1. Basic of Chemical Machinery & Equipments
Section 1 Materials of Chemical
Equipments
Section 2 Design of Chemical
Vessels
Section 3 Mechanical Design of
Typical Equipments
Reference:
Structural Analysis and
Design of Process Equipment

2. Section 1 Materials of Chemical Equipments
Chapter 1 Materials and Selection
1.1 Summarization

3. 1.2 Properties of Materials
Mechanical Properties
Physical Properties
Chemical Properties
Technical(processing) Properties

4. 1.Mechanical Properties:
Definition:
The capability of materials to resist
external forces, but does not deformation
beyond allowance or wreck.
Main Performance Index:
Five Index: Elasticity, Plasticity,
Strength, Hardness,
Toughness

5. Elasticity Elastic State(curve ob) i.proportional limit:σ ε a b c d . o
Tensile curve of Low Carbon steel
ii.elastic limit:

6. Strength: ultimate tensile stress σb yielding point σs, creep limit σn
creep rupture strength σD
fatigue limit (strength) σ-1
shrinkage P Ao
Stress=
(MPa) p do
Strain= l lo lo 4
Ao=
πdo2

7. When it is stretched to a certain degree,
there will be shrinkage ,and then break.
As Figure-1 showing:
i. Yielding State
(near point c)
Conditional Yielding
ii. Intensification State (curve cd)
T. S. (Tensile Strength)
iii. Shrink Neck State
(after d)

8. 1) Yielding Point σs (MPa)
it’s the minimum value in yielding state or the point in which the apparent plastic deformation appears.
*Conditional yielding point σ0.2
For the metal materials which have no apparent
yielding phenomena,it’s stipulated that:
σ0.2 = stress in 0.2% of residue elongation

9. *The stress of any point in the pressure vessel caused by pressure from medium should be below the elastic limit and cannot happen the plastic deformation.
2)Ultimate Tensile Stress σb (MPa)
抗拉强度 The maximum value of stress from the beginning of being stressed to the end of fracture.

10. i. Normal or low temperature:
considering: yield [yield/tensile] ratio: σs / σb σ σb
Yielding point
Generally speaking, σs <σb
σs/ σb ↓ , Plasticity ↑, Deformation ↑
σs/ σb ↑ , Plasticity↓, Deformation ↓
Strength Usage ↑ σs ξ
Elastic state
Plastic state

11. Temperature(0C)--1Cr18Ni9Ti
ii. Elevated temperature:
considering: σn and σD as well as the previous
Creep Rate
mm/mm*h(P con.)
Temperature(0C)--1Cr18Ni9Ti
10-6

12. 3) Creep Limit σn
#Creep phenomena:
蠕变 When the materials is in high temperature and in certain stress, the stress increases as the time is going.
#The temperature in which metals creep
Carbon steel > C
Alloy steel > C
Light metal and alloy > C
Pt, Sn Normal Temperature

13. # Creep Curve ε d c b a o τ

14. #Creep limit σn (MPa):
Definition: The ability of materials to resist
the slowly plastic deformation under high
temperature.
Under certain temperature, the creep
speed does’t excess the stress stipulated.
Stipulated creep speed: 10-7 mm / mm . H
10-6 mm / mm . H
1% straining within 105 hours
1% straining within 104 hours

15. 4) Creep Rupture Strength σD (MPa)
Definition: 持久强度 under certain temperature, the material cracks in a stress after a period of stipulated time. This stress is called creep rupture strength.

16. Stipulated time: 105 hours
Because the designed life time of chemical equipments is commonly 105 hours, the stress under which material cracks is said to be rupture strength.
Creep rupture strength is the ability to resist
cracking under certain temperature and
load. The stronger the ability is, the longer it
will endure under the same conditions.

17. 5) 疲劳极限(Strength) σ-1(MPa)
Fatigue phenomenon: the constructional
elements destruct under the alternate
load action.
Fatigue strength: the maximum stress,
under which the materials do not
happen fatigue destruction or failure
after infinite times of alternate load action.
Times of Fatigue Test: 106 ~ 108

18. 塑性 1)Definition: the ability of plastic deformation
but not destructing under external force.
2)Commonly used Index:
Percentage Elongation
Shrinkage of Sectional Area
Cold Bending Property
延伸率
After the unit of structure is cracked by tensile force, the ratio of the total stretched length and the origin length is called Percentage Elongation, described by δ%

19. Figure as following: lk — the gauge length after cracking, mm
l0— the origin gauge length, mm
△lk—the absolute length after

20. The meaning of Percentage Elongation:
i) The value of  reflects the degree of the
plastic deformation before the material cracks.
ii) The larger , the better the plasticity of material.
iii) Plastic material  > 5%; Low carbon steel  = 20~30%
iv) Hard brittle material  < 5%; Cast iron  = 1%

21. 断面收缩率（）
After the unit of structure is cracked, the ratio of the reduced area of the cross-section and the original (cross) sectional area is called Shrinkage of Sectional Area which is described by ψ%.
Fk—the minimum As after cracking ，mm2
F0—original sectional area As，mm2

22. The larger the , the better the plasticity of the material.
The  of Low Carbon Steel is about 60%.
Cold Bending Property
Welding joint R
With R increasing, the plasticity of materials will be better and better.

23. The real meaning of the Plastic Index:
Forming handling(process) and welding ease,
such as bending and rolling、forging press、cold impacting、welding and etc.
ii) Make the unit of structure to avoid cracking for deformation after bearing load.
iii) The Pressure Vessels and their spare parts
should have the characteristic.

24. 硬度 Definition: when something which is
harder than material itself is pressed on the surface of it, it will resist the pressure by deformation or be damaged, such abilities are called Hardness.
The Hardness Index:
Brinell Hardness (HB)
Rochwell Hardness (HR)
维氏 Hardness (HV)

25. F ——The area of the Indent, mm2
The test of HB: d D P
p ——Pressure, N
D——The diameter of
the rigid ball, mm
d ——The diameter of
the indent, mm
F ——The area of the Indent, mm2

26. The relationship of Hardness and Strength:
Generally, good Hardness leads to good
Strength and good resistance to wear and tear.
Experimental Value (MPa):
Low Carbon Steel b ≈ 36 HB
High Carbon Steel b ≈ 34 HB
Gray Cast Iron b ≈ 10 HB
Application of Hardness in Engineering

27. 冲击韧性ak 1)Definition: The ability of materials to resist
the impact load, i.e., the ability of
materials that will make plastic
deformation immediately and rapidly
when suddenly attacked by dynamic
loading.

