aterials are selected on the basis of service requirements, no-tably strength, so corrosion resistance (stability) may not bethe primary design consideration. Assemblies need to be strongand resilient to the unique loads and stresses imparted on them,

which can include significant temperature changes and thermal gradients formany high-temperature applications.

In making a choice, it is necessary to know what materials are availableand to what extent they are suited to the specific application. The decision isquite involved and the choice is significantly affected by the environmentand the intended use, be it a reactor vessel, tubes, supports, shields, springs,or others. Some problems may occur because of distortion and crackingcaused by thermal expansion/contraction; typically, a high-temperature alloymight change 4 in./ft from ambient to 1,000°C (1,832°F).

The user or designer needs to properly understand that the environmentdictates the materials selection process at all stages of the process or applica-tion. For example, an alloy that performs well at the service temperature maycorrode because of aqueous (dew point) corrosion at lower temperatures dur-ing off-load periods, or through some lack of design detail or poor mainte-nance procedures that introduce local air draughts that cool the system (e.g.,at access doors, inspection ports, etc.).

To provide as optimum performance as possible, it is necessary for a sup-plier to be aware of the application, and for the user to be aware of the gen-eral range of available materials. Otherwise, severe problems can result. Forexample, a catastrophic failure occurred within weeks for an ignitor, madewith Type 304 stainless steel (UNS S30400, iron, 19% Cr, 9% Ni, 0.08% C).Type 304 stainless steel would have been suitable for clean oxidizing condi-

CEP February 2001 www.aiche.org/cep/ 75

Materials

High temperatures,stresses, and the presence of elements such asoxygen, sulfur, orthe halogens canadd up to trouble.Here is how toscreen candidate alloys for such service.

Peter Elliott,Corrosion & MaterialsConsultancy, Inc.

Choose Materials forHigh-Temperature Environments

Choose Materials forHigh-Temperature Environments

To join an online discussion about this article

with the author and other readers, go to the

ProcessCity Discussion Room for CEP articles

at www.processcity.com/cep.

<Discuss This Article!>

M

Based on a paper presented at CORROSION/2000 (NACE International 55th Annual Conference and Exhibition), Mar.26–31, 2000, Orlando, FL, USA. © NACE International. All rights reserved.

76 www.aiche.org/cep/ February 2001 CEP

Materials

tions to about 900°C (1,650°F) incontinuous service, or 845°C(1,550°F) in intermittent (temperaturecycling) service (1). The failure oc-curred because of overheating withcontributions from sulfidation (hotcorrosion). The true cause of failurewas a material mix-up, because Type304 was not specified, but was inad-vertently used.

Mechanical limits of materialsIn considering traditional alloys, it

is important for the designer and userto be fully aware of the mechanicallimits of a material. For example, theASME Pressure Vessel Codes advisethat the maximum allowable stressshall not exceed whichever is thelowest of: (i) 100% of the averagestress to produce a creep rate of0.01% in 1,000 h; (ii) 67% of the av-erage stress to cause rupture after100,000 h; and (iii) 80% of the mini-mum stress to cause rupture after100,000 h.

These recommendations may bebetter appreciated by extracting typi-cal data for Type 304 intended for usein a pressure vessel up to 815°C(1,500°F). Based upon ASME tables,for a load of 17 MPa (2.5 ksi) at760°C (1,400°F), the expected designlife would be 24 yr; at 788°C(1,450°F), the life falls to 7 yr; and at815°C (1,500°F), it is only 2.2 yr.Thus, a short-term temperature excur-sion can have a significant effect onequipment life. Also to be noted isthat a small increase in loading, forexample, from 2.5 to 3 ksi at 760°C(1,400°F), can markedly reduce thelife expectancy, here, from 24 to 9 yr.

Overheating is the most commoncause of high-temperature corrosionfailure, but the temperature influenceon mechanical properties is of equalor even more significance in thatmany failures occur because of creepdeformation (creep voids) and ther-mal fatigue. Overheating can arise forvarious reasons, including an unex-pected accumulation of tenacious de-posits that can foul tubes in a heat exchanger.

