Process Engineering Equipment Handbook Episode 2 Part 8 pps

deceptively simple and is often misused. Surface preparation is particularly
important because defects can easily be masked by overpeening.
In the analysis of service-exposed components such as discs and blades, a
judicious compromise is often required on the surface preparation. Light glass bead
cleaning is often effective in removing surface deposits with minimal loss in
sensitivity; however, care must be taken not to overpeen the surface. Where
optimum sensitivity is required, such as in rotating blades, the parts should be
chemically etched after glass bead cleaning to remove metal peened over the
discontinuities.
LPI is designed to locate only discontinuities that are open to the surface. When
a penetrant is applied to the surface of a component, it is drawn into surface
discontinuities by capillary forces. After the excess penetrant has been removed
from the surface, the penetrant trapped by the defects is drawn back out by
capillary action and forms a detectable outline of the defect.
Over the years, many penetrants have been developed that vary in sensitivity
and application. As indicated in the enclosed information sheets from the
manufacturers, the penetrants are divided into water washable and post-
emulsifiable (solvent remover) types. Commonly used penetrants include ZL-17B or
Ardrox 970-P10 (water washable) and ZL-22A (solvent type). Care must be taken
to ensure that the correct combinations of penetrants, removers, and developers are
used. In addition, a test should never be repeated using a different penetrant type
because complete masking of the defects will occur.
Field inspections are particularly challenging because the inspection conditions
are generally not ideal and often the operator does not have all the equipment
desired. Although some compromises are often required, the inspector must ensure
that the sensitivity and validity of the test are not jeopardized.
Laser techniques. These can be used for inspection, calibration, and highest-
resolution surface mapping.
Computer-aided topography (CAT) scan. CAT scanners locate internal defects in
engine components. It is particularly useful for sophisticated components such as

blades and airfoils with internal passages and cavities.
Powder metallurgy
This involves molding of powdered alloy flux (somewhat like plasticine) to damaged
areas of a component (blades and vanes typically) and use of elevated temperatures
to make that flux integral with the parent material. Some sophisticated repair
shops develop their own equivalent process and do the work under license to OEMs
or sell the OEM (and other facilities) the right to use the process.
Welding
Traditional weld repairs could result in component warpage, which then requires
specialized heat treatment and associated jigs, which, in turn, extends repair times
and costs, with severe consequences for overall turbine maintenance.
᭿
Laser welding: Extremely accurate and much less heat intensive than
conventional repair, laser welding is particularly useful for turbine blades,
compressor blade leading edges, and other sensitive components.
Metallurgy; Metallurgical Repair; Metallurgical Refurbishment M-37
᭿
Weld repair using robotics*: The automation of turbine blade welding provides
both metallurgical benefits and production advantages. Heat-affected zone
cracking in sensitive superalloys, such as IN738 and IN100, can be eliminated
or greatly reduced by optimizing process control, and higher production yields
can be achieved when welding jet engine blades. However, the successful
implementation of automated processes requires careful consideration and
engineering of the technology package. In particular, the equipment packager
must be experienced in the technology associated with turbine blade welding and
incorporate appropriate tooling, measurement system, power source and robotic
controls.
᭿
Superalloy welding at elevated temperatures (SWET): OEMs often develop their
own proprietary process for this technology that is commonly used on superalloy

or directionally solidified materials such as turbine blades.
᭿
Dabber TIG (tungsten inert gas): A slightly older process that uses TIG to rebuild
knife edge seals with minimal heat warpage.
᭿
Plasma transfer arc: Similar to dabber TIG and used for the same components.
The exception to the “land-based turbine design approaches aircraft engine
technology standards” is evident in certain OEM models, such as Alstom’s GT11N2
and GT35. However, that is because both these models are designed to take the
punishment meted out by vastly inferior fuels or just be conservative enough to
require less training for end-user operators and maintenance staff. Alstom also
makes sophisticated models with metallurgy that will match those of the “dual”
(both aircraft engine and land-based engine) OEMs for users with different
requirements and less punishing fuels. However, Alstom also contracts powder
metallurgy repair, for instance.
All OEMs can enhance their “benefits to end user” objectives from some for
the preceding techniques, such as the ultimate time-saver laser machining. It
ultimately depends on the specifics of an end user’s application. The potentially
usable repair techniques on any end user’s selection play a huge role in determining
the turbine model’s overall maintenance costs and therefore the ultimate crux of
gas turbine selection, called “total costs per fired hour.”
Basic Fundamentals of Materials
The properties of the materials used in gas turbines are determined by their
composition and their prior processing and service history. To understand how these
factors work to govern alloy behavior, a basic understanding of some fundamental
principles of materials engineering is useful. This is largely a question of
understanding some of the terms used by metallurgists in describing material
behavior.
Turbine materials are governed by the laws of thermodynamics, which basically
means that changes that take place in the materials result in a reduction of the

energy state in the material. We often speak of the equilibrium or stable condition
of a material; this simply means the condition of lowest energy.
Given infinite time, all materials would end up in their equilibrium condition. In
M-38 Metallurgy; Metallurgical Repair; Metallurgical Refurbishment
* Source: Adapted from extracts from Lownden, Pilcher, and Liburdi, “Integrated Weld Automation for
Gas Turbine Blades,” Liburdi Engineering, Canada, ASME paper 91-GT-159.
practice, there are kinetic barriers to achieving equilibrium and most materials are
used in a metastable condition. The most common kinetic barrier is the rate of
diffusion (i.e., the speed at which atoms in a solid material can rearrange
themselves). Almost all of the metallurgical reactions that occur in turbine
materials occur at rates governed by the speed of diffusion. Examples include the
rate at which a coating interdiffuses with the base metal or the rate at which
strengthening particles grow in an alloy.
All of the materials used in gas turbines are crystalline in nature. This means
that the atoms of the elements that make up the alloy are arranged in regular
periodic arrays or lattices, with each atom occupying a site in the array. When we
refer to grain or crystal orientation, we are referring to the direction relative to this
crystal lattice. The mechanical and physical properties of materials depend on their
orientation.
In real materials, the crystals are not perfectly periodic, but contain various
lattice defects. Two of the most important of these are dislocations and grain
boundaries. Dislocations are an important class of planar defects, since their
presence within crystals leads to plastic deformation behavior. Most materials are
not used as a single crystal, but as polycrystals that consist of many individual
crystals with different orientation called grains. The interfaces between the
individual grains are grain boundaries. The size and degree of orientation between
grains and the nature of the grain boundaries are important in determining the
properties of a material.
Metallurgists control the nature of grains by the processing performed during
manufacture. In a polycrystalline material, grains will increase in size at elevated

