TheRoleofChlorineinHigh TemperatureCorrosioninWaste to EnergyPlants 14045

8/11/2019 TheRoleofChlorineinHigh TemperatureCorrosioninWaste to EnergyPlants 14045

1/14

The role of chlorine in high temperaturecorrosion in waste-to-energy plants

G. Sorell

G. Sorell Consulting Services, North Caldwell, New Jersey, USA

H igh tem perature corrosion has been a serious problem in m unicipal solid w aste (M SW ) incinerators sincethe em ergence of w aste-to-energy (W TE) plants in the 1960s. Early researchers conjectured that corrosionw as caused by sulfur com pounds, but it soon becam e evident that the dom inant corrosive species arechlorides, typically in com bination w ith alkali m etals (Na, K) and heavy m etals (Pb, Zn). Yet, m anyuncertainties rem ain w ith respect to the com plex interactions betw een m etallic m aterials of construction andtheir corrosion products w ith aggressive species in the com bustion atm osphere and in fireside deposits.Follow ing a review of historical background, M SW incineration technology and refuse boilerm aterials/corrosion, this paper w ill exam ine the causes and m echanism s of high tem perature corrosion inW TE plants, as well as the environm ental and alloy-related factors affecting m etal w astage. Attention w ill becalled to rem aining uncertainties regarding corrosion m echanism s, and to apparent incongruities andconflicting data on m aterials perform ance to help identify areas for further R& D .

(Keywords: waste incineration; chloride corrosion; alloy performance)

INTRODUCTION

O ver a quarter century ago, British researchers in the field offossil fuel fired boiler corrosion concluded that there is "adiversity of opinion concerning the role of chlorides in thecorrosion process, and at the present tim e the picture issom ew hat confused"l. Although the state of know ledge has been

greatly expanded since then, the role of chlorides in firesidecorrosion is by no m eans fully understood. Several unresolvedissues rem ain and need to be clarified according to a recentoverview of British research and experience w ith burning high-chloride coals2.

This situation is m irrored in the incineration of m unicipalsolid w aste, often referred to as refuse or garbage, perform ed inso-called w aste-to-energy plants. As with coal-fired com bustion,corrosion in refuse boilers has been intensively studied overm any decades. Yet, m ajor uncertainties rem ain as to the com plexinteractions betw een gaseous and condensed species w ith firesidem etallic surfaces. There is, how ever, universal agreem ent thatchlorine com pounds are the principal corrosive agents in M SWincineration, in contrast to corrosion in coal-fired pow er

generation w here sulfur com pounds are the m ain culprits. Thisdistinction is not surprising, considering that M SW usuallycontains higher concentrations of chlorine (0.5-2.0% ) than sulfur(0.1-0.4% ). The principal sources of chlorine in dom estic refuseare sodium chloride and polyvinyl chloride (PV C) plastic. Asshow n in Figure 1, the am ount of PV C-derived chlorides isprojected to keep on rising, portending that refuse boilercorrosion m ay becom e an even greater concern in future years.

0960-3409/97/03/00035-121997 Science and Technology Letters

Figure 1 Estim ated chlorine content of M SW derived from PV C(ref.3).

HISTORICAL PERSPECTIVE

European boiler m anufacturers who pioneered the developm entof W TE plants in the 1960s m odeled their designs on coal-firedboiler technology. Proceeding on the assum ption thatcom parable therm al efficiencies could be attained, these earlyunits w ere designed w ith high steam conditions ranging from450-540C (840-1000F) and 36.2-187.0 kg cm -2(500-2650psig)4-6. In m any cases, failures of carbon steel boiler tubes dueto corrosion w ere experienced during the firstyear of operation.The m ost severe attack reported occurred in a G erm anincinerator, w here a w astage rate of 40.6 m m yr-1(1.6 in yr-1) w asexperienced in the superheater4.

MATERIALS AT HIGH TEMPERATURES 137


2/14

N um erous corrosion failures in these first-generation W TEplants clearly indicated that corrosion w as a tar m ore seriousproblem than in coal-fired plants operating at com parableconditions. To achieve satisfactory tube life, designers ofrefuse-fired boilers w ere forced to accept substantial reductionsin steam tem peratures/ pressures. The adverse experience in theEuropean plants w as not lost on U S boiler m anufacturers, w hoaccordingly opted for very conservative steam conditions, rang-ing from 190-323C (375-613F) and 13.3-33.4 kg cm -2(175-460psig). Even these m odest steam conditions required tube m etaltem peratures above 260C (500F), w hich w as the upper lim it

recom m ended by leading researchers of M SW corrosion duringthese early years.

