7. low alloy steels for cryogenic applications
TRANSCRIPT
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Nofrijon
Sofyan, Ph.D.
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Introduction
Steel for cryogenic applications is a steel usvery low temperatures around -200 C.
At this very low temperature, the materials
commonly become brittle.
Because of that, for this low-temperature se
the materials are required to give a specifi
strength, ductility, and toughness.
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Carbon and alloy grades for low-temperatureare required to provide the high strength, duct
toughness in vehicles, vessels, and structures thaserve at -45C and lower.
At temperature below ambient, a metals behacharacterized somewhat by crystalline structur
The yield and tensile strengths of metals that cin the body-centered cubic from iron, molybdevanadium and chromium depend greatly ontemperature.
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These metals display a loss of ductility in a
temperature region below room temperatu
The tensile strength of metals with face-cen
cubic structures - aluminum, copper, nickel a
austenitic stainless steel - is more temperatu
dependent than their yield strength, and thoften increase in ductility as temperature d
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Cryogenic properties5
Transformation occurring in compositions that are nstable at room temperature, but metastable at crytemperatures can greatly alter their behavior.
For example, the combination of gross plastic defoand cryogenic temperatures can cause a normallyand tough stainless steel, such as 301, 302, 304, 3partially transform to bcc structure, resulting in animpairment of ductility and toughness.
A fully stable stainless steel 310 cannot be transfocryogenic temperatures.
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The 300 series steels offer a fine combination
toughness and weldability for service to the lo
temperatures. In the annealed condition, their strength prope
adequate for ground-based equipment but ina
for lightweight structures.
For aerospace applications, fabricators can ta
advantage of the alloys strain-hardening char
and use them in highly cold-worked condition.
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The principal shortcomings of cold-worked matare: low weld-joint efficiencies caused by anneduring welding and the transformation to martthat occurs during cryogenic exposure.
Selection of fully stable grade type 310, overtransformation problem.
Precipitation-hardening A286 stainless has eve
strength when cold worked before aging. The alloy steel recommended for cryogenic ser
9% nickel steel.
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It is satisfactory for service down to -195C
used for transport and storage of cryogeni
because of its low cost and ease of fabrica
Other alloy steels are suitable for service in
low-temperature range.
The steels A201 and T-1 can suffice to -45steels with 2.25% Ni can suffice to -59C, a
nickel steels with 3.5% Ni to -101C.
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Design for cryogenic applications9
Designers of cryogenic assemblies base thecalculations on the room-temperature prope
the material.
The reason is that it is the highest temperat
material will encounter.
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And it stands that if a higher-strength matestands up to super cold conditions were ava
designers might specify it.At 26C austenitic stainless steel has tensile
yield strengths that are 172 MPa greater tcorresponding strengths for type 304 stainl
At -100C its tensile and yield strength excthose of type 304 by 550 MPa and 276 Mrespectively.
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A grade with following chemical composition shgood mechanical properties at cryogenic tempC - 0.072%, Mn - 16%, P - 0.02%, S - 0.008%0.41%, Ni - 5.85%, Cr - 17.8%, N - 0.36%, FRemainder
The composition is given for plates with 12.7mthickness
The material combination of high strength, gootoughness, and weldability should prompt desispecify it for welded pressure vessels for the scryogens.
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Ductility and temperature12
Ductility is a critical property for cryogenicapplications.
In general, BCC metals such as Fe, Carbon
alloy steels, Molybdenum, and Niobium bec
brittle at low temperatures.
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FCC metals such as Cu, Ni, Cu-Ni alloys, Al
alloys, and austenitic stainless steels remain
at low temperatures.
Most plastics and elastomers become brittle
temperatures.
Ceramics and glasses are already brittle atemperature and become slightly more so a
cryogenic temperatures.
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Brittle materials14
In brittle materials, the maximum load is the sa
the yield strength,
the tensile strength
the breaking strength
Yield in brittle materials such as ceramics doesby the motion of dislocations but by planar de
as cracks.
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The effect of temperature on the stress-strain curve and
properties of an aluminum alloy.
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Brittle materials bend test16
The bend test is used to measure the properties ofmaterials where a flat specimen is put under load
The bend test for measuring the strength of brittleand the deflection, d, obtained by bending.
Brittle Materials
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Low alloy steel17
Low-alloy steels constitute a category of fematerials that exhibit mechanical propertiesuperior to plain carbon steels as the result additions of alloying elements such as nickechromium, and molybdenum.
Total alloy content can range from 2.07% ulevels just below that of stainless steels, whicontain a minimum of 10% Cr.
