structure and charictoristics of materials

8/2/2019 Structure and Charictoristics of Materials

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Note: The source of the technical material in this volume is the Professional

Engineering Development Program (PEDP) of Engineering Services.

Warning: The material contained in this document was developed for Saudi

Aramco and is intended for the exclusive use of Saudi Aramcos

employees. Any material contained in this document which is notalready in the public domain may not be copied, reproduced, sold, given,

or disclosed to third parties, or otherwise used in whole, or in part,

without the written permission of the Vice President, Engineering

Services, Saudi Aramco.

Chapter : COE10501 For additional information on this subject, contact

File Reference: S.B. Jones on 874-1969 or S.P. Cox on 874-2488

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Structure And Characteristics Of Materials


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Engineering Encyclopedia Materials & Corrosion Control


Saudi Aramco DeskTop Standards

CONTENTS PAGES

STRUCTURE OF METALS AND NONMETALS.................................................... 1

Crystalline-Metallic ......................................................................................... 1

Nonmetallic Materials ..................................................................................... 3

Plastics ................................................................................................. 3

Elastomers............................................................................................ 3

CHARACTERISTICS OF METALS AND NONMETALS....................................... 4

Tensile Strength............................................................................................... 4

Yield Strength.................................................................................................. 4

Ductility............................ ............................................................................... 4

Toughness........................................................................................................ 4

Hardness .......................................................................................................... 4

Strength at Low or Elevated Temperatures ..................................................... 5

Corrosion and Erosion Resistance................................................................... 5

Characteristics of Plastics................................................................................ 7

Thermoplastics..................................................................................... 7

Elastomers............................................................................................ 7

Thermosetting Plastics......................................................................... 7

Carbon and Low Alloy Steels .............................................................. 9

Cast Irons ............................................................................................. 9

Chromium-Molybdenum Steels........................................................... 9

Nickel Alloys ....................................................................................... 9


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Saudi Aramco DeskTop Standards

Copper Alloys ...................................................................................... 9

Aluminum ............................................................................................ 9

Titanium............................................................................................... 9

GLOSSARY ............................................................................................................. 11


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Saudi Aramco DeskTop Standards 1

STRUCTURE OF METALS AND NONMETALS

Metals and nonmetals are basic materials of construction for the Petroleum Industry. Their

proper selection, design, fabrication, or application and use in new construction or

maintenance are essential to safe, reliable operation of production, pipeline, and refiningfacilities.

Crystalline-Metallic

To be able to identify the structure and characteristics of metals, it is important to recognize

that metals have crystalline structures. In a crystalline structure the atoms are located in a

periodic or geometric arrangement. Figure 1, Crystalline-Metallic Structures, shows the three

most common crystalline structures:

Crystalline Structures: Examples:

Body-Centered Cubic Iron and Steels

Face-Centered Cubic Austenitic Stainless Steels

Hexagonal Close Packed Magnesium

As indicated above, metals are crystalline solids that have periodic or geometric arrangements

of atoms, i.e., they have long-range order.


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Body-Centered Cubic

Face-Centered Cubic

Hexagonal Close Packed

Figure 1. Cr ystalline-Metallic Structur es


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Nonmetallic Mater ials

In contrast to metallic materials, nonmetallic materials such as glass, plastics and elastomers

have a noncrystalline structure. The atoms making up these materials do not possess the

periodicity of a crystal, i.e., they have no long-range order.

Ceramics, which are also classified as nonmetallic materials, can exhibit a crystalline

structure. An example of a ceramic material is aluminum oxide (Al2O3).

Plastics

The American Society for Testing and Materials (ASTM) defines a plastic as a material that

contains as an essential ingredient an organic substance of large molecular weight, is solid in

its finished state, and at some stage in its manufacture or in its processing into finished articles

can be shaped by flow.

There are two types or classes of plastics:

Thermoplastics soften with increasing temperature and return to their original

hardness when cooled.

Thermosetters cannot be softened by heat and will char or burn as the

temperature is increased.

Plastics do not corrode like metals. Among the types of plastic deterioration are loss in

mechanical properties, swelling, softening, hardening, and color change.

Elastomers

Elastomers, such as natural and synthetic rubbers, have good elastic, resilience, and flexibility

properties. Certain elastomers have good chemical and abrasion resistance and are used in

corrosive environments.


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CHARACTERISTICS OF METALS AND NONMETALS

Some of the important characteristics of engineering materials are: tensile strength, yield

strength, ductility, toughness, hardness, strength at low or elevated temperatures, corrosion

and erosion resistance.