High-temperature alloys and uses

High-temperature alloys are typi-cally iron-, nickel- or cobalt-based al-loys containing >20% chromium (or30% for cobalt), which is sufficient toform a protective oxide against fur-ther oxidation. The basic alloys in-clude various additional elements thataid in corrosion resistance, notablyaluminum (typically >4% to developan alumina scale), silicon (up to 5%to develop an amorphous (glass-like)scale that is complementary to chro-mia), and rare earth elements (typi-cally <1%, e.g., yttrium, cerium, andlanthanum, that improve scale adhe-sion). Other additions, such as the re-active metals, the refractory metals,and carbon, primarily improve me-chanical properties. The beneficialand detrimental roles of common al-loying elements on the anticipatedperformance of alloys at high-temper-atures is covered by Agarwal andBrill (2).

Refractory metals — Molybde-num, which is a beneficial additionfor resisting aqueous chloride-in-duced pitting corrosion (found inTypes 316 and 317 stainless steels,and the 6%-Mo alloys), is prone tocatastrophic oxidation as tempera-tures exceed about 700°C (1,292°F),the point above which MoO3 formseutectic mixtures with iron, nickel,and chromium oxides. The oxideMoO3 melts at 795°C (1,462°F°).

Catastrophic oxidation rapidly ren-ders a metal into a useless powderyoxide. Damage is worse in stagnantconditions and appears to be exacer-bated when sodium oxide is present(e.g., from insulation). All of the re-fractory metals (tungsten, tantalum,niobium, and molybdenum) may ex-perience catastrophic oxidation. Sili-cide coatings have shown some tooffer some resistance to this catas-trophic (“pest”) oxidation.

Coatings — High-temperaturecoatings or surface modifications aregenerally based on chromium, alu-minum, or silicon, which, at hightemperatures, form protective oxides

rich in chromia, alumina, or silica, re-spectively. In more recent years, therehave been developments in applyingso-called alloy coatings, for example,the use of MCRALY (metal, chromi-um, aluminum, and yttrium) on steelsor other high-temperature alloy sub-strates. Efforts have also continued inweld overlay work, where a strongbase metal can support a corrosion-resistant surface-coated layer.

Applications — In consideringmaterials options, a thorough knowl-edge of the service applications(stress-bearing service; cyclic loadingor not; frequency of cycling; impactor erosion effects; thermal expansionand contraction) is needed.

Different high-temperature corro-sion processes are simultaneously in-volved in many common service ap-plications. Some of these are syner-gistic, which creates a formidablechallenge for users and alloy produc-ers. Some examples of the forms as-sociated with various applications aregiven in Table 1 (3, 4).

Types of high-temperaturecorrosion

There are certain distinguishingfeatures about the morphology ofhigh-temperature corrosion that aid indeciding upon the cause of damage.Some typical indications includethick scales, grossly thinned metal,burnt (blackened) or charred surfaces,molten phases, deposits of variouscolors, distortion and cracking, andmagnetism in what was first a non-magnetic (e.g., austenitic) matrix.

Damage varies significantly basedupon the environment, and will bemost severe when a material’s oxida-tion limits are exceeded, notablywhen an alloy sustains breakaway at-tack by oxygen/sulfur, halogen/oxy-gen, low-melting fluxing salts, moltenglasses, or molten metals, especiallyafter fires.

OxidationMany industrial processes involve

oxidation, i.e., a metal reacts in air toform and sustain a protective oxide.

CEP February 2001 www.aiche.org/cep/ 77

There can be several oxide products,some of which are less desirable, forexample, wustite, a defective oxide ofiron that forms rapidly at about540°C (1,000°F) on steel.

Most high-temperature alloys areoxidation resistant, so price, availabil-ity, experience, and the type of appli-cation usually dictate choice. Thereare no significant problems up to400°C (750°F), few up to 750°C(1,380°F), but the choice of success-ful alloys becomes somewhat limitedabove about 800°C (1,470°F).