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For many low-alloy steels, the primary func
the alloying elements is to increase hardena
order to optimize mechanical properties antoughness after heat treatment.
In some cases, however, alloy additions are
reduce environmental degradation under cespecified service conditions.
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Classification of low alloy steels19
As with steels in general, low-alloy steels can
classified according to:
Chemical composition, such as nickel steels,
chromium steels, molybdenum steels, chromi
molybdenum steelsHeat treatment, such as quenched and temp
normalized and tempered, annealed.
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Because of the wide variety of chemical comp
possible and the fact that some steels are used
than one heat-treated, condition, some overlapamong the alloy steel classifications.
Thus, four major groups of alloy steels can be
addressed: (1) low-carbon quenched and temp
(QT) steels, (2) medium-carbon ultrahigh-streng(3) bearing steels, and (4) heat-resistant chrom
molybdenum steels.
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Low-carbon quenched and tempered21
Low-carbon quenched and tempered steels
high yield strength (from 350 to 1035 MPa
high tensile strength with good notch toughn
ductility, corrosion resistance, or weldability
The various steels have different combinatiothese characteristics based on their intende
applications.
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However, a few steels, such as HY-80 and H
are covered by military specifications.
The steels listed are used primarily as plate
Some of these steels, as well as other, simila
are produced as forgings or castings.
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Medium-carbon ultrahigh-strength ste23
Medium-carbon ultrahigh-strength steels ar
structural steels with yield strengths that can
1380 MPa.
Many of these steels are covered by SAE/A
designations or are proprietary compositio Product forms include billet, bar, rod, forgin
sheet, tubing, and welding wire.
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Bearing steels24
Bearing steels used for ball and roller bear
applications are comprised of low carbon (
0.20% C) case-hardened steels and high ca
1.0% C) through-hardened steels.
Many of these steels are covered by SAE/Adesignations.
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Cr-Mo heat-resistant steels25
Chromium-molybdenum heat-resistant steels
0.5 to 9% Cr and 0.5 to 1.0% Mo.
The carbon content is usually below 0.2%.
The chromium provides improved oxidation
corrosion resistance, and the molybdenum instrength at elevated temperatures.
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They are generally supplied in the normaliz
tempered, quenched and tempered or ann
condition.Chromium-molybdenum steels are widely us
oil and gas industries and in fossil fuel and
power plants.
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Know how27
Knowing the type of low-alloy steel you have and matching icorrect filler metal is critical to achieving weld integrity.
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Low-temperature steel28
Designation Lowest usual
service
temperature,
(C)
Min Yield
Strength (MPa)
Tensile
Strength (MPa)
Min
Elongation,
L0= 50 mm
(%)
U
A442 Gr. 55 -45 221 379 - 448 26 Welded pressure v
tanks; refrigeration
equipment
A442 Gr. 60 -45 221 414 - 496 23
A516 Gr. 55 -45 207 379 - 448 27
A516 Gr. 60 -45 221 414 - 496 25
A516 Gr. 65 -45 241 448 - 531 23
A516 Gr. 70 -45 262 483 - 586 21
A517 Gr. F -45 690 792 - 931 16 Highly stressed ve
A537 Gr. A -60 345 483 - 620 22 Offshore drilling p
tanks, earthmovingA537 Gr. B -60 414 551 - 690 22
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Designation Lowest usual
service
temperature,
(C)
Min Yield
Strength (MPa)
Tensile
Strength (MPa)
Min
Elongation,
L0= 50 mm
(%)
U
A203 Gr. A -60 255 448 - 531 23 Piping for liquid p
A203 Gr. B -60 276 482 - 586 21
A203 Gr. D -101 255 448 - 531 23 Land-based storag
carbon dioxide, ac
ethylene
A203 Gr. E -101 276 482 - 586 21
A533 Gr. 1 -73 345 552 - 690 18 Nuclear reactor ve
ambient toughness
hydrostatic testingpetroleum equipm
A533 Gr. 2 -73 482 620 - 793 16
A533 Gr. 3 -73 569 690 - 862 16
A543 Gr. 1 -107 586 724 - 862 14 Candidate materia
toughness for heav
vessels
A543 Gr. 2 -107 690 793 - 931 14
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Ferritic cryogenic steels30
Ferritic cryogenic steels are nickel containing lo
steels designed to operate safely at temperatsubstantially below 0C and are characterizedgood tensile properties and high impact strengtemperatures.
The nickel content ranges from around 1.5 to 9although there are some fine grained carbon-manganese steels that may be operated attemperatures as low as -50C.
