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

Basic of Chemical Basic of Chemical Machinery & EquipmentsMachinery & Equipments

Section 1 Materials Section 1 Materials of Chemical Equipmentsof Chemical Equipments

1.1 Summarization1.1 Summarization

Chapter 1 Materials Chapter 1 Materials and Selectionand Selection

Mechanical Properties

Physical Properties

Chemical Properties

Technical(processing) Properties

1.2 Properties of Materials1.2 Properties of Materials

I. Definition:

The capability of materials to resist

external forces, but does not deformation

beyond allowance or wreck.

1.Mechanical Properties:

II. Main Performance Index:

Five Index: Elasticity, Plasticity,

Strength, Hardness,

Toughness

Elastic State(curve ob)

i.proportional limit:

o

pp F

P

o

ee F

P

σ

ε

abc

d

.

p

es

b

o

Tensile curve of Low Carbon steel

Elasticity

ii.elastic limit:

Strength:

lodo

p

p

PAo

Stress= (MPa

)

shrinkage

4Ao= πdo2 Strain= l

lo

ultimate tensile stress σb

yielding point σs, creep limit σn

creep rupture strength σD fatigue limit (strength) σ-1

i. Yielding State

(near point c)

o

ss F

P

ii. Intensification State (curve cd)

T. S. (Tensile Strength)

o

bb F

P

oF

P 2.02.0

Conditional Yielding

When it is stretched to a certain degree,

there will be shrinkage ,and then break.

iii. Shrink Neck State (after d)

As Figure-1 showing:

For the metal materials which have no apparent

yielding phenomena,it’s stipulated that:

σ0.2 = stress in 0.2% of residue elongation

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

*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.

抗拉强度 The maximum value of stress from the beginning of being stressed to the end of fracture.

2)Ultimate Tensile Stress σb (MPa)

σb

σs

Elastic state Plastic state

σ

ξ

Yielding point

i. Normal or low temperature:

considering: yield [yield/tensile] ratio: σs / σb

Generally speaking, σs <σb

σs/ σb ↓ , Plasticity ↑, Deformation ↑

σs/ σb ↑ , Plasticity↓, Deformation ↓

Strength Usage ↑

ii. Elevated temperature:

Creep Rate

mm/mm*h(P con.)

Temperature(0C)--1Cr18Ni9Ti

425 475 520 550

10-6 176 91 33 6

considering: σn and σD as well as the previous

3) Creep Limit σn

#The temperature in which metals creep

#Creep phenomena: 蠕变 When the materials is in high temperature and in certain stress, the stress increases as the time is going.

Carbon steel > 420 0CAlloy steel > 450 0CLight metal and alloy > 50-150 0C Pt, Sn Normal Temperature

τ

ε

o

ab

cd

# Creep Curve

#Creep limit σn (MPa):Definition: The ability of materials to resist the slowly plastic deformation under high temperature.Under certain temperature, the creepspeed does’t excess the stress stipulated.Stipulated creep speed: 10-7 mm / mm . H 10-6 mm / mm . H1% straining within 105 hours1% straining within 104 hours

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.

4) Creep Rupture Strength σD (MPa)

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.

5) 疲劳极限 (Strength) σ-1(MPa)

Fatigue strength: the maximum stress, under which the materials do not happen fatigue destruction or failure after infinite times of alternate load action.

Fatigue phenomenon: the constructional

elements destruct under the alternate

load action.

Times of Fatigue Test: 106 ~ 108

塑性

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%

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

%100%100 00

0

l

l

l

ll kk

lk — the gauge length after cracking, mm

l0— the origin gauge length, mm

△lk—the absolute length after cracking, mm

Figure as following:

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%

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

%100

F

FF k

Cold Bending Property

Welding joint

R

The larger the , the better the plasticity of the material. The of Low Carbon Steel is about 60%.

With R increasing, the plasticity of materials will be better and better.

i) 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.

The real meaning of the Plastic Index:

硬度I. 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.

II. The Hardness Index:

Brinell Hardness (HB)

Rochwell Hardness (HR)

维氏 Hardness (HV)

III. The test of HB:

d

D

P

)( )(

222 aMPdDDD

p

F

pHB

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

IV. 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

V. Application of Hardness in Engineering

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.

