Objectives

Question 1

Describe an Ionic Bond

Answer 1

One or more electrons wholly transferred from an atom of one element to the atom of another element. +/- polarity change attracts. “Transfer of electrons”

Question 2

Describe a Covalent Bond

Answer 2

A bond formed by shared electrons. One atom needs electrons to fill its outer shell so it shares those electrons with another atom. The electrons fill both atoms’ shells. “Sharing of electronics”

Question 3

Describe a Metallic Bond

Answer 3

Atoms do not share or exchange electrons in order to bond. Approximately one electron per atom are free to move throughout the metal and interact with many of the fixed atoms.

Question 4

Describe a Molecular Bond

Answer 4

A temporary weak charge when electrons of neutral atoms spend more time in one region of their orbit then another. “Van der Waals bond”

Question 5

Describe a Hydrogen Bond

Answer 5

Similar to the molecular bond, occurs when hydrogen atoms are willing to give up an electron to atoms of oxygen, fluorine or nitrogen.

Question 6

Describe an Amorphous type of solid

Answer 6

No regular arrangement of atoms or molecules.
-Exhibit properties of solids
-Have definite shape and volume
-Diffuse slowly
-Lack sharply defined melting points
-Solid but resemble liquids that flow slowly at room temperature
Examples: glass and paraffin

Question 7

Describe Crystalline Solids

Answer 7

Atoms in a pattern that periodically repeat in a three-dimensional lattice.
Forces associated with chemical bonding cause this repetition to produce properties such as:
- strength
- ductility
- density
- conductivity
- shape

Question 8

Describe Grain Structures

Answer 8

Arrangement of the grains in a metal - each grain has a crystal or lattice structure. Grain boundary is a region of misfit on interface between grains and is usually the diameter of 1-3 atoms. Grain size determines the properties of the metal. Smaller grain size = higher tensile strength, higher ductility. Larger grain size = good high temperature creep properties.

Question 9

Describe the Body-Centered Cubic (BCC) lattice structure

Answer 9

Eight atoms at the corners of a cube and one atom at the body center of the cube. Examples: ferrite, chromium, vanadium, molybdenum, tungsten. High strength, low ductility.

Question 10

Describe the Face-Centered Cubic (FCC) lattice structure

Answer 10

Eight atoms at the corners of a cube and one atom at the center of each of the faces of the cube. Examples: austenite, aluminum, copper, lead, silver, nickel, platinum, thorium. Lower strength, higher ductility than BCC metals.

Question 11

Describe Hexagonal Close-Packed (HCP) lattice structure

Answer 11

Top and bottom layers contain six atoms at the corners of a hexagon with one atom in the center, middle layer contains three atoms. Examples: beryllium, magnesium, zinc, cadmium, cobalt, thallium, zirconium. Not as ductile as FCC metals.

Question 12

Describe the Point Imperfections known as Vacancy Defects.

Answer 12

Missing an atom in a lattice position. Results from imperfect packing during crystallization-maybe due to increased thermal vibrations of atoms at higher temperatures.

Question 13

Describe the Point Imperfections known as Substitutional Defects

Answer 13

Impurity at a lattice position (alloy material added to metal)

Question 14

Describe the Point Imperfections known as Interstitial Defects

Answer 14

Impurity or atom at an interstitial site

Question 15

Describe the “Edge” Line Imperfection

Answer 15

Extra row or plane of atoms in crystal’s structure.

Question 16

Describe the “Screw” Line Imperfection

Answer 16

Tearing a crystal parallel to the slip direction (slip pattern similar to a screw thread)

Question 17

Describe the “Mixed” Line Imperfections

Answer 17

Orientation of dislocations varies from pure edge to pure screw and at intermediate points. May possess characteristics of each

Question 18

Describe Interfacial Imperfections

Answer 18

Large and occur over a two-dimensional area

Question 19

Describe Macroscopic Defects (Bulk Defects)

Answer 19

Three-dimensional material defects introduced during material refinement or fabrication. Most caused by foreign particles called inclusions. Others include voids (gas pockets, shrinking, etc), cracks from work stress and welding or joining defects.

Question 20

Describe the common characteristics of alloys

Answer 20

Stronger than pure metals.
Reduced electrical conductivity.
Reduced thermal conductivity.

Question 21

Identify the desirable properties of type 304 stainless steel

Answer 21

Extremely tough (18-20% Cr & 8-10.5% Ni)
Resists most, but not all, types of corrosion.

