Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
ĂN MÒN VÀ BẢO VỆ KIM LOẠI
CORROSION AND PROTECTION
OF METALS
TRONG CÔNG NGHỆ DẦU KHÍ
1
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
COURSE OBJECTIVES
When you complete this course, you will be able:
❑ To know the main characteristics and types of corrosion encountered in metallic
materials used in the chemical and oil and gas industries.
❑ To understand the corrosion problems.
❑ To evaluate the severity of the corrosion problems.
❑ To choose and to apply proper control procedures.
2
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
OUTLINE
1. IMPORTANCE OF ENGINEERED MATERIALS FOR PROCESS
PLANTS
2. GENERAL ASPECTS OF CORROSION
3. MECHANISM OF CORROSION
4. REFINERY INDUSTRY CORROSION
5. LOCALIZED CORROSION IN REFINERY – PROCESS UNIT PFD’S
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
IMPORTANCE OF ENGINEERED MATERIALS
FOR PROCESS PLANT
❑ Designing equipment is a multidiscipline exercise involving mechanical engineers,
stressing experts, draftsmen, materials/corrosion engineers,…
❑ The corrosion engineer has double important roles:
➢ Preventing the equipment which prematurely fails by corrosion
➢ Avoiding the over-specified designing in use of material
4
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
IMPORTANCE OF ENGINEERED MATERIALS
FOR PROCESS PLANT
THE CRITERIA FOR SELECTION OF MATERIALS
1. Corrosion resistance
5. Fabricability
2. Cost
6. Appearance
3. Availability
7. Maintenance
4. Strength
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
IMPORTANCE OF ENGINEERED MATERIALS
FOR PROCESS PLANT
THE CRITERIA FOR SELECTION OF MATERIALS
1. Corrosion resistance
❑ For any processing operation, there will be a range of materials which will offer a
corrosion resistance which is adequate (or more than adequate) for a particular job
❑ When considering corrosion resistance, the operational environment is the obvious one
❑ The other point must be whether the material will also offer corrosion resistance to the
chemicals used for cleaning and sanitizing
6
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
IMPORTANCE OF ENGINEERED MATERIALS
FOR PROCESS PLANT
THE CRITERIA FOR SELECTION OF MATERIALS
2. Cost
❑ Many of the materials originally considered will be eliminated on the grounds of
their high cost
3. Availability
❑ Availability is a less obvious feature of the material selection process
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
IMPORTANCE OF ENGINEERED MATERIALS
FOR PROCESS PLANT
THE CRITERIA FOR SELECTION OF MATERIALS
4. Strength
❑ Strength is a factor which is taken into account at the design stage, but as with all the
others, cannot be considered in isolation
❑ Many of the new stronger stainless steels, although more expensive than conventional
stainless steels, are less expensive when considered on a strength/cost ratio
8
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
IMPORTANCE OF ENGINEERED MATERIALS
FOR PROCESS PLANT
THE CRITERIA FOR SELECTION OF MATERIALS
5. Fabricability
❑ There is little point in considering materials which are either unweldable (or unfabricable)
or can only be welded under sophisticated conditions
6. Appearance
❑ Appearance may or may not be an important requirement
❑ Equipment located outside must be resistant to environmental weathering
❑ The application of protective sheathing – which could double the basic material cost.
9
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
IMPORTANCE OF ENGINEERED MATERIALS
FOR PROCESS PLANT
THE CRITERIA FOR SELECTION OF MATERIALS
7. Maintenance
❑ The equipment to be essentially maintenance-free or is some maintenance
❑ How long will the equipment operate without the need for major servicing
✓ When all these interrelated criteria are considered, the long list of possible starters
will be reduced to one or two
✓ The material initially rejected due to their high cost, for example, may have to be
reconsidered because of other factors.
10
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
GENERAL ASPECTS OF CORROSION
❑ In simplified technical terms: the corrosion has been defined as the
destruction of a metal by either chemical or electrochemical reaction with its
environment
✓ The useful life of oilfield equipment is often shortened as a result of corrosion.
✓ The great development have been made in corrosion detection and remedies as applied
to the oilfield or to the refinery.
11
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
GENERAL ASPECTS OF CORROSION
Some general statements concerning corrosion rates
✓ Carbon steel will usually corrode faster than corrosion resistant alloys used in the oil and gas engineering.
✓ The major corrodents (chất ăn mòn) present in the oil and gas engineering are carbon dioxide, hydrogen
sulfide, organic acids, hydrochloric acid, and oxygen dissolved in water.
✓ Films or scales at the interface between metal and corrodent influence corrosion rates.
✓ Environmental factors - such as chemical composition of water, temperature, and velocity - affect the rate of
corrosion.
✓ Impressed voltages and stray electrical currents (Điện thế áp đặt và dòng điiện rò) are often a source of
serious corrosion damage.
✓ Velocity of the flowing media plays an important role in erosion/ corrosion.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
GENERAL ASPECTS OF CORROSION
Economics of Corrosion Problem (details viewed in the textbook)
❑ Loss due to Corrosion
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
GENERAL ASPECTS OF CORROSION
Importance of Personnel in Corrosion-control Programs
❑ Certain of the principles of corrosion and corrosion-control procedures have been worked out
in corrosion research and engineering laboratories.
Theirs responsibilities:
✓ Recognition of the corrosion problem
✓ Record keeping related to corrosion phenomena
✓ Carrying out corrosion-control procedures
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Main types of corrosion in Oil and Gas Industry (9)
❑ 1. Erosion (Mài mòn)
✓ Direct metal removal by the cutting action of high-velovity abrasive particles.
✓ Erosion of flowlines at bend and joints by produced sand is the most common occurrence of metal
erosion in the petroleum industry.
❑ 2. Erosion Corrosion (Ăn mòn mài mòn)
✓ When erosion removes the protective film of corrosion products, corrosion can occur at faster rate.
✓ Under mild flow condition, sand may also cause erosion corrosion.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Main types of corrosion in Oil and Gas Industry (9)
❑ 3. Microbiologically-Influenced Corrosion – MIC (Ăn mòn do vi sinh vật)
✓ Known as microbial corrosion or biological corrosion, is the deterioration of metals as a result of the
metabolic activity of microorganisms.
✓ A dozen of bacteria known to cause microbiologically influenced corrosion of carbon steels, stainless
steels, aluminum alloys and copper alloys in waters and soils with pH 4~9 and temperature 10oC - 50oC.
✓ These bacteria can be broadly classified as aerobic or anaerobic Examples:
✓ Sulphate reducing bacteria (SRB): anaerobic and responsible for most instances of accelerated
corrosion damages to ships and offshore steel structures.
✓ Iron and manganese oxidizing bacteria are aerobic and are frequently associated with accelerated
pitting attacks on stainless steels .
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Main types of corrosion in Oil and Gas Industry (9)
❑ 4. Corrosion fatigue (Ăn mòn mỏi)
✓ Metal to alternating stresses (ứng suất – độ bền cơ khí) in a corrosive environment.
