Material technology

1
Sr. Manager(Prod)
National fertilizers Ltd, India,
An Expert for www.ureaknowhow.com
Fellow of Institution of Engineers India

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INTRODUCTIONINTRODUCTION
Materials plays very important role in any
industry
Selection of material is vital at design
stage itself
Wrong selection of material may lead to
catastrophic failures and outage of plants
& even loss of Human lives
Right selection of material leads to long
life of plant

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MAIN TOPICS
CLASSIFICATION OF MATERIALS
TYPES OF MATERIALS USED AT
VIJAIPUR
TYPES OF STEELS
SPECIAL MATERIALS IN USE
 NEW DEVELOPMENT
MATERIALS FOR UREA SERVICE

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CLASSIFICATION OF MATERIALS
C A R B O N S T E E L
L O W T E M P E R A T U R E C A R B O N S T E E L
A L L O Y S T E E L
S T A IN L E S S S T E E L
F E R R O U S
A L U M IN IU M
Z IR C O N IU M
C O P P E R
W H IT E M E T A L
N O N -F E R R O U S
M E T A L L IC
T E F L O N
R U B B E R
W O O D
N O N -M E T A L L IC

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MATERIALS
• There is a wide variety of materials use to
construct process equipment. The type of
material selected depends on its
compatibility with process conditions and
cost.
• The materials of choice can be divided
into the following general categories

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METALS
• The metals used in the process industries
can be generally divided into two groups,
ferrous and nonferrous. Ferrous metals
are arbitrarily defined as those containing
at least 50% iron.
• As a group they far exceed any other
group of metal alloys used in the process
industry.

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FERROUS ALLOYS
• The reason for popularity of ferrous alloys
is their relatively low cost, ready
availability and good workability. Ferrous
alloys are subdivided into cast irons,
carbon steels , low alloy steels, and
stainless steels.
• There are also tool steels, but these will
not be discussed as they are of limited
used in the process industry.

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CAST IRON
• Cast iron are iron alloys that have greater than 1.5%
Carbon content. These are four types.
1 .GRAY CAST IRON.-This type is used in applications
such as construction equipment requiring vibration
damping and wear resistance. Its gray appearance is
caused by the graphite particles spread through out its
mass. Gray cast iron has a low tensile strength and is
brittle, and it should not be used in high pressure
process vessels.
2. WHITE CAST IRON.-White cast iron has a much lower
silicon content than gray cast iron. No graphite particles
exist in its microstructure, and any carbon in the cast iron
is combined with iron in the form of iron carbide(Fe3C).
The metal is hard, extremely abrasive, brittle .

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Contd.
3. DUCTILE CAST IRON.-
When ductile cast iron is manufactured, small spherical
nodules of graphite are produced in its microstrure.This cause
it to be ductile rather than brittle. Ductile cast iron is used for
high strength pipes, valve bodies, pump casing, compressor
casings, crankshaft and machine tools.
4..WROUGHT CAST IRON
Prior to the nineteenth century, wrought iron was the only form
of iron used. It is basically pure iron low in the carbon but with
a few percent of slag remaining in the form of an iron silicate.
The slag form a fibrous structure within the wrought iron that
gives it excellent shock, vibration, and corrosion resistance.
wrought iron can be used for water pipe, air brake pipes, and
engine bolts.

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IRON CARBON EQUILIBRIUM DIAGRAM
TEMPERATURE
TEMPERATURE

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IRON CARBON EQUILIBRIUM DIAGRAM

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PROPERTIES
STRENGTH
HARDNESS
DUTILITY
TOUGHNESS

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STRENGTH
THE RESISTANCE OFFERED BY
MATERIAL ON APPLICATION OF
EXTERNAL FORCE IS CALLED
STRENGTH
HARDNESS
HARDNESS IS RESISTANCE
OFFERED BY MATERIAL TO
INDENTATION

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HARDNESS & ITS MEASURMENTSHARDNESS & ITS MEASURMENTS
• Several indentation method, give hardness
value in terms of absolute units, briefly a given
load is applied to a specimen for a specific
time ,removed and the area of indentation is
then measured.
• HARDNESS = Load
• Area(kg/mm2
).
1.Brinnel Hardness Test.
2. Vickers or Diamond pyramid hardness(DPH).
3. Rockwell Hardness Test.

