MATERIALS & CONSTRUCTION PART A Flashcards
1
Q
The overriding
considerations when selecting engineering materials for chemical process plant?
A
High temperature strength
Ability to resist corrosion
2
Q
Who is responsible for recommending materials
that will be suitable for the process conditions?
A
Process Designer
3
Q
Who must also consider the requirements of the
mechanical design engineer
A
Process engineer
4
Q
The material selected by the process engineer must have?
A
- Sufficient strength
- Easily worked
5
Q
What material should be selected?
A
Most economical that satisfies both process and mechanical requirements
6
Q
The material selected will be a material that gives ?
A
lowest cost over the working life of the plant allowing for maintenance and replacement
7
Q
What are other factors to be considered when selecting a material?
A
Product contamination
Process safety
8
Q
The most important characteristics to be considered when selecting a material of construction are? (7)
A
Mechanical Properties
Effect of temperature on mechanical properties
Corrosion Resistance
Any special properties required
Ese of Fabrication
Availability in standard sizes
Cost
9
Q
Under mechanical properties
A
Strength
Stiffness
Toughness
Hardness
Fatigue
Creep resistance
10
Q
Measured through tensile strength
A
strength
11
Q
Measured through elastic modulus (Young’s Modulus)
A
Stiffness
12
Q
Measured through fracture resistance
A
Toughness
13
Q
measured through wear resistance
A
Hardness
14
Q
Under effect of temperature on mechanical properties particularly the effects of:
A
high temp
low temp
thermal cycling
15
Q
Under ease of fabrication
A
Forming
Welding
Casting
15
Q
Under Special properties required
A
Thermal conductivity
Electrical resistance
Magnetic properties
16
Q
Under Availability in Standard sizes
A
Plates
Section
Tubes
17
Q
What materials are satisfactory in all fabrication operations?
A
Nickel and Monel
18
Q
Material with the highest annealing temp
A
Nickel
19
Q
A measure of the basic strength of a material
A
Tensile Strength/Stress
20
Q
the maximum stress that the material will withstand, measured by a standard
tensile test
A
Tensile Strength/Stress
20
Q
Older name of Tensile strength/stress
A
Ultimate Tensile Strength (UTS)
21
Q
the stress to cause a specified permanent extension
A
Proof stress
22
Q
Metals/Alloy that has the highest tensile strength
A
Monel
23
Percentage of proof stress
0.1%
24
What codes are calculated from Tensile strength/stress
ASME Boiler and Pressure Vessel (BPV)
European EN 13445 Pressure vessel code
25
Hardest metal/alloy
Monel
26
Ability to resist bending and buckling
Stiffness
27
Function of elastic modulus of the material and the shape of the cross-sectional area of the member (the second moment area)
Stiffness
28
Slope=
Stiffness
29
The stress beyond which a material becomes plastic
Yield point
30
An indication the tendency for an element to return to its original form after being subjected to a force
Stiffness
31
Measures how much stress can be applied to an element before it deforms permanently or fractures
Strength
32
Measures a material's resistance to surface deformation
Hardness
33
Associated with tensile strength
Toughness
34
Measure of the material's resistance to crack propagation
Toughness
35
What ductile materials stop the propagation of crack by local yielding at the crack tip. They have crystal structure
Steel
Aluminium
Copper
36
The crystal structure of the ductile materials stop the propagation of crack by?