28. 2) Impact Toughness
Ak—— Impact Work, J
F —— The sectional area of the
notch in the unit, cm2

29. The larger is a k , the better is the ability of materials to resist the impact load.
Hard Brittle Materials’ a k ＜＜
Plastic Materials’ a k
The relationship between Toughness and
Plasticity:
Generally, stronger toughness makes stronger plasticity; but strong plasticity may not make strong toughness .
For Mediate and Low Pressure Vessels,
a k≥30～35J/cm2 , commonly a k＞60 J/cm2.

30. 2.Physical Properties: a. Modulus of elasticity (E) (M Pa)
Nature of E:
1) It’s the index of materials’ ability to resist
elastic deformation. E↑ , ability to resist
deformation↑. E of steel is about 2 ╳ 105
（M Pa） .
2) For the same material, T ↑ , E↓ .

31. b. Poisson’s Ratio 
(For steel:  ≈ 0.3)
′—— transverse stress
 —— longitudinal stress

32. c. Thermal Expansion Coefficient ()
Physical Meaning of :
When T increases by 1℃, the increasing
length per unit length is called Thermal
Expansion Coefficient.
Application of  in Engineering.

33. 3.Chemical Properties: Definition: It’s the chemical stability of
materials in medium, i.e. , it’s the nature that
whether the materials react with medium
chemically or electro-chemically leading to
corrosion.
Two index:
Corrosion Resistance
Resistance to Oxidation

34. 耐腐蚀性
—— the ability of metal materials to resist the corrosion caused by the medium (such as atmosphere, water vapor, electrolyte).
b. 抗氧化性
1）Resist to high temperature oxidation;
2）Resist to oxide etch by other gaseous medium, such as water vapor, CO2 , SO2 , etc.

35. 4.Technical (Processing) Properties:
A. Definition: All performances in physical,
chemical and mechanical
properties when materials are
in processing, they make the
Technical or Processing
Properties of the materials.
B.Contents: as following

36. Casting Property
——Fluidity, Congealing Shrinkage Rate
Forging Property
——Resistance to Thermal Fragment,
Resistance to Oxidation, Thermo-plasticity.
Welding Property
——Fluidity of parent material and
welding flux in the melting state, Congealing,
Shrinkage Rate, Thermo-plasticity.
Machining Property——Hardness, Brittleness.
Heat Treatment Property
——Heat Treatment Feasibility.
Cold Bending Property——Plasticity, Toughness.

37. Review of 1.2: Properties of Materials: Four kinds
(1)Mechanical Properties
(2)Physical Properties
(3)Chemical Properties
(4)Technical (Processing) Properties
What are their indexes respectively and what is the meaning of them all?
How to calculate them all?

38. 1.3.Carbon Steel and Cast Iron The Classification of
A. According to their Chemical Components :
Iron Carbon Alloy:
(>95%)Fe +(0.05% ~ 4%)C
+(~1%)(impure steel and cast iron)

39. Pure Iron Steel Cast Iron 0.02 2 4 C%
B. According to the Carbon Content:
Steel C%=0.02~2%
Cast Iron C%>2%
Engineering Pure Iron C%<0.02%
Pure Iron
Steel
Cast Iron
0.02 2 4 C%

40. of iron-carbon alloy steel
1.3.1 The structure
of iron-carbon alloy steel
1. The structure of metal
چThe micro-structure of metal
(Structure in brief)
Grain
Grain Boundary

41. Different structure cause different performance of materials.
Thick plate-like
Graphite
Low strength
Thin plate-like
Mediate strength
Spherical
High strength

42. 2. Isomeric Transformation of Pure Iron
同素异构
is the phenomenon that the crystal
configuration changes with the temperature
in the state of solid.

43. Classification:
t < 910℃ Cubic Lattice in Bulk Center,
called “x-Fe”
t > 910℃ Cubic Lattice in Face Center,
called “y-Fe”
The transformation accomplishes in 910℃
without T changing.

44. The transformation is as following:
-Fe
-Fe
910℃

45. 3.Carbon and its existing form in steel
The basic types of C existing in iron-carbon alloy:
Dissolution
Chemical Combination
Blending

46. Dissolution
C dissolute in the lattice of Fe to form
Solid Solution
—— Fe-C Solid Solution.
Solvent—— the element without changing
in lattice，Fe is the solvent
Solute —— the element dissolving in
solvent，C is the solute

47. Two kinds of common-used Solid Solution
The solid solution formed by C dissolving in
-Fe is called Ferrite.
Characteristics:
Because the gap between atoms is small, the capacity to dissolve C is weak.
Solubility of C
At room temperature
0.006 %
723 ℃
0.02 %(maximum)

48. Properties:
Low strength
Low hardness
Good plasticity
Good toughness

49. 奥氏体 (A):
The solid solution formed by C dissolving in
-Fe is called Austenite, it is denser than Ferrite.
The lattice of C keeps in that of -Fe, i.e.
Cubic Lattice in Face Center.
Characteristics:
Because the gap between atoms is large, the capacity to dissolve C is strong.
Solubility of C
723 ℃
0.8 %
1147 ℃
2.06 %(maximum)

50. Properties:
High strength
High hardness
Good plasticity
Good toughness
No ironic magnetism

51. The transformation between F and A:
The irons that dissolve C will take the
transformation between -Fe and  -Fe in
different temperature.
723 ~ 910℃
Ferrite (F)
Austenite (A)
Both F and A have good plasticity and they
are the structural basis of steels’ characteristic
of excellent plasticity.

52. Chemical Combination
C and Fe form the metallic compound
——Iron Carbide (Fe3C) whose crystal
structure is called 渗碳体 indicated
by “C”.
C + 3Fe Fe3C
Characteristics:
The carbon content of Cementite is high,
the mass proportion is 6.67%.
b)Hard and brittle (HB=78.4MPa)

53. Almost no plasticity and toughness
Low break-down strength (b≈35 MPa )
The Cementite is semi-stable compound, it will decompose into Fe and C at certain conditions, the extricated C exists in the form of graphite.
Fe3C C Fe

54. Mechanical Blending (Mixture)
The alloy whose components are blending together in the state of liquid cam solidify into two types of mechanical mixtures:
Mixture formed by two solid solutions;
Mixture formed by a solid solution and metallic compound.