temperatures and thus grain growth will occur during high temperature heat
treatments. Grain sizes can be reduced by introducing plastic work into a material.
At high temperatures, the resulting strain energy drives the process of
recrystallization, which results in the formation of smaller grains during heat
treatments or hot-working operations.
Engineering materials are almost exclusively mixtures of two or more elements,
which are called alloys. Alloying elements can dissolve in the matrix of the principal
elements to form a solid solution, in which the dissolved element is randomly
distributed in the crystal lattice. The alloying elements can also react with the
matrix to form a compound that has a specific arrangement of atoms of each
element.
Commonly both solid solutions and compounds will coexist within the same
material as different phases. The stability of specific phases within a given alloy
system varies with the composition and the temperature. Kinetics also determine
which phases form within an alloy. Many reactions are sluggish enough that
the stable phase may not form initially and the alloy may exist in metastable
condition for some length of time. By using chemistry and heat treatment to
control the phases formed by an alloy, metallurgists can alter the strength of
materials.
Three principal types of deformation take place upon the application of loads
to turbine materials. Elastic deformation is instantaneous reversible deformation
that results from the distortion of the crystal lattice. Plastic deformation is the
irreversible deformation that takes place instantaneously through the movement
of dislocations through the crystal matrix. Creep deformation takes place by a
variety of diffusion-controlled processes over time, resulting in continuing strain
under the applied load.
At sufficiently high loads or after a critical amount of deformation has taken
place, fracture of a material will occur. Fracture can be broadly classed as ductile
or brittle. In turbine materials under most conditions, fracture occurs by the
Metallurgy; Metallurgical Repair; Metallurgical Refurbishment M-39

formation and linkage of internal cavities formed either by creep or plastic
deformation.
When cyclic loads are applied to a material, cracking and fracture may occur by
the process of fatigue. On a microscopic scale, fatigue occurs by localized plastic
deformation, resulting in the initiation and growth of macroscopically brittle cracks.
The resistance of a material to deformation and fracture depends on its
composition and microstructure. The size of grains, the size and distribution of
second phases, and the effects of alloying elements on the crystal lattice of the
matrix all influence the mechanical behavior of the alloy.
Exposure of alloy surfaces to operating conditions results in surface reactions
between the alloy and the environment. Oxidation and hot corrosion occur at
elevated temperatures through direct reaction with oxygen and other environmental
contaminants. Aqueous corrosion occurs in wet environments through dissolution
reactions.
Material Selection for Gas Turbines
This subsection is with specific reference to gas turbine materials, the most severe
thermal application in a plant.
The materials used in gas turbines or jet engines span the range of metallurgical
alloys from high-strength steel, to lightweight aluminum or titanium, to temperature-
resistant nickel or cobalt superalloys. In a gas turbine, the temperatures can vary
from ambient to gas temperatures in excess of the melting point of superalloys and,
therefore, the materials in the different sections must be selected on the basis of
their capability to withstand the corresponding levels of stress and temperature.
The following summary outlines the materials used in the different components of
the gas turbine, along with a rationale for their selection.
Compressor rotor
The temperature in a typical compressor will range from ambient to approximately
800°F (425°C). The discs and blades rotate at high-speed and are, therefore, highly
stressed and subjected to aerodynamic buffeting or fatigue. In industrial turbines,
the discs are generally made from high strength alloy steel and the blades from

martensitic stainless steel. However, in jet engine derivatives, lighter materials
such as aluminum and titanium are used for the blades and vanes in the front of
the compressor. In some cases, the last stages of the compressor can run
significantly hotter and more creep-resistant materials must be used such as A286
and IN718.
Turbine discs
Turbine discs are highly stressed in the rim area where the blade root attachment
occurs and in the hub of bored discs where high burst strength is required. The
discs are forged from high-strength steels in advanced industrial turbines and iron
or nickel base superalloys such as A286 and Inconel 718 for the jet engines. The
disc rim is generally isolated from the hot gas path and cooled to as low as 600°F
(315°C) for alloy steel discs to ensure adequate material strength and creep
resistance.
Combustion cans
The flame temperature in a burner generally exceeds 3000°F (1650°C). The
temperature is moderated by mixing with cooler compressor discharge air that flows
M-40 Metallurgy; Metallurgical Repair; Metallurgical Refurbishment
around the combustion chamber and through the slots in the walls to keep metal
relatively cool [approximately 1500°F (815°C)]. The combustor cans are generally
fabricated from nickel base sheet superalloys such as Hastelloy X, Nimonic C263,
and Inconel 617. These alloys have good weldability and oxidation resistance.
Turbine vanes
The stationary vanes in a turbine act as guides for the hot gas to ensure that it
enters the blade’s airfoil at the right angle and with minimal pressure loss. The
applied stresses are generally low; however, they are subjected to turbine inlet gas
temperatures which, in some engines, exceed the melting point of the material
[2500°F (1370°C)]. The vanes are generally made from cobalt base alloys such
as FSX414 and X45, which have good castability and excellent oxidation and
thermal shock resistance. In advanced designs, the vanes are cast with integral
cooling passages to reduce the metal temperature. The cobalt base alloys are