The large disparity betw een early European and U S plants isillustrated in Figure 2. Betw een 1960 and 1972, the 11 EuropeanW TE plants put into service w ere designed w ith steamtem peratures averaging 497C (926F), as com pared to 235C(456F) for the six U S facilities that started up betw een 1965 and1974. Respective differences in average steam pressure w ereeven larger, w ith the European plants topping U S installationsm ore than three-fold.

Several of these early U S plants experienced unexpectedlysevere corrosion, notw ithstanding their low steam conditions.This w as attributed to a variety of factors, am ong them excessiveboiler tube m etal tem peratures and locally reducing atm ospheres.Since then, im provem ents in furnace and boiler design, m aterialsupgrading, and better controlled operation have perm itted aprogressive increase in steam conditions. This is reflected in thedesign of 15 large W TE plants, utilizing boilers from 10 differentm anufacturers, that started up in the U S in 1990-1992. Steamconditions in these m odern U S plants range from 399-463C(750-865F) and 46.6-64.3 kg cm -2(650-900 psig), w hich is com -parable to m odern European facilities.

The historic trend in W TE plant design in Europe and the U Sdiffers m arkedly from the path taken in Japan. D uring the sam e1990-1992 tim e fram e, the 24 W TE

plants that w ent into operation in Japan had com paratively m ildsteam conditions ranging Iron, ZU 6-300 C, (406-527F) and18.6-32.0 kg cm -2(250-440 psig)9. The greater conservatismreflected by the Japanese plants apparently signals a greaterem phasis on plant reliability and availability than on m axim izingpow er production. The therm al efficiency of m ost JapaneseW TE plants is 10-15% , com pared to about 20% for U S facilities.These figures are far below the typical 33% efficiency attained incoal-fired pow er stations, w hich routinely operate at 538C(1000F) superheat/reheat cycles, and in supercritical units, up to245 kg cm -2(3500 psig).

The situation in Japan is expected to change m arkedly w ith thecom pletion in 1999 of an 8-year program to develop highefficiency w aste-fired pow er generation10,11. This cooperativegovernm ent/private sector initiative is being conducted underthe auspices of the N ew Energy D evelopm ent O rganization(N ED O ), w ith the objective to design and dem onstrate W TEplants having a therm al efficiency of 30% . A key com ponent ofthis landm ark project is developm ent of new corrosion-resistantalloys and com posites, notably for superheaters, that can w ith-stand the high tem peratures necessary to attain this highefficiency level. This alloy developm ent effort, carried out bym ajor Japanese alloy producers and boiler vendors, is directed bythe Japan Research and D evelopm ent Center for M etals.

M SW IN C IN E R A TIO N T E C H N O LO G Y

The tw o com peting concepts in com m on use for M SWincineration are m ass-burn and refuse-derived fuel (RD F),described in greater detail elsew here3,12-14. M assburn incineratorsburn as-received unprepared refuse, w hile in RD F facilities theraw refuse is first separated, classified, and shredded intofist-sized chunks. In recent years, several fluidized bedincinerators have been put into service for com busting andco-com busting M SW .

M ass-burn and RD F plants both em ploy grates throughw hich prim ary air is introduced, and w hich transport the

Figure 2Steam conditions in European and US WTE plants (ref. 8).

138 MATERIALS AT HIGH TEMPERATURES

The role of chlorine in high temperature corrosion in waste-to-energy plants: G. Sorell


3/14


burning refuse through the furnace toward an ash dump.

Mass-burn grates come in a large variety of proprietary stoker

designs, most of which use sloped and stepped metal grates

consisting of reciprocating or other moving action grate bars

that churn the refuse to facilitate combustion. RDF plants

employ traveling grate stokers, with part of the combustion

taking place in suspension firing above the grate. All MSW

incinerator designs introduce copious amounts of secondary

air to complete the combustion process.

