Kuppan T. Heat Exchanger Design Handbook

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804

Table

Nickel Alloy Product

Forms

and Specifications [206,207]

Alloy

Nickel 200

MONEL alloy 400

MONEL alloy R-405

Monel alloy 450

Monel alloy K-500

INCONEL alloy 600

INCONEL alloy 601

INCONEL alloy 617

INCONEL alloy 625

INCO alloy C-276

INCONEL alloy 7 18

INCONEL alloy X-750

INCO alloy G-3

INCO alloy

INCOLOY alloy

800

INCOLOY alloy

800

INCOLOY alloy 825

INCO alloy 020

INCO alloy 330

Standard product forms

Round, flats, pipe, tube, plate, sheet, forging

stock, strip, and wire

Round, hexagon, flats, forging stock, pipe,

tube, plate, sheet, strip, and wire

Round, hexagon, flats, and wire

Round, hexagon flats, forging stock, pipe,

tube, plate, sheet, and wire

Round, hexagon, flats, forging stock, pipe,

tube, plate, sheet, strip, and wire

Round, hexagon, extruded section, flats, forg-

ing stock, pipe, tube, plate, sheet, strip,

and wire

Round, flats, forging stock, pipe, tube, plate,

sheet, strip, and wire

Round, forging stock, extruded section, plate

sheet, strip, pipe, tube, and wire

Round, flats, forging stock, extruded section,

pipe, tube, plate, sheet, strip, and wire

Round, forging stock, tube, pipe, plate, sheet,

strip, and wire

Round, flats, extruded section, pipe, tube,

forging stock, plate, sheet, strip, and wire

Round, flats, extruded section, forging stock,

plate, sheet, strip, pipe, tube, and wire

Round, plate, sheet, strip, pipe, tube, and

wire

Round, extruded section, flats, forging stock,

plate, sheet, strip, and wire

Round, flats, forging stock, pipe, tube, plate,

sheet, strip, and wire

Round, flats, forging stock, pipe, tube, plate,

sheet, strip, and wire

Round, flats, forging stock, pipe, tube, plate,

sheet, strip, and wire

Round, flats, forging stock, pipe, tube, plate,

sheet, strip, and wire

Round, flats, forging stock, pipe, tube, plate,

sheet, strip, and wire

Chapter

Spec.

ASTM(B)/ASME( SB

)

160-163, 366, B725,

B730

127, 163-165, 564

164, B165

1, 171, 359, 395, 466,

467, 543

Code Cases 1192, N-119

163, 166-168, 516, 517,

564, Code cases 1827,

N-20

B 166-B 168, Code Case

1500

166

443, 444, 446, 564,

B704, B705, B751,

Code Cases 1409,

N-

188

574, 575, 619, 622, 626

637, 670, Code Cases

N-

62, N-47, N-119

637, Code Cases N-62,

N-60, N-119

581, 582, 619, 622, 626

435, 572, 619, 622, 626

163, 407-409, 514, 515,

564, 751, Code Cases

1325

163, 407, 408, 409, 514,

515, 564, Code Cases

1987

163, 423-425, 424, 425,

B704, B705

462464,468

511, B512, 536, 535,

B546, 710

Material Selection

and

Fabrication

805

Table

ASTM Specification

for

Nickel

Alloy

Tubular Products

ASTM

Description

UNS No.

spec.