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Indenter
Specimen
surface
h1 h2
Pre load
Pre load
Main Load
+
d
D
I
Brinnel
Vickers Or
DPH
Knop
Indentation shapes for various indentation hardness test method
Measuring sequence in Rockwell Hardness Test
HV=1.8544F/D2
.BH= F
( ΠD)(D-√D2
-d2
)
F=Load

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DUCTILITY
• IT IS A MEASURE OF THE AMOUNT OF
PLASTIC DEFORMATION A MATERIAL
CAN TAKE UNDER TENSILE FORCE
WITHOUT FRACTURE
• RATIO OF ELONGATION OF MATERIAL
AT FRACTURE TO ORIGINAL LENGTH
• BRITTLENESS IS THE PROPERTY
OPPOSITE TO DUCTILITY

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TOUGHNESS
• THE AMOUNT OF ENERGY ABSORBED
BY A MATERIAL AT THE TIME OF
FACTURE UNDER IMPACT LOADING
• IT IS CAPACITY TO TAKE IMPACT
LOAD

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ROLE OF DIFFERENT ELEMENTS USED
IN STEEL ALLOYS
1.CHROMIUM(Cr):
“It is strong Carbide former and form complex series of
carbides compound of chromium and iron.”
(a)It is essential for formation of passive film
to resist corrosion.
(b)It helps to raise the critical Temperature of steel.
(c)It improves hardness and wear resistance.
2.NICKEL:
(a)It improves toughness,ductility and ease in
welding.
(b)It improves resistance to Fatigue failure.
(c)It is austenitic stabilizer.

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3.MOLYBDENUM:
(a)It increases corrosion resistance in presence of
chlorides.
(b)It prevents Pitting and Crevice corrosion.
4.CARBON:
(a)It permits the hardenability by heat treatment.
(b)It gives the strength at high temperatures.

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5.NITROGEN:
(a)It enhances pitting resistance.
(b)It is a supplement of Carbon in Low Carbon Steels.
(c)It improves Pitting and Crevice Corrosion resistance.
6.MANGANESE:
(a)It prevents to form Iron Sulphide which is harmful
in steels.
(b)It promotes forgeability of steel.

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Copper
• Increases strength up to about 12 %.
Higher concentration cause
brittleness. Copper improve the
elevated temperature properties and
machinability. Used in concentration
of about 0.5% or less, produces a
tenacious self sealing oxide film on a
metal surface.

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7.PHOSPHORUS:
1.IT IS ADDED IN LOW CARBON STEELS UPTO
0.12%.IT DISSOLVES IN FERRITE AND INCREASES
STRENGTH AND HARDNESS.
2.IT IMPROVES THE MACHINABILITY.
8.SILICON
1.IT IS ADDED IN STEELS AS ADEOXIDISER DURING
CASTING OF IGNOTS.
2.IT DISSOLVES IN FERRITE INCREASING STRENGTH
AND HARDNESS WITHOUT LOWERING THE DUCTILITY

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CARBON STEEL
• The characteristic difference between cast
iron and carbon steel is the carbon
content.
• Carbon steel has less than 1.5 % carbon.
• It is easy to fabricate and has better
strength than cast iron.
• It is easier to weld than cast iron.
• The main disadvantage in using carbon
steel is its susceptibility to corrosion.

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TYPES OF CARBON STEEL
LOW CARBON STEEL
MEDIUM CARBON STEEL
HIGH CARBON STEEL

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LOW CARBON STEEL
CONTAIN UPTO 0.3% CARBON
KNOWN AS SOFT OR MILD STEEL
NOT RESPONSIVE TO HEAT TREATMENT
SCREW, NAIL, NUTS,BOLTS, WASHERS,
WIRE FRAMES