generally weldable and minor weld repairs are often allowed. In some designs,
the cobalt base alloys have been replaced with more creep-resistant nickel base
alloys such as IN738, Rene 80, and IN939, which are significantly harder to weld
repair.
Turbine blades
Turbine blade airfoils are subjected to the most severe combination of applied
stresses due to centrifugal and bending loads and high temperatures. The blade
materials must have excellent strength and creep resistance, as well as oxidation
resistance. In advanced units, the blades are cooled by internal passages to
moderate the metal temperature and improve blade life. The blades are generally
precision forged or cast from nickel base alloys such as Udimet 520, IN738, Rene
80, and Mar M247 and can be manufactured as either equiaxed, directionally
solidified, or single crystal castings. These materials have poor weldability and
repairs must be approached with extreme caution.
Service life for turbine components
Once in service, critical gas path components require care and attention to optimize
their life potential. Often, turbine users choose to abdicate their responsibility in
this critical area and elect to rely solely on the manufacturer for guidance. However,
this can lead to premature component replacement of failures if components are
neglected or improperly assessed.
A gas path component management program basically involves the detailed
characterization of components at established intervals. For example, during major
overhauls, representative blades are removed and destructively tested for corrosion,
microstructure, and remaining creep life. The data are tabulated and a life trend
curve established for the material. This will provide the user with specific
information on how the engines are standing up rather than rely on someone
else’s data and provide advance warning of impending problems with corrosion or
creep.
Creep damage can be detected in turbine blades by judicious testing of samples
from the airfoil and by metallurgical inspection. With prolonged service exposure

at high temperature and stress, cavities are formed at the grain boundaries of the
material that, with time, will grow in number and size and eventually join to form
a crack. However, if creep voiding can be detected prior to surface crack formation,
the parts can be rejuvenated by hot isostatic pressing (HIP).
Metallurgy; Metallurgical Repair; Metallurgical Refurbishment M-41
During HIP, the parts are subjected to a combination of pressure and temperature
that collapses any internal cavities and diffusion bonds the surfaces back together.
Tests have shown that, in most materials, HIP is capable of fully restoring the
properties and, therefore, offers the opportunity to recycle and extend the life of
serviced blades.
Steam-turbine metallurgy
Steam turbines operate in far less demanding service than gas turbines as the
following list of typical steam turbine materials illustrates.
Typical steam turbine materials
Part Identification Material Commerical Equivalent
Steam rings — 650 psig/750°F Carbon steel ASTM A216 grade WCB
— 900 psig/950°F Alloy steel ASTM A217 grade WC6
— 1500 psig/950°F Alloy steel ASTM A217 grade WC9
Valve chests — 650 psig/750°F Carbon steel ASTM A216 grade WCB
— 900 psig/950°F Alloy steel ASTM A217 grade WC6
— 1500 psig/950°F Alloy steel ASTM A217 grade WC9
Cylinders Carbon steel ASTM A216 grade WCB
Nozzle blocks Carbon steel ASTM A212 grade A
Stainless steel AISI 416
Sovernor valve Stainless steel AISI 410
Sovernor valve stem Stainless steel AISI 410
Shafts Alloy steel AISI E4340
Discs — standard forged Alloy steel ASTM A294 class 5
— integral with shaft Alloy steel ASIS E4340
Blading Stainless steel AISI 403

Bearing brackets Carbon steel ASTM A216 grade WCB
Manufacture
Superalloys
The term superalloy is popularly used to define a material having structural
strength above 1000°F (540°C). The development of these temperature-resistant
materials in the early 1940s was a primary catalyst for jet engine development. The
two technologies have been interrelated ever since and, as the temperature
capability of materials was improved, so did the turbine efficiency. The enclosed
graph illustrates the strength improvements obtained through alloy development
and how the chemistry and microstructure became more complex with each
evolution.
Basically, superalloys can be categorized into three chemical families: iron base,
nickel base, and cobalt base. All alloys contain additions of chromium and
aluminum for oxidation resistance and variations of aluminum, titanium,
molybdenum, and tungsten for strength. The nickel base superalloys offer the
highest strength and are generally chosen for rotating blade applications. The
cobalt base alloys, although weaker, offer better environmental resistance and are
generally chosen for stationary vane applications.
From a metallurgical point of view, all superalloys exhibit an austenitic or
g
microstructure that, unlike steel, does not undergo any transformation as it is
heated to its melting point. The alloys derive their strength from three principal
mechanisms:
M-42 Metallurgy; Metallurgical Repair; Metallurgical Refurbishment
1. Solid solution hardening of the
g
matrix resulting from the coherency strains or
stiffening effect or larger atom elements such as chromium, molybdenum, and
tungsten.
2. Precipitation of small

g
¢ particles Ni
3
(Al, Ti) throughout the matrix act as
obstacles to dislocations or strain flow. The
g
¢ phases precipitate on cooling from
the solution temperature and during aging treatments.
3. The formation of blocky carbides at the grain boundaries act to pin the grain
boundary and prevent grain boundary sliding during creep.
Manufacture: Castings and Forgings
There are two main routes by which superalloys are manufactured into turbine
components: casting and forging.
Forged parts are made by hot-working cast ingots or powder metallurgy compacts
into billet or bar and eventually into the final shape. Since it involves significant
plastic deformation, considerable refinement of grain size can be achieved through
recrystallization; however, the alloy must also have good ductility at the forging
temperature. Consequently the higher strength superalloys cannot be manufactured
by forging. Turbine discs, some turbine blades, and compressor components are
made by forging.
Cast parts are formed by pouring molten alloy into near-net-shape molds and
allowing them to solidify. The investment casting process used allows extremely
complex shapes, including cooling passages, to be cast in. Molds are made by
depositing a ceramic layer around a wax form and melting the wax to form a cavity,
while ceramic cores are used to cast internal passages. Because the process does
not involve the deformation of the alloy, ductility is not an important consideration.
Turbine blades and vanes are commonly made by casting.
A modification of the investment casting process is used to produce directionally
solidified and single crystal components. To produce components in these forms,
alloy is cast into molds that are subsequently withdrawn from a furnace at a