Simple iron-chromium (or iron-chromium-molybdenum) alloys be-come less useful as service tempera-tures increase, which is where theType 300 series austenitic stainlesssteels, (304, 309, 310, 314, 330, 333,etc.) and certain ferritic stainlesssteels (410 and 446) find many appli-cations. For more arduous serviceconditions at higher temperatures,these alloys are surpassed by nickel-or cobalt-based formulations, includ-ing many of the more robust alloysthat are mechanically alloyed to im-

prove strength and to control (that is,minimize) grain growth at elevatedtemperatures.

Certain alloys (usually those withrare earth additions) are more re-silient to oxidation under thermal cy-cling (shock) conditions. Some appli-cations do not allow an alloy to fullydevelop its steady-state condition,thus, performance is dictated by thetransient (not-so-protective) surfacescales. Transient effects will becomeapparent should failure analysis beperformed.

Caution should be given to iron-chromium-nickel alloys that can beprone to sigma-phase formation be-tween 540–800°C (1,000–1,470°F),which results in premature brittle fail-ure. Molybdenum-containing alloys(Types 316 and 317 stainless steelsand the 6%-Mo alloys) can be proneto catastrophic oxidation above about680°C (1,256°F).

SulfidationSulfurous gases are common to

many applications, including fuel

combustion atmospheres, petrochemi-cal processing, gas turbines, and coalgasification. Sulfides (e.g., sulfurvapor, hydrogen sulfide) can be verydamaging, because metal sulfidesform at faster rates than do metal ox-ides. Sulfides have low melting pointsand produce voluminous scales (scalespallation).

With mixed corrodant environ-ments (oxygen and sulfur), alloy per-formance is based upon a subtle inter-play between oxide and sulfide for-mation. Oxides are more stable; sul-fides form more rapidly (due to kinet-ics). Thus, oxides, sulfides, or bothmay form. If deposits are also pre-sent, then conditions at the metal sur-faces are reducing compared to areasexternal to the deposits. Damage canbe extensive.

Mixed sulfur-and-oxygen gasescan invoke very high corrosion ratesdue to breakaway attack, typicallyabove about 600°C (1,110°F) fornickel-based alloys, 920°C (1,688°F)for cobalt-based, and 940°C (1724°F)for iron-based formulations. Break-

Table 1. Typical process conditions causing corrosion.Process or Components Temperature Type(s) of corrosion

O S C Cl F N Slag Melt OthersSteam reforming tubes To 1,000°C • •Steam cracking tubes: ethylene To 1,000°C • •Vinyl chloride crackers 650°C •Hydrocrackers: heaters 550–600°C • •Coke calcining recuperators 815°C • • •Cat cracking regenerators To 800°C •Flare-stack tips 950–1,080°C • • • Cl2; marine corr.CS2 furnace tubes 850°C • • DepositsMelamine/urea reactors 450–500°C •Reactors in Ti production 900°C • •Nitric acid: catalyst grids 930°C • • •Linings for Al pyrohydrolysis To 1,000°C • • •Nuclear processing reactors 750-–800°C • •HTGR* (gas-cooled) reactors 750–950°C •Oil-fired boilers/superheaters 850–900°C • • • • Fuel ash attackGas-turbine blades 950+°C • • • • • DepositsWaste incinerators 470–500°C • • • • • • Liquid metals; depositsFluidized-bed combustors >600°C • • • • • High-Cl coalGlass: recuperators 1,090°C • • • •Hot-dip galvanizing 455°C • Molten Zn

* HTGR is high-temperature gas reactor.

away attack is commonly associatedwith sulfur and excess air. Once thefirst-formed oxide is lost or de-stroyed, sulfides can invade thechromium-depleted substrate, thus,causing accelerated attack to occur.

Stainless steels and iron-based al-loys are preferred over high-nickel al-loys, because nickel is prone to form-ing the low-melting nickel-nickel sul-fide eutectic, Ni-Ni3S2, which melts at635°C (1,175°F). Eutectics of cobaltand iron occur at higher temperatures,880°C (1,616°F) and 985°C(1,805°F), respectively.

Alloys can be weakened by inter-nal corrosion, most noticeably whenmobile species are present, such aslow-melting sulfides, which are typi-fied by localized dull uniform grayphases within the alloy matrix. Attimes, liquid-appearing phases arefound in the metallurgy.