✓ At the point of greatest stress, the corrosion product film becomes damaged allowing localized
corrosion to take place
➢ Leading to crack initiation and crack growth by a combination of mechanical and corrosive action.
➢ Because of this combined action, corrosion fatigue is greater at low stress cycles
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Main types of corrosion in Oil and Gas Industry (9)
❑ 5. Hydrogen embrittlement and Stress Corrosion
(Sự giòn do Hydro và Ăn mòn ứng suất)
✓ When H2S is present, corrosion cells generate FeS and H2
atomic hydrogen.
✓ The layer of FeS promotes the movement of hydrogen into
the metal and accumulation generate tremendous
pressure.
✓ Reducing the ductility (độ dẻo) of metal
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Main types of corrosion in Oil and Gas Industry (9)
❑ 6. Sulfide Stress Corrosion (SSC) – Ăn mòn ứng suất do Sulfua
✓ Hydrogen embrittlement combined with static or cyclic stress
can lead the failure of metal by
✓ Corrosion fatigue
✓ Stress corrosion.
Static Stress: A stress in which the force is
constant or slowly increasing with time
Ứng suất tĩnh là ứng suất trong đó lực tác dụng
không đổi hoặc tăng chậm theo thời gian
Cyclic stress: distribution of forces (a stress) that
changes over time in a repetitive fashion
Ứng suất lặp lại (chu kỳ) khi lực tác động thay đổi
lặp lại theo thời gian
❑ 7. Chloride stress cracking (CSC) – Nứt ứng suất do Clorua
✓ Under tensile stress (ứng suất kéo)
✓ Exposed to saline water at high temperature
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Main types of corrosion in Oil and Gas Industry (9)
❑ 8. Stress Corrosion Cracking (SCC) – Ăn mòn nứt dưới ứng suất
✓ Combined with Sulfide Stress Corrosion (SSC), Chloride Stress
Cracking (CSC) and corrosion fatigue
✓ Start at a pit or a crevice – Bắt đầu tại một hố hay một vết nứt
✓ The zone around the tip becomes plastic under stress allowing a
crack develop.
✓ Chlorine ions, as catalyst to corrosion, immigrate into the crack
accelerating the process.
✓ The crack within the plastic zone is another site for H2
embrittlement.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Main types of corrosion in Oil and Gas Industry (9)
❑ 9. Localized Pitting Corrosion – Ăn mòn điểm cục bộ
✓ Producing holes or small pits in a metal but the bulk of the surface remains
unattacked.
✓ Pitting is often found in situations where resistance against general corrosion is
conferred by passive surface films (Màng thụ động trên bề mặt) and where
these passive films have broken down.
✓ Pitting attack induced by the present of Chloride ion (Cl -) and microbial activity,
such as Sulfate Reducing Bacteria (SRB).
✓ Pitting can be one of the most dangerous forms of corrosion because it is
difficult to anticipate and prevent, difficult to detect, occurs very rapidly, and
penetrates a metal without causing it to lose a significant amount of weight.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Predominant Corrosion Types in various sectors of the Oil and Gas Industry
CRA: Corrosion-Resistant Alloy – Hợp kim chịu ăn mòn
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Predominant Corrosion Types in various sectors of the Oil and Gas Industry
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Predominant Corrosion Types in various sectors of the Oil and Gas Industry
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Predominant Corrosion Types in various sectors of the Oil and Gas Industry
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Predominant Corrosion Types in various sectors of the Oil and Gas Industry
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Predominant Corrosion Types in various sectors of the Oil and Gas Industry
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
❑ Corrosion of metals and alloys in aqueous solution, or
in any other ionically conducting medium, takes place by
electrochemical mechanisms.
❑ An electrochemical corrosion reaction requires four
elements: an Anode, a Cathode, a Metallic conductor,
and an Electrolytic conductor (ACME)
1. At Anode site: Me → Men+(aq) + ne2. Migrating of ne- by metallic conductor to cathode region
3. At Cathode site, ne- are consumed by the depolarizers
(chất khử phân cực) as H+, O2 or cation of more-noble metal
present in the solution (electrolytic conductor) in contact:
Oxygen: O2 + H2O + 4e- → 4OH-(aq)
Acid: 2H+ (H3O+) + 2e- → H2
Cation of more-noble metal (Cu2+): Cu2+ + 2e- → Cu
…
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
❑ At Anode:
✓ A metal ion leaves the metal surface and goes into solution.
✓ The metal leaves electrons behind on the metal surface.
✓ The metal is oxidized, i.e., it loses electrons at the anode.
✓ This process is corrosion.
✓ A typical anodic (corrosion) reaction can be written as:
Me → Men+(aq) + ne-
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
❑ Electrolyte solution – Electrolyte conductor:
✓ Ionically conducting electrolyte carries the metal ions from the anode to the cathode.
✓ Mostly liquids, but they may be solids.
✓ A higher concentration of ions → higher electrical conductivities.
✓ Contains two types of ions: anions and cations.
✓ Anions are negatively charged, and move towards the anode, where they may get
oxidized (i.e., they lose electrons).
✓ Cations are positively charged and they move towards cathode, where they may
get reduced (i.e., they gain electrons) → Depolarizers in corrosion (H3O+ & O2).
✓ Metallic ions may in some cases leave the solution and deposit on the cathode.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
❑ At Cathode:
✓ The cathodic reaction can be written as: Men+(aq) + ne- → Me
✓ The electrolyte may contain several other species that could undergo reduction instead of the
metal ion.
✓ Commonly occurring other species include hydrogen ions and dissolved oxygen. Therefore,
depending on the pH, hydrogen ion reduction or oxygen reduction may take place:
Oxygen: O2 + H2O + 4e- → 4OH-(aq)
Acid: 2H+ (H3O+) + 2e- → H2
❑ Metal conductor
✓ Carrying the electrons left by the metal ions at the anode site to the cathode site for the reductive
reaction .
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
➢ The absence of any one of ACME prevents corrosion.
➢ In the presence of all four elements a balance is established, so that the rate of anodic
reaction (corrosion) is equal to that of cathodic reaction (reduction).
➢ Anodes, Cathodes, and Metallic conductors exist in a metal, so when a metal
comes in contact with an electrolyte corrosion can potentially take place.
➢ Two more things should be known before corrosion control strategies can be developed:
✓ Does corrosion take place under given conditions?
✓ At what rate does it take place?
ELECTROCHEMICAL BASIC
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
➢ ELECTROCHEMICAL THEORY BASIC
✓ Fast comparison of corrosion possibilities of different metals by referring on Energy Required
to Convert Ore to Metal (Chuyển hóa quặng thành kim loại) table:
✓ Comparing relative energy requirements for converting ores into
metals (Gibbs free energy change - G).