)( )(

221

cmJ

F

HHG

F

Aa kk

Ak—— Impact Work, J

F —— The sectional area of the

notch in the unit, cm2

2) Impact Toughness

The larger is a k , the better is the ability of materials to resist the impact load.

For Mediate and Low Pressure Vessels,

a k≥30 ～ 35J/cm2 , commonly a k ＞ 60 J/cm2.

The relationship between Toughness and

Plasticity:

Generally, stronger toughness makes stronger plasticity; but strong plasticity may not make strong toughness .

Hard Brittle Materials’ a Hard Brittle Materials’ a kk ＜＜ ＜＜ Plastic Materials’ a Plastic Materials’ a kk

a. Modulus of elasticity (E) (M Pa)

E

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 10╳ 5 （ M Pa ） . 2) For the same material, T ↑ , E↓ .

2.Physical Properties:

b. Poisson’s Ratio

'

(For steel: ≈ 0.3)

′—— transverse stress —— longitudinal stress

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.

）C/1(

tl

ltll

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:a. Corrosion Resistance b. Resistance to Oxidation

a. 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.

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

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.

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?

1.3.Carbon Steel

and Cast Iron

The Classification of Carbon Steel and Cast IronA. According to their Chemical

Components :

Iron Carbon Alloy:

(>95%)Fe +(0.05% ~ 4%)C

+(~1%)(impure steel and cast iron)

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 Iron0.02 2 4 C%0

1.3.1 The structure of iron-carbon alloy steel 1. The structure of metal The micro-structure of metalچ (Structure in brief)

GrainGrain Boundary

Different structure cause different performance of materials.

Thick plate-like Graphite

Low strength

Thin plate-like Graphite

Mediate strength

Spherical Graphite

High strength

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.

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.

-Fe -Fe910℃

The transformation is as following:

The basic types of C existing in iron-carbon alloy:

3.Carbon and its existing form in steel

DissolutionChemical CombinationBlending

A. 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

Two kinds of common-used Solid Solution

Solubility of C

At room temperature 0.006 %

723 ℃ 0.02 %(maximum)

铁素体 (F):

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.

• Properties:

Low strength

Low hardness

Good plasticity

Good toughness

asab MPMP 170~90,280~200

aMPHB 0.8~5.5

%40~30

2/5.2~8.1 mMJak

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)

• Properties:

High strength

High hardness

Good plasticity

Good toughness

No ironic magnetism

The transformation between F and A:

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.

The irons that dissolve C will take the

transformation between -Fe and -Fe in

different temperature.

B. 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:

a)The carbon content of Cementite is high,

the mass proportion is 6.67%.

b)Hard and brittle (HB=78.4MPa)

c) Almost no plasticity and toughness

d) Low break-down strength (b≈35 MPa )

e) 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 + 3Fe

C. Mechanical Blending (Mixture)

The alloy whose components are blending together in the state of liquid cam solidify into two types of mechanical mixtures:

a) Mixture formed by two solid solutions;

b) Mixture formed by a solid solution and metallic compound.

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)

Conclusion and review of 1.3.1:

The three basic structural types are

showed as following:

Ferrite (F)

Austenite (A)

Cementite (C)

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

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.

A. 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.

1.Manganese (Mn):

B. Mn > 0.8%

—— the alloy element intentionally Function: Mn can disolve in the

ferrite to form the solid solution strengthening the effect of ferrite.

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.

2.Silicon (Si):

The existing form in the steels:

Forming solid solution with Ferrite.

or Remaining in the steels in the form of

deoxidation product——SiO2

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”.

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%

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”.

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%

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.

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.

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”.

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.

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)

Methods:

Improve the environment of smelting.

Clear up the moisture content in the feed.

Purify the steel liquid.

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?

1.According to the content of carbon (C%): Low Carbon Steel

Medium Carbon Steel

High Carbon Steel

1.3.3 Classification anddesignation of the equipments

i. 低碳钢 (C<0.25%)

Low strength and good plasticity,

used in chemical vessels in welding and

mechanical units with low loads.