55. For example: 珠光体 (P)、Ladeburite (L) is a kind of Mechanical Mixture.
Pearlite (P) = Ferrite (F) + Cementite (C)
Ladeburite (L) = Austenite (A) + Cementite (C)

56. Conclusion and review of 1.3.1:
The three basic structural types are
showed as following:
Ferrite (F)
Austenite (A)
Cementite (C)

57. in the Carbon Steels and their effects
1.3.2 The impure elements
in the Carbon Steels and
their effects
The main impure elements are:
Mn Si S P O N H

58. Mn is useful element.
Si is useful element.
S is harmful element.
P is harmful element.
O is harmful element.
N is harmful element.
H is harmful element.

59. 1.Manganese (Mn): Mn < 0.8% —— the common existing impure element
Coming from the deoxidizing and desulfurizing agent in the process of smelting.
Function: eliminating S and O2.
They won’t effect the properties of steels if the content of both are little.

60. Mn > 0.8% —— the alloy element intentionally
Function: Mn can disolve in the ferrite to form the solid solution strengthening the effect of ferrite.

61. 2.Silicon (Si): Si < 0.5% —common existing impure element
Coming from the deoxidizing agent and ore.
Function:
Ability of deoxidation is stronger than Mn.
2FeO + Si  2 Fe + SiO2
Si can dissolve in the Ferrite and improve
the strength and hardness of steels.

62. The existing form in the steels:
Forming solid solution with Ferrite.
or Remaining in the steels in the form of
deoxidation product——SiO2

63. 3.Sulphur (S): Originating in the fuels in ore or which
are used in the process of smelting
——called Coke.
The existing form:
FeS (S doesn’t dissolve in Fe)
Function:
The low-melting-pointed compound
(985ºC) formed by FeS and Fe makes the steel unit crack in the process of hot-working, this phenomenon is called “Hot Brittle”.

64. Controlling of the content of S:
Common Steel
S＜0.055～ 0.07%
High Grade Steel
S＜0.03～ 0.045%
Super High Grade Steel
S＜0.02～ 0.03%

65. 4.Phosphorus (P): Originating in the ore. Function:
P in steels can dissolves in -Fe and improves the strength of steels in normal atmospheric temperature & brittleness, but dramatically reduces their plasticity and toughness, this phenomenon is called “Cold Brittle”.

66. When the content of P in the steel is P=0
When the content of P in the steel is P=0.3%, the impact toughness ak = 0.
Controlling of the content of P: P ＜ 0.06%

67. 5.Oxygen (O): Originating in the air. Existing form:
O2 always exists in the steels in the form of non-metallic inclusion, such as FeO, SiO2 , MnO, MgO, Al2O3, etc.

68. Function:
These oxidations is in the steels as solid grains which are hard but brittle and damage the continuity of basic structure of steels sharply reducing the mechanical property of steels.
Eliminating the O2 in the process of smelting.

69. 6.Nitrogen (N): Originating in the air. Function:
Low Carbon Steels with high-content of N2
are particularly lack of resistance to
corrosion.
Easy to form the air bubble to be loose.
Cause the phenomenon of “Age-hardening”.

70. Methods:
Adding Al and Ti to form AlN and TiN as if making the N fix in the steels (called N-fixed Treatment), this will eliminate the age-hardening.

71. 7.Hydrogen (H):
Originating in moist feed in steel-melting stove, pouring system and the moist air, etc.
Function:
Making the steels to be brittle
(H-Brittle)
Making the steels to be seriously defective
(Fish-eye)

72. Methods:
Improve the environment of smelting.
Clear up the moisture content in the feed.
Purify the steel liquid.

73. Review of 1.3.2: What are the impure elements?
Mn, Si, S, P, O, N, H
What are their respective function
in steels (which are harmful and
which are useful) ?
What are “Age-hardening”, “Fish-eye”, etc.? What is the factor to form them?

74. designation of the equipments
1.3.3 Classification and
designation of the equipments
1.According to the content
of carbon (C%):
Low Carbon Steel
Medium Carbon Steel
High Carbon Steel

75. Low strength and good plasticity,
used in chemical vessels in welding and
mechanical units with low loads.

76. ii. Medium Carbon Steel (C=0.25%~0.6%)
Medium strength and plasticity, used
as the important units of shaft, gear, top
cap of high pressure equipments and so on.

77. High strength and hardness, poor
iii. High Carbon Steel (C>0.6%)
High strength and hardness, poor
plasticity, used as string, wire line and so on.

78. 2.According to the smelting
methods:
Full Killed Steel
Boiling Steel
Semi-killed Steel

79. i.镇静钢 —completely deoxidized steel
Deoxidation by the strong deoxidizer Si
to reduce the content of oxygen to be
less than 0.01%, commonly it will be
0.002~0.003%.

80. Tough structure, uniform texture and solid.
The Pressure Vessels’ steels should apply the full killed steels.
Using ‘Z’ to indicate the designation or none.

81. ii.沸腾钢 —incompletely deoxidized steel
Deoxidation by the strong deoxidizer Mn
to reduce the content of oxygen to be
0.03~0.07%.
Loose structure, inferior texture.
Commonly used in Support, Frame and the
like unimportant units.
Designation is ‘F’.
iii. Semi-killed半镇静钢 —between the previous two
Designation is ‘b’.

82. 3.According to the quality:
Common Steel
High Grade Steel
Super High Grade Steel

83. i. 普通碳素钢
The content of the harmful elements
S & P can be a little more to be
(S≤0.055%, P≤0.045%)

84. Three kinds of the old designation of
Common Steels (GB700-79)：
A——merely assuring the mechanical
properties (A1, A2, A3, ……A7)
B——merely assuring the chemical
components (B1, B2, B3, ……B7)
C——assuring both of the previous
points (C1, C2, C3, ……C5)

85. The new designation of Common Steels (GB700-88): For example:
Q 235 — A. F
The quality
grade of steels
The deoxidized method
The value of the steels’ yielding
point with the unit of “MPa”
The first letter of the Chinese spell of the word “屈”

86. Designation Z B D C
b.Z
Q275
F.b.Z A
Q255
Q235
Q215
Q195
Deoxidized
Method
Grade

87. ΘFull Killed Carbon Steel Plate:
The applying range of the Common Steels in
the chemical equipments:
ΘFull Killed Carbon Steel Plate:
*Q235-A——suitable under the condition of
P≤1.0MPa, t=0~350ºC, S≤16mm.
The media shouldn’t be used in the
Pressure Vessels with media
ultra-hazardously toxic or
high-hazardously toxic or
with media as liquified
petroleum gas.