Alloys containing aluminum, sili-con, and cobalt are useful in sulfidiz-ing environments. Many alloys classi-fied as candidates for sulfidation dowell only if oxides are first able toform. Preoxidation can be of value.

HalogenationHalogen attack is commonly man-

ifested as a combination of scale spal-lation with internal alloy damage in-cluding voids that form as a result ofhighly volatile species (5). Material

performance is dictated by the uniqueproperties of the halides, includinghigh vapor pressures, high volatility(vaporization), low melting points,mismatched expansion coefficientswith metal substrates, and the effectsof displacement reactions wherebyoxide or sulfide are thermodynami-cally favored over the halides.

Alloy performance is greatly af-fected by oxidizing or reducing con-ditions. For oxidizing atmospheres orfor vapors jointly present with oxy-gen (or air), there is an opportunityfor reduced corrosion rates (kinetics)associated with oxide formation, al-though the scale may later be disrupt-ed by the volatile halides, especiallyif iron-based alloys are used. Nickelalloys are generally favored for halo-gen atmospheres, since iron-based al-loys are more vulnerable, due to theirvolatile products, e.g., FeCl3. Siliconadditions are useful if oxidizing envi-ronments prevail, but not for reducingconditions. Preoxidation is not nor-mally a benefit for reducing halogenattack.

What makes halogens differentfrom other oxidants is their high mo-bility and diffusivity into a metal, re-sulting in internal damage of thealloy matrix. Fluorine can penetratetwice the distance of chlorides,which means that the predominantmode of damage in fluorine-contain-

ing gases is by means of internal attack. Halide products are also hygro-

scopic (3), so it is not unusual to dis-cover local protrusions on a metalthat have been removed during ser-vice. In laboratory studies, it is com-mon to find that a surface apparentlyfree from chlorides (removed duringmetallographic preparation) is laterfound to show them. This is becausethe chlorides have been leached outfrom deep under the voided areas inthe metal.

CarburizationSeveral environments are synony-

mous with carburization, includingpyrolysis and gas-cracking processes,reforming plants, and heat-treating fa-cilities that involve carbon monoxide,methane, and hydrocarbon gases.Damage is usually manifested as in-ternal carbides, notably in grainboundaries and is generally worstabove 1,050°C (1,922°F). When car-burizing conditions alternate with ox-idizing ones, carbides can becomeoxidized to oxides, which yields car-bon monoxide that can weaken thegrain boundaries in an alloy. Such analloy fails by “green rot,” a name thatdescribes the green fractured surfacethat results (chromium oxide).

Strongly carburizing atmospheres(i.e., those that have a carbon activity>1) can cause a metal to form coke-like layers, often of a dusty form.This form of attack, termed metaldusting, commonly occurs between425–800°C (790–1,470°F) and can bevery rapid (in days not months).Damage is either general or localized(pitting), as dictated by the ability ofthe alloy to form a surface oxide (6).

Materials

78 www.aiche.org/cep/ February 2001 CEP

Above: Tube failure due to local overheating.

Left: Burst tube walls due to overheating.

Carbon steels and alloy steels arenormally uniformly thinned by metaldusting; more highly alloyed materi-als usually display local outgrowthsof coke emerging through small pitsthat broaden with time.

Cast iron-nickel-chromium alloysare widely used for carburizing appli-cations, including the more recent al-loys containing 1–2% silicon and1.5% niobium (the HP Mod alloys)(4, 6). High-nickel alloys (with lowsolubility for carbon) find many ap-plications for carburizing conditions.Stronger nickel-based alloys withhigh chromium and silicon contentsare useful in more demanding envi-ronments. Highly alloyed ferriticstainless steels (that are able to morerapidly form a thin oxide film) tend tooutperform austenitic steels.

NitridingRelatively little is reported about

nitridation other than material perfor-mance is weakened (embrittlement)as a result of the formation of internalnitrides in the alloy (4). It is commonto expect damage with nitrides at700–900°C (1,290–1,650°F). Nitridesappear generally as needle-like pre-cipitates in the alloy matrix.

