CPO Basic Corrosion Course 1

CORROSION POLICY AND OVERSIGHT OFFICE OF THE SECRETARY OF DEFENSE

FOR ACQUISITION, TECHNOLOGY, AND LOGISTICS

BASIC CORROSION OVERVIEW:

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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

Introduction

Which of these show corrosion?

The deterioration of a material, usually a metal, or its

properties because of a reaction with its environment.

Definition of Corrosion

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)

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




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)


Lost Production and Downtime



Product Contamination


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


Loss of Product


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


Loss of Efficiency


Corrosion Allowance on offshore platform leg in Cook Inlet, Alaska


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


Increased Capital Costs


An oil containment boom deployed by the U.S. Navy

surrounds New Harbor Island, Louisiana


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


Accidents Indirect Costs of Corrosion (1 of 4)


Accidents

Indirect Costs of Corrosion (2 of 4)

Natchitoches, Louisiana, 1965


Accidents


Parking Garage Collapse, St. Paul, MN

Caused by Corrosion of Reinforcing Steel, St. Paul,

Minnesota


Appearance



Environmental Cost


Better direct assessment efforts

Better designs


Changes in Engineering Practice

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

Polarization

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

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

Atmospheric Corrosion

What are the four classifications of atmospheric

corrosion?

Industrial

Marine

Rural

Indoor

Combined Effects


Above-ground Storage Tank


Industrial

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


Marine

Few strong chemicals

Potential for stress corrosion

cracking from:

– Dusts – fertilizers

– Gases – ammonia (NH3)


Rural

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


Indoor

Condensed water necessary for metallic corrosion at low

temperatures

Hydrocarbon-wetted metal surfaces prevent or limit

corrosion

Water

Overview

Effects of Mineral Deposits (1 of 3)

Water

Water


Water


Leaks on bottom of 3% AFFF mixture lines

Fluid velocities affect corrosion rates

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

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

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

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

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

Metallurgy Fundamentals

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




Claiborne Avenue Bridge from Lower 9th Side Photo by

Infrogmation © CC-BY-2.5

General Attack

Introduction

http://commons.wikimedia.org/wiki/Category:CC-BY-2.5





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

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)

Galvanic corrosion of galvanized piping in connection

with bronze valve

Galvanic Corrosion

Galvanic Coupling of Two or More Metals (2 of 2)

Galvanic Corrosion

Environmental Effects on 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

Definition

Material selection

Modification of environment

Protective coatings

Electrochemical techniques

Design

Pitting Corrosion

What are some ways to control 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

Definition

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)

Definition

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

Can lead to catastrophic failure

Inspectors must find cracks before they reach critical

flaw size

Environmental Cracking

Definition

Tensile stress

Alloy composition and structure

Corrosion environment

Corrosion potential

Temperature

Environmental Cracking

Control

All metals and many other materials can degrade due to

corrosion fatigue

Corrosion fatigue

Definition

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



Use conventional methods of corrosion control

– More corrosion-resistant alloys

– Corrosion inhibitors

– Cathodic protection

Corrosion Fatigue

Control

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

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

Dealloying

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

Fretting Corrosion

Examples:

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

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

Corrosion Control

Protective Coatings

Role of Paint, Protective Coatings, and Linings on Storage Tank

Cost Breakdown

Surface Preparation

Permits and Scaffolding

Materials

Inspection and OtherCosts

Protective Coatings

Applying Protective Coating to Existing Structure

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

Protective Coatings

Barrier Coatings

Protective Coatings

Inhibitive Coatings

Protective Coatings

Sacrificial (Galvanic) 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

Surface Preparation

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

Protective Coatings

Geometric and Access Considerations

Surface Preparation

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

Coating Degradation (1 of 3)

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

Wraps and Linings

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

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

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

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

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

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”

Inspection

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

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?

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

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

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


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.


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


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

Ultrasonic (1 of 3)

Techniques

Sound waves detecting different patterns in the part

Inspection

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

CPO Basic Corrosion Course 1

Documents

Transcript of CPO Basic Corrosion Course 1