Local yielding at the crack tip
37
In this materials, the local yielding does not occur, that's why they are brittle
Cast irons
Glass
38
T/F: Brittle Materials are strong in tension but weak in compression
F
39
Under ____ any incipient cracks present are closed up
Compression
40
Technique developed that allowed the use of brittle materials in situations where tensile stress would normally occur
Use of pre-stressed concrete and
Glass-fibre-reinforced plastics in Pressure vessel construction
41
Are induced to counteract external stresses
Internal stresses
42
Curve downward
Load deflection
43
Horizontal side to side
Tendons stressed
44
Horizontal to center
Prestress forces
45
Curve upward to center
Prestress deflection
46
Indication of a material's ability to resist wear
Hardness
47
Hardness is measure using
Brinell Madness Test
48
An important property if the equipment is being designed to handle abrasive solids, or liquids containing suspended solids that are likely to cause erosion
Hadness
49
Hard to hardest
Lead
Pure aluminium
Copper
Soft brass
Hardened aluminium
Mild steel
Annealed chisel steel
White cast iron
Nitrided surface
Glass
Rhenium diboride
50
T/F: The higher the impression diameter the lower the Brinell Number
True
51
Is likely to occur in equipment subject to cyclic loading
Fatigue
52
Examples where fatigue occurs
Cracks in bicycle frame
Helical gear
Spring
Steering arm
53
Gradual extension of a material under a steady tensile stress over a prolonged period of time
Creep
54
Usually only important at high temperatures like with steams and gas turbine blades
Creep
55
For a few materials like ____ the rate of creep is significant at moderate temperatures
Lead
56
_____ Will creep under its own weight at room temperature and ___ must be supported at frequent intervals
Lead
Lead linings
57
Reported as the stress to rupture in 100,000 hours at the test temperature
Creep strength
58
____ and ____ of metals decrease with increasing temperature
Tensile strength and elastic modulus
59
____ and ____ of metals decrease with increasing temperature
Tensile strength and elastic modulus
60
Tensile strength and elastic modulus of metals ____ with increasing temperature
Decrease
61
Tensile strength of mild steel (low carbon, C<0.25%) is 450 Pa at 25°C falling to ___ @500°C
210 Pa
62
Young's Modulus of Mild steel is 200,000 Pa at 25°C and falls to _____ at 500°C
150,000 Pa
63
SA-285 Plain Carbon Steel plate cannot be used to construct a pressure vessel with design temperature
> 900°F or 482°C
64
If any pressure vessel designed to for use above 900°F, what must be used
Killed steel or Alloy
65
Maximum allowable stress used in design is always based on the?
Design temperature
66
Are superior in sufficient strength at the design temperature that gives an economic and mechanically feasible wall thickness
Stainless steel than carbon steels
67
Will be important if the material is subjected to high stresses at elevated temperatures
Creep resistance
68
Special alloys that are used for high temperature equipment such as furnace tubes in environments that do not contain silphur
Inconel or incoloy
69
A these temperatures, metals that are normally ductile can fail in a brittle manner
Less than 10°C
70
Serious disasters have occurred through the failure of this at low temperatures
Welded carbon steel vessels
71
The phenomenon of _____ is associated with the crystalline structure of the metals
Brittle failure
72
Are more liable to brittle failure
BCC
73
For this low temperature equipment, austenitic steel (FCC) or aluminium (Hex) should be specified
Cryogenic plant
Liquefied - gas storage
74
Austenitic steel has
FCC
75
Aluminium alloys has ____ structure
Hexagonal lattice
76
Example of V-notch impact tests
Charpy test
77
Are used to test the susceptibility of materials to brittle failure
Charpy test
78
Is a complex phenomenon and is dependent on plate thickness and residual stress present after fabrication as well as the operating temperature
Brittle fracture of welded structure
79
General wastage of material
Uniform corrosion
80
Dissimilar metals in contact
Galvanic corrosion
81
Localized attack
Pitting
82
An electrochemical process
Metallic corrosion
83
Four components necessary to set up an electrochemical cell
Anode
Cathode
Conducting medium
Completion of the electrical circuit
84
Corroding electrode
Anode
85
Passive, non-corroding electrode
Cathode
86
Corroding fluid
Electrolyte
87
Cathodic areas can arise in many ways
Dissimilar metals
Corrosion products
Inclusions in the metals such as slag
Less well - aerated areas
Areas of differential concentration
Differential strained areas
88
The more or less uniform wastage of material by corrosion, with no pitting or other forms of local attack
Uniform corrosion
89
If the corrosion of a material can be considered to be Uniform, the life of the material in service can be predicted from experimentally determined?
Corrosion rates
90
Expressed as penetration rate in inches per year or mils per year
Corrosion rates
91
1 mill = inches?
10^-3
92
Can be expressed as weight loss in milligrammes per square decimeter per day
Corrosion rates
93
In here, the corrosion rate is measured by the reduction in weight of a specimen of known area over a fixed period of time
Corrosion testing
94
Of judging corrosion rate in mdd, it must be remembered that the penetration rate depends on ?