✓ This means that metals have a high Energy level they have a
tendency to corrode. Therefore:
✓ Magnesium has a greater tendency to corrode
✓ Gold has a smaller tendency to corrode
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
➢ ELECTROCHEMICAL THEORY BASIC
✓ The ΔG is related to the potential as: G = -nFE*
where E is the potential according to the Nernst-Latimer Equation:
E* = E0 +
RT
ln Q
nF
✓ For corrosion reaction: Me → Me2+ + 2e
E*Fe2+/Fe = Eo,Fe2+/Fe +
RT
ln [Fe2+]
2F
✓ For reduction reaction: 2H+ + 2e → H2
E*2H+/H2 = Eo,2H+/H2 +
RT
ln [H+]
F
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
➢ ELECTROCHEMICAL THEORY BASIC
✓ The standard redox potentials of ions (Eo) are referred to the hydrogen potential i.e.,
➢ The potential for reducing hydrogen ions from a concentration (activity) of 1 g-mole/l at
25oC to gas at 1 atmospheric pressure is zero.
✓ The standard redox potential (Eo) is the potential of a metal in contact with its own ions at a
concentration of 1 g-mole/l activity at 25oC.
✓ The standard potential helps us to understand the corrosion tendency of metals.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
Standard Electrode Potentials in Aqueous Solution at 25°C
Half-Reaction
Standard Potential
E° (volts)
Li+(aq) + e- → Li(s)
-3.04
K+(aq) + e- → K(s)
-2.92
Ca2+(aq) + 2e- → Ca(s)
-2.76
Na+(aq) + e- → Na(s)
-2.71
Mg2+(aq) + 2e- → Mg(s)
-2.38
Al3+(aq) + 3e- → Al(s)
-1.66
2H2O(l) + 2e- → H2(g) + 2OH-(aq)
-0.83
Zn2+(aq) + 2e- → Zn(s)
-0.76
Cr3+(aq) + 3e- → Cr(s)
-0.74
Fe2+(aq) + 2e- → Fe(s)
-0.44
Cd2+(aq) + 2e- → Cd(s)
-0.40
Ni2+(aq) + 2e- → Ni(s)
-0.23
Sn2+(aq) + 2e- → Sn(s)
-0.14
Pb2+(aq) + 2e- → Pb(s)
-0.13
Fe3+(aq) + 3e- → Fe(s)
-0.04
2H+(aq) + 2e- → H2(g)
0.00
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
Standard Electrode Potentials in Aqueous Solution at 25°C (Cont.)
Standard Potential
E° (volts)
Half-Reaction
Sn4+(aq) + 2e- → Sn2+(aq)
Cu2+(aq)
e-
+
→
Cu+(aq)
ClO4-(aq) + H2O(l) + 2e- → ClO3-(aq) + 2OH-(aq)
e-
AgCl(s) +
→ Ag(s) +
Cl-(aq)
0.15
0.16
0.17
0.22
Cu2+(aq) + 2e- → Cu(s)
0.34
ClO3-(aq) + H2O(l) + 2e- → ClO2-(aq) + 2OH-(aq)
0.35
IO-(aq) + H2O(l) + 2e- → I-(aq) + 2OH-(aq)
0.49
Cu+(aq) + e- → Cu(s)
0.52
→
0.54
I2(s) +
2e-
2I-(aq)
ClO2-(aq) + H2O(l) + 2e- → ClO-(aq) + 2OH-(aq)
Fe3+(aq)
→
0.59
Fe2+(aq)
0.77
Hg22+(aq) + 2e- → 2Hg(l)
0.80
Ag+(aq)
+
+
ee-
→ Ag(s)
0.80
Hg2+(aq) + 2e- → Hg(l)
0.85
ClO-(aq) + H2O(l) + 2e- → Cl-(aq) + 2OH-(aq)
0.90
2Hg2+(aq) + 2e- → Hg22+(aq)
0.90
NO3-(aq) + 4H+(aq) + 3e- → NO(g) + 2H2O(l)
0.96
Br2(l) +
2e-
→
2Br-(aq)
O2(g) + 4H+(aq) + 4e- → 2H2O(l)
1.07
1.23
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
Standard Electrode Potentials in Aqueous Solution at 25°C (Cont.)
Half-Reaction
Standard Potential
E° (volts)
Cr2O72-(aq) + 14H+(aq) + 6e- → 2Cr3+(aq) + 7H2O(l)
1.33
Cl2(g) + 2e- → 2Cl-(aq)
1.36
Ce4+(aq) + e- → Ce3+(aq)
1.44
MnO4-(aq) + 8H+(aq) + 5e- → Mn2+(aq) + 4H2O(l)
1.49
H2O2(aq) + 2H+(aq) + 2e- → 2H2O(l)
1.78
Co3+(aq) + e- → Co2+(aq)
1.82
S2O82-(aq) + 2e- → 2SO42-(aq)
2.01
O3(g) + 2H+(aq) + 2e- → O2(g) + H2O(l)
2.07
F2(g) + 2e- → 2F-(aq)
2.87
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
➢ ELECTROCHEMICAL THEORY BASIC
✓ Considering a situation in which copper and zinc pieces each immersed separately in their
own ions of unit activity (1 g-mole/l ) are electrically connected together → A galvanic cell
✓ Standard electrode potentials:
▪ E*Cu2+/Cu = +0.34V (Cathode)
▪ E*Zn2+/Zn = - 0.76V (Anode)
▪ EMF
= +0.34 – (-0.76) = 1.1 V
(ElectroMotive Force - Sức điện động)
✓ when copper and zinc are short-circuited, an ACME is
established with zinc undergoing oxidation (corrosion) and
copper ions undergoing reduction.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
➢ ELECTROCHEMICAL THEORY BASIC
✓ In practice, both anode and cathode can exist on the same metal sample, which can also
act as the metallic conductor (ACM)
✓ When the metal is immersed in an electrolyte, all four elements (ACME) are established,
and a potential is developed.
✓ This potential is called the corrosion potential (Ecorr) (Điện thế ăn mòn) and is different
from the standard redox potential (Eo).
✓ Measurement of the corrosion potential is the fundamental primary step for
understanding the corrosion tendency.
✓ Practically, one cannot measure the potential of a single electrode, but can measure only
the difference between the potentials of two electrodes.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
➢ ELECTROCHEMICAL THEORY BASIC
✓ How can we measure the corrosion potential?
✓ Using a reference electrode (điện cực so sánh) so the corrosion potential is
reported with respect to a reference electrode.
▪ Standard hydrogen electrode (SHE) ,
Eo = 0 V
▪ Saturated calomel electrode (SCE),
Eo = +0.241 V
▪ Silver/Silver chloride (Ag/AgCl) electrode,
Eo =+0.197 V
▪ Copper/Copper sulfate (CCS) electrode.