controlled rate. By controlling the solidification of the casting, the grains are forced
to grow in one direction and by using a crystal selector at the base of the casting,
the casting can be made as a single crystal. Such components have improved creep
and thermal fatigue resistance because there are no grain boundaries oriented
perpendicular to the principal stress direction. Because of their high cost, such parts
are typically limited to first-stage turbine blading.
Metering, Fluids; Metering Pumps (see Fuel Systems)
Mist Eliminators (see Separators)
Mixers (see Agitators; Centrifuges)
Monitoring (see Condition Monitoring)
Motors (see Electric Motors)
Motors M-43
N
Noise and Noise Measurement (see Acoustic Enclosures, Turbine)
Noise Silencing and Abatement (see Acoustic Enclosures, Turbine)
Nondestructive Testing (FP1, MP1, X Ray) (see Metallurgy)
Nozzles
Nozzles can mean nozzles in the airfoil sense, i.e., inlet guide vanes on gas turbines
or steam turbines. See Metallurgy.
Nozzles can also be used to eject (see Ejectors) or spray. Spray-nozzle applications
are too numerous to itemize and must be customized for each application. Spray
nozzles in gas-turbine fuel systems, for instance, are typically for one-, two-, or dual-
phase fuel streams (gas; gas and liquid; or gas, liquid, and a mixture of gas and
liquid). Spray nozzles can also be used extensively in metallurgical processes such
as plasma coating.
Increasingly, for uniform flow distribution, spray patterns are CNC system
controlled. A robot that sprays plasma is one such example. This robotic CNC or
PLC control system is generally customized for most applications.
N-1
O

Oil Analysis
Some plants have oil-sample analysis done on oil samples taken from oil drains on
their turbomachinery packages. Metallic particulate content is trended for a clue
as to what problems may occur. For instance, rising content of babitt may
indicate bearing wear and/or incipient bearing failure. The problem of using this
technique with rotating machinery is that most of this machinery turns so fast, the
machine may fail between sampling analyses. Oil analysis has a far better chance
of detecting deterioration in slower reciprocating machines, provided the samples
are analyzed expeditiously.
Oil Sands; Synthetic Crude; Tar Sands; Shale
Oil sands and tar sands are synonyms for the same material. Synthetic crude
results from processing oil sands. Shale is similar to oil sand in that it is a category
of soil/rock that contains oil that can be extracted.
Certain areas of the world have large deposits of oil sands (northern Alberta,
Canada) or shale (China and the United States) that oil can be extracted from,
either by mining the soil and processing it or directing leaching steam into the
ground. The latter process recovers only about 60 percent of the oil. The former
process can recover more oil but is expensive to design and build because of the
high level of corrosion and erosion problems experienced.
This technology is significant to process engineers in that it provides useful
information on what equipment can survive the harshness of this process: such
equipment would be suitable for similarly demanding processes elsewhere. Figure
O-1 is a simplified line diagram of synthetic crude manufacture from processing oil
sands.
Reference and Additional Reading
1. Soares, C. M., Environmental Technology and Economics: Sustainable Development in Industry,
Butterworth-Heinemann, 1999.
Oxygen Analysis
Oxygen analyzers used to have applications in turbine and boiler design; they
monitored fuel/air ratios. Now the zirconium oxide probe for oxygen analysis is

found to have applications in process operations as well, where turbines are
involved. These applications give the probe some predictive solving potential, which
most rotating machinery engineers might depend on other indicators (such as
vibration analysis) for.
O-1
Oxygen Analysis Produces Profitable Power Plants*
A recent survey of instrument engineers from European power companies has
indicated that many have expanded the utility of the ZrO
2
oxygen probe beyond its
traditional use as a tool to optimize fuel/air ratios.
Most operators of large boilers have come to realize that significant stratification
can exist in the ductwork carrying flue gases. (See Fig. O-2.) By installing an array
of O
2
probes, and averaging the outputs, an average signal is generated that is
suitable for use in automatically trimming fuel/air ratios.
While averaging for control purposes is increasingly common, many operators
demand a trend display of each individual probe. By watching the relative O
2
values,
many operators feel that they can detect problems with fouling at individual
burners, slag accumulation, or even problems with coal fines at a pulverizer. The
O
2
measurement is increasingly taking on a “predictive maintenance” function.
᭿
Air heater leakage. An increasing number of customers are utilizing the O
2
measurement to detect seal leakage at air preheaters. This is particularly

effective when utilized with rotating units. Air leakage at the preheater is not
only a strong indicator that maintenance is required, it negatively affects thermal
heat rate efficiency. See Fig. O-3.
O-2 Oxygen Analysis
FIG. O-1 The production of synthetic crude oil. (Source: Syncrude Canada Limited.)
* Source: Adapted from extracts from Simmers, “Oxygen Analysis Produces Profitable Power Plants,”
IPG, January 1998.
᭿
Flue gas recirculation. One NO
x
reduction strategy is to mix some flue gas into
the combustion air prior to the burner, preventing the formation of thermal NO
x
.
An O
2
analyzer placed downstream of the mixing point can be utilized to maintain
a specific final O
2
set-point. (See Fig. O-4.)
It should be noted that the ZrO
2
sensing cell is mildly sensitive to pressure
changes, whereby each 10 mm of H
2
O pressure = 1 percent change in reading
(not a 1 percent change in O
2
). Some windboxes may experience pressures high
enough to require a pressure balancing accommodation to compensate.

᭿
NO
x
predictor. Thermal NO
x
is dependent in great part on the amount of O
2
available, as well as temperature at the burner. Increasing numbers of stations
are watching O
2
levels as an indication of NO
x
production. (See Fig. O-5.)
Oxygen Analysis O-3
FIG.
O-2 Most operators realize that significant stratification can exist in ductwork carrying flue
gases. (Source: Simmers.)
FIG. O-3 Oxygen measurement can be used to detect seal leakage in air heaters. (Source:
Simmers.)
Ozone*
Industrial activity and motor vehicle emissions produce ozone, a greenhouse gas.
As desired ozone levels are legislated toward, its effects need to be familiar to
process and industrial engineers.
Two problems to be considered are ground-level and stratospheric ozone. (As a
sample country for data comparisons, Canada has been selected.)
It is important not to confuse the problem of ground-level ozone pollution with
O-4 Ozone
FIG. O-4 Using O
2
measurement to control NO