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MEDIUM CARBON STEEL
 CONTAINS CARBON 0.3 TO 0.6%
 HARDER AND MORE TENSILE STRENGTH THEN
LOW CARBON STEEL
 BETTER MACHINIG QUALITIES AND MORE
RESPONSIVE TO HEAT TREATMENT
 SHAFTS, CONNECTING RODS, SPINDLES,
MACHINE PARTS

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HIGH CARBON STEEL
CONTAINS 0.6% TO 1.7% CARBON
HIGHER TENSILE STRENGH AND HARDER
READILY RESPOND TO HEAT TREATMENT
HAND TOOLS, CHISELS, PUNCHES, FILES,
CUTTING TOOLS, RAIL ROAD WHEELS

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MATERIALS FOR VARIOS
NETWORKS
NETWORK MATERIAL GRADE
COOLING
WATER, STEAM
CONDENSATE
CARBON
STEEL
API 5L Gr.B
STEAM UP TO
3750
C
CARBON
STEEL
ASTM A
106Gr.B
STEAM MORE
THAN 400 0
C
ALLOY
STEEL
ASTM A335
Gr.P11 & P22

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STAINLESS STEEL
• “A steel that has 12% or more chromium is
considered a stainless steel.”
• “Another criterion defining a stainless steel is its
Passivity.”
• PASSIVITY.- “Passivity is the ability of a metal
to form an impervious surface coating which
inhibits corrosion resulting from the
electrochemical reaction of the metal with the
surrounding environment.”
• “Stainless Steels exhibit passivity in oxidizing
environment.”

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Professional organization and their
Scope of Concern
Abbreviatio
n
organization Scope of
Concern
ASTM America
Society of
Testing & Material
Provides testing
procedures for a
wide variety of
material
ASME American society
of mechanical
engineers
Provides a list of
recommended
metal & welding
material

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AISI American iron & steel
Institute
Provides standard
descriptions for cs
& alloy.
SAE Society of automotive
engineers
Provides a four
digit system and
alloy steels used
in high production
item
CDA Copper development
association
Instituted a
numerical system
for identifying
copper.
ANSI AmericanNational
Standard Institute
Provides safety &
design criteria

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Corrosion as function of Chromium
• “Following figure
shows the corrosion
rate as a function
chromium content in
an iron chromium
alloy.”
Corrosion rate of
iron-Chromium
alloys exposed to an
intermittent water
spray at room
temperature

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Effect of Chromium
Stainless steels are chromium containing steel alloys.
The minimum chromium content of the standardized
stainless steels is 10.5%. Chromium makes the steel 'stainless'
this means improved corrosion resistance,
as can be seen in the chart.

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IRON-CHROMIUM PHASE
DIAGRAM
• Following figure shows the phase diagram
for iron chromium in all proportions.
• With chromium contents between 20 and
70% ,the “sigma” microstructure is formed.
• SIGMA MICROSTRUCTURE.- “This
microstructure is hard, brittle and poor
corrosion resistance.”

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IRON CHROMIUM
PHASE DIAGRAM
TEMPERATUREIN0
C
2054266408711090131515381760

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TYPES OF STAINLESS STEEL
• There are three general types of
stainless steel of interest to the
process engineer.
1. FERRITIC STAINLESS STEEL
2. AUSTENITIC STAINLESS STEEL
3. MARTENSITIC STAINLESS STEEL

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FERRITIC STAINLESS STEEL
• Ferritic stainless steel has a
• carbon content of 0.2% or less.
• Chromium content 11-18% .
• Although it can not be heat treated and
has poor tensile and impact strength, it
better corrosion resistance than
martensitic stainless steel.
• It is suitable for use with strong oxidizing
acids such as Nitric acid.

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IRON CHROMIUM PHASE DIAGRAM WITH CARBON 0.2%
FERRITIC S.S. Far from sigma
phase

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FERRITIC STAINLESS STEEL
 HIGHLY RESISTANT TO STRESS CORROSION
CRACKING SHOW AN INCREASES AS RESULT
OF COLD WORK
 THEY ARE MEGNETIC, HAVE GOOD DUTILITY
READILY WELDABLE, NON MEGNETIC
 WELDING IS DIFFICULT
 SS 430(17% Cr) USED FOR AUTOMOTIVE TRIMS
AISI % C % Mn % P % S % Si % Cr
430 0.12 1.0 0.04 0.03 1.0 14 to 18

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MARTENSITIC STAINLESS
STEEL
• Farritic stainless steel has a
• Carbon.-1.2% or less. and
• Chromium.-12-18%.
• It has better hardenability and strength
than does ferritic stainless steel.
• It is used as cladding to carbon steel for
some process vessels .