A schematic of a typical mass-burn MSW incinerator is

shown in Figure 3. Except for the feed system and the lower

furnace area, the basic design is similar to that employed in

fossil fuel fired power plants. The radiant boiler consists of a

membrane waterwall combustion chamber, followed by

convective heat extraction in superheaters and economizers.

Air pollution control systems in US WTE plants

predominantly utilize semi-dry scrubbers (spray dryers) and

either fabric filters or electrostatic precipitators. In Europe and

Japan, many WTE plants continue to rely on wet scrubbers to

control particulate, acid gas emissions and volatile metals.

REFUSE BOILER MATERIALS AND CORROSION

CONTROL

Corrosion protection and control is a critical aspect of WTEplant technology and is closely governed by cost

considerations. Following the traditional approach taken with

fossil fuel fired boilers, designers of WTE plants strive to limit

the use of alloy materials by resorting to

Figure 3Schem atic of m ass-burn refuse incinerator.

favorable design configurations and refractory linings to

reduce metal wastage. Such linings, in the form of silicon

carbide monolithics15

and fired shapes16

, are used to good

advantage for protecting the lower waterwall in mass-burn

units, but have proved unsuitable for RDF installations

because of excessive risk of slagging. On the debit side,

refractory linings reduce heat transfer and add to the

maintenance burden. For added protection against

abrasion-corrosion close to the grate, this zone is often fitted

with wear-resistant blocks made of cast alloys or ceramics.

An effective method for protecting and restoring carbon

steel waterwall tubing is by means of alloy 625 weld overlay

17

.An estimated 16,000 m2 (170,000 ft

2 ) of alloy 625 weld

overlay has been applied in over 100 US refuse boilers. The

most corrosion-prone location in mass-burn incinerators is the

high heat flux zone directly above the refractory-lined portion,

which is often subject to flame impingement. A typical

corrosion failure of a steam generation waterwall tube is

illustrated in Figure 4. Corrosion of unprotected carbon steel

tubing in this vulnerable location has led to numerous

in-service failures within the first year of operation in several

US WTE plants.

Superheater tubing is customarily made of carbon or low

Cr-Mo steel, and fitted with high alloy tube shields for added

protection against erosion-corrosion. This approach has met

with only limited success in high temperature superheatersbecause of short shield life and resultant corrosion of the

exposed tube. Moreover, shields

Figure 4W aterwall tube failure in M SW incinerator.



4/14


m ay becom e dislodged, w hich can lead to corrosionexacerbatingflow blockages. Several prom inent U S refuse boiler vendorsroutinely specify alloy 825 for hot sections of superheaters.Experience has generally been favorable, as gauged from oneplant's reported experience of a 10-year survival rate of 95% oftheir alloy 825 superheater tubes18. As another option, som eW TE plant operators are now utilizing alloy 625full-circum ference w eld overlayed superheater and screen tubes.

An alternative or supplem ental approach to alloy upgradingfor controlling corrosion/erosion is by m eans of conservativedesign features4,13,19-23. This strategy is favored particularly byEuropean boiler vendors, as an outgrow th of the disastrouscorrosion experience in their first-generation W TE plants. Theprim ary design-related stratagem for corrosion m itigation isreducing tube m etal and gas tem peratures. This can beaccom plished by accepting low er steam conditions and bydecreasing the tem perature of the com bustion gases entering theconvection section. O ther beneficial design features includeem pty and/or w ater-screened gas passes, parallel-flow finishingsuperheaters, low gas velocities in convection banks, andm echanical tube rappers (instead of sootblow ers). O n the debitside, som e of these design features reduce energy efficiency andincrease furnace size. Boiler vendors and W TE plant operatorsrem ain divided as to w hether the initial cost prem ium for alloyconstruction is com pensated by the boiler's m ore com pactconfiguration and greater energy production.

An im portant design consideration for reducing corrosion isthe use of m easures to im prove com bustion characteristics. H ighon the list are provisions for a generous supply and gooddistribution of overfire air, and prom otion of strong turbulencein the furnace. In that regard, it should be recognized thatcontrolling and stabilizing com bustion conditions in M SWincinerators is inherently m uch m ore difficult than infossil-fueled plants. The difficulty arises from thenon-hom ogeneity and variability of refuse w ith respect tocom position, heat content and m oisture.