Nickel- and cobalt-rich alloys ap-pear to be first-choice candidates forresisting nitride attack, because of thelow solubility of nitrogen in these

base metals. Iron tends to be detri-mental, as do aluminum and titaniumin low concentrations. Silicon forms abrittle intermetallic compound withnitrogen and can contribute to scalespallation, especially in applicationsat low oxygen concentrations (poten-tials), where thin oxides can form,and during thermal cycling.

Molten productsDeposits are a common product in

many high-temperature applications,including boilers, waste incinerators,fluidized-bed combustors, and gasturbines. A whole series of reactionsis possible should deposits becomemolten and no single mechanism canbe applied generally to characterizesuch damage (7).

The mechanisms of molten prod-uct corrosion are complex. The typesof damage include fuel-ash corrosion— sulfates, including acid and basicfluxing reactions (8), and vanadicslag attack (9) — molten salt corro-sion (chlorides, nitrates, and carbon-ates) (4), and molten glass corrosion.Liquid metal attack is yet anotherspecial category (4).

Fuel-ash or ash/salt-deposit cor-

rosion stems from high-temperaturecorrosion processes associated withfuel combustion products in boilers,waste incinerators, and gas turbines.Thus, products can include variousdeposits (oxidizing or reducing) withactive contributions from oxygen,sulfur, halogens, carbon, and nitrogen(4, 7). Typically, alloy matrices dis-play intergranular attack (oxides andchlorides) beneath disturbed oxidelayers possibly fused with molten de-posits and internal sulfides within thealloy-affected zone.

Hot corrosion is generally regardedas attack in the joint presence of sulfurand oxygen. Typically, attack is consid-ered to be triggered by molten alkalimetal salts that melt above 700°C(1,290°F). Sodium sulfate, with a melt-ing point of 884°C (1,620°F), derivedfrom sodium chloride and sulfur fromthe fuel, is considered to be closely in-volved in the mechanism of hot corro-sion (8). This mechanism is consideredto have four stages: oxidation (incuba-tion); mild sulfidation; oxide failure;and catastrophic attack (internal sul-fides via a porous voluminous complexoxide/deposit layer). Hot corrosion isan irreversible autocatalytic process.

CEP February 2001 www.aiche.org/cep/ 79

Above: Thermal fatigue crack in boiler tube. Top: Tube fouling in anincinerator plant due to

carryover of deposits.

Bottom: Through-metalperforation in tubing from a

carbon black plant.

Materials

80 www.aiche.org/cep/ February 2001 CEP

Table 2. Guide to candidate materials.

Corrosion Mode Basic Alloy Types Candidates* Notes and Cautions

Oxidation Fe-Ni-(Co) >20% (30%) Cr. 304, 321,309, 310, 800(HT), 803, Wide choice dictated byStabilized to minimize 430, 446,HR120, 330, 85H, 333, application and function;sensitization. Al, Si beneficial. 600, 601(GC), 602CA, 617, 625, Mechanical properties; Rare earth additions aid scale 253MA, 353MA, DS, 214, MA956, Thermal cycle (shock);retention. MA754, X, etc. Transient vs. steady state;

Internal oxides. Beware σ;W, Mo — catastrophic oxidation.

Sulfidation Fe- with high Cr (Al) alloys. 9–12%Cr steels: 309, 310, 330, Sulfur vapor, H2S, etc. — (Reducing gases 800(HT), 803, HR120, 85H, no oxides. Beware of Ni/Ni3S2no oxides) 253MA, 353MA, MA956, 446, 671, eutectic; coatings can help.

6B, 188, etc.

Sulfidation Fe-Cr-based alloys. Oxide As above with 153MA, 601, HR160, SO2, SO3 , etc. — risk of(Oxidizing gases) formation a benefit. MA754, MA956, 333, 556, etc. breakaway attack with oxides

Preoxidization may help. and sulfides; Al coatings. (See hot corrosion.)

Carburization Wide use of cast alloys. HH, HK, HPMod, 309, 310, 330, 333, Internal carbides withFor worse conditions, use 85H, 800(HT), 803, DS, HR160, 600, intergranular attack; Casthigh-Ni alloys with Cr, Si. 601, 253MA, 602CA, 617, 625, 690, tubes benefit from smooth(Low solubility of C in Ni is MA754, MA956, X, 556, 706, 718, I.D. surfaces.benefit for Ni alloys.) 750, etc. Metal dusting (at lower

temperatures). Green rot (with intermittent O2-C).