E3751

General

requirements

for

nickel

and

nickel

alloy

seam-

less and

welded

tubes

B163

Specification

for

seamless

nickel

and

nickel alloy

con-

N02200, NO220 1, N04400,

denser

and

heat

exchanger

tubes

N06600, N06690, N08800,

N08810, NO8825

B468

Welded

chromium-nickel-iron-molybdenum-copper,

co-

N08028, N08024, NO8026

lumbium-stabilized alloy

tubes

B5 15

Welded

nickel-iron-chromium

alloy

tubes

for general

N08800, NO88 10

corrosion

resisting

and

low-

high-temperature

ser-

vice

B5 16

Welded

nickel-iron-chromium

alloy

tubes

for

general

NO6600

corrosive

service

and

heat-resisting applications

B626

Welded nickel

and

nickel cobalt

alloy

tube

N10001, N10665, N10276,

N06455, N06007, N06975,

N08320, N06985, N06002,

N06022, N06030, N06059,

NO803

N30556, NO6230

B720

Seamless cold-worked

tubes

nickel alloy

for

use

NO8310

condenser

and

heat-exchanger

service

25.1

Galvanic Corrosion

The element nickel (passive) is nobler than iron and copper in the electrochemical series.

25.2

lntergranular Corrosion

Nickel-chromium alloys with carbon content above 0.2% exposed to temperatures between

1100 and 1500°F (593 to 816°C) will be sensitized, resulting in chromium carbide precipitation

in grain boundaries. This leaves areas adjacent to the boundaries low in chromium and suscepti-

ble to intergranular corrosion. Such corrosion can be counteracted in three ways [209]:

Select low-carbon alloy and consumables.

2. Select titanium- and columbium-alloyed base metal and welding consumables.

Solution anneal the weldment at 2000-2200°F (1093-1204°C) to dissolve precipitated

carbides.

25.3

Stress Corrosion Cracking

There is a possibility that welded joints in nickel-rich alloys will suffer SCC if in contact with

strong caustic soda, fluorosilicates, and certain mercury salts [79]. Nevertheless, nickel alloys

have very good resistance to

SCC

in alkalies and solutions containing chloride ions, definitely

much better than the austenitic stainless steels. Important information on SCC of nickel and

nickel-base alloys includes [177]:

(1)

low-carbon nickel (0.02% C max) is recommended for

use in contact with caustics if the service temperature is above 850°F (455"C), (2) nickel-iron

alloys and nickel-chromium-iron alloys containing upto

40%

nickel can fail by SCC on expo-

sure to hot chloride solutions, (3) sensitized Ni-Cr-Fe alloys containing higher amounts of

nickel may be subjected to polythionic acid SCC at ambient temperature, (4) aqueous solutions

806

Chapter

of mercury salts are found to produce cracking in highly stressed Ni-Cu alloys,

(5)

high-nickel

alloys are susceptible to SCC in aerated hydrofluoric acid vapors and in hydroflurosilicic acid,

and

(6)

in addition

normal measures, complete annealing of nickel welds and annealing

Monel

400

at 1100 to 1200°F

(595

650°C)

are recommended as a means of eliminating

residual stresses that could cause

SCC.

In hydrofluoric acid service, stressed alloy

400

should

not be exposed to aerated acid vapors.

NICKEL AND NICKEL-BASE ALLOYS: WELDING

The solid-solution-strengthened (non-age-hardenable) wrought nickel and its alloys can be arc

welded under conditions similar to those used in the arc welding of austenitic stainless steels.

The precipitation-hardenable (PH) alloys like Monel

K-500,

Inconel

700,

Alloy 7

18,

and

Inconel

X-750

require special welding procedures because of their susceptibility to cracking.

Residual welding stress and stress induced by precipitation cause cracking in the base metal

or heat-affected zone on aging or in service, at temperatures above the aging temperature. If

precipitation-hardenable alloys undergo any operation that introduces high residual stresses,

welding should be done after annealing.

26.1

Considerations While

Welding

Nickel

While welding nickel and nickel-base alloys, greater care such as precleaning and cleanliness

are required to prevent contamination-induced cracking or porosity, or embrittlement due to

sulfur and lead [209,210]. As nickel content increases, the weld puddle viscosity increases; the

coefficient of expansion decreases, as does weld penetration

[209].

Additional considerations

should include effect

minor elements on weldability, susceptibility to cracking in the weld

bead caused by high heat input or excessive welding speeds, and SCC of certain welded

structures in service. These welding considerations are discussed next.