The use of alkaline additives used by som e plants for curbingem issions has not proven effective for corrosion control. To thecontrary, addition of calcium com pounds (lim e) m ay actually

aggravate corrosion24,25

. Co-com bustion of M SW w ith sulfur orhigh-sulfur coal has been reported as a m ethod for suppressingcorrosion, as w ill be discussed later. To the best know ledge, thism easure is not being pursued, probably because of concern thatintroducing large quantities of sulfur w ould overtax the em issioncontrol system .

CAU SES O F CO RRO SIO N IN M SW

IN CIN ERATO RS

Corrosion in refuse boilers has been intensively studied datingback to the em ergence of W TE facilities in the 1960s. Thelargest body of w ork has been conducted by a Battelle team ledby K rause7,8,24,26-34, m ostly through grants from the U SEnvironm ental Protection A gency (EP A). M ore recent studiesconducted by Battelle researchers w ere funded by the ElectricPow er Research Institute (EPRI)3,5,35,36 and jointly by theAm erican Society of M echanical Engineers (ASM E) and the U SD epartm ent of Energy (D O E)13.

M ajor studies have also been carried out by the


prom inent U S refuse boiler vendors Babcock & W ilcox37-41,Foster W heele6,21,42-45and AB B Com bustion Engineering46-49.Im portant contributions tow ard advancing the state ofknow ledge on incinerator corrosion have recently com e out ofJapan9-11,50-56, m ost of them associated w ith the aforem entionedN ED O project. Valuable insights into the fundam ental aspectsof incinerator corrosion have been contributed by researchers inuniversities and research institutess57-64. Also notew orthy is thestrong continuing w ork effort focused on m aterials developm ent,testing and perform ance carried out by m ajor alloyproducers,prom inently including H aynes, Inco, K rupp VD M , M itsubishi,Sandvik and Sum itom o.

Recognition that chlorine in the refuse is the prim ary sourceof corrosion problem s cam e slow ly to the M SW incineratorcom m unity4. W hen the pioneer W TE plants ran into severecorrosion problem s, these w ere attributed to the fluxing actionof m olten sulfates, pyrosulfates and alkali iron trisulfates, thecorrosive species responsible for corrosion in high tem peraturecoal com bustion environm ents65. This view has been largelydiscredited as an explanation for refuse boiler corrosion.A lthough sulfur com pounds are still recognized as playing a con-tributory role, it is now accepted that corrosion in M SWincinerators is strongly chloride dom inated. The aggressivespecies m ost responsible are chlorides of alkali m etals (N a, K)and heavy m etals (Zn, Pb, Sn). Chloride-rich ash deposits tend to

have far low er m elting points than sulfatic deposits, w hichdictates the low er steam conditions in W TE plants com pared tocoal-fired pow er stations.

The influential role of chlorides on corrosion becam eincreasingly evident as study after study detected chlorides at them etal/scale interface, usually at higher concentrations than in thegas-side layer. Chloride corrosion in M SW incinerators proceedsvia gas phase attack and, far m ore im portantly, underneathdeposits containing solid and/or m olten chlorine com pounds.

Gaseous corrosion

Essentially all chlorine com pounds in M SW are converted tohydrogen chloride in the com bustion environm ent. The am ountof H Cl in refuse incinerator flue gases ranges from about 400 to1500 ppm , based on the rule of thum b that each 0.1 % Cl in thew aste generates around 80 ppm H Cl. D irect gas-phasechloridation of steels to iron chloride is not considered asignificant factor. In fact, therm odynam ic analysis predicts thatthis reaction is unlikely to proceed in M SW com bustion atm os-pheres66. Experim ents w ith iron- and nickel-base alloys in asynthesized incinerator gas atm osphere show ed a sharp increaseof attack w ith progressive am ounts of H Cl up to 10% 67.H ow ever, the actual corrosion rate w as negligible at the low H Cl

concentrations likely to be encountered in refuse boilers. It canthus be concluded that direct gas-phase chloridation is a m inorconcern in M SW incineration, except possibly under localizedstrongly reducing conditions or at exceptionally hightem peratures.