Nitridation Ni-alloys rather than Fe. Avoid 309, 800(HT), 330, 446, 188, 230, Internal nitrides (e.g., AlN) can high Cr levels. Use low Al and 600, 602CA, 625, 253MA, etc. weaken alloy; Thin oxide at lowlow Ti levels (nitride formers). oxygen partial pressure Si promotes scale spalling. reduces nitridation.

Halogenation: Ni alloys generally better 800H, 333, 200, 201, 207, 600, Volatile products; Internal chlorination, than Fe. Benefits: Cr (not HF), 601, 602CA, 214, N, H242, B3, etc. attack with voids;fluorination, etc. Al, Si (with oxygen). Hygroscopic products

Preoxidation not beneficial. (e.g., chlorides); Scale spallation.

Fuel ash corrosion FeCrMo alloys at lower 309, 310, 800(HT), 600, 601, 602CA, Applications dictate alloy,temperatures; CRAs† for S, O, 625, 825, 253MA, 353MA, MA754, or coating: Gas turbinesC — subject to application. MA758, MA956, IN657, 671, etc. (strong + CRA†); vanadicHigh Cr, Al, Si useful (also slag (high-Cr + Si).as coatings).

Molten salts Ni alloys generally favored; As with halogens, sulfidation: Intergranular attack,some high-Cr alloys; depends on nature of salts internal voids, andNiCrMoW alloys for molten (acidic/basic). probable embrittlement. chlorides.

Molten glass Ni- or some Co-/high-Cr 600, 601, 602CA, 671, 690, Complex fluxing reactions;alloys; Some refractories. MA758, etc. oxidation; sulfidation;

chlorination; fluorination, etc.

Liquid metals Fe-alloys with Cr, Al, Si 309, 310, 85H, 253MA, etc. Dissolution or alloying effects;usual first choices (subject to Intergranular attack;liquid metal, e.g,. Liq. Na, K, Depends on system.molten Zn, Pb, etc.)

Complex Synergy of processes. CRAs† or coatings Seek input from suppliers; Environments Consider online tests/monitoring.

Note: This is a general, not exhaustive, guide.

* Not in any preferred order.† CRAs are corrosion-resistant alloys.

Vanadic slag corrosion occurs fol-lowing combustion of certain low-grade or residual fuel oils that are ofhigh vanadium, sulfur, and alkalimetals. The molten sodium vanadylvanadates typically flux away protec-tive oxides and then rapidly dissolvethe metal. Many high-temperature al-loys cannot survive 100 h at 900°C(1,652°F) in vanadic slags (9).Vanadic attack can be managed bylowering temperatures (if possible),using fuel-oil additives (such as mag-nesium and calcium oxides), or byspecifying high-chromium alloys. Sil-icon-rich coatings are beneficial andappear to complement the role ofchromium (9).

Molten glass typically induces in-tergranular attack with voids (fromvolatile halides) and sulfides. Oxidesare generally fused into the glass. At-tack is commonly rapid, and highchromium-nickel-based alloys areusually employed. Iron-rich alloyscan be prone to severe attack due totheir ability to form low-meltinghalides (e.g., FeCl3).

Molten salts, used for heat treatingapplications, nuclear engineering,solar cells, and metal extraction, gen-erally promote intergranular attack inalloys, often with voids and internallow-melting products (halides).

A common feature in most high-temperature aggressive environmentsis the synergy of the reactants onewith each other (Table 1). Wastagecan be easily measured, but the mech-anism(s) are not as easy to determine.As a minimum, a rigorous study andanalysis of the morphologies shouldhelp to establish the rate-controllingprocess, which should help to betterdefine the type of alloy that could beconsidered as a candidate. The broadexpertise of the material suppliersshould be fully explored in the questfor a suitable choice. Monitoring trialsusing test spools are recommendedwherever they can be used.