x
formation. (Source: Simmers.)
FIG. O-5 Using O
2
to predict NO
x
formation. (Source: Simmers.)
* Source: Environment Canada. Adapted with permission.
the thinning of the stratospheric ozone layer. About 90 percent of atmospheric ozone
occurs in the stratosphere, a layer that extends from about 15 to 50 km above the
Earth’s surface. There it performs the critical function of absorbing harmful
ultraviolet (UV) radiation emitted by the sun. At present the stratospheric ozone is
thinning and providing plants and animals with less protection from the harmful
effects of excess UV radiation than in the past. This is an urgent problem; however,
it is not the topic of the fact sheet.
The ozone problem at the Earth’s surface is accumulation rather than depletion.
The normal state of affairs at ground level is for ozone to form and almost
immediately break down, at the same rate at which it is being produced, by
releasing one oxygen atom. Figure O-1 shows the chemical cycle involving oxygen
(O
2
) and two of the nitrogen oxides (NO
x
) (in this case, nitric oxide and nitrogen
dioxide), sunlight, and high temperatures that governs the formation and
breakdown of ground-level ozone. Problems arise when volatile organic compounds
(VOCs) (see “Chemical precursors of ground-level ozone” for a description of VOCs)
are added to the mix (Fig. O-6).
Because the buildup of ozone at ground level depends upon the concentration of
other pollutants, as well as temperature and sunlight, ozone levels usually peak in

the late afternoon of hot summer days and can persist into the evening and night.
Just how much ozone builds up varies considerably from year to year and from
region to region, but summers that are hotter than normal generally produce more
episodes of ozone pollution.
Chemical Precursors of Ground-Level Ozone
Ozone is a secondary pollutant in that it is not emitted directly to the atmosphere.
Nitrogen oxides and VOCs, both of which are emitted by natural processes and
human activities, are called ozone precursors because they must be present for
ozone to form (Fig. O-7).
Nitrogen oxides
This group of nitrogen-oxygen compounds includes the gases nitric oxide, nitrogen
dioxide, and nitrous oxide. Natural sources of nitrogen oxides are forest fires, lightning,
Ozone O-5
FIG.
O-6 Urban smog. (Source: Environment Canada.)
and bacterial action in the soil. About 95 percent of human-caused emissions of
nitrogen oxides come from the combustion of gasoline, diesel fuel, heavy fuel oil,
natural gas, coal, and other fuels, notably in motor vehicles, heavy equipment,
turbines, industrial boilers, and power plants (Fig. O-8).
Volatile organic compounds
The term volatile organic compounds (VOCs) is used to describe carbon-containing
gases and vapors that are present in the air, with the major exceptions of carbon
dioxide, carbon monoxide, methane, and chlorofluorocarbons. VOCs are given off by
trees and other vegetation, particularly in heavily forested areas. The combustion
of fossil fuels, especially in cars and trucks; certain industrial processes; and the
evaporation of some liquid fuels and solvents found in cleaning solvents, oil-based
paints, varnishes, stains, and thinners are important sources of human-caused
VOCs (Fig. O-9). Releases of VOCs lead to ground-level ozone pollution when these
emissions occur in the presence of nitrogen oxides (Fig. O-7).
Effects of Ground-Level Ozone

Effects on human health
Ozone is a very irritating and harmful gas. It adversely affected lung function in
young, normal subjects who exercised for 6 h in concentrations as low as the present
Canadian 1-h objective of 82 parts per billion (ppb). (A part per billion is a unit of
measure used to describe the concentration of atmospheric gases. In this case, the
unit represents one molecule of ozone in one billion molecules of all gases in the
O-6 Ozone
FIG. O-7 In unpolluted air, ground-level ozone forms and breaks down in a steady cycle. Scenario b shows one way that
pollutants disrupt the natural equilibrium. (Source: Environment Canada.)
Ozone O-7
FIG. O-8 Estimates of nitrogen oxide emissions due to human activities in Canada during 1985–2005. (Source: Environment
Canada.)
FIG. O-9 Estimates of VOC emissions due to human activities in Canada during 1985–2005. (Source: Environment Canada.)
air.) When lung function is affected, ozone has probably caused inflammation in
the lung.
Scientific studies show that after a few days of continuous exposure to ozone,
respiratory discomfort disappears. However, although little is known of the long-
term effects of repeated ozone exposure on humans, recent research on animals
suggests that it may lead to irreversible changes in lung function.
When ozone levels exceed 82 ppb, there is evidence that more people are
admitted to hospitals with acute respiratory diseases. In 1987 it was reported that
high ozone levels coincided with increased admission of patients with acute
respiratory disease to 79 hospitals in southern Ontario. However, it is difficult to
separate the effects of ozone from those of sulfate in these epidemiological studies.
Furthermore, the health effects of individual pollutants may be intensified when
two or more pollutants occur together.
High concentrations of ozone may affect the health of people and vegetation and
corrode materials.
Heavy exercise for 2 hours at an exposure of 120 ppb may lead to coughing,
shortness of breath, and pain on deep inhalation in healthy adults. Exposures above

120 ppb have resulted in dryness of the throat, shortness of breath, chest tightness
and pain, wheezing, fatigue, headache, and nausea.
People working or exercising outdoors inhale larger quantities of air and may
suffer more during episodes of ozone pollution. Children are more susceptible
because they spend more time outside than adults. Studies showed that children
at summer camps in Canada and the United States where they were exposed to a
typical summer mix of pollutants, including ozone, experienced a measurable
decline in lung function.
Ozone causes similar decreases in lung function in people who have asthma as
in those who do not, but the loss is more likely to be serious in those whose lungs
are already unhealthy. In clinical studies, people with asthma do not respond to
ozone differently than any other population. However, there is recent evidence that
when asthmatics are exposed to ozone their sensitivity to allergens is heightened.
Lung function is known to decline with age. Studies of the exposure of human
populations to ozone have noted an increase in the rate at which lung function
declines. Scientists are researching whether long-term exposure is causing changes
in human cells and tissues.
The savings that could be achieved by cutting ground-level ozone pollution are
likely considerable.
Effects on vegetation
Ozone is now viewed as the most important pollutant affecting vegetation.
Canadian research on the impact that ozone is having on farming has focused
mainly on southern Ontario, where ozone levels are typically highest. Estimates of
the cost of reduced yields in southern Ontario range from $17 to $70 million,
depending on the number of ozone events. Ozone damage to crops also occurs in
other regions. Value of lost production in the Fraser Valley has been estimated as
$8.8 million annually.
Ozone damages leaf tissue. Leaves may become mottled with yellow, exhibit small
black or white spots, develop larger bronze-colored, paper-thin areas, or exhibit
other visible symptoms. Inside the leaf, ozone can inhibit metabolic activity, destroy

