7. Low Alloy Steels for Cryogenic Applications

7/29/2019 7. Low Alloy Steels for Cryogenic Applications

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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.

7. Low Alloy Steels for Cryogenic Applications

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