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IRON –CHROMIUM PHASE
DIAGRAM FOR 1.0% CARBON
Martensitic S.S.
Far from
sigma phase

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MARTENSITIC STAINLESS STEEL
(Chemical Requirements)
AISI % C % Mn % P % S % Si % Cr
410 0.15 1.0 0.04 0.03 1.0 11.5 to
13.5
420 0.15 1.0 0.04 0.03 1.0 12 to 14

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AUSTENITIC STAINLESS STEEL
• “Austenitic stainless steel is a more complex
material because the addition of NICKEL (3.5 to
22%) allows it to retain its austenitic microstructure
at all temperature
• It has a high tensile strength and best impact
strength, ductility and corrosion resistance of all the
stainless steel over a very wide range of
temperatures.
• All stainless steels are susceptible to pitting from
exposure to high chloride concentration.
However,austanitic steel with high Molybdenum
content(1 to 3 %)have improve resistance to pitting.

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Austenitic Steels in High Temperature Service
The austenitic alloys have a face centered cubic structure
which has a better corrosion resistance compared to the
ferritic steels. The austenitic structure is normally not stable
in irons below 700 C, but adding nickel to the steel makes
the austenitic phase stable down to room temperature.
These alloys are basically chromium nickel steels.
Chromium is used in these alloys to make the steel
corrosion resistant, whereas nickel stabilizes the even
more corrosion resistant austenitic structure. Silicon and
aluminum are added to increase the oxidation resistance.
Titanium and niobium, as well as boron, nitrogen, tungsten,
vanadium and cobalt can be added to increase the creep
strength due to precipitation strengthening. Manganese can
be used to substitute nickel as an austenite former.

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Fe-Cr-Ni Ternary diagram for an
18% Cr alloy with the austenitic S.S
Austenitic S.S.

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AUSTENETIC STAINLESS STTEEL
AISI % C %
Mn
% Si % Cr % Ni % Mo
304 0.08 2 1.0 18 to 20 8 to 10.5 -
304L 0.03 2 1.0 18 to 20 8 to 10.5 -
309 0.2 2 1.0 22 to 24 12 to 15 -
310 0.2 2 1.0 24 to 26 19 to 22 -

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AISI % C %
Mn
% Si % Cr % Ni % Mo
316 0.08 2 1.0 16 to 18 10 to 14 2 to 3
316L 0.03 2 1.0 16 to 18 10 to 14 2 to 3
321 0.08 2 1.0 17 to 19 9 to 12 Ti >5xC
347 0.08 2 1.0 17 to 19 9 to 12 Nb >5xC

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AISI USES
304 DM Water, Lube oil, waste water, CO2
304L VACUUM SECTION
309 Its filler wire & electrodes are used to weld
Carbon Steel with Austenitic Stainless Steel
316L M.P. & L.P. SECTIONS, HYDROLYSER
SECTION

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MATERIALS FOR
CARBAMATE SERVICE
CARBAMTE IS HIGHLY CORROSIVE
IN NATURE AT HIGH PRESSURE &
TEMPERATURES
ALL OVER THE WORLD LICENSERS
OF UREA PLANTS ARE SEARCHING
OR COST EFFECTIVE & BETTER
CORROSION RESISTANT MATERIALS

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MATERIALS FOR
CARBAMATE SERVICE
TITANIUM
ZIRCONIUM
316l MOD OR 316L UG OR 3RE60
2RE69 OR 25Cr.-22Ni.-2Mo. (UNS
S31050)
DUPLEX STEEL