Tensile Str ength

Tensile strength refers to the maximum load that a material can withstand without rupturing.

Loads are normally expressed in MPa or lbs/in2

(psi).

Figure 2 compares the tensile strength and five other characteristics of eleven important

engineering materials.

In the oil industry, equipment and piping must be capable of resisting the effects of pressure

and mechanical loads at both ambient and elevated temperature.

Yield Strength

Yield Strength refers to the maximum load that a material can resist without permanent plastic

deformation. Loads are normally expressed in MPa or lbs/in2

(psi).

In the oil industry, materials with high yield strength are needed for the fabrication of items of

equipment and piping. Equipment and piping must be capable of resisting the effects of

pressure and mechanical loads at both ambient and elevated temperature.

Ductility

Ductility refers to the ability of a material to deform plastically without fracturing. Ductility is

measured by elongation or reduction in area.

Toughness

Toughness refers to the ability of a material to absorb impact energy and deform plastically

prior to fracture. Toughness is measured by a notch impact test.

In the oil industry, tough (high-ductility) materials are used to fabricate equipment and piping

components that will be in low-temperature service. Low-temperature service is normally

defined as design temperatures below -29.5 C (-20.5 F).

Hardness

Hardness refers to the ability of a material to resist penetration by an indenter. Hardness data

are sometimes used to estimate tensile strength.


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Principle uses for hard materials include:

Hoppers handling coke are lined or constructed of hard, erosion resistant

materials to minimize the abrasive action of coke fines.

Shafts for pumps, turbines, compressors and valve stems are made of materials

hardened by heat treatment.

Strength at Low or Elevated Temperatu r es

Metallic materials that maintain their strength at both low and elevated temperatures are

ideally suited for use in the oil industry. In fact, this attribute is a prerequisite for their use in

industrial applications.

Materials that maintain their useful properties at extremes of temperature are used for the

fabrication of items of equipment and piping found in a refinery or other industrial plant.Examples of items of equipment include pressure vessels, heat exchangers, valves and items

of rotating machinery such as pumps, compressors and turbines.

Corrosion and Erosion Resistance

Engineering materials can be made to resist corrosion or erosion when exposed to corrosive

and/or abrasive environments by alloying and heat treatment. By incorporating certain

metallic elements, materials which are inherently corrosion and erosion resistant are

produced. Heat treatments which increase hardness are often used to increase a materials

erosion resistance. In general, materials that exhibit high hardness are usually more erosion

resistant than soft materials.

Materials that resist corrosion and erosion are used for equipment and piping exposed to

environments that include: sour crude oil, produced water containing sand, corrosive

chemicals such as acids, sour gases, rich amines, high temperature hydrocarbons and catalyst

fines. It is important to note that this list is not all inclusive.


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Carbon and Low AlloysSteels

Cast Irons

Cr-Mo Steels

Stainless Steels: Austenitic

Ferritic

Martensitic

Duplex

Nickel Alloys

Copper Alloys

Aluminum

Titanium

TensileStrength

Yield

Stre

ngth

Ductility

Hard

ness

High-Te

mp

Strength

Corrosio

n

Resist

ance

G

P

G

G

G

G

G

G

P-M

P-M

M-G

G

P

G

G

G

G

G

G

P-M

P-M

M-G

G

P

G

G

M-G

P

M-G

G

G

M

M

M

M-P

M

M-G

M-G

G

M-G

G

P

P

M

M

M

G

G

G

G

G

G

P

P

M

P

P-M

M

G

G

M-G

G

G

M-G

M

G

G = Good ; M = Moderate ; P = Poor

Figure 2. Cha racter istics of Engineering Mater ials


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Cha racteristics of Plastics

Thermoplastics

Thermoplastics such as fluorocarbons (teflon, KEL-F), polyethylene, and polypropylene havegood resistance to many corrosive media, but limited service temperature range compared to

many metals. Uses include buried raw water piping and associated valves, valve seals and

gaskets, tape, valve diaphragms, and linings.

Elastomers

Elastomers such as Nitrile (Buna-N), Styrene-butadiene (Buna-S), Chloroprene (Neoprene),

Fluorocarbon (Viton), etc. have good resistance to many corrosive media. In the oil and

petrochemical industries they are used in the form of hose, tubing, seals, O-Rings, gaskets,

and occasionally tank linings. A significant limitation associated with these materials is that

they are not suitable for elevated temperature service. Neoprene, Buna-N, and Buna-S arelimited to temperatures below about 121 C (250 F). Viton, which is a fluoroelastomer can

be used at tempertures up to 260 C (500 F). Elastomers exhibit poor strength, and

consequently should never be used to fabricate pressure-retaining components, unless the

material is reinforced.