Effects of Minor Elements on Weldability

Calcium and cerium are used as deoxidizers. Small additions of aluminum and titanium also

serve as deoxidizers. These elements tend to contribute to the formation of oxide films, and

slag spots on the weld surface. In multipass welding, such tenacious slag films should be

removed between passes to avoid weld defects.

Precleaning and Surface Preparation

Cleanliness is the single most important requirement for successful joining of nickel alloys

[210]. Welding, brazing, soldering, and any postheating must be performed only on base metal

that is clean and completely free of surface contaminations. Surface contaminations due to

manufacturing processes, like grease, oil, paint or lacquers, cutting fluids, machine lubricants,

marking crayons and inks, and shop dirt, must be removed completely either by chemical or

by vapor degreasing. Vapor degreasing or swabbing with perchloroethylene or other suitable

solvents can remove oil- or grease-base shop dirt. Paint and other materials not soluble in

degreasing solvents may be removed by methylene chloride, or alkaline cleaners. Alkaline

cleaners that contain sodium sesquisilicate or sodium carbonate must be removed prior to

welding. Wire brushing will not remove the residue completely. The best method is spraying

or scrubbing with hot water.

Surface Oxide Removal

Nickel oxide melts at a higher temperature than the base metal. Therefore, oxides should be

thoroughly removed from the surfaces to be welded because they can inhibit wetting and result

807

Material Selection and Fabrication

in lack of fusion. Oxides are normally removed by grinding with an aluminum oxide or silicon

carbide wheel or a carbide burr, machining, abrasive blasting, or pickling. Any cleaning tools,

including wire brushes and carbide burrs, should be clean and free from metals that may be

transferred to the base metal. Wire brushes used for cleaning should be made of austenitic

stainless steel. However, they will not remove tenacious surface oxides from welds. It merely

polishes the oxide.

Weld Metal Porosity

Surface contaminations, poor welding techniques, improper shielding, and the presence of hy-

drogen, carbon dioxide, nitrogen, and oxygen gases often cause porosity in nickel weldments.

To overcome this problem, electrodes/filler metals containing deoxidizers are a necessity. The

deoxidizers combine chemically in the molten weld with inorganic compounds, which then

float on the surface.

Joint Designs

Molten nickel-alloy weld metals do not flow and wet the base metal as readily as

carbon-

steel and stainless-steel weld metals. The operator must place the metal at the proper location

in the joint. Therefore, the joint must be sufficiently open to permit proper manipulation of the

electrode, and deposition of the weld beads. Suggested joint designs for butt joints in nickel

alloys (except submerged arc welding) are shown in Fig. 29.

Preheat and Interpass Temperatures

Guidelines on preheat and interpass temperatures are:

In general, preheat is not required for welding nickel base alloys. However, the area to be

welded should not be below about 60°F (16°C) to avoid moisture condensate that could

produce weld metal porosity.

The interpass temperature may be limited to 200°F (93°C). Cooling mediums used to

reduce interpass temperature should not introduce contaminants that will cause weld dis-

continuities. Examples are traces of oil in compressed air and mineral deposits from the

water spray.

Heat Input

High heat input during welding may result in constitutional liquation, carbide precipitation, or

other metallurgical phenomena. Some degree of annealing and grain growth can take place in

the heat affected zone. These, in turn, may cause cracking or loss of corrosion resistance, or

both.

Hot Cracking

Weldments of nickel base alloys are susceptible to liquation cracking or hot cracking. This

takes place particularly when welding conditions of high restraint are present, as in circumfer-

ential welds that are self-restraining. Therefore, all weld bead surfaces should be slightly con-

vex. Convex beads are virtually immune to center-line cracking; flat and concave beads are

particularly susceptible to center-line cracking. Excessive width to depth or depth to width

ratio can also result in cracking. Measures to overcome hot cracking include (1) limit heat input

during welding,

(2)

obtain fairly small grain sizes in the microstructures, and

(3)

minimize the

amount of deleterious minor elements such as sulfur and phosphorus that are known to cause

hot cracking.