It is interesting to note that H Cl m ay actually act as acorrosion inhibitor in som e reducing-sulfidizing gas m ixtures. Inlaboratory exposures sim ulating utility boiler substoichiom etriccom bustion gases containing 500 ppm H 2S, the addition of 350ppm H CI w as found to substantially reduce corrosion rates ofcarbon and low alloy


5/14


steels41

. Similar observations were made with simulated coal

gasification atmospheres containing 1% H2S, where additions

of 600 ppm HCl sharply reduced the corrosion rate of low

alloy steel68

. The inhibitive effect was ascribed to chlorine in

the sulfide scale acting to slow the outward diffusion of Fe to

form the sulfide.

Deposit-induced corrosion

Corrosion in refuse boilers takes place primarily beneath

deposits consisting of corrosive salts, usually admixed with a

large fraction of ash constituents. In the lower furnace areawhere local reducing conditions are common, deposits are

characteristically rich in chlorides. At higher elevations and in

the convection section, deposits contain progressively larger

amounts of sulfates, which are more stable than chlorides

under oxidizing conditions. Consequently, a sizable fraction of

chloride corrosion products is converted to sulfates. Deposition

processes are varied, but generally include vapor condensation,

physical deposition of flyash, and reaction of gaseous species

with previously formed deposits. The cohesion of deposits

may be promoted by fusion or sintering of molten or

semi-solid alkali, alkaline earth, and heavy metal sulfates,

chlorides, phosphates and carbonates38,39

.

Corrosion by condensed species is especially severe when

these consist of molten salt eutectics, due to their fluxingaction on protective scales. Significantly, deposit induced

corrosion can be severe even in the absence of molten species.

The proposed reaction sequences and mechanisms explaining

such "dry" deposit attack will be examined in the section on

corrosion mechanisms.

Mechanically-assisted corrosion

The simultaneous action of abrasion and erosion on com-

ponents exposed in corrosive WTE plant environments

synergistically accelerates metal wastage13

. Rates of attack

caused by such conjoint action can easily be an order of

magnitude greater than corrosion alone. Abrasion-corrosion isencountered on the waterwall along the grate line in mass-burn

plants, caused by the wearing action of the churning refuse.

Erosion-corrosion is confined largely to the convection bank,

where gas velocities are higher than in the radiant furnace

zone. The erosion component results from impingement by

flyash particles, and by high-velocity steam blast in sootblower

lanes. Mechanically-assisted corrosion is best controlled by

appropriate design features and protective barriers, as noted

earlier.

CORROSION MECHANISMS

Corrosion in chloride-contaminated combustion environments

is governed by competing oxidation-chloridation reactions,

which in turn are closely dependent on the type of metal and

adjacent micro-environment. The specific factors influencing

the relative dominance of oxidation vs chloridation are

thermodynamic factors (rates of formation, relative stability of

products, vapor pressures, etc.) as well as kinetics which, in

turn, relate to physico-chemical properties of the product

(density, volume, diffusivity, expansion coefficients, etc.) and

also to the product integrity, i.e. its adhesion and cohesion60

. In

oxidizing-chloridizing environments, it is of crucial

importance which attack mode predominates because, unlike

oxides, chlorides are ineffective corrosion barriers.

Thermodynamic analysis

Researchers exploring the mechanisms of corrosion in MSW

incineration environments rely heavily on thermodynamic

analyses, largely by means of thermochemical stability

diagrams exemplified in Figure 5. While useful for

determining equilibrium phases of metallic elements, such

diagrams often fail to accurately predict corrosion products

and scales that may actually form in complex multi-componentenvironments because these depend on the specific reaction

path and alloy composition. The shortcomings of stability

diagrams are of even greater consequence with volatile species

because stability diagrams do not take into account the vapor

pressure of volatile species that may be in equilibrium with

condensed phases63

. Thus, in chloride-contaminated com-

bustion environments, chlorides are often found at the

metal-scale interface even though oxide corrosion products are

thermodynamically stable in the gas phase. Notwithstanding

these limitations, thermodynamic analysis is used to good

advantage by corrosion researchers. For that purpose,

thermodynamics-based computer programs can provide a

valuable tool for predicting species in the flue gas and flyash

based on fuel chemistry and boiler operating conditions39.

Reaction kinetics

In mechanistic studies of chloride corrosion, it is essential to

factor in reaction kinetics, since these determine the rate of

transport of gaseous chloride species by diffusion through

pores and cracks in otherwise protective oxide scales.