88. *Q235-B——suitable under the condition of
P≤1.6MPa, t=0~350ºC, S≤20mm.
The media shouldn’t be used in the
Pressure Vessels with media
ultra-hazardously toxic or
high-hazardously toxic.
*Q235-C——suitable under the condition of
P≤2.5MPa, t=0~400ºC, S≤30mm.

89. ΘBoiling Carbon Steel Plate:
*Q235-AF——suitable under the condition
of P≤0.6MPa, t=0~250ºC, S≤12mm.
The media shouldn’t be used in the
Pressure Vessels with media media,
ultra-hazardously toxic or
high-hazardously toxic or
combustible.

90. ii. 优质碳素钢
Seriously control the content of S & P to be (S & P≤0.04%)
Uniform texture, good surface quality, superior properties than Common Steels.
The number in designation indicates the percentage of the average content of C:
08：C=0.08% : C=0.2%

91. Steels that commonly contain Mn (without indicating Mn)
Designation:
Steels that commonly contain Mn
(without indicating Mn) ……
Steels that contain more Mn
(Mn=0.7~1.2%) (indicating Mn)
30Mn Mn ……

92. iii. 超级优质碳素钢
(1)S & P≤0.03%
(2)Both the texture and properties of this
kind of steels’ are superior to that of
High Grade Steel.

93. (3) Designation: adding the letter ‘A’ after
the designation, such as 20A, 25A …...
(4) Indication of steels with different usage
by the letter of Chinese spelling:
Boiling Steel: g such as 20g
Vessel Steel: R such as 20R

94. Review of 1.3.3: Classification and designation of the
equipments according to:
(1)Content of carbon
(2)Smelting methods
(3)Quality
What are the concrete steels under each
of the previous titles?
How to explain the designation?

95. 1.3.4 Heat Treating of Steels
1.Bring forward the problem:
Find out the method and path of altering the properties of steels
2.热处理的目的
Eliminating some shortages of steels
Improving some properties of steels

96. Intensifying the metallic materials,
3.热处理的优点
Intensifying the metallic materials,
fully developing the potential of materials,
lightening the mass of equipments and
guaranteeing the security and expected life
of equipments.

97. Heat treatment is the technical process or
4.热处理的定义
Heat treatment is the technical process or
treatments to steels in solid state according to
the scheduled requirements like heating,
keeping warm and cooling, their aims are to
vary the internal structure and gain the
desired properties.

98. 5.Basic Theories of heat treatment:
When the basic components of steels (Fe) is heated to a certain degree, its lattice structure of steel will vary from one form to another as the temperature.
Ferrite (F) and Austenite (A) are both the solid solution of Fe, so they have the lattice structure of iron.

99. 6.Processing steps of heat treatment:
Heating Keeping warm Cooling
Temperature/ºC
Time
Keeping warm
Cooling
Heating

100. Cooling media and way of cooling:
Cooling in furnace
Cooling in still air
Cooling in oil
Cooling in water
Cooling in brine
Cooling Capacity
Cooling Speed

101. 7.Heat Treating Process of steels:
Annealing
Normalizing
Quenching
Tempering

102. i. 退火 正火
(1)The function of annealing and normalizing
*Lowering hardness, improving plasticity,
making steels apt to the cold-work.
*Homogenizing the steel structure, refining
the grain, developing the mechanical
properties.
*Clearing up the internal stress, resisting
the deformation of workpieces.

103. (2)The selection of annealing and normalizing
*Aimed mainly at improving the
machinability, normalizing is better for
Medium or Low Carbon Steels; while
annealing for High Carbon Steels.

104. *Aimed mainly at developing the
mechanical properties and never need
any other heat treatments, normalizing
is better.
*From the aspect of economy, normalizing
is better than annealing.

105. ii. 淬火
(1)Process
Heating the steel pieces to the
quenching temperature, cool them
quickly in the quenching agents after
the warm-keeping treatment, then the
Austenite changes into the Matensite.

106. (2)Quenching Temperature
*Hypo-eutectoid Steel (C<0.8%)
heating above the A3 line 30~50ºC
*Hyper-eutectoid Steel (C>0.8%)
heating above the A1 line 30~50ºC

107. (3)Quenching Agent
*Mineral Oil, Water, and Brine.
*Generally speaking:
Carbon Steel, cooling in water and brine.
Alloy Steel, cooling in oil.

108. (4)Quenching Function
——developing the hardness, strength
and wear (abrasion) resistance.
*The emergency cooling in quenching is apt
to make flaw in the steel pieces, so the
tempering is commonly needed to clear
up the stress after quenching.
*Quenching and Tempering are always
combined to the technical process.

109. iii. 回火
(1)Process
Heat the steel pieces which are already
quenched to the certain temperature
(T<Tcritical), cool them quickly in still air
after the warm-keeping treatment.
(2)Purpose
Reduce or clear up the internal stress of
workpieces after quenching, stabilize the
internal structure and gain the different
mechanical properties.

110. (3)Types of Tempering
*Tempering at low temperature
——after quenching, tempering
between 150~250ºC.
Function——reduces the internal stress
and brittleness of quenching
steels, and at the same time
keeps the high hardness and
high wear resistance.
Usage ——in spares of various tools and
ball bearing after carburation.

111. *Tempering at medium temperature
——after quenching, tempering
between 300~450ºC.
Function——reduce the internal stress,
reach the limit of high
strength and high elasticity.
Usage——in the treatment of various
spring.

112. *Tempering at high temperature
——after quenching, tempering
between 500~680ºC.
Function——gain the certain strength, have
higher plasticity and impact
toughness, i.e. excellent overall
mechanical properties.
Quenching + Tempering ——Thermal Refining
Usage——important spares, such as gear,
rod, crank shaft, etc.