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These grades of steel are generally found and gas and petrochemical industries wher
are used for the handling and storage of lipetroleum gases (LPG) at temperatures dowapproximately -100C and, in the case of nickel steel, down to -196C.
They are also found in the gas processing infor the production and handling of gases sucarbon dioxide and oxygen.
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Some cryogenic steels32
Steel Type
Specification
(Plate)
Min service
temperature C
Typical stora
processing a
Fine grained Al killed C/Mn
steel
EN10028-3
P460NL2
-50 Ammonia, pro
1.5% Ni steel EN10028-4 15NiMn6 -60 Ammonia, pro
disulphide
2.5% Ni steel ASTM A203 GrB -60 Ammonia, pro
disulphide
3.5% Ni steel ASTM A203Gr E
EN10028-4 12Ni14
-101 Carbon dioxide
5% Ni steel EN10028-4 X12Ni5 -130 Ethylene (LEG
9% Ni steel ASTM A353/A553Tp1
EN10028-4 X8Ni9
-196 Methane (LNG
Austenitic stainless steel ASTM 304L
EN10088-1 1.4305
-273 Nitrogen, hydr
A l
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Applications33
The choice of which steel to use forany particular application depends
not only on the temperature but
also on such aspects as section
thickness required by design and
the possibility of stress corrosion.
W ldi f i
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Welding for cryogenic34
The applications of these steels require that th
mechanical properties, in particular the toughnwelds and their associated heat affected zoneor are very close to those of the parent metals
The fabrication of the cryogenic steels into pip
and vessels therefore requires careful selectionwelding consumables and close control of weldparameters.
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Manual metallic arc (SMAW) electrodes matchcomposition and Charpy-V impact strength of grained carbon manganese steels at -50C ca
obtained, for example, AWS A5.5 E7018-1 ealthough the addition of a small amount of nic1%, will give added confidence in achieving threquired toughness.
Matching C/Mn composition MAG (GMAW), f(FCAW) and submerged arc (SA) consumablesgive adequate toughness at -50C and requirprovide the required as-welded toughness.
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Natural gas is more efficiently stored and
transported in liquid phase, which involves t
the material to temperatures below -163 This requires economic and materials that w
at low temperatures, such as steel to 9% N
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This material has been developed to have g
toughness and impact resistance at low
temperatures to prevent the spread of cracductility and strength traction.
Metallurgy and weldability of the steel for
cryogenic applications, general welding an
precautions, need to be taken into account
a weld with this steel.
C i t ll
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Cryogenic metallurgy38
The most critical property of steels for cryogen
applications is their tenacity. Ferritic materials show a change in their mecha
behavior when exposed to low temperatures, amanifested by a reduction in the toughness of
characterized by a change from ductile to britbehavior as the temperature decreases belowcritical temperature of transition.
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This temperature can not be assessed on al
materials depending on their crystal structu
case of steels, this temperature is presentedferritic steels while not shown in the austenit
W ldi f t l t 9% i k l
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Welding of steel to 9% nickel40
Usually these steels are welded in the cond
after heat treatment.
The preparation of the board must be done
carefully, should be avoided sharp edges t
induce no magnetization in the plates.
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Surfaces must be carefully cleaned with ace
some organic solvent to remove contaminan
can cause defects in the weld.Aspects in the manufacture of welding:
Evaluation of the welding processes to use
Material supply to useWelding Procedure
Welding processes
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Welding processes42
Evaluation of welding processes to employ: W
processes such as submerged arc welding (SAWshielded metal arc welding gas (GMAW), arc electrode tungsten (GTAW) and coated electrowelding (SMAW) can be employed, however tSMAW process turns out to be a viable and fle
weld in any position or material and field. For these processes are commonly used basic
electrodes.
Filler material
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Filler material43
Input materials to vary from those of ferriti
high percentage of Ni (80Ni/20Cr/0.26C)are generally used in high temperature
applications.
Ferritic alloys around 12% Ni are cheap, bare not accepted for the sizes of storage ta
today.
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The primary objective in selecting the filler meget a counterpart to the base metal that is tenductile to reduce residual stresses in the HAZ (haffected zone) (elongation > 35%), and with acoefficient of thermal expansion low and similabase metal to prevent thermal fatigue in the u
Because the liquid natural gas tanks are subjec
continual expansion and contraction, the constathermal expansion filler materials should be simthe base material.
References
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References
W.D. Callister, Jr.. Fundamentals of Materials S
and Engineering, John Wiley & Sons, Inc., New2001
R.C. Reed: The Superalloys, Fundamentals andApplications, Cambridge University Press, Cam
UK, 2006. J.R. Davis: Heat-Resistant Materials, ASM Speci
Handbook, 1997.