Eo =+0.314 V
✓ The corrosion potential measured against one reference electrode can be
converted into that against another reference electrode.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
➢ ELECTROCHEMICAL THEORY BASIC
✓ Reference Electrodes (4)
SHE
SCE
(Ag/AgCl)
Electrode
CCS Electrode
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
➢ ELECTROCHEMICAL THEORY BASIC
✓ Polarization and Over potential (Phân cực và Quá thế)
Eo,C
c < 0
Ecor.
a > 0
Eo,A
✓ Equilibrium potential for cathodic reaction:
Eoc
✓ Equilibrium potential for anodic reaction:
Eoa
✓ Real (Mixte) potential = Corrosion Potential:
Ecor
✓ Cathodic Over potential
ηc = Ecor – Eoc < 0
✓ Anodic Over potential
ηa = Ecor – EoA > 0
→ Ecor on the surface of Anode and Cathode
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
➢ ELECTROCHEMICAL THEORY BASIC
✓ Rate of corrosion (Tốc độ ăn mòn)
▪ Corrosion rates are proportional to the rate of electron
transfer between two electrodes.
▪ The rate of electron transfer is represented as current (Icor).
▪ Normally, the current over the surface area is measured and
reported as current density (icor).
▪ Depending on the type of resistance that limits the reaction
rate, there are two different kinds of polarization
❖ Activation polarization (Activation control) : Tafel Eq.
❖ Concentration polarization and (Diffusion control)
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
✓ ELECTROCHEMICAL THEORY BASIC
✓ Rate of corrosion
✓ Activation polarization (η) increases with current density in accord with Tafel
Equation:
✓ The Tafel constant is given by:
i
 =   log
io
2.3RT
β=
αnF
io: exchange current density
: Tafel slope
: Charge transfer coefficient
✓ Sometimes the mass transport within the solution may be rate determining – in such
cases we have concentration polarization
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
✓ ELECTROCHEMICAL THEORY BASIC
✓ Rate of corrosion –
▪ Schematic anodic and cathodic
polarization curves for a metal corroding in
acid solution:
▪ Determination of the density of corrosion
Ecorr,2
and also the corrosion potential.
icorr,2
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
✓ ELECTROCHEMICAL THEORY BASIC
✓ Rate of corrosion
✓ Schematic anodic polarization curves
for a metal that show passive behavier
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
➢ ELECTROCHEMICAL THEORY BASIC
3
✓ Iron Pourbaix diagram
1. Fe2++ 2e− ⟶ Fe(s) (no pH dependence)
2
2. Fe3+ +e− ⟶ Fe2+ (no pH dependence)
4
3. 2Fe3++3H2O⟶ Fe2O3(s)+6H+ (pure acid-base, no redox)
4. 2Fe2++3H2O⟶ Fe2O3(s)+6H++2e−
(slope = -0,059x6/2 = -0,178 mV/pH)
5. 2Fe3O4(s)+H2O⟶3Fe2O3 + 2H++ 2e−
5
1
(slope = -0.059 x 2/2 = -0,059 mV/pH)
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Electrochemical nature of corrosion
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
General corrosion
➢ The anodic and cathodic reactions on the metal surface do not partition and occur
simultaneously over the entire surface.
✓ Corrosion proceeds uniformly over the entire surface.
➢ In reality, the uniform or general corrosion seldom occurs.
✓ General corrosion in the oil and gas industry is corrosion of acidizing pipes in the
presence of hydrochloric acid .
✓ Many factors convert uniform corrosion into localized corrosion: corrosion of
surface layers, Extraneous materials (sand, clay particles, Chloride ion…), velocity,
and metallurgy.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
General corrosion
✓ Passive layers:
✓ If the product of the corrosion reaction dissolves in the environment, corrosion continues
to take place uniformly.
✓ Beyond a certain point, due to solution saturation, some products may deposit back
onto the surface.
✓ If the deposition occurs uniformly, then the surface is fully covered and no corrosion
reaction takes place → passive or protective layer
✓ In reality, the surface layers (known as passive layers) are formed discontinuously, and at
various thicknesses at various locations in the structure.
Neither uniform corrosion nor intact surface layer formation
occurs all the time in practice.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Galvanic corrosion
➢ Galvanic corrosion occurs when dissimilar metals or alloys are electrically in contact
with one another and are immersed in a conductive solution.
✓ A potential difference exists between two dissimilar metals in contact in a solution.
✓ The less corrosion resistant material becomes the anode and the more corrosionresistant material becomes the cathode, leading to galvanic corrosion
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Galvanic corrosion
➢ The galvanic effect of connecting dissimilar metals is highest at the junction between them.
➢ The galvanic effect decreases progressively with distance.
➢ The anode-cathode relative area affects galvanic corrosion; a large cathode surrounding a
smaller anode creates conditions for accelerated galvanic corrosion
✓ To minimize galvanic corrosion, metals close to one another in the galvanic series are
chosen.
✓ Small anode and large cathode are avoided.
✓ Electrically connected dissimilar metals are insulated from the electrolyte by coating →
the anodic areas is replaced relatively easily.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Pitting corrosion
✓ When the percentage of the cathodic area is larger than that of the anodic area, corrosion
takes place in small area with the large areas acting as cathode.
✓ This phenomena causes pitting corrosion: the extreme form of localized attack resulting
in holes in the surface.
✓ During pitting corrosion, amount of metal lost is small, but is lost from a relatively small
area, so pitting is one of the most destructive and insidious forms of corrosion.
✓ Pits may form in various shapes, with irregular walls.
PITTING CORROSION MAY BE CONTROLLED BY APPROPRIATE MATERIAL SELECTION
AND BY ADDITION OF CORROSION INHIBITORS
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Khoa Hóa
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MECHANISM OF CORROSION
Pitting corrosion
✓ Typical Shapes of Pits
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Pitting corrosion
➢ Pitting corrosion is a process that consists of three stages:
✓ Formation of surface layer on the steel surface;
✓ Initiation of pits at localized regions where layer breakdown occurs;
✓ Pit propagation and eventual penetration of the material.
➢ Surface layers generally form adjacent to the metal, Example: by the reaction between
the metal or alloy and the atmosphere (Al, Ti, SS).
➢ Such a layer is compact, adherent to the metal surface, and protects it from further
corrosion → primary passive or simply passive layer.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Pitting corrosion
➢ When exposed to certain environments, a compact and adherent surface layer may
form, as a consequence of a corrosion reaction between the metal and the environment.
➢ This layer is commonly known as a precipitated layer, secondary layer, or salt layer.
✓ The secondary layer incorporate anions and cations from the solution and is
porous, thick and formed on top of primary layer
➢ Neither primary nor secondary surface layers are static.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
MECHANISM OF CORROSION
Pitting corrosion
✓ General Features of Passive Layers.
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Khoa Hóa
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MECHANISM OF CORROSION
Pitting corrosion
➢ The pits initiate at localized regions where passive breaks down.
➢ Initiation of pits depends on passive layer composition, thickness and the presence of
extraneous ions, such as chloride ions.
➢ The pit initiation is a random process with respect to space and time.
➢ When a pit stabilizes, large local cathodes surround a small anode, it propagates
continuously until failure occurs.