113. Review of 1.3.4: Types of Heat Treatments: What are their definition?
(1)Normalizing
(2)Annealing
(3)Quenching
(4)Tempering
What are their definition?
What are their functions in the
improvement of mechanical
properties of materials?

114. 1.3.5 Cast Iron 1.The chemical components of commonly used cast iron:
95% Fe + (2.5% ~ 4%) C + ( ~1%) Purities
2.Structure:
Pealite + Cementite + Ladeburite + Graphite

115. 3.Properties and Characteristics: Excellent casting property
Good machinability
Good wear resistance
Excellent property to reduce vibration
Low plasticity and brittleness
Low tensile strength and high (ultimate)
compression strength

116. 4.Properties and Designation of commonly used cast iron:
Gray cast iron (HT)
Spherical graphite cast iron (QT)
High-silicon cast iron (G)

117. i. 灰口铁 (HT)
(1)Properties and characteristics
*C exists in the form of plate-like graphite
*Gray fracture
*Low mechanical properties
*Excellent corrosion resistance in H2SO4
and NaOH

118. (2)Designation HT 150 — 330 HT 200 — 400 Tensile Strength
b (MPa)
Bending Strength
bb (MPa)

119. ii. 球墨铸铁 (QT)
(1)Properties and characteristics
*C exists in the form of spherical graphite
*Have better strength and a certain
plasticity and toughness, its overall
mechanical properties are close to
that of steels.
*Better corrosion resistance than that of
HT except when it is in the acid
solution.

120. Elongation Percentage
(2)Designation
QT 400 — 15 QT 450 — 10 QT 450 — 10
Tensile Strength
b (MPa)
Elongation Percentage %

121. iii. High-silicon cast iron (G)
(1)Properties and characteristics
*Adding amount of Si (14.5~18%) to
improve the corrosion resistance of
the cast iron.

122. Highly corrosion resistant media:
nitric acid, sulfuric acid,
phosphorus acid, acetic acid
Medium corrosion resistant media:
hydrochloric acid, 草酸(甲酸), 蚁酸
Corrosive media:
caustic soda, hydrofluoric acid

123. *Low tensile strength, good hardness, brittle
and easy cracking.
*Impact non-resistant, hard to cut and cast only.
(2)Designation
ST Si 15 R
Content of Si is 15%
Mixing lanthanide

124. Review of 1.3.5: Types of commonly used cast iron:
(1)Gray cast iron (HT)
(2)Spherical graphite cast iron (QT)
(3)High-silicon cast iron (G)
What are their properties and
characteristics?
How to explain their designations?

125. 1.4.
Common Low Carbon Steel
and Special Steel
used in Chemical Equipments

126. 1.4.1 Problems 1.Shortages of Carbon Steel:
i. Low strength and yield ratio (s/ b) σs σb σ ε
σs/σb of Carbon Steel
is small
σs/σb of Alloy Steel
is large

127. The strength comparison between Carbon Steel and Alloy Steel
Material
σ s
(MPa)
σ b
(Mpa)
σ s / σ b
Carbon
Steel
Q235-AR
240
400
0.6 20
250
0.62
Alloy
16MnR
360
520
0.69
15MnV
540
0.74
18MnMoNbg
650
0.8

128. ii. Low strength at high temperature
The strength comparison (at high T)
between Carbon Steel and Alloy Steel σ S
(Mpa)
Material
(mm)
20℃
400℃
450℃
500℃
Q235-A
20~40
230
125 — C
20g
26~36
115
16Mn
27~36
310
190
170 A
18MnMoNbR
16~38
520
420
390
350

129. 2.Necessity to the development of modern industry and Science
iii. Poor hardenability
iv. Inferior special physical and chemical
properties
2.Necessity to the development
of modern industry and Science
& Technology

130. 1.4.2 Effect of Alloy Elements
to the properties of steels
1.Alloy elements:
i. Definition
The elements that are added on
purpose to develop the structure and
characteristics of steels.
ii. Main alloy elements
Cr Ni Mn Si Al Mo
V Ti Cu B Nb W Re

131. 2.Alloy Steel Definition
合金钢 Alloy steels are those steels that contain the alloy elements which develop the properties of steels.

132. 3.Characteristics of the main alloy elements:
i. Cr
(1)Cr>13%, corrosion resistance dramatically
(2)Strength, hardness, wear resistance,
oxidation resistance and hardenability all
(3)Plasticity and toughness
(4)Adds strength at high temperature

133. ii. Ni
(1)Enlarge the range of corrosion resistance
of stainless steel, especially improve the
resistance to base.
(2)Broad the -phase region as to be the
element that form the austenite.
(3)Develop the strength as well as keep
excellent properties of plasticity and
toughness.
(4)Improves strength at high T(热强性?)

134. iii. Mn
(1)Develop the strength and impact
toughness at low temperature.
(2)Broad the -phase region.
(3) Counteracts sulfur brittleness.
(4)Increases hardenability.

135. iv. Si
(1)Develops strength and fatigue
durability at high temperature.
(2)Improve heat resistance
(3)Resistant to the corrosion of such media
as H2S and so on.
(4)If amount of Si is too much,
plasticity and impact toughness both
(5)Strengthens steel
(6)Increases hardenability

136. v. Mo
(1)Develop the resistance of stainless
steels to the chloride anion Cl-.
(2)Enhances H corrosion resistance.
(3)Improve the heat resistance.
(4)Raises grain-coarsening temperature.
(5)Mo<0.6%, plasticity .
(6)Counteracts tendency toward temper
brittleness.(要否?)

137. vi. Al
(1)Restricts grain growth.
(2)Develops the impact toughness.
(3)Resistant to the corrosion caused by H2S.
(4)Improves the oxidation and heat resistance.
(5)Cheap, common substitute for Cr among
heat-resistant steels.

138. vii. Ti
(1)Restricts grain growth.
(2)Develops strength and toughness.
(3)Improves the oxidation and heat resistance.
(4)Stablizes C to prevent the
“inter-crystalline corrosion”.
(5)Prevents formation of austenite in high
chromium steels; prevents localized
depletion of chromium in stainless steel
during long heating.(英文书上的,要否?)