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TITANIUM
USED FOR LINING & TUBE MATERIAL OF
AMMONIA STRPPER IN SNAM PROGETTI’S
UREA PLANTS
 USED FOR LINING OF UREA REACTORS
OF TOYO PLANTS AT PANIPAT &
BHATINDA
ADVANTAGES :
PASSIVATION AIR IS NOT REQUIRED
STRIPPER BOTTOM TEMPERATURE
CANBE KEPT UPTO 210 0
C

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TITANIUM
DISADVANTAGES :
IS NOT MAINTENANACE FRIENDLY
ERROSION OF TUBES ENDS RESULTING
IN BYPASSING
“Titanium & Zirconium Hexagonal
closed packed”

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316L MOD & 2RE69
THESE ARE TAILOR MADE GRADES OF
AUSTENETIC STAINLESS STEEL TO SUIT
REQUIRED SPECIFICATIONS OF
PURCHASER

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USES OF 316L MOD & 2RE69
316L MOD
• REACTOR LINING
• CARBAMTAE
SEPERATOR LINING
• H.P. SECTION PIPING
• CARBAMATE
CONDENSOR LINING
IN UREA-I
• TUBES OF
CARBAMTAE
CONDENSOR
2RE69
• AMMONIA STRIPPER
LINING
• CABAMATE
SEPERATOR LINING &
TUBES IN UREA-II
• ADDITIONAL
REACTOR TRAYS IN
UREA-I PLANT

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CHEMICAL COMPOSITION
316L MOD & 2RE69
316L MOD
• CARBON : < .
02 %
• CHROMIUM : 18 %
• NICKLE : >13 %
• MOLY : 2-2.6 %
• MAGNESE : 1.5-2 %
• SILICON : 0.4 %
• SULPHUR : 0.01 %
• PHOSPHORUS :
0.015 %
• N MAX : 0.10 %
2RE69
CARBON : < .02 %
CHROMIUM : 24-26 %
NICKLE : 21-23 %
MOLY BEDNUM : 2-2.6 %
MAGNESE : 1.5-2 %
SILICON : 0.4 %
SULPHUR : 0.015 %
PHOSPHORUS : 0.02 %
N MAX : .1-.15%

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316L MOD & 2RE69
METALLOGRAPHIC PROPERTIES :
 MATERIAL IN CONTACT WITH PROCESS FLUID
SHALL HAVE AUSTENITIC STRUCTURE
 FERRITE CONTENT SHALL NOT EXCEED 0.6%
EXCEPT FOR MANUAL WELDS, FOR WHICH 1%
IS ALLOWED
“SIGMA PHASE SHALL BE ABSENT”
 CHROMIUM CRABIDES MAY BE PRESENT IN
MINIMUM AMOUNTS ONLY

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316L MOD & 2RE69
METALLOGRAPHIC PROPERTIES :
 MATERIAL SHALL PASS HUEY TEST & SHALL BR
PERFORMED ACORDING TO ASTM A262
PRACTICE ‘C’ AND MAXIMUM CORROSION RATE
ALLOWED SHALL BE:
TYPE OF
MATERIAL
CORROSION
RATE
MM/YEAR
DEPTH OF
ATTACK
MICRON
316L MOD
25-22-2
0.6
0.3
90
70

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RATE OF CORROSION( as per Huey Test)
MATERIAL CORROSION RATE
MM/YEAR
ZIRCONIUM 0.005
TITANIUM 0.06
25-22-2 0.3
316L MOD 0.6
HUEY TEST-Metal sample is boiled in 65% HNO3
for 48 Hrs(5times) to estimate corrosion rate
1mm=40mils
(mpy)

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ADVANTAGES
EXCELLENT ERROSION AND CORROSION
RESISTANT
COST EFFECTIVE
MAINTENANACE FRIENDLY
LIMITATIONS:
TEMPERATURE IS LIMITED TO 207 0
C
PASSIVATION AIR IS REQUIRED

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MATERIAL OF CONSTRUCTION FOR
MAJOR EQUIPMENTS IN UREA
PLANT
1.REACTOR:
2.STRIPPER: LINE 1 (Retired)
(a)Liner--------------Ti
(b)Ferrules-----------2RE-69
(c)Tubes --------------Ti(3.5mm)
(d)Internals ----------2RE-69
(e)Shell --------------C S
(a)Shell ------------CS.
(b)Liner------------316LM
(c)Trays----------316L.
(d)Addl & Replaced Trays--------2 Re-69