✓ Mostly the pit growth rate decreases progressively with time as the passive layers
reform at its tip
✓ Sometimes pit growth rate accelerates if its tip continues to be an anode, and the
cathode to anode ratio increases → known as autocatalytic pit growth
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
✓ Evaluation of a corrosion type includes of:
1. Description of Damage
2. Affected Material
3. Critical Factors
4. Affected Units or Equipment
5. Appearance or Morphology of Damage
6. Prevention / Mitigation
7. Inspection and Monitoring
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
Refinery Steels
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Galvanic Corrosion
✓ Description of Damage
▪ A form of corrosion that can occur at the junction of dissimilar metals
when they are joined together in a suitable electrolyte, such as a moist or
aqueous environment, or soils containing moisture.
✓ Affected Material
▪ All metals with the exception of most noble metals.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Galvanic Corrosion
✓ Affected Units or Equipment
▪ Galvanic corrosion can occur in any unit where there is a conductive fluid and
alloys are coupled.
▪ Heat exchangers are susceptible if the tube materialis different from the
tubesheet and/or baffles, particularly if salt water cooling is utilized.
▪ Buried pipelines, electrical transmission support towers and ship hulls are
typical locations for galvanic corrosion.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Galvanic Corrosion
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Atmospheric Corrosion
✓ Description of Damage
▪
A form of corrosion that occurs from moistureassociated with atmospheric
conditions. Marine environments and moist polluted industrial environments with
airborne contaminants are most severe. Dry rural environments cause very little
corrosion.
✓ Affected Materials
▪ Carbon steel, low alloy steels and copper alloyed aluminum.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Atmospheric Corrosion
✓ Affected Units or Equipment
▪ Piping and equipment with operating temperatures sufficiently low to allow
moisture to be present.
▪ A paint or coating system in poor condition.
▪ Equipment may be susceptible if cycled between ambient and higher
or lower operating temperatures.
▪ Equipment shut down or idled for prolonged periods unless properly
mothballed.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Atmospheric Corrosion
✓ Affected Units or Equipment
▪ Tanks and piping are particularly susceptible. Piping that rests on pipe
supports is very prone to attack due to water entrapment between the pipe and
the support.
▪ Orientation to the prevailing wind and rain can also be a factor.
▪ Piers and docks are very prone to attack.
▪ Bimetallic connections such as copper to aluminum electrical connections
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Atmospheric Corrosion
✓ Atmospheric Corrosion of an LPG line in close proximity to a cooling tower.
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢
Corrosion Under Insulation (CUI)
✓ Description of Damage
✓ Corrosion of piping, pressure vessels and structural components resulting from
water trapped under insulation or fireproofing.
✓ Affected Materials
✓ Carbon steel, low alloy steels, 300 Series SS, and duplex stainless steels.
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢
Corrosion Under Insulation (CUI)
✓ Affected Units or Equipment
▪ All insulated piping and equipment are susceptible to CUI under conditions noted
above even on piping and equipment where the insulation system appears to
be in good condition and no visual signs of corrosion are present.
▪ Examples of locations where CUI can occur are listed below:
▪ CUI can be found on equipment with damaged insulation, vapor barriers,
weatherproofing or mastic, or protrusions through the insulation or at insulation
termination points such as flanges.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢
Corrosion Under Insulation (CUI)
✓ Affected Units or Equipment
▪ Equipment designed with insulation support rings welded directly to the vessel wall (no
stand-off); particularly around ladder and platform clips, and lifting lugs, nozzles and
stiffener rings.
▪ Piping or equipment with damaged/leaking steam tracing.
▪ Localized damage at paint and/or coating systems.
▪ Locations where moisture/water will naturally collect (gravity drainage) before
evaporating (insulation support rings on vertical equipment) and improperly
terminated fireproofing.
▪ Vibrating piping systems that have a tendency to inflict damage to insulation
jacketing providing a path for water ingress.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
✓ Corrosion Under Insulation (CUI)
✓ Affected Units or Equipment
✓ Dead legs (vents, drains, and other similar items).
✓ Pipe hangers and other supports.
✓ Valves and fittings (irregular insulation surfaces).
✓ Bolted-on pipe shoes.
✓ Steam tracer tubing penetrations.
✓ Termination of insulation at flanges and other piping components.
✓ Insulation jacketing seams located on the top of horizontal piping or
✓ improperly lapped or sealed insulation jacketing.
✓ Termination of insulation in a vertical pipe.
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢
Corrosion Under Insulation (CUI)
✓ Affected Units or Equipment
▪ Caulking that has hardened, has separated, or is missing.
▪ Bulges or staining of the insulation or jacketing system or missing bands. (Bulges
may indicate corrosion product buildup.)
▪ Low points in piping systems that have a known breach in the insulation system,
including low points in long unsupported piping runs.
▪ Carbon or low-alloy steel flanges, bolting, and other components under insulation in
high-alloy piping systems.
▪ Locations where insulation plugs have been removed to permit piping thickness
measurements on insulated piping and equipment should receive particular
attention.
▪ The first few feet of a horizontal pipe run adjacent to the bottom of a vertical run.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢
Corrosion Under Insulation (CUI)
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢
Corrosion Under Insulation (CUI)
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢
Corrosion Under Insulation (CUI)
CUI of CS level bridle
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢
Cooling Water Corrosion
✓ Description of Damage
✓ General or localized corrosion of carbon steels and other metals caused
by dissolved salts, gases, organic compounds or microbiological activity.
✓ Affected Materials
✓ Carbon steel, all grades of stainless steel, copper, aluminum, titanium and
nickel base alloys.
✓ Affected Units or Equipment
✓ Cooling water corrosion is a concern with water-cooled heat exchangers
and cooling towers in all applications across all industries
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Cooling Water Corrosion
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢
Boiler Water Condensate Corrosion
✓ Description of Damage
▪ General corrosion and pitting in the boiler system and condensate return piping.
✓ Affected Materials
▪ Primarily carbon steel, some low alloy steel, some 300 Series SS and copper
based alloys.
✓ Affected Units or Equipment
▪ Corrosion can occur in the external treatment system, deaerating equipment,
feedwater lines, pumps, stage heaters and economizers as well as the steam
generation system on both the water and fire sides and the condensate return
system.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Boiler Water Condensate Corrosion
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢
CO2 Corrosion
✓ Description of Damage
▪ Carbon dioxide (CO2) corrosion results when CO2 dissolves in water to form
carbonic acid (H2CO3). The acid may lower the pH and sufficient quantities
may promote general corrosion and/or pitting corrosion of carbon steel.
✓ Affected Materials
▪ Carbon steel and low alloy steels.
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ CO2 Corrosion
✓ Affected Units or Equipment
▪ Boiler feedwater and condensate systems in all units are affected.
▪ Effluent gas streams of the shift converters in hydrogen plants can be affected.
Corrosion usually occurs when the effluent stream drops below the dew point,
approximately 149°C. Corrosion rates as high as 1000 mpy have been observed.
▪ (Overhead systems of regenerators in CO2 removal plants are affected.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ CO2 Corrosion
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Flue-Gas Dew-Point Corrosion
✓ Description of Damage
▪
Sulfur and chlorine species in fuel will form sulfur dioxide, sulfur trioxide and
hydrogen chloride within the combustion products.