139. viii. V
(1)Developes high-temperature strength.
(2)Increases hardenability.
(3)Restricts grain growth.
(4)Keeps the strength and improve the
plasticity.
(5)Resists tempering (英文书上的,要否?)

140. S P H WR IT CR OR HR FD GR Cr Ni Mn Si H2S Mo HCl Al Ti in-c V Re A E

141. Interpretation: AE——alloy element S ——strength P ——plasticity
H/WR ——hardness and wear resistance
IT ——impact toughness
CR ——corrosion resistance
OR ——oxidation resistance
HR ——heat resistance
FD ——fatigue durability
GR ——grain refining H ——hardability
in-c ——inter-crystalline

142. Review of 1.4.2: The main alloy elements:
Cr Ni Mn Si Al Mo
V Ti Cu B Nb W Re
What are their characteristics?
What are their functions in the improvements of mechanical properties of steels?

143. 1.4.3 Common Low Alloy Steel 1.Definition:
普通低合金钢 They are the steels that are formed by adding a few alloy elements at the basis of
Common Low Carbon Steel.

144. 2.Composition: (1)C<0.2% 3.Structure: (2)Alloy elements *Mn 1~1.5%
*Si Cr Ti V Nb Ni Al… ~ 0.6%
3.Structure:
Ferrite + Pearlite

145. 4.Properties and characteristics:
i. High strength and large yield ratio
ii. Excellent welding property
iii. Good resistance to the corrosion of
atmosphere
iv. Perfect properties at low temperature

146. (New Designation GB/T1591-94)
16Mn 16MnR 16Mng 15MnV 15MnVR
15MnVg 09Mn2V 18MnMoNbR
The number ahead is the percentage of the C content, such as 16Mn (C = 0.16%).

147. Indicate the main alloy elements, the number thereafter is the percentage of that element. If it is less than 1.5%, it can be omitted.
Content of alloy elements:
1.5 ~ 2.49% Sign as “2” ~ 3.49% Sign as “3” ~ 4.49% Sign as “4”

148. 1.4.4 Boiler Steel & Vessel Steel
1.Steels specially used in the
manufacture of boilers and vessels.
2.There are some special requirements
for boiler steel and vessel steel.

149. 3.Commonly-used Designation:
i. Boiler Steel
20g 22g 12Mng 16Mng 15MnVg
14MnMoVg 18MnMoNbg
ii. Vessel Steel
Q235-AR 20R 16MnR 15MnVR
09MnVR MnMoNbR

150. Corrosion (Acid) Resistant Steel
1.4.5 Stainless Steel and
Corrosion (Acid) Resistant Steel
不锈钢 Stainless Steels are the kind of alloy
steels which are resistant to the
corrosion caused by atmosphere,
water or other soft caustic media.

151. 耐酸钢 Acid Resistant steels are the kind of alloy steels which are resistant to the corrosion
caused by acid or strong caustic media.
As a rule, we called them both “Stainless Steel”.
Examples:
*Chromium Stainless Steel
*Chromium-nickel Stainless Steel

152. 1.Chromium Stainless Steel:
i. Component
< 0.2% C + (13 ~ 28%) Cr + Fe
ii. Construction
Ferrite or Martensite
(no Austenite even at high temperature)

153. iii. Theories of corrosion resistance
(1)In the oxidizing medium, a oxide skin
Cr2O3 which is stable and tight will be
formed, it has an effect on passivation,
i.e. there is a passivation layer on the
surface of the steels.
(2)The degree of corrosion resistance
depends on the content of C and Cr.
The more Cr, the better the resistance
The less C, the better the resistance

154. iv. Commonly-used Chromium Stainless Steel
1Cr Cr Cr Cr Cr17Ti
v. Designation
(1)The first number:
Average C content 平均含C量的千分数
0：C < 0.1% 1: C≤0.15% 2: C≈0.2%
(2)The second number:
percentage of the average content of Cr

155. 2.Chromium-nickel Stainless Steel:
i. Component
≤ 0.14% C + ( 17~19% ) Cr + ( 8 ~11%) Ni + Fe
Briefly called “18 — 8” Steel
Typical Designation: 1Cr18Ni9Ti
ii. Construction
Single austenite structure at normal temperature

156. iii. Characteristics
(1)High strength and good plasticity
& toughness
(2)Large range of suitable temperature
-196℃ ~ 800 ℃
(3)Excellent technical properties
(4)Good corrosion resistance

157. ΘNon-corrosive media:
cold phosphorus acid, nitric acid, acetic acid,
hydrogen sulfide, sulfate, nitride, base liquid,
petroleum chemicals, etc.
ΘCorrosive media:
hydrochloric acid, dilute sulfuric acid (<10%),
hot phosphorus acid, oxalic acid (草酸),
melting caustic potassium, melting caustic
alkali, Cl-, bromine (Br), iodine (I), etc.

158. (5)Inter-crystalline corrosion easily occurs
between 400~800 ℃
Θ晶间腐蚀 Definition of inter-crystalline corrosion:
It is the phenomenon that
the corrosion occurs between two
crystalline surfaces and causes the
grain boundary continuously damaged.
ΘNature:
It’s a kind of local and selective
corrosive damage.

159. ΘOccurring in:
Austenitic stainless steels
ΘReason:
Lack of Cr element in the grain boundary
ΘAustenitic stainless steels (C<0.14%):
*At high temperature (1050ºC)
C distributes completely in whole alloy.

160. *Between 400~800℃ C + Cr + Fe (Cr . Fe)23C6 Cr% Cr＜12.5% Cr lacking
Separate out along the grain boundary
Cr%
Grain
(Cr . Fe)23C6
Cr lacking region
boundary
Cr＜12.5%
Cr lacking
Corroding
minicell
Cr lacking
region —
Anode
Inter-crystalline
Corrosion occurs
Grain —
Cathode

161. ΘDamage:
To be brittle, even softly beating can makes
it break into dust. Have very low strength.
ΘPreventive measures:
*Solution heat treatment ——
quenching again (1100~1150ºC) to
dissolve C and Cr into the austenite.
*Reduce the content of C ——
preventing C to combine with Cr, then less
Cr will be separated out.
For example: 0Cr18Ni9 (C ≤ 0.08%)
00Cr18Ni9 (C ＜ 0.03%)

162. *C stabilization treatment ——
adding Ti or Nb to form TiC or NbC to
stabilize C.
For example: 1Cr18Ni9Ti 1Cr19Ni11Nb
*Add microelement ——
adding B can vary the nature of grain
boundary to prevent (Cr . Fe)23C6 to be
separated out.