Question 22

Describe Strength

Answer 22

Ability of a material to resist deformation.
Maximum load that can be borne before failure is apparent.
Nominal stress is included when quoting a material’s strength.

Question 23

Describe Ultimate Tensile Strength

Answer 23

The maximum resistance a material presents to fracture.
UTS = Max load ÷ Area of original cross section = PSI

Question 24

Describe Yield Strength

Answer 24

The stress where a predetermined amount of permanent deformation occurs. The stress where plastic deformation occurs.

Question 25

Describe Ductility

Answer 25

The ability of a material to deform easily on application of a tensile force.
The ability of a material to withstand plastic deformation without rupture.
The ability of a material to elongate in tension.

Question 26

Describe Malleability

Answer 26

A metals ability to display large deformation or plastic response when subjected to compressive force

Question 27

Describe Toughness

Answer 27

The work required to deform 1in³ of metal until it fractures.
The way a material reacts under sudden impacts.
- Shape of metal and the material composition determines toughness

Question 28

Describe Hardness

Answer 28

Property of a metal that enables it to resist plastic deformation, penetration, indentation and scratching.

Question 29

Describe Heat Treatment

Answer 29

A metallurgical process that changes properties of the metal. When hardness and tensile strength go up, toughness and ductility go down.

Question 30

Describe Quenching

Answer 30

Faster cooling, smaller grain size = harder metal.
Cooling rate depends on method of cooling and size of the metal.
Uniform cooling prevents distortion.

Question 31

Describe Annealing

Answer 31

Slow heating and soak, then slow cool. -Softens steel and improves ductility. -Stress relief.
-Refines grain structure.

Question 32

Describe Coldworking

Answer 32

Plastic deformation in a particular temperature region over a particular time period such that the work hardening is not relieved.
-Lowered ductility.

Question 33

Describe Hotworking

Answer 33

A process where metal deformation occurs above re-crystallization temperature, preventing work hardening from occurring.

Question 34

Describe General Corrosion

Answer 34

Involving water and steel (or iron), results from chemical action where steel surface oxidizes forming iron oxide or rust.

Question 35

Describe Galvanic Corrosion

Answer 35

To dissimilar metals with different electrical potentials are in electrical contact in an electrolyte. The larger the potential difference, the greater the galvanic corrosion rate.

Question 36

Describe Stress Corrosion Cracking and how to prevent it

Answer 36

Intergranular attack corrosion that occurs at the grain boundaries of a metal under tensile stress. Cracks then occur at inter/trans-granular paths which leads to further corrosion.
To prevent:
- proper system & component design
- reduce stress
- remove hydroxides, chlorides, oxygen
- avoid stagnant areas & crevices
- use Inconel

Question 37

Describe Chloride Stress Corrosion and how to prevent it

Answer 37

Intergranular corrosion that occurs in austenitic stainless steels under tensile stress in the presence of oxygen, chlorides and high temperatures.
To prevent:
- maintain low chloride ion content
- maintain low oxygen content
- use low carbon steels

Question 38

Describe Caustic Stress Corrosion (CSS) and how to prevent it

Answer 38

Cracks initiate and grow along grain boundaries then extensive crack branching occurs along grain boundaries. Carbon steels are susceptible to CSS. High tensile stress from fabrication is the driving force. Inconel is known for getting CSS.

Question 39

Describe Hydrogen Embrittlement

Answer 39

Another form of stress corrosion cracking, hydrogen or methane gas forms at grain boundaries building up internal pressure and rupturing in the form of tiny cracks causing steel to lose its strength and ductility.

Question 40

Describe Fatigue Failure

Answer 40

A material’s tendency to fracture by means of progressive brittle cracking under repeated alternating or cyclic stresses of an intensity considerably below the normal strength. Thermal fatigue is the most common (cyclic changes in temperature).
To prevent:
- operate plant in a controlled manner
- heat up and cool down limits
- pressure limits
- pump curves

Question 41

Describe Work-Hardening

Answer 41

Straining a material beyond the yield point.
Increasing stress produces additional plastic deformation, causing metal to become stronger and more difficult to deform.
-Makes a material stronger, but less ductile.
-Can be used to treat metal.

Question 42

Describe Creep

Answer 42

At elevated temperatures and constant stress or load, material slowly deforms.
Rate of creep depends on stress and temperature.
To limit creep:
- stay within acceptable creep rate limits for component lifetime.
- creep becomes a concern at extremely high temperatures and pressures