▪ At low enough temperatures, these gases and the water vapor in the flue gas
will condense to form sulfurous acid, sulfuric acid and hydrochloric acid
which can lead to severe corrosion.
✓ Affected Materials
▪ Carbon steel, low alloy steels and 300 Series SS.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Flue-Gas Dew-Point Corrosion
✓ Affected Units or Equipment
▪ All fired process heaters and boilers that burn fuels containing sulfur have the potential
for sulfuric acid dew point corrosion in the economizer sections and in the stacks.
▪ Heat-Recovery Steam Generators (HRSG‟s) that have 300 Series SS feedwater
heaters may suffer chloride-induced stress corrosion cracking from the gas side (OD)
when the temperature of the inlet water is below the dewpoint of hydrochloric acid.
▪ 300 Series SS feedwater heaters in HRSG‟s are potentially at risk if the
atmosphere of the combustion turbine includes chlorine. Cooling tower drift from cooling
towers that use chlorine based biocides may blow into the combustion turbine and
lead to potential damage in the feedwater heaters.
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Microbiologically Induced Corrosion (MIC)
✓ Description of Damage
▪ A form of corrosion caused by living organisms such as bacteria, algae or fungi.
▪ It is often associated with the presence of tubercles or slimy organic substances.
✓ Affected Materials
▪ Most common materials of construction including carbon and low alloy steels, 300
Series SS and 400 Series SS, aluminum, copper and some nickel base alloys.
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Microbiologically Induced Corrosion (MIC)
✓ Affected Units or Equipment
▪ MIC is most often found in heat exchangers, bottom water of storage tanks, piping with
stagnant or low flow, and piping in contact with some soils.
▪ MIC is also found in equipment where the water has not been removed or
equipment has been left outside and unprotected.
▪ Product storage tanks and water cooled heat exchangers in any unit where cooling
water is not properly treated can be affected.
▪ Fire water systems can be affected.
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Microbiologically Induced Corrosion (MIC)
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Soil Corrosion
✓ Description of Damage
▪ The deterioration of metals exposed to soils is referred to as soil corrosion.
✓ Affected Materials
▪ Carbon steel, cast iron and ductile
✓ Affected Units or Equipment
▪ Underground piping and equipment as well as buried tanks and the bottoms of above
ground storage tanks.
▪ Ground supported metal structures.
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
✓ Soil Corrosion
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
✓ Caustic Corrosion
✓ Description of Damage
✓ Localized corrosion due to the concentration of caustic or alkaline salts
that usually occurs under evaporative or high heat transfer conditions.
However, general corrosion can also occur depending on alkali or
caustic solution strength.
✓ Affected Materials
✓ Simarily carbon steel, low alloy steels and 300 Series SS.
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Caustic Corrosion
✓ Affected Units or Equipment
▪ Caustic corrosion is most often associated with boilers and steam
generating equipment including heat exchangers.
▪ Similar concentrating effects of caustic may occur where caustic is added to
crude unit charge.
▪ Accelerated localized corrosion can occur in preheat exchangers, furnace
tubes and transfer lines, unless the caustic is effectivel y mixed in the oil
stream.
▪ Units that use caustic for removing sulfur compounds from product streams
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ Caustic Corrosion
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
✓ High Temperature Corrosion (>200oC) – Oxidation
✓ Description of Damage
✓ Oxygen reacts with carbon steel and other alloys at high temperature converting
the metal to oxide scale.
✓ It is most often present as oxygen is in the surrounding air (approximately 20%) used for
combustion in fired heaters and boilers.
✓ Affected Materials
✓ All iron based materials including carbon steel and low alloy steels, both cast and
wrought.
✓ All 300 Series SS, 400 Series SS and nickel base alloys also oxidize to varying
degrees, depending on composition and temperature
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion (>200oC) – Oxidation
✓ Affected Units or Equipment
▪ Oxidation occurs in fired heaters and boilers as well as
other combustion equipment, piping and equipment that
operates in high temperature environments when metal
temperatures exceed about 538°C
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion (>200oC) – Oxidation
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Sulfidation
✓ Description of Damage
▪ Corrosion of carbon steel and other alloys resulting from their reaction with
sulfur compounds in high temperature environments. The presence of hydrogen
accelerates corrosion. This mechanisms is also known as sulfidic corrosion.
✓ Affected Materials
▪
All iron based materials including carbon steel and low alloy steels, 300 Series
SS and 400 Series SS.
▪ Nickel base alloys are also affected to varying degrees depending on
composition, especially chromium content.
▪ Copper base alloys form sulfide at lower temperatures than carbon steel.
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
✓ High Temperature Corrosion – Sulfidation
✓ Affected Units or Equipment
✓ Sulfidation occurs in piping and equipment in high temperature environments
where sulfur-containing streams are processed.
✓ Common areas of concern are the crude, FCC, coker, vacuum, visbreaker and
hydroprocessing units.
✓ Heaters fired with oil, gas, coke and most other sources of fuel may be
affected depending on sulfur levels in the fuel.
✓ Boilers and high temperature equipment exposed to sulfur-containing gases can be
affected.
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Sulfidation
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Sulfidation
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Khoa Hóa
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Fuel Ash Corrosion
✓ Description of Damage
▪ Fuel ash corrosion is accelerated high temperature wastage of materials that occurs when
contaminants in the fuel form deposits and melt on the metal surfaces of fired heaters, boilers
and gas turbines (538°C).
▪ Corrosion typically occurs with fuel oil or coal that is contaminated with a combination of
sulfur, sodium, potassium and/or vanadium.
▪ The resulting molten salts (slags) dissolve the surface oxide and enhance the transport
of oxygen to the surface to reform the iron oxide at the expense of the tube wall or
component.
✓ Affected Materials
▪ All conventional alloys used for process heater and boiler construction are susceptible.
▪
Alloys of the 50Cr-50Ni family show improved resistance.
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Fuel Ash Corrosion
✓ Affected Units or Equipment
▪ Fuel ash corrosion can occur in any fired heater or gas turbine utilizing fuels
with the aforementioned contaminants.
▪ Fuel ash corrosion is most often associated with fired heaters burning vanadium
and sodium contaminated fuel oils or residue.
▪ Heater tubes are sometimes not affected because their skin temperatures are cooler
than the threshold melting point of the slags in most heaters. Tube hangers and
supports, however, operate hotter and can suffer severe fuel ash corrosion.
▪ Some gas turbines suffer blade corrosion when switched over to burning fuel oil.
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REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Fuel Ash Corrosion
✓ Affected Units or Equipment
▪ In some cases, coking of the heater tubes may cause operators to increase heat
flux that may push some components above the threshold temperature where
fuel ash corrosion is possible.
▪ Since the melting points of these liquid species are around 538° C and
higher in the superheaters and reheaters, any unit that has metal
temperatures above the melting point of the sulfates may have the problem.