Candidate alloysChoice should be based on careful

considerations, including, primarily,

the function of the component or ves-sel. As might be expected, there aremany candidates, yet, from these thechoice is often reduced to one of two,once the total range of properties isfully explored. Factors to be consid-ered include mechanical properties(strength, flexibility, fatigue life),physical properties (expansion andcontraction, reflectivity, magnetism,etc.), availability (shape and form),and price (economic decision basedon overall costs and fabrication, etc.).

As a convenience, some generally

recommended alloys and alloy typesfor various high-temperature environ-ments are summarized in Table 2.This table is intended only as a guide;no order of merit is to be interpretedfrom the sequence of listings (oromissions) in this table. Also, thealloy lists are not meant to be inclu-sive, but, rather, merely typical exam-ples of what has worked in the field.

To sum upIdeally, the material choice is

based on known data and experience,which implies communication be-tween a user and a supplier. A betterknowledge of anticipated componentrequirements in addition to corrosionbehavior provides for a better choiceand the expectation of more reliableservice.

Proper identification and recordingof damage from prior systems is apositive benefit in deciding upon analternative alloy or coated system.Wherever possible, and certainly fornew and complex environments, test-ing is to be recommended. ◆

CEP February 2001 www.aiche.org/cep/ 81

Literature Cited1. Rothman, M. F., ed., “High Tempera-

ture Property Data: Ferrous Alloys,”ASM International, Metals Park, OH, p.9.26 (1989).

2. Agarwal, D. C., and U. Brill, “MaterialDegradation Problems in High Tempera-ture Environments,” Industrial Heating,p. 56 (Oct. 1994).

3. Elliott, P., “Practical Guide to High-Temperature Alloys,” Materials Perfor-mance, 29 (4), p. 57 (Apr. 1989).

4. Lai, G. A., “High-Temperature Corro-sion of Engineering Alloys,” ASM Inter-national, Metals Park, OH (1990).

5. Hussain, M. S., “Aspects of Hot Corro-sion Attack on High-Temperature Materi-als,” PhD thesis, University of Manchester(1984); C. J. Tyreman, “The High Tem-perature Corrosion of Metals and Alloysin HF-containing Environments,” PhDthesis, University of Manchester (1986).

6. Grabke, H. J., “Carburization — AHigh Temperature Corrosion Phe-nomenon,” Publication No 52, MaterialsTechnology Institute of the ChemicalProcess Industries, Inc., St. Louis(1998).

7. Elliott, P., “Materials Performance inHigh Temperature Waste CombustionSystems,” Materials Performance, 33(2), p. 82 (1993).

8. Goebel, J. A., et al., “Mechanism forHot Corrosion of Nickel Base Alloys,”Met. Trans., 4 (1), p. 261 (1973).

9. Elliott P., and T. J. Taylor, “Some As-pects of Silicon Coatings Under VanadicAttack,” in “Materials and Coatings toResist High Temperature Oxidation andCorrosion,” A. Rahmel and D. R.Holmes, eds., Applied Science Publish-ers, London, p. 353 (1978).

P. ELLIOTT is president of Corrosion &

Materials Consultancy, Inc., Colts Neck, NJ

((732) 303-0538; Fax: (732) 303-0591;

E-mail: pelliott@monmouth.com). The

company provides professional engineering

services, notably in materials utilization and

corrosion control. C&MC offers a wide range

of technical support, including metallurgical,

analytical, corrosion testing, and evaluation

services. Elliott has 30 years’ experience as

a corrosion and materials engineer,

especially in troubleshooting and failure

analysis. He is the author of over 90

technical papers dealing with materials

performance, high-temperature corrosion,

environmental corrosion, risk assessment,

and technology transfer. He is a NACE

International Fellow and Corrosion

Specialist, and serves on several NACE

committees; he also presents a NACE

seminar on high-temperature corrosion. He

is a Fellow and past chairman of the Institute

of Corrosion, a Fellow of the Institute of

Materials, a chartered engineer, and a

member of ASM International. He has also

presented over 100 lectures to international

conferences and professional societies.

Elliott holds a BSc in metallurgy, and an MSc

and PhD in chemical metallurgy from the

University of Manchester, U.K.