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STRIPPER
LINE- 1&2
(a)Top&Bottom Domes ----------2RE-69
(b)Tubes ----------------------------Bimetallic
2.0mm 2RE69 & 0.7mm Zr
(c)Ferrules --------------------------2RE-69
(d)Internals -------------------------2RE69
(e)Shell ------------------------------C S

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3.CARBAMATE CONDENSER ( E-5)
(a) Tubes -----------------2 RE-69
(b)Dome ----------------Liners---316L
Liners(Replaced)---2RE-69
4.MV-2 --------------316L
5.MV-3
--------------304L

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Construction :-
1. Kettle type construction
2. Carbamate + vapors inlet through a mixer
condenser ,Inlet and outlet passes
separated by Partition plates
3. Material of Construction
– Channel /tube sheet liner - 2 RE 69
– Tubes - 2 RE 69
– Partition plate - SS 316 L M
– Changed new petal - 2 Re -69
Carbamate Condenser

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7.MV-6& -------------------304L
MV-7
8.Hydrolyser ---------------316L
9. C-2 -------------------------------304L
Contd.
6. Pre-Concentrator
E14 A –(Tube &Cell)----------------316L
E-14B(Tube)---------------------------304L
(Cell)----------------- ------------------CS.

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ALLOY C P S Si Mn Cr Ni Mo N
304 0.08 0.045 0.030 1.0 2.0 18-20 8-10.5
304L 0.03 0.045 0.030 1.0 2.0 18-20 8-12
316 0.08 0.045 0.030 1.0 2.0 16-18 10-14 2-3
316L 0.03 0.045 0.030 1.0 2.0 16-18 10-14 2-3
316LN 0.02 0.015 0.010 0.40 1.70 17.5 14 2.6 0.18
2RE-69 0.02 0.015 0.010 0.40 1.70 25 22 2.1 0.12
HVD-1 0.05 CU-1.5 0.02 0.038 1.25 25.16 8.5 2.5
MATERIALS OF CONSTRUCTION(COMPOSION IN Wt%)

67
“DUPLEX” STAINLESS STEEL
• “A DULEX steel is characterized by a
microstructure containing both Ferritic
phase with a BCC crystallographic
structure and an Austenitic phase with a
FCC structure.”
• The Ferritic phase is normally 40-60%,
mainly introduced in the wrought alloys by
a careful balance of the critical alloying
elements.

68
BCC.-Body centered cubic “ High strength low ductility.”
e.g.-Ferrite(α-iron),Cr,V,Mo,W etc.
FCC-(Body centered cubic). “Low strength high ductility.”
e.g. Austenite( γ-iron),Al,Cu,Pb,Ag,Au,Ni,Pt etc.
HCP-(hexagonal closed packed) HCP metal are not
ductile as FCC metal
e.g.-Be,Mg,Zn,Cd,Co,Tl,Zr. Etc
The HCP cell consists three layers of atom The top
and bottom layers contain six atom at the corner of
the hexagonal and one atom at the centre of each
hexagonal. The middle layer contains three atoms
nestled between the atom of the top & bottom layers
hence the name close packed.

69
DUPLEX STEELS
MIXTURE OF AUSTENITE & FERRITE
HIGHER STRENGTH & BETTER
RESISTANCE TO CHLORIDES
Cr: 18-27%, Ni: 4-7%, Mo: 2-4%

70
DUPLEX STTEEL
%
C
%
Mn
% Si % Cr % Ni % Mo
HVD-1
(EJ-1)
0.0
8
2 1.0 26 to
27
7 to 9 2 to 3
FR-
255
0.0
3
2 2.0 26 5 3
Cu 2 %
USE SPINDLES & SEATS OF UREA GRADE
VALVES( in Urea Plant EJ-1)

71
Stress Corrosion Cracking
A particular problem for the common austenitic
grades (e.g. 304 and 316) is stress corrosion cracking (SCC).
Like pitting corrosion this occurs in chloride environments, but
it is possible for SCC to take place with only traces of
chlorides, so long as the temperature is over about 60°C,
and so long as a tensile
stress is present in the steel, which
is very common. The ferritic grades are virtually immune
from this form of attack, and the duplex grades are highly
resistant. If SCC is likely to be a problem it would be
prudent to specify a grade from these branches
of the stainless family tree.