▪ For oil-fired boilers, fuel oils that do not contain vanadium are less prone to liquid
ash corrosion.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Fuel Ash Corrosion
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Corrosion Fatigue
✓ Description of Damage
▪ A form of fatigue cracking in which cracks develop under the combined effects of
cyclic loading and corrosion. Cracking often initiates at a stress concentration
such as a pit in the surface. Cracking can initiate at multiple sites.
✓ Affected Materials
▪ All metals and alloys.
105
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Corrosion Fatigue
✓ Affected Units or Equipment
▪ Rotating equipment, deaerators and cycling boilers, as well as any equipment
subjected to cyclic stresses in a corrosive environment. Some examples include:
▪ Rotating Equipment
▪ Galvanic couples between the impeller and the pump shaft or other corrosion
mechanisms may result in a pitting problem on the shaft.
▪ The pitting can act as a stress concentrator or stress riser to promote cracking.
▪ Most cracking is transgranular with little branching.
106
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Corrosion Fatigue
✓ Affected Units or Equipment
▪ Deaerators
▪ Residual welding and fabrication stresses, stress risers and the normal
deaerator environment could produce multiple corrosion fatigue cracking
problems.
▪ Cycling Boilers
▪ A cycling boiler may see several hundred cold starts over its useful life
which, because of differential expansion, continually cracks the protective
magnetite scale, allowing corrosion to continue.
107
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Corrosion Fatigue
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Amine Corrosion
✓ Description of Damage
▪ Amine corrosion refers to the general and/or localized corrosion that occurs
principally on carbon steel in amine treating processes. Corrosion is not
caused by the amine itself, but results from dissolved acid gases (CO2 and
H2S), amine degradation products, Heat Stable Amine Salts (HSAS) and
other contaminants.
✓ Affected Materials
▪ Primarily carbon steel.
▪ 300 Series SS are highly resistant.
109
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Amine Corrosion
✓ Affected Units or Equipment
▪ Amine units are used in refineries to remove H2S, CO2 and mercaptans from
process streams originating in many units including the crude, coker, FCC,
hydrogen reforming, hydroprocessing, and tail gas units.
▪ The regenerator reboiler and the regenerator are areas where the temperature
and turbulence of the amine stream are the highest and can cause significant
corrosion problems.
▪ The rich amine side of the lean/rich exchangers, hot lean amine piping, hot rich
amine piping, the amine solution pumps, and the reclaimers are also areas
where corrosion problems occur
110
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Amine Corrosion
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Ammonium Bisulfide Corrosion (Alkaline Sour Water)
✓ Description of Damage
▪ Aggressive corrosion occurring in hydroprocessing reactor effluent streams and in
units handling alkaline sour water.
▪ Several major failures have occurred in hydroprocessing reactor effluent
systems due to localized corrosion.
✓ Affected Materials
▪ Carbon steel is less resistant.
▪ 300 Series SS, duplex SS, aluminum alloys and nickel base alloys are more
resistant, depending on ammonium bisulfide (NH4HS) concentration and velocity.
112
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Ammonium Bisulfide (NH4HS) Corrosion (Alkaline
Sour Water)
✓ Affected Units or Equipment
▪ Hydroprocessing Units
▪ NH4HS salts precipitate in the reactor effluent streams when
temperatures drop to within the range of 49°C to 66°C.
▪ Fouling and/or velocity accelerated corrosion
▪ FCC Units
▪ NH4HS concentrations are usually less than 2 wt % but high velocities
and/or the presence of cyanides can remove protective iron sulfide scales.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Ammonium Bisulfide Corrosion (Alkaline Sour Water)
✓ Affected Units or Equipment
▪ Sour Water Strippers (SWS)
▪ High concentrations of NH4HS in stripper overhead piping, condensers,
accumulator and reflux piping, and possible presence of cyanides.
▪ Amine Units
▪ High concentrations of NH4HS may be found in regenerator overheads and
reflux piping depending on unit operation.
▪ Delayed Coker
▪ High concentrations of NH4HS may be found in the gas concentration plant
downstream of the fractionator tower.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Ammonium Bisulfide Corrosion (Alkaline Sour Water)
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Ammonium Chloride Corrosion
✓ Description of Damage
▪ General or localized corrosion, often pitting, normally occurring under
ammonium chloride or amine salt deposits, often in the absence of a free water
phase.
✓ Affected Materials
▪ All commonly used materials are susceptible, in order of increasing resistance:
carbon steel, low alloy steels, 300 Series SS, Alloys 400, duplex SS, 800, and 825,
Alloys 625 and C276 and titanium.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Ammonium Chloride Corrosion
✓ Affected Units or Equipment
▪ Crude Tower Overheads
▪ Tower top, top trays, overhead piping and exchangers may be subject to fouling
and corrosion. Deposits may occur in low flow zones due to ammonia
and/or amine chloride salts condensing from the vapor phase.
▪ Top pumparound streams may be affected if ammonia or amine chloride
salts are present.
117
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Ammonium Chloride Corrosion
✓ Affected Units or Equipment
▪ Hydroprocessing
▪ Reactor effluent streams are subject to ammonium chloride salt fouling and
corrosion. Water washing may be required if exchanger fouling or loss in duty
occurs.
▪ Catalytic Reforming
▪ Reactor effluent streams and the H2 recycle system are subject to ammonium
chloride salting and corrosion.
▪ FCC and coker fractionator overheads and top pumparounds are subject to ammonium
chloride corrosion and salting.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – High Temp H2/H2S Corrosion
✓ Description of Damage
▪ The presence of hydrogen in H2S-containing hydrocarbon streams increases the
severity of high temperature sulfide corrosion at temperatures above about
260°C. This form of sulfidation usually results in a uniform loss in thickness
associated with hot circuits in hydroprocessing units.
✓ Affected Materials
✓ In order of increasing resistance: carbon steel, low alloy steels, 400 Series SS, and 300
Series SS.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – High Temp H2/H2S Corrosion
✓ Affected Units or Equipment
▪ This form of corrosion occurs in piping and equipment in units where high
temperature H2/H2S streams are found including all hydroprocessing units such
desulfurizers, hydrotreaters and hydrocracking units.
▪ Noticeable increases in corrosion may be found downstream of hydrogen
injection points.
120
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – High Temp H2/H2S Corrosion
121
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Hydrofluoric (HF) Acid Corrosion
✓ Description of Damage
▪ Corrosion by HF acid can result in high rates of general or localized corrosion and
may be accompanied by hydrogen cracking, blistering and/or HIC/SOHIC (Stress
Orientated Hydrogen Induced Cracking).
✓ Affected Materials
▪ Carbon steel, copper-nickel alloys, Alloy 400.
▪ Other nickel base alloys such as Alloy C276 have also been used in some
applications.
▪ Low alloy steels, 300 Series SS and the 400 Series SS are susceptible to
corrosion and/or cracking and are generally not suitable for HF service.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Hydrofluoric (HF) Acid Corrosion
✓ Affected Units or Equipment
▪ Piping and equipment in the HF alkylation unit, flare piping and downstream
units exposed to acid carryover are also affected.