Sulfur Embrittlement

Nickel combines with sulfur at elevated temperature to form a brittle sulfide. This phenomenon

takes place preferentially at the grain boundaries, and is exhibited when the material is stressed

808

Chapter

\("O"r

V-groovr

U~groovr

Ooublr

U-groove

Standard design

Drllled

for

root

gas

purge

UIiFICCEPTABLE

60"

leeo

\ /

BUTT

Figure

Nickel welding: (a) joint design except

SAW;

(b) groove in backup bar; and (c) acceptable

bead profile shape.

(From

Refs.

209

and 210.)

809

Material Selection and Fabrication

or bent. Nickel is the most affected, nickel-copper less, and nickel-chromium-iron the least.

Prior to carrying out any operation involving high-temperature operations such as welding,

brazing, hot forming, PWHT, etc., the surfaces should be cleaned throughly and should be free

from sulfur-bearing substances. For more details refer to ASME Code Section VIII, Div. 1,

NF-14.

Lead Embrit tlement

Lead causes embrittlement in all nickel-base alloys in much the same manner as sulfur. There-

fore lead-containing fluids or lubricants should be removed from the surfaces.

Design for Penetration

Nickel alloys give lower weld penetration than ferrous materials. Increasing amperage beyond

the recommended range will not significantly increase the penetration of the arc, but

will

cause harm. The harmful effects due to over amperages are [210]: (1) overheating of the

electrode and the resulting flux flaking off as heat breaks down the binder, and (2) puddling

of the molten weld metal and resultant loss of deoxidizers, leading to porous welds.

Welding Fixtures

Proper fixturing and clamping is required to hold the workpieces firmly in place, minimize

buckling, maintain alignment, and, when needed, provide compressive stress in the weld metal.

A backing bar or any portion of a fixture that might be contacted by the arc should be made

of copper. Since copper has high thermal conductivity, an inadvertent arc touch on the copper

will not result in fusion of the bar to the weldment. A groove in the backup or chill bar (Fig.

29b) allows weld metal penetration and avoids entrapment of gas or flux at the weld root

[210].

Good

Bead Shape

Increased puddle viscosity can cause poor wetting and lack of fusion along bead edges. With

low penetration in materials of high nickel content, the angle between the base metal and weld

bead edge should be greater than 100" to facilitate good tie-ins with subsequent beads [209].

Nickel alloy beads should be slightly convex. Avoid flat and concave beads. Susceptibility to

center-line cracking during solidification increases as flat or concave beads become stressed in

root passes [210]. Acceptable bead profile shape is shown

Fig. 29c.

Carbide Precipitation

Like some austenitic stainless steels, nickel-chromium and nickel-iron-chromium alloys with

carbon content above 0.2% exposed to temperatures between 1100 and 1500°F (593 to 816°C)

will be sensitized due to carbide precipitation in the weld HAZ. Such sensitization does not

result in accelerated attack in most environment. In general, carbide precipitation is overcome

by these measures [209]:

Use low-carbon base alloy and consumables.

Select titanium- or columbium-stabilized alloy base metal and consumable.

Solution anneal the weldment at 2000-2200°F (1093-1204°C) to dissolve carbide precipi-

tate.

Pitting Corrosion of Weldments

resist pitting and crevice corrosion, weldments must have smooth surfaces and be chemi-

cally homogeneous on a microscopic level. Molybdenum imparts pitting resistance to nickel-

chromium alloys. Use filler metal with sufficient molybdenum; even in the event of iron dilu-

tion, enough molybdenum will impart greater resistance to weld metal than that of base metal.

810

Chapter

For this reason, many base metals with

or 6% MO have been welded with filler metal such

as Inconel 112 (60% Ni) electrode and Inconel 625 filler metal, both containing

[209].