the walls of cells, damage chlorophyll, and reduce photosynthesis. The plant as a
whole may grow 10–40 percent more slowly, age prematurely, lose its leaves during
the growing season, and produce pollen with a shorter life span.
O-8 Ozone
The effects of ozone on ecosystems are difficult to measure, because species vary
in their susceptibility. In forest ecosystems, exposure to ozone may lead to increased
vulnerability to disease and other stresses, increased mortality of individuals, and
eventually to overall decline of affected species. Both the degree of, and reasons for,
the decline in forest health in eastern North America are still debatable, but ozone
is believed to be partly responsible for the reported decline of red spruce, sugar
maple, and white birch. (See Fig. O-10.)
Damage to materials
Ozone can lead to the development of cracks in products made of rubber or synthetic
rubber, such as tires, boots, gloves, and hoses. Continued exposure to high levels of
ozone can cause these products to disintegrate completely. Ozone accelerates the
fading of dyes; damages cotton, acetate, nylon, polyester, and other textiles; and
accelerates the deterioration of some paints and coatings.
It is difficult to pin down the costs of this type of ozone damage. The economic
impact in the United States has been estimated at $1 billion, but a similar estimate
has yet to be prepared for Canada.
Ambient Air Quality Objective for Ozone
An air quality objective is a statement of the concentration of a specified air
pollutant that should not be exceeded beyond a specified length of time, in order to
provide adequate protection against adverse effects on humans, animals, plants,
and materials. Pollution control agencies routinely monitor the levels of air
pollutants and compare the levels with air quality objectives. This allows them to
measure their progress in controlling air pollution.
The maximum acceptable level for ground-level ozone in Canada is set at 82 ppb
over a 1-h period (see Fig. O-11). An “episode” occurs when the average ozone
concentration exceeds 82 ppb for 1 h or more. Ozone episodes in Canada typically

last from one to a few days. It is considered that natural levels of ozone in
unpolluted conditions would range between 15 and 25 ppb.
Ozone O-9
FIG.
O-10 Grape leaf with ozone exposure damage. (Source: Environment Canada.)
The federal government has provisionally adopted the number of days per year
when ozone concentrations exceed the 1-h air quality objective as its indicator for
ground-level ozone (Environment Canada, Indicators Task Force 1991). The
objective of the National Environmental Indicators Project is to develop credible,
understandable indicators of environmental conditions. These numbers will help
decision-makers to make choices consistent with sustainable development and to
evaluate the country’s progress toward that goal.
Emission Control Options
Measures to control ground-level ozone concentrations focus on the reduction of
emissions of nitrogen oxides and VOCs.
Because ground-level ozone is a secondary pollutant, formed by the reaction of
primary pollutants, measures to control ground-level ozone concentrations focus
on the reduction of emissions of nitrogen oxides and VOCs. The amount of ozone
formed depends on the ratio of nitrogen oxides to VOCs in the atmospheric mixture.
Under certain conditions, ozone formation could be limited more effectively by
controlling nitrogen oxides more than VOCs, and under other conditions the reverse
could be true. The complex nature of the problem has made evaluation of control
strategies difficult. Computer models are needed to predict the degree of ozone
formation based on particular atmospheric conditions. As warm temperatures and
O-10 Ozone
FIG. O-11 Maximum 1-h ozone concentrations for Canadian cities, based on an average of the three highest years during
1983–90. (Source: Environment Canada.)
Ozone O-11
sunlight are needed for ozone formation, it is especially important to reduce summer
daytime emissions.

International focus for the control of nitrogen oxides and VOCs
International protocols: In 1988, Canada and 24 other countries signed a protocol
to stabilize emissions of nitrogen oxides at 1987 levels by 1994. Canada, the United
States, and 19 European countries signed another protocol in November 1991 to
reduce the emission of VOCs and their transport across international boundaries.
The protocol commits Canada to a 30 percent reduction in annual VOC emissions
in the Lower Fraser Valley and Windsor–Quebec Corridor by 1999 based on 1988
levels. Canada is also committed to a national freeze on VOC emissions at 1988
levels by 1999 (United Nations Economic Commission for Europe 1991).
The Canada–U.S. Air Quality Accord: In March 1991, Canada and the United
States signed an Air Quality Accord. This agreement addresses the acid rain
problem and provides for the study and control of those air pollutants that
commonly move across the Canada–U.S. border. Annexes will be developed to
specifically address urban smog.
International Joint Commission recommendations on air quality in the Detroit–
Windsor–Port Huron–Sarnia Region: In March 1992, the International Joint
Commission (IJC) highlighted the need for governments to phase out emissions of
air toxics in the region. Among 19 recommendations, the IJC promoted development
of a joint regional ozone control strategy that includes emission controls for
mobile and stationary sources, including coke ovens. A common ground-level ozone
standard has also been recommended for the region.
Canada’s management plan for nitrogen oxides and VOCs
A national plan has been developed for the management of nitrogen oxides and
VOCs.
A national plan for the management of nitrogen oxides and VOCs has been
developed by federal and provincial governments through the Canadian Council
of Ministers of the Environment. Initiated in 1988 as a coordinated approach
to reducing levels of ground-level ozone throughout the country, the plan was
developed in consultation with industry, public interest groups, and environmental
groups. It aims for consistent attainment of the 1-h ground-level ozone air quality

objective of 82 ppb by the year 2005. Implementation is occurring in several phases:
Phase I (in place by 1995):
a. National Prevention Program: The program outlines 31 initiatives that will
reduce emissions of nitrogen oxides and VOCs, including the following:
᭿
Energy-conservation and product-improvement measures:
᭿
Energy efficiency standards in equipment and appliances
᭿
Energy audits by industry
᭿
Reductions in emissions when surface coatings are applied and when
adhesives, sealants, and general solvents are used
᭿
Public education to promote informed consumer choice and an environmentally
responsible lifestyle including:
᭿
Energy-conserving driving habits and alternative transportation modes,
such as cycling, walking, and ridesharing
᭿
Energy conservation
᭿
The use of energy-efficient products
᭿
The construction of energy-efficient homes and businesses
᭿
Improved solvent use and recycling
᭿
Source control initiatives:
᭿