▪ Most equipment is made from carbon steel with the exception of the HF
acid rerun/regenerator tower and the acid relief neutralizer vessel which are
usually made partially or completely from Alloy 400.
▪ High corrosion rates have been observed:
▪ In piping and equipment operating above 66°C;
▪ In dead legs including inlets to relief valves, as well as small bore vents and
drains;
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Hydrofluoric (HF) Acid Corrosion
✓ Affected Units or Equipment
▪ Condensing overhead vapors in piping and exchangers off top of the
Isostripper (iC4stripper), Depropanizer and HF Stripper/Propane Stripper;
▪ On flange faces;
▪ Heat exchanger bundles that heat acid-containing streams such as the acid
vaporizer.
▪ Severe fouling due to iron fluoride corrosion product has been observed in the
piping, heat exchangers and in the tops of the Isostripper and Depropanizer
towers.
124
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
✓ High Temperature Corrosion – Hydrofluoric (HF) Acid Corrosion
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Naphthenic Acid Corrosion (NAC)
✓ a. Description of Damage
▪ A form of high temperature corrosion that occurs primarily in crude and
vacuum units, and downstream units that process certain fractions or cuts that
contain naphthenic acids.
✓ b. Affected Materials
▪ Carbon steel, low alloy steels, 300 Series SS, 400 Series SS and nickel base
alloys.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Naphthenic Acid Corrosion (NAC)
✓ Affected Units or Equipment
▪ Crude and vacuum heater tubes; crude and vacuum transfer lines; vacuum bottoms
piping, AGO circuits; HVGO and sometimes LVGO circuits. NAC has also been
reported in the LCGO and HCGO streams on delayed coking units processing high
TAN feed.
▪ Piping systems are particularly susceptible in areas of high velocity, turbulence
or change of flow direction, such as pump internals, valves, elbows, tees and
reducers as well as areas of flow disturbance such as weld beads and thermowells.
127
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Naphthenic Acid Corrosion (NAC)
✓ Affected Units or Equipment
▪ Crude and vacuum tower internals may also be corroded in the flash zones, packing
and internals where high acid streams condense or high velocity droplets
impinge.
▪ NAC may be found in hot hydrocarbon streams downstream of the crude and
vacuum units, upstream of any hydrogen mix points.
128
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Naphthenic Acid Corrosion (NAC)
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
✓ High Temperature Corrosion – Sour Water Corrosion
✓ Description of Damage
▪ Corrosion of steel due to acidic sour water containing H2S at a pH between 4.5 and 7.0.
Carbon dioxide (CO2) may also be present.
▪ Sour waters containing significant amounts of ammonia, chlorides or cyanides may
significantly affect pH.
✓ Affected Materials
▪ Primarily affects carbon steel.
▪ Stainless steels, copper alloys and nickel base alloys are usually resistant.
✓ Affected Units or Equipment
▪ Acid sour water corrosion is a concern in overhead systems of FCC and coker gas
fractionation plants with high H2S levels and low NH3 levels.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Wet H2S Damage
✓ Description of Damage
▪ Four types of damage that result in blistering and/or cracking of carbon steel
and low alloy steels in wet H2S environments.
▪ Hydrogen Blistering
▪ Hydrogen Induced Cracking (HIC)
▪ Stress Oriented Hydrogen Induced Cracking
▪ Sulfide Stress Cracking
✓ Affected Materials
▪ Carbon steel and low alloy steels.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Wet H2S Damage
✓ Affected Units or Equipment
▪ Blistering, HIC, SOHIC and SSC damage can occur throughout the refinery
wherever there is a wet H2S environment present.
▪ In Hydroprocessing units, increasing concentration of ammonium bisulfide above
2% increases the potential for blistering, HIC and SOHIC.
▪ Cyanides significantly increase the probability and severity of blistering, HIC
and SOHIC damage.
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
✓ High Temperature Corrosion – Wet H2S Damage
✓ Affected Units or Equipment
✓ The vapor recovery sections of the fluid catalytic cracking and delayed coking units.
✓ Typical locations include fractionator overhead drums, fractionation towers,
absorber and stripper towers, compressor interstage separators and knockout
drums and various heat exchangers, condensers, and coolers.
✓ Sour water stripper and amine regenerator overhead systems are especially prone
to wet H2S damage because of generally high ammonia bisulfide concentrations and
cyanides.
✓ SSC is most likely found in hard weld and heat affected zones and in high strength
components including bolts, relief valve springs, 400 Series SS valve trim,
compressor shafts, sleeves and springs
133
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Wet H2S Damage
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Wet H2S Damage
135
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Carbonate Stress Corrosion Cracking
✓ Description of Damage
▪ Carbonate stress corrosion cracking (often referred to as carbonate cracking) is
the term applied to surface breaking cracks that occur adjacent to carbon steel welds
under the combined action of tensile stress in systems containing a free water
phase with carbonate, where some amount of H2S is also present.
▪ The environments include the outside surface of buried pipelines; and piping and
equipment containing aqueous carbonate solutions used in the carbon dioxide (CO2)
removal facilities associated with hydrogen reformers.
✓ Affected Materials
▪ Carbon steel and low alloy steels.
136
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Carbonate Stress Corrosion Cracking
✓ Affected Units or Equipment
▪ Carbonate cracking has been most prevalent in the fluid catalytic cracking unit main
fractionator overhead condensing and reflux system, the downstream wet gas compression
system, and the sour water systems emanating from these areas. Both piping and vessels are
affected.
▪ Carbonate cracking has also been observed in SWS units of the side pumparound type in
the pumparound return line to the SWS tower; on the OD (process side) of highly cold worked
SA179 condenser tube u-bends; and in the floor of tank storing sour water from an FCC unit.
▪ Carbonate cracking has also occurred in piping and equipment in Catacarb (The Catalytic
Process for Acid Gas Removal) and CO2 removal facilities of hydrogen manufacturing units
137
Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
REFINERY INDUSTRY CORROSION
Refinery industry corrosion
➢ High Temperature Corrosion – Carbonate Stress Corrosion
Cracking
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PGS. TS. Nguyễn Đình Lâm
PROCESS UNIT PFD’S
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PGS. TS. Nguyễn Đình Lâm
PROCESS UNIT PFD’S
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PGS. TS. Nguyễn Đình Lâm
PROCESS UNIT PFD’S
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PGS. TS. Nguyễn Đình Lâm
PROCESS UNIT PFD’S
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PGS. TS. Nguyễn Đình Lâm
PROCESS UNIT PFD’S
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PGS. TS. Nguyễn Đình Lâm
PROCESS UNIT PFD’S
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PGS. TS. Nguyễn Đình Lâm
PROCESS UNIT PFD’S
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LOCALIZED CORROSION IN REFINERY – Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
PROCESS UNIT PFD’S
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LOCALIZED CORROSION IN REFINERY – Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
PROCESS UNIT PFD’S
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LOCALIZED CORROSION IN REFINERY – Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
PROCESS UNIT PFD’S
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Khoa Hóa
PGS. TS. Nguyễn Đình Lâm
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