Strain Age Cracking

Most of the

precipitation-hardenable

alloys are susceptible to strain age cracking. Alloys con-

taining columbium have a better resistance to cracking because of the slower hardening re-

sponse of the columbium precipitate than the aluminum or titanium precipitate.

26.2 Welding

Methods

Typical arc welding processes employed for welding nickel and nickel base alloys are

gas

tungsten arc welding (GTAW), gas metal arc welding (GMAW), and shielded metal arc weld-

ing (SMAW). Submerged arc welding (SAW) and plasma arc welding (PAW) have limited

applicability. The GTAW process is preferred for welding the precipitation-hardenable alloys,

although GMAW and SMAW can also be used. Reference 21 1 details the welding of nickel

and nickel-base alloys.

Gas Tungsten Arc Welding

GTAW is widely used for joining thin sections of nickel alloys, for the root pass of pipe

welds, and where flux residues are harmful. This process is the principal welding method for

precipitation hardenable alloys. Argon, helium or a mixture of the two are the recommended

shielding gases. Since presence of oxygen, carbon dioxide or nitrogen cause porosity

the

weld metal, they should be avoided. GTAW usually requires shielding of the weld root. If a

complete penetration weld is made in the open, the weld metal exposed on the underside of

the bead will be oxidized. Various shielding methods employed to protect the rootside include,

grooved backup bars, inert gas backup shielding, and a backing flux.

Shielded Metal Arc Welding

SMAW is primarily used for welding commercially pure nickel and solution-strengthened

nickel alloys 1/16 in (1.6 mm) thick and over. The

precipitation-hardenable

alloys are seldom

welded with SMAW process, because the alloying elements that contribute to precipitation

hardening are difficult to transfer across the arc.

Gas Metal Arc Welding

GMAW is used

weld the solution-strengthened nickel alloys except high-silicon casting

alloys. Many precipitation-hardenable alloys may also be welded. Spray, pulsed spray, globu-

lar, or short-circuiting filler metal transfer may be used. The protective shielding gas is usually

argon or argon mixed with helium. Use dcrp for all methods of metal transfer with GMAW.

Submerged Arc Welding

Submerged arc welding (SAW) can be used for joining

solid-solution-strengthened

nickel

alloys. Monel

400

is mostly welded by this process.

is especially useful for welding thick

sections. SAW uses dc with sp or rp. SAW process cannot be used for welding the precipita-

tion-hardenable alloys.

Oxyacetylene Welding

The oxyacetylene flame is the only gas flame that burns hot enough, 5000-6300°F (2760-

3482"C),

to join nickel alloys. Oxyacetylene welding gives good results in all welding posi-

tions. It is a cheap process. To weld nickel-base alloys, use a slightly reducing flame.

strongly reducing flame is not recommended when welding nickel alloys containing chromium,

to avoid carbon pickup in the weld. Oxidizing flame is not recommended to weld (1) nickel-

Material Selection and Fabrication

copper alloys, because, the oxidizing flame forms cuprous oxide, which dissolves

the molten

metal, which causes weld brittleness and reduces corrosion resistance, and (2) high-chromium

alloys, because an oxidizing flame produces chromium oxide that is not readily soluble

the

flux [211].

26.3 Postweld Heat Treatment

Nickel and nickel-base alloys generally do not experience any metallurgical changes, either

the weld metal or

the heat-affected zone, that affect normal corrosion resistance. Hence, no

postweld heat treatment is normally required. However, heat treatment may be necessary in

circumstances such as

(1)

to meet specification requirements, or (2) for stress relief of a welded

structure to avoid age hardening or SCC of the weldment used to contain hydrofluoric acid

vapor or caustic soda. If welding induces moderate to high residual stresses, the precipitation-

hardenable alloys require a stress-relief anneal after welding and before aging.