72
Types of Stress
• “Stresses occur in any material that is subject to a load
or applied force, Stress is the internal resistance, or
counterforce, of a material to the restoring effect of an
external force or load.” There are many types of stresses
,but they can all be generally classified in in one as six
categories-
1 .Residual stress,
2. structural stress.
3. pressure stress,
4. Flow stress,
5. Thermal and
6. Fatigue stress.

73
Residual Stresses
• “Residual stress are due to manufacturing
process that leave stress in a material. Welding
leaves residual stresses in the metal welded.
stress associated in welding are further
discussed later in this module.”
• STRUCTURAL STRESSES- “Structural stresses
are produced in the structural member because
of the weights they support. The weight provide
the loadings. These stresses found in the
building foundation and frame works, as well as
machinery parts.”

74
PRESSURE STRESSES
• “Pressure stresses are stresses induced in vessels
containing pressurized material. The loading is provided
by the same force producing the pressure. In a Reactor
facilities. The Reactor vessel is a prime example of
pressure vessel.”
• FLOW STRESSES -“Flow stresses occur when a mass
of flowing fluid induces a dynamic pressure on a conduit
wall. The force of the fluid striking the wall acts as the
load. This type of stress may be applied unsteady
fashion when flow rate fluctuate. Water hammer is a
example of transient flow.”
• FATIGUE STRESSES- “Fatigue stresses are due to
cyclic application of a stress." The stress could be due to
vibration or thermal cycling.”

75
‘THERMAL STRESSES”THERMAL STRESSES”
• “Thermal stresses exist whenever temperature
gradient are present in a material.” “Different
temperature produce different expansion and
subject material to internal stress." This type of
stress is particularly noticeable in mechanism
operating at high temperature that are cooled by
cold fluid.
• Example-Compressors intercoolers.
Practically in 41 stream E-27 tubes thermal
stresses cracking corrosion found in 1997.All the
tubes have been changed, after this SCC.

76
STRESS CORROSION
CRACKING
• Practical experience of 41-E-27 Tube
leakage was found in 1997,due to SCC.
• Based on practical experience in
combination with laboratory test a stress
corrosion cracking has been compiled to
make to make selection easier .,following
fig.
• It shows that even a very small amount (a
few ppm) of chloride may result in
cracking of austenitic grade like 304L and
316L.

77
Stress corrosion cracking (SCC) Resistance of various SS.in
oxygen bearing Neutral chloride solution . Testing time 1000 hrs.
applied stress equal to yield strength. Open circle mean no SCC
for SAF 2507.

78
Advantages of Duplex S.S.
• Good resistance to “chloride stress corrosion
cracking.”(CSCC).
• The duplex stainless steel also offer
resistance to general and pitting corrosion.
• Good resistance to erosion and abrasion.
• There are numerous cases where plant
equipment properly fabricated from duplex
SS has operated with full immunity in chloride
containing environment where types
304,304L, 316,316Lhave failed due to stress
corrosion cracking.

79
NEW DEVELOPMENT IN DUPLEX
• First generation duplex.-The first generation
duplex containing.-
• Cr-25 %.
• Ni-5 %, and
• Mo-1.5 % and Nitrogen ---Nil
• There is no Nitrogen. Because Carbon Content
upto 0.2%.There is a considerable loss in
corrosion resistance during welding
• Therefore ,a post weld heat treatment is required
to assure good prosperities.

80
SECOND GENRATION DUPLEX
• The second generation duplexes have low
carbon levels, assuring resistance to
irregular attack(IGA) The nitrogen
contents are usually more than 0.1%.in
addition to improving pitting and crevice
corrosion.
• Cr.----25 %,Ni.—5 %, Mo.-1.5 %.N- 0.1%.