163. (6)氢蚀 Pitting corrosion occurs in the media
containing [Cl-]
ΘMechanism:
[Cl-] intrudes into the flaw of passivation
film (Cr2 O3) and reacts with metallic ion to
form strong acidic salts ([M+] + [Cl-] → MCl)
which can dissolve the passivation film ——
the locally corroded film becomes a “passive-
active” minicell —— with corrosion taking
place.

164. ΘDamage:
Fast corrosion speed easily perforates the
thin (only several mini-meter thick) stainless
steel by corrosion.
ΘPreventive measures:
*Adding some alloy elements
The most effective elements to improve the
pitting corrosion resistance: Cr, Mo
Secondarily effective elements: Ni, Si, N, Re

165. *Cr≥25%, pitting corrosion won’t occur.
2%Mo improve pitting corrosion
resistance dramatically, Mo and [Cl-]
form the protective film (MoOCl2) which
can prevent the passivation film being
perforated.
*Materials resistant to the corrosion of [Cl-]:
high Cr-Ni stainless steel containing Mo
such as: 1Cr18Ni12Mo2Ti
00Cr20Ni30Mo2Nb
000Cr30Mo2

166. and Low-temperature Steel
1.4.6 Heat-resisting Steel
and Low-temperature Steel
1.Heat-resisting Steel:
i. Characteristics
(1)Excellent high-temperature oxidation
resistance (excellent high-T chemical
stability)
(2)Good high-T mechanical properties
(strength at high T热强性？)

167. ii. Elements added
Cr Mo V Ti W Si Ni Al
iii. Commonly-used heat-resisting steel
(1)Oxidation resistant steel——
*mainly resistant to oxidation, but has
low strength.
*used in the parts that are heated directly
(800~1000℃) but small loaded.
such as: heating tube support, nozzle, etc.
*commonly used steels’ designation:
Cr13SiAl Cr25Ti Cr17Ti Cr25Ni12

168. (2)热强钢——
*mainly resistant to creep but also resistant
to oxidation.
*used in the parts that are loaded at high T.
such as: heating tube, reactor, etc.
*commonly used steels’ designation:
12CrMo Cr5Mo 1Cr18Ni9Ti Cr25Ni20

169. 2.Low-temperature Steel:
i. Working temperature
< -20℃ Low temperature
-20 ~-40 ℃ Non-cryogenic temperature
< -40 ℃ Cryogenic temperature
ii. Characteristics
(1)Excellent low-temperature toughness
(2)Excellent processing workability and
weldability

170. iii. Requirements of structure
(1)Low content of C (0.08~0.18%) ——
form homogeneous ferritic structure.
(2)Homogeneous austenitic structure is
desirable at cryogenic temperature.
iv. Elements added
Mn Al Ti Nb Cu V N

171. Specifications of Steels
1.4.7 Varieties and
Specifications of Steels
1.Plates (Sheet Materials):
2.Tubes(Tubular Products):

172. 3. Shapes (Section Materials): i. Flat Steel (bar)
ii. I-Steel (beam or section)
iii. L-Iron (Angle Steel)
4. CCS (Cast Carbon Steel) & FS (Forged Steel)

173. Corrosion & Protection of Chemical Equipments
1.5.
Corrosion & Protection of
Chemical Equipments
1.5.1 Harm of corrosion

174. 1.5.2 Evaluation Methods of the Corrosion of Metal
1.According to the weight changes: h t m2 F p1 p0 K g
g/cm2·h
Time of corrosion action —
Contact Area of corrosive
media and test piece
WT after corrosion
WT before corrosion
Corrosion Rate

175. 2.According to the corrosion degree:
mm/year
Ka—Thickness variation per year mm/year
—Metallic density g/cm3 g F h

176. 3.Three Grades’ Standard of Metallic Resistance to Corrosion:
Grade I: Ka < 0.1 mm/year (corrosion resistant)
Grade II: Ka = 0.1 ~ mm/year (available)
Grade III: Ka > mm/year (unavailable)

177. 1.5.3 Chemical Corrosion
1.Definition:
化学腐蚀 The corrosion caused by chemical reactions between metals and drying gas or non-electrolyte solution (非电解质溶
液?) is called Chemical Corrosion.

178. 2.Characteristics: i. Corrosion products are on the metallic surface
ii. No electric current in the cause of corrosion
iii. The two natures of the products from
chemical reactions:
(1)Stability —— Passivation
(2)Unstability —— Activation

179. 3.Examples of Chemical Corrosion:
i. Metallic high temperature oxidation
(1)Oxidation resistance:
oxidized rapidly at high T
forming oxidation film
stopping oxidation

180. Stable Stable Unstable (2)High temperature oxidation of carbon steel
and cast iron:
T > 300 ℃ oxidation surface appears
T < 570 ℃ oxidation layer forms
inner layer Fe3O4
outer layer Fe2O3
Stable
T > 570 ℃ oxidation layer forms
layer I: Fe2O3
layer II: Fe3O4
layer III: FeO
Stable
Unstable

181. Composition of ironic oxidation layer
Fe2O3
Fe3O4
FeO Fe
T < 570 ℃
T > 570℃
Composition of ironic oxidation layer

182. (3)Solutions:
Adding some Cr Si Al to form stable
oxidation film of Cr2O3 SiO2 Al2O3 which
can prohibit the oxidation reaction from
proceeding.

183. ii. High temperature decarburization
oxidation and decarburization both exist
Fe3C + O2  3Fe + CO2
Fe3C + CO2  3Fe + 2CO
Fe3C + H2O  3Fe + CO + H2

184. (2)Result
*Cementite Ferrite
with Strength, hardness and Fatigue
Strength all decreasing.
*Forming the air bubble which is the crack
initiation point.
(3)Prevention
Adding Al or W

185. iii. 氢腐蚀 (hydrogen brittleness)
At relevant low temperature and pressure
(T≤200 ℃, P ≤5MPa), H2 won’t
corrode the carbon and alloy steels
apparently.
At high T and P, the corrosion actions of
H2 to steels are obvious.

