubber lining being glued onto interior of large-diameter pipe

Protective Coatings

 Debonded liner caused by rapid pressure

release in fluid piping system

 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

 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

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

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

 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?

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”

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

 Visual (VI)

 Radiographic (RT)  Ultrasonic (UT)

 Eddy-current (ET)

 Liquid penetrant testing (PT)  Magnetic particle (MT)

 Positive material identification (PMI)  Thermographic

Inspection

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

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

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

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.

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

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

Ultrasonic (1 of 3) Techniques

 Sound waves detecting different patterns in the part

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

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

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

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

 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) (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

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

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

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

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

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

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

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

 This course covered:

– The definition of corrosion.

– The economic, environmental, and safety significance of corrosion.

– Why metals corrode.

– The differences between inspection and monitoring.