81
THIRD GENERATION DUPLEX
• The third generation duplex contains
about 0.2% copper.
• Cr.-25 % Ni.-4.0 % Mo-Nil. Cu.-0.2%
• “A third generation developed in
SWEDON, has recently been introduced
Alloy 2304.” and SAFUREX.
• HVD-1 is also 3rd
generation Duplex S.S.
and developed by Snampogetti.

82
SUPERFERRITIES
• These are highly resistant to chloride
pitting and crevice corrosion. They have
found extensive applications as tubing for
power plant condensers, and heat
exchanger handling chloride solution,
such as Sea water. Having a ferrite
microstructure. They have a very high
resistance to CSCC. In addition they are
suitable for use in organic acids, dilute
reducing acids.

83
contd
• Alloy 29-4C(UNS S44735) containing-
• Cr -20 %
• Mo -4.0 %
• Alloy Sea –cure (UNS S44660)
• Cr-26 %
• Mo 3.0 %
• Ni1.0 %

84
DUPLEX DEVELOPED BY
STAMICARBON &TEC(ACES)
DP3 UREA
GRADE(DP12)
R4 UREA
GRADE(R5)
Cr 24.8-26 24-26
Ni 6.5-7.5 6.0-6.7
Mo 2.5-3.2 1.2-2.0

85
SAFUREX(STAMICARBON)
• Safurex is jointly developed by SANDVIK
& STAMICARBON and designated
SafurexTM.
can allow lower Oxygen content
for passivation.

86
Chemical composition and PRE No
for various Duplex & S.S.
Grade Cr Ni Mo N PRE Microstru
cture
2 Re 60(UG) 18.5 4.9 2.7 0.07 28 Duplex
SAF 2304 23 4.5 - 0.1 24 Duplex
SAF 2205 22 5.5 3.2 0.18 35 Duplex

87
Grade Cr Ni Mo N PRE Microstruc
ture
SAF 2507 25 7 4 0.3 43 Duplex
AISI 304L 18.5 10 - - 18 Austenitic
AISI 316L 17.5 13 2.1 - 24 Austenitic
Sanicro 28 27 31 3.5 - 38 Austenitic
Contd.

88
“Selection for Fabrication”
Again it is usually the case that grades are selected for
corrosion resistance and then consideration is given to how
the product can be fabricated. Fabrication should be considered
as early as possible in the grade selection process, as it greatly
influences the economics of the product.
Table lists some common
grades and compares their relative fabrication characteristics.
These comparisons are on arbitrary 1 to 10 scales,
with 10 indicating excellent fabrication by the particular method.
Table . Common Grades and Their Relative Fabrication
Characteristics

89
Grade Formability Machinability Weldability
303 1 8 * 1
304 8 5* 8
316 8 5* 8
416 1 10 1
430 4 6 2
2205 5 4 5
3CR12 5 6 6
* Improved Machinability versions of these grades offer higher
machinabilities in some products.

90
CORROSION RATE IN STRIPPER
1000 10000ppm O2
0.010.11.0
Corrosionratemm/yr
DUPLEX
316LS.S.
2RE 69

91
HOW TO GAUGE RESISTANCE
TO PITTING
• The resistance of a particular grade of
stainless steel to pitting and crevice
corrosion is indicated by its Pitting
Resistance Equivalent number or
PRE, as shown in table . The PRE
can be calculated from the
composition as:
PRE = %Cr + 3.3 %Mo + 16 %N
PRE is also known as LCR-Localized Corrosion Resistance

92
A higher PRE value , hower,cannot be used as a direct
selection criterion. For selection of material in chloride-
containing solution a diagram showing the critical pitting
temperature. Has to be used

93
Table. Pitting Resistance Equivalent Number or PRE for
Various Grades
Grade
Class PRE
3CR12 ferritic 11
430 ferritic 17
303 austenitic 18*
304/L austenitic 18
316/L austenitic 24
2205 duplex 34
904L austenitic 34
S31254 austenitic 43
S32750 duplex 43
S32520 duplex 43
*The calculated PRE for 303 is wrong, due to sulphur in
the composition.

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