Density of the material
95
Corrosion rate of ferrous metals
100 mdd = 0.02 ipy
96
1 ipy = mm per year
25
97
What can be considered as an acceptable rate of attack will depend on the __ of the material, the ____ particularly as regards to safety and the ____ of the plant
Cost
Duty
Economic life
98
If the corrosion rate of inexpensive metals like carbon and low alloy steels less than 0.01 ipy, the more expensive alloy's like brasses and aluminium will be
0.01/2
99
If the corrosion rate indicates only short exposures then the design engineer should
Allow for frequent inspection of the plant and periodic replacement of the affected equipment
100
Uniform corrosion affects in two ways
Reduces the on-stream factor
Increase the maintenance cost
101
Number of days of production per year
On-stream factor
102
T/F: usually the impact of the frequent shutdown and replacement is so negative that the use of more expensive alloys
With better corrosion resistance can be justified
T
103
What must be added to the minimum vessel wall thickness to comply with PV codes
Allowances for expected corrosion over the plant life
104
T/F: the corrosion allowance can be economically or mechanically prohibitive if the corrosion rate is high
T
105
T/F: the corrosion allowance should be atleast equal to the expected corrosion loss during the desired life of of the vessel
T
106
Corrosion depends on
Temperature
Concentration of corrosion fluid
107
Increase in temperature usually (not always) ____ the rate of corrosion
Increases
108
Corrosion rate will depend on other factors that are affected by temperature like
Oxygen solubility
109
As an example, the corrosion of mild steel in sulphuric acid, where the rate has unacceptably high in dilute acid and at concentrations above 70%, but is acceptable at intermediate concentration
Complex effects
110
* If dissimilar metals are placed in contact in an electrolyte, the
corrosion rate of the anodic metal will be ______, as the metal
______ in the electrochemical series will readily act as a _____
increased
lower
cathode
111
What is an example of metal that at certain conditions form natural protective film in oxidizing environments?
Stainless steel
112
The state of forming a natural protective film is called
Passive
113
” indicates the absence of the protective film
Active
114
Minor shifts in position in the series can be expected in other
electrolytes, but the series for _______ is a good indication of the
combinations of metals to be avoided.
sea water
115
* If metals that are widely separated in the galvanic series have to be
used together, they should be electrically _______ from each other,
breaking the conducting circuit
insulated
116
Alternatively, if _____ of the anodic material can be accepted,
the _______ of this material can be ________to allow for the
increased rate of corrosion.
sacrificial loss
thickness
increased
117
will depend on the relative areas of the anodic and
cathodic metals.
Corrosion rate
118
T/F: A high cathode to anode area should be avoided
T
119
are used to protect underground steel pipes.
Sacrificial anodes
120
highly localized corrosion that forms pits in the metal surface
Pitting
121
T/F: If a material is liable to pitting, penetration can occur prematurely and
corrosion rate data are not a reliable guide to the equipment life.
T
122
Causes of Pitting
Not uniform composition of metals
Impingement of bubbles
Aerated medium
123
Example of not uniform composition of metals
Presence of slag in welds
124
occurs during cavitation in pumps, which is an
example of erosion-corrosion
Impingement of bubbles
125
the oxygen concentration will be lower at the bottom of a
pit, and the bottom will be anodic to the surrounding metal, causing
increased corrosion and deepening of the pit
Aerated medium
126
When attack is caused by aerated medium, how can pitting be reduced?
Good surface finish
127
the preferential corrosion of material at the grain (crystal) boundaries
Intergranular Corrosion
128
In this corrosion, though the loss of material will be small, it can cause the catastrophic
failure of equipment
Intergranular corrosion
129
a common form of attack on alloys but occurs rarely with pure metals
Intergranular corrosion
130
* The attack is usually caused by a differential couple being set up between
impurities existing at the grain boundary.
* Impurities will tend to accumulate at the grain boundaries after heat treatment.
Intergranular Corrosion
131
Classic example of intergranular corrosion
Weld decay of unstabilized stainless steel
132
caused by the precipitation of chromium carbides at the grain
boundaries in a zone adjacent to the weld, where the temperature has
been between 500–800°C during welding
Weld dacay of unstabilized stainless steel
133
can be avoided by annealing after welding
Weld decay
134
can be avoided by annealing after welding
By using low carbon grades
grades stabilized by the addition of tatnium or niobium
weld decay
135
136
Corrosion rate and form of attack can be changed if the material is under ?
Stress
137
Generally, the ____ will not change significantly within normal design stress values
Rate of attack
138
Stress corrosion cracking can occur with some combination of ____,____ and ___
Metal
Corrosive media
Temperature
139
The general name given to a form of attack in which cracks are produced that grow rapidly, and can cause premature, brittle failure of the metal
Stress corrosion cracking
140
Conditions necessary for Stress corrosion cracking to occur
Simultaneous stress cracking and corrosion
Specific corrosive substance particularly the presence of Cl-, OH- NO3- and NH4+ ions
141
Can cause cracking
Mild stress
142
Examples of mild stress
Residual stresses from fabrication and welding
143
Examples of corrosion cracking
Season cracking of brass cartridge cases
Caustic embrittlement of steel boilers
Stress corrosion cracking of stainless steels in the presence of chloride ions
144
How can stress corrosion cracking be avoided?