New emission standards for cars and light trucks
᭿
Caps on emissions of nitrogen oxides from trains
᭿
Emission guidelines for new sources, i.e., power plants, industrial boilers,
and compressor engines, as well as for storage tanks for volatile liquids,
chemical processes used by industry, commercial and industrial coating
applications, printing, degreasing, and dry cleaning.
b. Remedial programs: The plan identifies 27 sample regional initiatives for
reducing ozone, which could be implemented in the three ozone problem areas:
the Lower Fraser Valley, the Windsor–Quebec Corridor, the Southern Atlantic
Region. Most initiatives involve the installation, retrofit, or enhancement of
emission-control technologies for existing sources.
c. Study initiatives: The plan outlines 24 research initiatives aimed at determining
the most effective control strategies for limiting the formation of ground-level
ozone. Ambient air monitoring, modeling, and studies of industrial processes and
emission sources will help to determine what controls on emissions of nitrogen
oxides and VOCs will be necessary in Phases II and III of the plan.
d. Federal–provincial agreements: Federal–provincial agreements will establish
the responsibilities of the respective governments for specific remedial actions
required to reduce ground-level ozone concentrations. The agreements will also
set out interim targets for emission reductions.
Phases II and III: Phase II of the management plan will establish emission caps
for problem areas for the years 2000 and 2005. To meet these caps, it is likely that
additional steps, over and above the initiatives laid out in Phase I, will be needed.
Phase III will make final adjustments to emission caps and control programs.
Implementation of Phase I of the NO
x
/VOC management plan should be a
significant step toward solving the country’s ground-level ozone problem by 2005.

Maximum ground-level ozone concentrations should be reduced by 15–35 percent
as a result of predicted Canadian and U.S. emission reductions. In addition, joint
Canada–U.S. emission reductions will lead to a 40–60 percent reduction in the time
during which the maximum acceptable ground-level ozone objective (82 ppb) is
exceeded in the regions of greatest concern.
Some regional remedial measures already underway
᭿
The Montreal Urban Community has passed regulations that require dry cleaning
and printing facilities, surface-coating applications, and metal degreasing
operations to control emissions. Substantial reductions have been achieved.
᭿
The B.C. Motor Vehicle Branch is implementing mandatory vehicle emission
testing starting in late 1992 under the Air Care Program. As a condition of annual
license renewal, all light-duty vehicles in the province’s Lower Mainland will be
inspected for exhaust emissions and emission-control systems. Those not meeting
the standards will undergo repairs.
Global efforts to address stratospheric ozone depletion have been underway since
1981. The Vienna Convention for the Protection of the Ozone Layer entered into
force on September 22, 1988. As of March 1, 1989, thirty-seven countries,
representing the vast majority of the industrialized nations of the world, had
ratified this Convention. The Convention provides the framework for cooperative
activities, including the exchange of data or information related to the ozone layer.
This Convention provides for the subsequent creation of protocols (free-standing
O-12 Ozone
treaties) for matters such as control of specific pollutants or families of pollutants.
The first such protocol created was the Montreal Protocol on Substances that
Deplete the Ozone Layer.
The Montreal Protocol was signed in Montreal, Canada on September 16, 1987.
It is clearly a watershed in cooperative and collaborative international undertakings.
It introduces many new features never before established in international law.

The Montreal Protocol had two requirements for entry into force; namely, 11
signatures of ratification by countries and these countries must represent at least
two-thirds of global consumption of the controlled substances. The Montreal
Protocol entered into force on January 1, 1989, and as of March 1989 had already
attained 33 ratifications, again representing most of the industrialized states of the
world.
On May 1988, Environment Canada published its first Control Options Report,
titled: “Preserving the Ozone Layer: a first step.” This report set out a series of
options to implement regulations to meet Canada’s obligations under the Montreal
Protocol.
The Montreal Protocol calls for a 50 percent cutback in the 1986 levels of
consumption of five chlorofluorocarbons (CFC 11, 12, 113, 114, and 115) and a freeze
at 1986 consumption levels of three brominated fluorocarbons called Halons (Halon
1211, 1301, and 2402). At a series of United Nations Environment Programme
(UNEP) meetings held in The Hague, Netherlands, in October 1988, the world’s
leading scientists expressed the consensus viewpoint that the Antarctic hole will
remain unless the emissions of controlled CFCs are reduced by at least 85 percent
from 1986 levels. The target reductions contained in the Montreal Protocol are
currently undergoing international review. This review is expected to culminate in
amendments that will tighten the Montreal Protocol. Canada contributed to both
the organization and conduct the UNEP meeting in The Hague and fully supports
the notion of reducing consumption further.
On February 20, 1989, the Federal Government of Canada announced that it had
set as its objective the complete elimination of controlled CFCs within the next 10
years. It also called on the rest of the world to set as its common target a reduction
of no less than 85 percent by no later than 1999. The Minister of the Environment
further announced that the following actions would be taken to achieve the
Canadian objective.
1. Implement the protocol
As a first step, regulations will be enacted under the Canadian Environmental