27 TITANIUM: PROPERTIES AND METALLURGY

Titanium is a reactive, nontoxic, and low-density metal. Titanium and its alloys are used in

major applications for which their inherent properties justify their selection: (1) for corrosion

resistance, and (2) where specific strength is of major advantage. Titanium “bridges the design

gap” between aluminum and steel, and offers a combination

many of the most desirable

properties of each. Its light weight with specific gravity lying between aluminum and steel

(approx. 60% of steel) gives a high strength-to-weight ratio. For example, the strength-to-

weight ratio for annealed Ti-6A1-4V (grade

is about 7.81 (density is 0.160 lb/in7 and yield

strength is 125 ksi), whereas

is about 1.25 for annealed stainless steels. Increases

strength,

as with other materials, are achieved by the addition of alloying elements such as Al, Cu,

MO,

Si, V and Zr. It is known for its excellent corrosion resistance due to a stable, tenacious oxide

film formed on its surface. Corrosion failures with titanium are rare and usually associated

with weld defects. All titanium alloys contain minute amount of interstitial elements such as

carbon, oxygen, nitrogen, and hydrogen.

27.1 Properties that Favor Heat-Exchanger Applications

The combination of high strength, stiffness, good toughness at cryogenic temperature, immu-

nity to corrosion in wet chlorine, excellent corrosion resistance to many chemicals, and erosion

resistance allows widespread use of titanium and titanium alloys from cryogenic (-423°F) to

moderately high temperature (1000’F). Titanium is used as heat-exchanger material

chemi-

cal industries, refinery, absorption refrigeration and air conditioning, refinery heat exchangers,

brine heat exchangers, desalination plants, power-plant surface condensers, and auxiliary ex-

changers. Titanium finds its widest use in chemical process industries as process equipment,

wet scrubbers, heat exchangers, valves, pumps, and piping systems. Almost all nuclear stations

the world over have standardized on the use of titanium as tube material. It is available

various product forms including sheets, plates, cladded plates, pipes, tubes, including U-bend,

and enhanced tubes (integral fin tube, applied fin tube, and corrugated and rope tube).

The arguments against titanium are its high price, high quality standards, sensitivity to

fouling, corrosion fatigue, and possibility of hydrogen embrittlement if cathodic protection in

excess is applied

[

1091. For fixed-baffle spacing, titanium tube heat exchangers are susceptible

to flow-induced vibration due to its low modulus

elasticity and the use of thin-walled sec-

tions for cost considerations. However, this can be overcome by reducing the baffle spacing.

Chapter

27.2

Alloy

Specification

Titanium specification and grades include Grade 1, Grade 2, Grade

Grade 4, Grade

Grade

Grade 7, Grade

Grade 11, and Grade 12. Grades 1, 2,

and 4 apply to commercidly

pure titanium

(98.5

99.5%)

and differ in the amounts of interstitials like oxygen, nitrogen,

carbon, and iron. By varying these interstitials elements, the unalloyed titanium grades can be

strengthened. The higher the grade, the greater is the amount of oxygen and the greater is the

metal's strength. Grades

7, 11, and 12 are titanium alloys. Various ASTM grades, alloy

designations, compositions, and metallurgical phases present are given in Table

46;

characteris-

tics and applications areas are given in Table 47. An important source book on titanium is the

Titanium Handbook

[212]; also see Schutz et al. [213].

27.3 Titanium Grades and

Alloys

Unalloyed Grades

Pure titanium has low tensile strength and is extremely ductile. Dissolved oxygen and nitrogen

markedly strengthen the metal, and carbon and iron to a lesser extent. Grade

is purer and

therefore more ductile, and finds use where severe forming is required; Unalloyed titanium

mill products of Grade

most widely used and more ductile, find use where severe forming

is required; this grade has outstanding resistance to general and other forms of corrosion in

many environments, but it is not resistant to crevice corrosion

[

1051. Grade

provides slightly

higher strength due to its higher percentage of interstitial elements [215].