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.

iii. High Carbon Steel (C>0.6%)

High strength and hardness, poor

plasticity, used as string, wire line and so on.

2.According to the smelting methods:

Full Killed Steel Boiling Steel Semi-killed Steel

i. 镇静钢 — completely deoxidized steel

a. 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%.

b. Tough structure, uniform texture and solid.

c. The Pressure Vessels’ steels should apply the full killed steels.

d. Using ‘Z’ to indicate the designation or none.

ii. 沸腾钢 — incompletely deoxidized steel

a. Deoxidation by the strong deoxidizer Mn

to reduce the content of oxygen to be

0.03~0.07%.

b. Loose structure, inferior texture.

c. Commonly used in Support, Frame and the

like unimportant units.

d. Designation is ‘F’.

iii. Semi-killed 半镇静钢 — between the previous two Designation is ‘b’.

3.According to the quality:

Common Steel

High Grade Steel

Super High Grade Steel

i. 普通碳素钢

a. The content of the harmful elements

S & P can be a little more to be

(S≤0.055%, P≤0.045%)

b. 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)

c. The new designation of Common Steels

(GB700-88):

For example: Q 235 — A. F

The first letter of the Chinese spell of the word “ 屈”The first letter of the Chinese spell of the word “ 屈”

The value of the steels’ yielding point with the unit of “MPa”

The value of the steels’ yielding point with the unit of “MPa”

The quality grade of steels

The quality grade of steels

The deoxidized method

The deoxidized method

Designation

Z Z

BD C B B

b.Z

Q275

F.b.Z

A

Q255

F.b.Z

A

Q235

F.b.Z

A

Q215

F.b.Z

Q195

Deoxidized Method

Grade

d. 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.

*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.

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.

ii. 优质碳素钢a. Seriously control the content of S & P to

be (S & P≤0.04%)

b. Uniform texture, good surface quality, superior properties than Common Steels.

c. The number in designation indicates the percentage of the average content of C:

08 ： C=0.08% 20: C=0.2%

d. Designation: Steels that commonly contain Mn (without indicating Mn)

08 10 15 20 22 25 30 35 45 50…… Steels that contain more Mn (Mn=0.7~1.2%) (indicating Mn) 30Mn 40Mn ……

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.

(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

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?

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

1.3.4 Heat Treating of Steels

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.

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.

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.

6.Processing steps of heat treatment:

Heating Keeping warm CoolingT

emp

erat

ure

/ºC

Time

Keeping warm

CoolingHeating

Cooling media and way of cooling:

Cooling in furnaceCooling in still air Cooling in oilCooling in waterCooling in brine

Cooling Capacity Cooling Speed

7.Heat Treating Process of steels:

Annealing

Normalizing

Quenching

Tempering

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.

(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.

*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.

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.

(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

(3)Quenching Agent

*Mineral Oil, Water, and Brine.

*Generally speaking:

Carbon Steel, cooling in water and brine.

Alloy Steel, cooling in oil.

(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.

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.

(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.

*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.

*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.

Review of 1.3.4:Types of Heat Treatments: (1)Normalizing (2)Annealing (3)Quenching (4)Tempering

What are their definition?What are their functions in the improvement of mechanical properties of materials?

1.The chemical components of commonly used cast iron: 95% Fe + (2.5% ~ 4%) C + ( ~1%) Purities

2.Structure: Pealite + Cementite + Ladeburite + Graphite

1.3.5 Cast Iron

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

4.Properties and Designation of commonly used cast iron:

Gray cast iron (HT)

Spherical graphite cast iron (QT)

High-silicon cast iron (G)

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

(2)Designation

HT 150 — 330 HT 200 — 400

Tensile Strength b (MPa)

Tensile Strength b (MPa)

Bending Strength bb (MPa)

Bending Strength bb (MPa)

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.

(2)Designation

QT 400 — 15 QT 450 — 10 QT 450 — 10

Tensile Strength b (MPa)

Tensile Strength b (MPa) Elongation Percentage

%

Elongation Percentage%

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.