186. Mechanism of hydrogen corrosion:
Stage I —— “Hydrogen brittleness stage”
H disperses inward and dissolves.
Stage II —— “Hydrogen attack stage”
Chemical reaction vary the
structure of steels:
Fe3C + 2H2  3Fe + CH4

187. 1.5.4 Electrochemical Corrosion
1.Definition:
电化学腐蚀
The corrosion caused by electrochemical
reactions between metals and electrolytes is
called Chemical Corrosion.

188. 2.Mechanism: Anode reaction —— Me  Me+ + e
Electron movement —— eanode  ecathode
Cathode reaction —— D + ecathode  [D e]

189. 3.Conditions of electrochemical corrosion:
i. There is potential difference on the parts of
metallic surface or between different metals.
ii. The parts which have potential difference
are connected with each other or the anode
is connected with cathode.
iii. The metal with potential difference is in
the electrolyte or the electrolyte where the
anode and cathode are connected with each
other.

190. 4.Inter-crystalline corrosion
i. Definition
晶间腐蚀
It is the phenomenon that
the corrosion occurs between two
crystalline surfaces and causes the
grain boundary continuously damaged.
ii. Nature
It’s a kind of local and selective
corrosive damage.

191. iii. Occurring in
Austenitic stainless steels
iv. Reason
Lack of Cr element in the grain boundary
v. Austenitic stainless steels (C<0.14%)
*At high temperature (1050ºC)
C distributes completely in whole alloy.

192. *Between 400~850℃ C + Cr + Fe (Cr . Fe)23C6 Cr% Cr＜12.5% Cr lacking
Separate out along the grain boundary
Cr%
Grain
(Cr . Fe)23C6
Cr lacking region
boundary
Cr＜12.5%
Cr lacking
Corroding
minicell
Cr lacking
region —
Anode
Inter-crystalline
Corrosion occurs
Grain —
Cathode

193. 5.Stress corrosion (SC Fracture)
i. Definition
应力腐蚀
The destruction is caused
by both corrosive media and the
tensile stress action, this kind of
damage is called Stress Corrosion.

194. ii. Initiation Circumstances
Carbon steel and various kinds of Alloy steel (such as austenitic stainless steel) are in the media listed as following:
(1)High concentrated chloride solution above
80℃
(2)High temperature and pressure water at
150~300 ℃
(3)High temperature and concentrated caustic
solution

195. Stage I: Breeding stage (孕育阶段?)
iii. Mechanism
Stage I: Breeding stage (孕育阶段?)
The primary destruction
(mechanical crack) is formed in metallic
surface under the co-action of corrosion
and tensile stress.

196. Stage II: Corrosion crack’s extension stage
Corrosive media dissolve the
passivation film in the cracks to form
anode with the film becoming cathode, the
electrochemical corrosion therefore occurs.
The crack extents rapidly under the co-action
of this corrosion and tensile stress.

197. Stage III: Breaking stage

198. iv. Prevention measure
(1)Decrease or clear up the stress concentration
(2)Select the stress corrosion resistant materials:
Two-phase stainless steel ——
austenite + small amount (about 5%) of Ferrite
such as: 1Cr18Mn10Ni5Mo3N
0Cr17Mn13Mo2N
0Cr21Ni5Ti

199. 1.5.5 Types of metallic corrosion
1.Uniform (General) Corrosion:
i. Corrosion is over the whole metallic surface
ii. Effect and danger are small
iii. Remaining enough corrosion allowance in
designation can still assure the strength
and expected life of equipments

200. 2.Local Corrosion: i. Corrosion is at the local region in metals
ii. Very dangerous
iii. Remaining the corrosion allowance in
designation has no effect.

201. iv. Categories of Local Corrosion
(1)Seam Corrosion
(2)Pitting Corrosion
For example:
the pitting corrosion of Cr-Ni stainless
steel in the media containing [Cl- ]

202. (3)Stress Corrosion
(4)Inter-crystalline Corrosion
For example:
the inter-crystalline corrosion of
Cr-Ni stainless steel under certain conditions

203. 1.5.6 Corrosion Resistant Measures in Metallic Equipments
1.Selecting materials reasonably

204. 2.Adding the lined protection
i. Metallic lining: stainless steel,
other metals(Cu Al Ti Cr Ni)
ii. Nonmetallic lining: plastics,
rubbers, enamelware, etc.

205. + -
iii. Coating
iv. Adding corrosion
buffering agents
v. Electrochemical
protection
such as:
cathodic protection
Cathodic Protection
Apparatuses

206. Mechanism of cathodic protection:
阴极保护
The protected metallic devises are
polarized into cathodes by the direct current
(DC) from outer electrical power supply
taking the auxiliary electrode as the anode.
When the potential of cathode < that
of anode, the corrosion will be prohibited.

207. of Chemical Equipments
1.6. Materials Selection
of Chemical Equipments
1.6.1 General Principles
1.Suitable Mechanical Properties:
Strength, hardness, plasticity, etc.
2.Good Corrosion Resistance
3.Economic and rational

208. 1.6.2 Others 1.Pressure Vessels commonly use Full-killed Steels
2.Common Alloy Steels are preferred
3.Q235- A and 16Mn can’t be used to
fabricate the vessels in which the
liquified petroleum gas is held.
4.The C content of Welded Vessels’
materials should be C < 0.24%.

209. Austenite A3 A1
Ferrite +
Pearlite
1667
1333
Temperature ºF
Iron-iron carbide equilibrium diagram
Percent carbon of weight
0.8
0.2
0.4
0.6

210. The lattice structure of steel varies from one
form to another as the temperature changes.
This is illustrated in the above figure. Between
room temperature and 1333ºF, the steel consists
of what s known as “ferrite and pearlite”.
Ferrite is a solid solution of a small amount of
carbon dissolved in iron. Pearlite, which is
shown in the figure, is a mixture of ferrite and
iron carbide. The carbide is very hard and
brittle.

211. In the previous figure between line A1
(lower critical temperature) and A3 (upper
critical temperature) the carbide dissolves
more readily into the lattice that is now
called “Ferrite and austenite”. Austenite is a
solid solution of carbon and iron that is
denser than ferrite.

212. Above line A3 the lattice is uniform
in property with the austenite the main
structure. The actual temperature for this
austenite range is a function of the carbon
content of the steel as shown in the figure.