Ther mosetting Plastics

Thermosetting plastics such as epoxies, phenolics and polyesters are resistant to various

corrosive media and have relatively good mechanical properties. Fiber-reinforced plastics

(FRP) are thermosetting resins that are filled or reinforced with cloth, mat or chopped fibers.

The resulting composite material not only has good resistance to corrosive species, but alsopossesses very good mechanical properties. This enables FRP materials to be used in Code

construction for pressure-retaining components. An example of an FRP material is fiberglass

reinforced epoxy. FRP materials are used for the fabrication of underground storage tanks,

pressure vessels, pipes, ducts, and small water or chemical injection pumps.


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Figure 3 summarizes the principal uses of several typical engineering materials.

Carbon and Low-Alloy Steels Cast Irons Chromium-Molybdenum Steels

Stainless Steels Nickel Alloys Copper Alloys Aluminum Alloys Titanium Plastics:

Thermoplastic

Thermosetting Fiber-Reinforced Plastics

Elastomers

Pressure

Vessels

HeatE

xcha

ngers

Piping

Pumps

Storag

eTa

nks

Structural

Ste

el

Valves

Claddings

Coatin

gs

Lining

s

Gasketa

ndSeals

(O-Rings)

Figure 3. Pr inciple Uses of Engineering Mater ials


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Some brief examples of typical engineering materials used in the Petroleum Industry are:

Carbon and Low Alloy Steels

Carbon and low alloy steels exhibit good strength, ductility, and moderate corrosionresistance. Carbon and low alloy steels are used extensively in pressure vessels, heat

exchangers, piping, pumps, storage tanks, and structural steel.

Cast Irons

Cast irons exhibit poor ductility but reasonable corrosion and erosion resistance in nonsaline

cooling water systems. Cast irons are used for certain pump casings, impellers, and valves.

Chromium-Molybdenum Steels

Chromium-molybdenum steels exhibit good strength at elevated temperatures, good

resistance to hydrogen attack, and adequate sulfidation resistance at elevated temperatures.

Chromium-molybdenum steels are used for pressure vessels, heat exchangers, piping, and

furnace tubes.

Stainless Steels: Austenitic, Ferritic, Martensitic, Duplex

Stainless steels exhibit good strength at low and elevated temperatures, good corrosion

resistance to many media. Stainless steels are used for pressure vessels, heat exchangers,

piping, furnace tubes, pumps, instruments.

Nickel Alloys

Nickel alloys exhibit good strength, ductility at low temperatures, good corrosion resistance

for certain media. Nickel alloys are used for pressure vessels, heat exchangers, piping at low

temperatures, and in certain corrosive environments.

Copper Alloys

Copper alloys exhibit good corrosion resistance in cooling water service when kept clean.

Copper alloys have good thermal conductivity, but comparatively low strength, and limited

service temperature use. Applications for copper alloys include heat exchanger tubes,

tubesheets, pipes, valves, and pumps.

Aluminum

Aluminum is a lightweight material which exhibits limited corrosion resistance and has a

limited application temperature range. Aluminum is used in aircraft and as an external fin

material on air-cooled heat exchangers.


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Titanium

Titanium exhibits good strength-to-weight ratio, excellent corrosion resistance to brackish

water and certain very corrosive process media. Titanium uses include heat exchangers (all

components), and piping.


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GLOSSARY

atoms The smallest particle of an element that can exist either alone

or in combination.

characteristics A special quality found in a material.

corr osion resistance The ability of a material to resist deterioration or degradation

due to the environment.

crystalline Denotes a solid composed of atoms arranged in a pattern

which is repetitive in three dimensions. Most common metals

are crystalline.

ductility The ability of a metal to deform plastically without fracturing,

as measured by elongation or reduction in area in a tensile test,cupping height in an Erichsen test, or bend radius in a bend

test.

erosion resistance The ability of a material to resist deterioration or degradation

due to the abrasive action of a moving stream.

hardness That property which measures the ability of a material to resist

penetration by an indenter. Hardness data can sometimes be

related to the tensile strength of a metal.

structure The regular or random arrangement of atoms in a material.

tensile str ength The ultimate strength of a material in tension.

toughness The ability of a material to absorb energy and deform

plastically before fracturing, as measured by the energy

absorbed in a notch impact test.

yield str ength The strength at which a metal or alloy shows significant plastic

deformation.

structure and charictoristics of materials

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