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

*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%Content of Si is 15%

Mixing lanthanide Mixing lanthanide

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?

1.4.

Common Low Carbon Steel

and Special Steel

used in Chemical Equipments

1.Shortages of Carbon Steel: i. Low strength and yield ratio (s/ b)

σs

σb

σ

ε

σs/σb of Carbon Steel is small

σσb

σs

εσs/σb of Alloy Steel is large

1.4.1 Problems

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

20 250 400 0.62

Alloy

Steel

16MnR 360 520 0.69

15MnV 400 540 0.74

18MnMoNbg 520 650 0.8

ii. Low strength at high temperature

The strength comparison (at high T)

between Carbon Steel and Alloy Steel

σS (Mpa) Material

S(mm)

20℃400℃450℃500℃

Q235-A 20~40 230 125 — —CS 20g 26~36 125 115 —

16Mn 27~36 310 190 170 —AS 18MnMoNbR 16~38 520 420 390 350

230

iii. Poor hardenability

iv. Inferior special physical and chemical

properties

2.Necessity to the development of modern industry and

Science & Technology

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

1.4.2 Effect of Alloy Elements to the properties of steels

2.Alloy Steel

Definition 合金钢 Alloy steels are those steels that

contain the alloy elements which develop the properties of steels.

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

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 ?)

iii. Mn

(1)Develop the strength and impact

toughness at low temperature.

(2)Broad the -phase region.

(3) Counteracts sulfur brittleness.

(4)Increases hardenability.

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

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 ?)

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.

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 ?)

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 ?)

A

E S P H

WR

IT CR OR HR FD GR H

Cr

Ni

Mn

Si H2S

Mo Mo<0.6% HCl

Al H2S

Ti in-c

V

Re

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

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?

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.

1.4.3 Common Low Alloy Steel

2.Composition: (1)C<0.2%

(2)Alloy elements

*Mn 1~1.5%

*Si Cr Ti V Nb Ni Al… 0.015 ~ 0.6%

3.Structure: Ferrite + Pearlite

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

5.Designation (GB1591-88) (New Designation GB/T1591-94)

16Mn 16MnR 16Mng 15MnV 15MnVR15MnVg 09Mn2V 18MnMoNbRThe number ahead is the percentage of the C

content, such as 16Mn (C = 0.16%).

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” 2.5 ~ 3.49% Sign as “3” 3.5 ~ 4.49% Sign as “4”

1.Steels specially used in the

manufacture of boilers and vessels.

2.There are some special requirements

for boiler steel and vessel steel.

1.4.4 Boiler Steel & Vessel Steel

3.Commonly-used Designation: i. Boiler Steel

20g 22g 12Mng 16Mng 15MnVg

14MnMoVg 18MnMoNbg

ii. Vessel Steel

Q235-AR 20R 16MnR 15MnVR

09MnVR 18MnMoNbR

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.

1.4.5 Stainless Steel and

Corrosion (Acid) Resistant Steel

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

1.Chromium Stainless Steel:

i. Component

< 0.2% C + (13 ~ 28%) Cr + Fe

ii. Construction

Ferrite or Martensite

(no Austenite even at high temperature)

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

iv. Commonly-used Chromium Stainless Steel

1Cr13 2Cr13 0Cr13 0Cr17 0Cr17Ti

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

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

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

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.

(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.

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.

*Between 400~800℃ C + Cr + Fe (Cr . Fe)23C6

Anode

Cr ＜ 12.5%

Inter-crystallineCorrosion occurs

Separate out along the grain boundaryCr%

Cr lacking

Corroding minicell

Cathode—Grain

—Cr lacking region

Grain

(Cr . Fe)23C6

Cr lacking region

Grainboundary

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%)

*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.

(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.

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

*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

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？ )

1.4.6 Heat-resisting Steel

and Low-temperature Steel

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

(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

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

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

1.Plates (Sheet Materials):

1.4.7 Varieties andSpecifications of Steels

2.Tubes(Tubular Products):

4. CCS (Cast Carbon Steel) & FS (Forged Steel)

3. Shapes (Section Materials): i. Flat Steel (bar)

ii. I-Steel (beam or section)

iii. L-Iron (Angle Steel)

1.5.