Alloy Grades

Titanium is not as widely used in the alloyed form in chemical process industries, the

exception being titanium-0.2% palladium alloy (Grade 7) to enhance corrosion resistance

in mildly reducing solutions and high-temperature chloride solutions. Typical applications

extend to hydrochloric, phosphoric, and sulfuric acid solutions and areas of service where

the operating conditions

vary

between oxidizing and mildly reducing conditions

[

114,

161. The presence of palladium has no other significant effect on the physical or mechani-

cal properties of titanium and it makes titanium costlier.

Table

Titanium Grades, Composition, and Structure

Grade UNS no. Description Phase

Grade

50250

Unalloyed titanium

Grade 2

50400

Unalloyed titanium

Grade 3

50550

Unalloyed titanium

Grade 4

50700

Unalloyed titanium

Grade

56400

Ti-6A1-4V

a-P

Grade

56401

Ti-6A1-4V

ELI"

a-P

Grade 6

54520 Ti-5A1-2.5Sn

Grade 6

54521

Ti-5A1-2.5Sn

ELIa

Grade

52400

Ti-0.20 Pd

Grade

56320

Ti-3A1-2.5 V

Near

Grade

52250

Ti-0.20 Pd

Grade 12

53400

Ti-O.3Mo-O.8Ni

Near

'Extra-low interstitials grade.

52550

and

52700

are titanium alloy

castings.

Material Selection and Fabrication

Table

General Characteristics of Titanium Alloys, and Applications

141

Alloy General characteristics

Applications

Grade

Highest purity, lowest strength and

Used in continuous service up to

high ductility, cold formability,

425°C (800°F) and for plate heat ex-

good corrosion resistance among the

changers (PHE).

four ASTM unalloyed grades due to

low interstitials.

Grade 2

Workhorse for industrial applications

Continuous service up

425°C

requiring good ductility and corro-

(800°F)

and

intermittent service

sion resistance. Minimum yield

540°C (1004°F). Piping, tubu-

strength of 275MPa, which is com-

lar heat exchangers, values, tanks,

parable

those of annealed austen-

vessels.

itic stainless steels.

Grade

Lower iron limits than Grade 4. Im-

Same as Grade 2. Higher strength than

proved strength with reasonable duc-

Grade

Tubesheets and valves.

tility, good corrosion resistance.

Grade

Highest strength of the unalloyed

Often used interchangeably with Grade

ASTM grades. Moderate formabil-

The strength-to-weight ratio is

ity, outstanding corrosion and fa-

higher than

301

stainless steels up

tigue resistance in saltwater.

15°C (600°F). Tubular heat ex-

changers, piping, vessels.

Grades, 7 and

Better resistance to crevice corrosion

Special corrosion application. Tubular

at low pH and high temperature

heat exchangers, vessels, valves, gas-

than corresponding unalloyed

Grades

and 2.

keted plate heat exchangers.

Grade 12

Stronger and more resistant to crevice

Application requiring moderate

corrosion at higher temperatures

strength and enhanced corrosion re-

than unalloyed Ti grades. Less ex-

sistance such as heat exchangers,

pensive than Grades

and 1

but it

does not offer the same crevice cor-

rosion resistance at low pH (pH

3).

pressure vessels, chlorine cells, and

salt evaporators.

In near neutral brines, crevice corro-

sion resistance are similar to Grades

and 11.

Grade

50%

higher strength than unalloyed

Excellent cold formability and

Used in tubular forms.

Grade 6 A medium-strength alloy with excel-

lent weldability. It has good oxida-

The primary use is for cryogenic appli-

cations, in which the EL1 grade has

tion resistance and intermediate

strength at service temperatures up

good strength and toughness for low

temperature. It has been replaced by

to 480°C (896°F).

Grade

(Ti-6A1-4V)

other appli-

cations.

Grade

It is the most widely used Ti alloy.

The alloy is most commonly used in

ses.

Aeorspace industry, medical prosthe-

the annealed condition. It is harden-

able in sections up to 25.4 mm (1

in) with yield strengths

high as

140 MPa (165 ksi).