Protection Act to implement the current control requirements set out in the protocol.
These are a freeze in consumption at 1986 levels (CFCs on July 1, 1989, and Halons
on January 1, 1992) and a two-step reduction in annual consumption of CFCs to 50
percent of 1986 levels by 1999.
2. Regulate a reduction in chlorofluorocarbon consumption of at least 85 percent
Draft regulations recently released call for at least an 85 percent reduction of the
controlled CFCs by no later than 1999. Consultation on what is achievable is
expected to increase the percentage reduction and tighten the time frame.
3. Prohibit specific CFC uses
As a third step, draft regulations have been released for discussion purposes that
would prohibit the use of ozone-depleting substances for nonessential uses or where
substitutes are available. For example, the import, manufacture, and sale of aerosol
Ozone O-13
products containing controlled CFCs (with the exception of certain medical and
industrial applications for which alternatives are not yet available or for which fire
safety is a particular concern); food packaging foam including food and beverage
containers containing or manufactured with controlled CFCs; portable handheld
fire extinguishers for home use containing Halons; and small pressurized canisters
that contain CFCs, including refrigerants, air horns, and party streamers, will be
prohibited by January 1, 1990. As safe alternatives become available, a similar
prohibition will apply to the following aerosol products: release agents for molds
used in the production of plastic and elastomeric materials, cleaners and solvents
for commercial use on electrical or electronic equipment, and products used in
mining applications where fire hazard is critical.
4. Further control measures
As a fourth step, this comprehensive control options report has been prepared to
focus discussion on the earliest possible prohibition dates for remaining CFC uses.
Some examples of prohibition dates proposed in this report are as follows:
1. Rigid foams
a. Insulating foams

᭿
Polyurethane (1992–1994)
᭿
Polystyrene (1990–1991)
᭿
Phenolic (1991–1992)
b. Packaging
᭿
Food (1990)
᭿
Other (1990–1991)
2. Flexible foams
a. Car seats, furniture cushions, etc. (1990–1992)
3. Refrigeration
a. New refrigeration and air-conditioning equipment (1994–1999)
b. Existing equipment maintenance (as replacements are available)
4. Solvents
a. Electronic (1991–1994)
b. Metal cleaning (1990–1991)
c. Dry cleaning (1991–1992)
5. Others
a. Hospital sterilants, optical coatings (1990–1994)
As these remaining uses are prohibited, the total allowable quantities of controlled
CFCs produced and consumed in Canada will be lowered.
This Control Options Report, “Preserving the Ozone Layer: A Step Beyond the
Montreal Protocol,” describes the most promising options to control ozone-depleting
substances for each process group and product group including rigid and flexible
foams, refrigeration and air conditioning, solvents, sterilants, aerosols, and fire
suppression systems in which controlled CFCs and Halons are used. The control
options comprise three main categories:

᭿
Emission controls
᭿
Chemical and process substitutes
᭿
Product substitutes
O-14 Ozone
Depletion of Ozone in the Stratosphere
As excess ozone at lower atmospheric levels is a problem, reduced ozone in the
stratosphere is also dangerous to life. Industry is therefore being pressured to take
steps to alleviate this problem. Some background information follows.
Figure O-12* describes effects of ozone on vegetation and health.
Benefits and costs
†
The benefits of the Montreal Protocol consist of two components. For benefits
associated with reduced damage to materials, reduced damage to agricultural
productivity, and reduced damage to fish stocks, estimates of the dollar amounts of
benefits are shown. For health impacts, including reduced incidence of skin cancers,
reduced fatal skin cancers, and reduced cataract incidence, estimates of averted
health effects are shown. In both cases, the framework for producing the estimates
is the same. Effects are estimated for the scenario in which no controls on the
consumption of ozone-depleting substances are implemented relative to the
alternative scenario represented by the introduction of the Montreal Protocol.
The overall benefits of the Montreal Protocol are shown in summary form in Table
O-1. This table shows quantified dollar benefits of $459 billion plus a reduction in
skin cancer cases of 3.4 million, 129 million fewer cataract cases, and more than
330,000 reduced fatalities.
Montreal Protocol costs are also substantial but small relative to benefits. The
present discounted value of protocol costs over the time period from 1987 to 2060
total $235 billion. Although substantial, these costs are less than the quantifiable

benefits from reduced damages to agriculture, fishing, and materials. The benefits
from averted health effects are extremely large in relation to the costs. If reduced
fatalities from skin cancers alone are considered, the number of cases averted from
1987 to 2060 is 333,500.
Costs of Replacing Ozone-Depleting Substances
‡
Overview and methodology
The methodology for assessing the costs of implementing the Montreal Protocol
focuses on the economic costs of the controls that have been introduced. In the
economics literature, this is frequently referred to as assessing the real resource
costs of the policy. See Table O-2.
As an example, consider refrigeration and air-conditioning services. Assume in
this example that a constant quantity of these services will be produced—that is,
there are no price impacts on this quantity. Prior to the regulation, CFCs are used
as refrigerants throughout this sector. As a result of the introduction of the Montreal
Protocol, a number of changes are made in this sector to reduce and then
eliminate CFCs. The economic cost of the regulation is the difference in the cost
of producing these outputs prior to the control and after it is introduced.
In this cost methodology, the real resource costs that are relevant consist of the
additional quantity of resources needed to produce this constant level of output.
Ozone O-15
* Source: Environment Canada, “Preserving the Ozone Layer: A Step Beyond,” April 1989. This report
was written with specific reference to Canada, but provides applications information for readers
anywhere.
†
Source: Adapted from extracts from Environment Canada, “Montreal Protocol 1987 to 1997: Global
Benefits and Costs of the Montreal Protocol on Substances That Deplete the Ozone Layer.”
‡
Source: Environment Canada SOE Sheet 92-1, written with specific reference to the U.S.–Canada Air
Quality Agreement and Ozone Levels in Canada.

Other private sector costs may be incurred that are not reflected in the economic
costs described above. If the price of CFCs increases, for example, due to regulatory
restrictions on quantity, some private sector users will register this as an increased
cost. This is not a economic cost, however, because no additional input resources
are required to produce the output in question. Viewed somewhat differently, the
price increase is not an economic cost because the additional costs of the purchasers
are exactly offset by the additional revenues of the producers.
In any regulatory scenario, we would expect to observe both real resource cost
impacts and price impacts as described above. Economists refer to the price effects
as transfers in that they involve transfers from one group in society to another. In
O-16 Ozone
FIG.
O-12 Effects of ozone on vegetation and health. (Source: Environment Canada.)