Corrosion & Protection of

Chemical Equipments

1.5.1 Harm of corrosion

1.5.2 Evaluation Methods of the Corrosion of Metal

htF

pp 210 /mg K

ht

m2F

p1

p0

K

g

g

g/cm2·h

Time of corrosion action—

Contact Area of corrosive media and test piece—

WT after corrosion—

WT before corrosion—

Corrosion Rate—

1.According to the weight changes:

2.According to the corrosion degree:

yearF

KFt

yearF

p

year

hKa

KK

76.81000

36524

mm/year

Ka—Thickness variation per year mm/year

—Metallic density g/cm3

hFP

VandhFV __

F

ph

3.Three Grades’ Standard of Metallic Resistance to Corrosion:

Grade I: Ka < 0.1 mm/year (corrosion resistant)

Grade II: Ka = 0.1 ~ 1.0 mm/year (available)

Grade III: Ka > 1.0 mm/year (unavailable)

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.

1.5.3 Chemical Corrosion

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

3.Examples of Chemical Corrosion: i. Metallic high temperature oxidation

(1)Oxidation resistance:

oxidized rapidly at high T

forming oxidation film

stopping oxidation

(2)High temperature oxidation of carbon steel

and cast iron:

Stable

Unstable

Stablelayer I: Fe2O3

layer II: Fe3O4

layer III: FeO

T > 570 oxidation layer forms ℃

inner layer Fe3O4

outer layer Fe2O3

T < 570 oxidation layer forms℃

T > 300 oxidation surface appears℃

T < 570 ℃ T > 570℃

Fe2O3

Fe3O4

FeO

Fe

Composition of ironic oxidation layer

(3)Solutions:

Adding some Cr Si Al to form stable

oxidation film of Cr2O3 SiO2 Al2O3 which

can prohibit the oxidation reaction from

proceeding.

ii. High temperature decarburization

(1) T > 700 ℃ oxidation and decarburization both exist

Fe3C + O2 3Fe + CO2

Fe3C + CO2 3Fe + 2CO

Fe3C + H2O 3Fe + CO + H2

(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

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.

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

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

1.5.4 Electrochemical Corrosion

2.Mechanism: Anode reaction —— Me Me+ + e

Electron movement —— eanode ecathode

Cathode reaction —— D + ecathode [D e]

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.

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.

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.

*Between 400~850℃ C + Cr + Fe (Cr . Fe)23C6

Anode

Cr ＜ 12.5%

Inter-crystallineCorrosion occurs

Separate out along the grain boundaryCr%

Cr lacking

Corroding minicell

Cathode—Grain

—Cr lacking region

Grain

(Cr . Fe)23C6

Cr lacking region

Grainboundary

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.

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

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.

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.

Stage III: Breaking stage

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

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

1.5.5 Types of metallic corrosion

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.

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- ]

(3)Stress Corrosion

(4)Inter-crystalline Corrosion

For example:

the inter-crystalline corrosion of

Cr-Ni stainless steel under certain conditions

1.Selecting materials reasonably

1.5.6 Corrosion Resistant

Measures in Metallic

Equipments

2.Adding the lined protection

i. Metallic lining: stainless steel,

other metals(Cu Al Ti Cr Ni)

ii. Nonmetallic lining: plastics,

rubbers, enamelware, etc.

iii. Coating

iv. Adding corrosion

buffering agents

v. Electrochemical

protection

such as:

cathodic protection

+-

Cathodic Protection

Apparatuses

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.

1.Suitable Mechanical Properties: Strength, hardness, plasticity, etc.

2.Good Corrosion Resistance3.Economic and rational

1.6. Materials Selection of Chemical Equipments

1.6.1 General Principles

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%.

1.6.2 Others

Austenite

A3

A1

Ferrite

Austenite+

Ferrite

Pearlite+

1667

1333

Tem

per

atu

re º

FIron-iron carbide equilibrium diagram

Percent carbon of weight

0 0.80.2 0.4 0.6

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.

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.

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.