Depending on the relative amounts oxides and chlorides

formed, corrosion can obey either a paralinear rate law (a

combination of weight gain due to oxidation and weight loss

due to volatile chloride formation) or a linear law due to

chloridation alone69

. One of the effects of chlorine is that itchanges the morphology of the oxide scale to create porosity,

leading to more rapid attack even if the amount of chlorides

formed is negligible62

. Such voids at the metal/oxide interface

promote scale spallation as well as internal attack by

subsurface penetration of chlorides. An astute analysis of

reaction kinetics operative in oxidation-chloridation, including

schematics describing different cases, has been developed by

Grabke58

.


Figure 5Therm ochem ical stability diagram for m etal-oxygen-chlorine system at400C.


6/14


Corrosion under solid deposits

To account for the presence of chlorides and sulfates in refuse

boiler deposits and associated "dry" deposit attack, Battelle

researchers proposed a number of chemical reactions

involving chlorine and sulfur species7,29

. Those involving

principally chlorine compounds are shown below. Similar

reactions can take place with sodium and potassium, since

Na2O and K2O are both refuse combustion products.

Na2O + 2HC1 2NaC1 + H2O (1)

4NaCl + 2S02+ O2+ 2H2O 2Na2SO4+ 4HC1 (2)

4HC1 + O2 2H2O + 2O2 (3)

C12+ Fe FeC12 (4)

4FeCI2+ 3O2 2Fe2O3+ 4O2 (5)

The release of HCl and particularly C12 (reaction (5)) was

conjectured to take place directly adjacent to the metal surface,

and therefore play a critical role in the corrosion mechanism.

In that connection, it is noted that Cl2 is far more corrosive

than HCI. As suggested by earlier studies70

, the chloridation of

iron by highly corrosive elemental chlorine (reaction (4)) is

selfperpetuating, since fresh C12continues to be generated by

reaction (5). The presence of a FeCl2corrosion product layer

in contact with the metal is judged to be particularly damaging

because it promotes scale disruption or spallation as a

consequence of massive growth stresses generated by the

six-fold volume expansion relative to the consumed metal2.

More recent studies by Battelle34

indicate that a similar

chlorine corrosion/regeneration cycle may proceed via FeC13formation. As shown in reactions (6) and (7), it is possible for

the ferrous iron corrosion product to be oxidized to the ferric

state which, when oxidized, liberates chlorine.

4FeC12+ 4HC1 + O2 4FeC13+ 2H2O (6)

4FeC13+ 302 2Fe2O3+ 4O2 (7)

Additional routes for chlorine release during the corrosion

process entail direct oxidation of FeC12 (reaction (8)) or via

ferrite formation (reaction (9))57

. A further refinement of the

self-sustaining chloride corrosion cycle was made by Grabke,

who terms this corrosion mechanism "active oxidation"57,59

.

3FeC12+ 2O2 4Fe3O4+ 3O2 (8)

2Fe2O3+ 4NaC1 + O2 2Na2Fe2O4+ 2O2 (9)

Chlorine liberation at the metal surface can similarly take

place with alloy and stainless steels, whereby chromia is

converted to alkali chromate (reaction (10)).

8NaC1 + 2Cr2O3+ 502 4Na2CrO4+ 4C12 (10)

Chemical interactions between metals, corrosion products,

deposits and the combustion atmosphere are, of course, not

restricted to chlorine compounds, but also involve other

chemical species contained in MSW. Among these, sulfur

compounds are the most influential, although they themselves

are not primary corrosive agents. As shown in reaction (2),

through its chlorine liberating action, S02 plays an indirect

though important role in promoting corrosion. The limits of

this a er do


not permit a closer examination of the sulfur chemistry in

refuse combustion. An indication of the complexity of some of

these possible interactions between chlorine and sulfur

compounds is depicted in Figure 6.

Corrosion by molten species

Attack by molten ash-salt mixtures in MSW combustors is

essentially a form of hot corrosion71

, wherein chlorine rather

than sulfur compounds are the primary aggressive species. The

term 'hot corrosion' was originally restricted largely to

sulfidation-oxidation attack of superalloys encountered in gas

turbines, but has been broadened in current usage toencompass other manifestations of accelerated oxidation of

metal surfaces exposed in a high temperature gaseous

environment and coated by a thin fused salt film. As an

extension of Rapp's fluxing model of hot corrosion, an

'apparent' acid-base chemistry has been postulated to account

for fused chloride attack of austenitic stainless steels and

Ni-base alloys in simulated waste incineration environments51

.