Selecting materials that are not susceptible in the specific corrosion environment
Relieving stress by post-weld heat treatment
145
The premature failure of materials in corrosive environments caused by cyclic stresses
Corrosion fatigue
146
T/F: even mildly corrosive conditions can markedly reduce the fatigue life of a component
T
147
Can occur in any corrosive environments and does not depend on the specific combination of corrosive Substance and metal
Corrosion fatigue
148
T/F: Materials with high resistance to corrosion must be specified for critical components subjected to cyclic process
T
149
The increased rate of attack caused by a combination of erosion and corrosion
Erosion Corrosion
150
If a fluid stream contains suspended particles or where there is high____ and ____, erosion will tend to remove the products of corrosion and any ____ and the rate of attack will be markedly _____
Velocity
Turbulence protective film
Increased
151
Can be used to prevent erosion Corrosion at the inlet to heat exchanger tubes
Plastic inserts
152
Corrosion is normally associated with
Aqueous solutions
153
Oxidation can occur in
Dry conditions
154
They will oxidize rapidly at high temperatures and their use is limited to temperatures below ___
Carbon and low alloy steels
480°C
155
Is the most effective alloying element to give resistance to oxidation, forming a tenacious oxide film
Chromium
156
____ is formed by Chromium to give resistance to oxidation
Tenacious oxide film
157
Should be specified to temperatures above 480°C in oxidizing atmospheres
Chromium alloys
158
Can be used up to 650°C
Type 304L stainless steel (18% Cr)
159
Is stabilized by niubiom and can be used up to 850°C
Type 347 Stainless steel
160
Can be used as along as sulphur is not present
High nickel alloys
161
A very common corrosive contaminant in gas processing, oil refining and energy conversion
Sulphur
162
Present in reducing environment as H2S
Sulphur
163
Causes sulphidation of metals
Sulphur
164
An example of material that must withstand sulphiding and oxidizing at high temperatures
Furnace tube
165
Can attack chromium oxide scale that protects the alloy
Sulphur
166
Causes breakaway corrosion particularly for high nickel alloys
Sulphur
167
Loss of ductility caused by the absorption of hydrogen in metal
Hydrogen embrittlement
168
Important when specifying steels for use in hydrogen reforming plant
Hydrogen embrittlement
169
Have a great resistance to hydrogen embrittlement than plain carbon steels
Alloy steel
170
A chart showing the suitability of various alloys steels for use in hydrogen atmosphere as a function of hydrogen partial pressure and temperature is given in?
National Association of Corrosion Engineers
171
Below ___ plain carbon can be used
500°C
172
To select the correct material of construction what must be clearly defined
Process environment to which the material will be exposed
173
In addition to .ain corrosive chemicals present, consider the following
Temperature
Pressure
pH
Trace impurities present
Aeration amount
Stream velocity & agitation
Heat transfer rates
174
Affects corrosion rates and mechanical properties
Temperature
175
Causes stress corrosion
Trace impurities present
176
Forms differential oxidation cells
Aeration amount
177
Causes erodion-corrosion
Stream velocity & agitation
178
Related to differential temperature
Heat transfer rates
179
Other sources of corrosion data
Rabald 1968
NACE 1974
Hamner 1974
Green and Perry 2007
Lai 1990
Schweitzer (2004,1989,2006)
DECHEMA Corrosion Handbook 2005
The ASM Handbook of Corrosion Data
180
Can be used for preliminary screening of materials likely to be suitable
Corrosion guides
181
T/F: If the published data indicate that a material is satisfactory, it is guaranteed that it will be suitable for the process environment being considered
F
182
T/F: Slight changes in process conditions or presence of unsuspected trace of jmpurities cannot change the rate of attack or nature of corrosion
F
183
Guides show clearly those materials that are manifestly ___
Unsuitable
184
If actual plant experience Is not available ___ and ___ under simulated plant conditions will help in the selection of sustaible materials
Pilot plant tests and laboratory corrosion tests
185
Perform preliminary tests like
Inserting coupons of different materials into an apparatus that resists corrosion before testing plant components
186
Reduce the likelihood of component failure and possible release of chemicals during testing
Preliminary tests