The corrosiveness of chlorides stems to a large degree from

their low melting points, especially eutectic mixtures of alkali

and heavy metal chlorides associated with waste incinerators.

A listing of possible molten chloride salt mixtures in MSW

incinerator deposits is given in Table 1. While it is unlikely

that these exact mixtures will be encountered in practice, the

tabulated values give a good indication of the low meltingpoints of fused deposits on corroded refuse boiler tubes.

Compounding the aggressiveness of chlorides is their low

vapor pressure. It is generally accepted that high rates of attack

can be anticipated at temperatures where the vapor pressure

attains or exceeds a value of 104

atmospheres, designated as

T464,73. A plot of T4. temperatures of several metal chlorides,

together with their melting point (TM), is shown in Figure 7.

Significantly, T4's tend to be appreciably lower than TMs,

reinforcing the observation that chlorides can cause high rates

of attack even in the absence of fusion. The proposed

mechanism whereby this occurs holds that high vapor pressure

chloride corrosion products cause volatilization of molecules

from the scale to the vapor, while there is simultaneous scale

growth by diffusional transport64.

Other species that may potentially form in oxidizing-

chloridizing environments are metal oxychlorides. These are

conjectured to have an even greater corrosion-

Figure 6Possible chem ical reactions on corroding refuse boiler tube (ref. 7).


7/14


Table 1Possible m olten chloride m ixtures in M SW incinerator deposits (w eight % )

Figure 7M etal chloride m elting points and tem peratures where chloride vaporpressure equals 104atm ospheres (ref. 73).

exacerbating effect than chlorides because oxychlorides are farm ore unstable and volatile than respective m etal chlorides60,69.This applies particularly to refractory m etals at elevatedtem peratures. For exam ple, m olybdenum oxychlorides havevapor pressures 10-20 orders of m agnitude greater thanm olybdenum chlorides in equilibrium w ith oxides and the test

environm ent. This extrem ely high volatility explains the poorcorrosion resistance of alloys having high m olybdenum contentsexposed in an atm osphere containing 20% O 2and 2% C12at900C (1652F)61. Fortunately such severe conditions are notencountered in M SW incinerators.

EN VIRO N M EN TAL FACTO RS IN FLU EN CIN GCH LO RID E ATTACK

The principal environm ental factors influencing the severity ofchloride corrosion are chloride concentration,

gas and m etal tem peratures, and the presence of oxidants in theatm osphere.

Chloride concentration

Battelle w as the first to conduct a system atic study on thecorrosion effects of chlorine content in M SW 8. Probe tests w ithPV C-spiked refuse at tem peratures from 204C (400F) to538C (1000F) show ed that additions of 2% PV C increasedcorrosion rates of carbon steel by 40-150% and that there w asalso a steep rise in chloride concentration of probe deposits.O ther researchers have observed a positive correlation betw een

corrosion and the chloride content in deposits10,53,56, asexem plified in Figure 8.

Gas and metal

Both m etal and flue gas tem peratures are im portant param etersaffecting corrosion in w aste-fired boilers. Flue gas tem peraturesdeterm ine the types of volatile species that can be transported inthe gas, as w ell as the m axim um tem perature of any deposits.Tube m etal tem peratures determ ine the location and m inim umtem perature of such deposits, and thus have a decisive influenceon corrosion3,35. As show n in Figure 9, gas tem peratures m ayexert a stronger corrosion-accelerating influence than m etaltem peratures. A sim ilar trend w as discerned from m ore recenttest data from three M SW incinerators, plotted in Figure 10.G enerally speaking, a corrosion accelerating influence w ithincreasing tem peratures has been discerned in nearly all refuseboiler corrosion studies10,11,38,45,55,74. A notable exceptionw as revealed by

Figure 8Effect of chloride content in deposits oncorrosion of carbon steel inM SW incinerators (ref. 10).

Figure 9Effect of tem perature on corrosion of carbon steel in M SW incinerator(ref. 31).



8/14


a laboratory study using chloride-rich ash, in which generally

higher weight losses of steels and alloys were observed at

450C (842F) than at 550C (1022F)54

. This was especially

surprising considering that 550C is above the ash melting

point. This reverse temperature effect was rationalized on the

basis that lead oxide in the ash may have catalyzed the release

of chlorine from the dry ash via the Deacon reaction (reaction

(3)).

Another temperature-related variable influencing boiler

tube corrosion is heat flux. The importance of this factor wasrevealed by a field study investigating a serious waterwall

failure in a RDF boiler47

. Maximum tube wastage occurred in

the overfire air region where heat fluxes calculated from

thermocouple readings ranged from 46,000 to

67,000 Btu/h1

ft2

, about 2-3 higher than in other furnace

zones. In mass-burn units, the highest heat flux and also the

most corrosion vulnerable area is the bare waterwall zone just

above the refractory-lined area.

Oxidants in furnace atmosphere

Accelerated waterwall tube wastage in coal-fired boilers has

long been closely associated with the presence of carbon

monoxide in localized reducing zones, brought on by

incomplete combustion due to an inadequate supply or poor

mixing of combustion air. When WTE plants first ran into

severe corrosion problems, it was naturally assumed that

MSW incinerator corrosion would be similarly governed, and

that substoichiometric CO-containing atmospheres are

detrimental. While this remains the consensus to this day, the

picture is clouded by some seemingly contradictory findings,

as explained below. However, in general, oxidizing conditions

characterized by ample excess oxygen tend to suppress corro-

sion. The positive effect of oxygen in retarding corrosion


has been demonstrated in simulated incineration atmos-

pheres55,75

. Water vapor content in the combustion atmosphere

can exert a similar corrosion-suppressing effect, as shown in

Figure 11.

In several laboratory studies, the unexpected discovery was

made that corrosion of steels coated with or immersed in

chloride-containing salt deposits was greater under oxidizing

than under reducing conditions40,53,66

. The results from two

laboratory tests, presented in Figures 12 and 13, appear to

negate the long-held position that reducing conditions are

more damaging. This paradox can be explained by the fact that

reducing conditions raise the vapor pressure of alkali chlorides

and thus enhance their formation and deposition but, that once

formed, these deposits are more corrosive under oxidizing

conditions. This finding suggests that alternating

Figure 11Effect of O 2or H 20 on corrosion in M SW incineration environm ents(ref. 75).

0.1 1 10 100Figure12Corrosion of salt-coated carbon steel coupons in sim ulated M SWincinerator flue gases (ref. 66).

Figure 13 Corrosion of salt-em bedded steel coupons in sim ulated M SWincineration flue gas at 316C (ref. 40).

Figure 1 0Effect of tem perature on corrosion of Fe-base and N i-base alloys (ref. 11).


9/14


oxidizing/reducing conditions characteristic of unstablecom bustion conditions in the low er furnace area m ay prom oteespecially rapid attack.

Heavy metals in waste stream

Intensive laboratory studies of refuse boiler deposit chem istries,conducted by Foster W heeler during the early days of M SWincineration, concluded that Pb and Zn w ere im portantcontributors to corrosion42,43,44. Since then, m any otherresearchers have confirm ed the detrim ental effect of Pb, Zn andSri in exacerbating corrosion by chloride-containing

deposits10,11,37,38,53,55. H eavy m etal chlorides significantly depressthe m elting point of ash deposits; for exam ple, raising the Pb0 +ZnO content from 2% to 8% has been show n to low er them elting point by 50C (90F)11. Som e studies suggest that Zn ism ore detrim ental than Pb, w hile others find the opposite. Leadappears to be particularly harm ful to stainless steels; in one seriesof tests, Type 304 S.S. corroded m ore rapidly than carbon steel38.Indicative of the detrim ental role of zinc is the close resem blancebetw een the corrosion responses of a w ide range of alloys testedin condensing ZnCl2 vapor and in an incinerator burning refusecontaining significant am ounts of zinc14,76.

It has recently been discovered that copper m ay yet beanother corrosion-aggravating heavy m etal contained in M SWLaboratory studies w ith m ixtures of alkali chlorides and heavy

m etal oxides in oxidizing-chloridizing atm ospheres have revealedthat CuO m ay actually be m ore harm ful than Zn077. To accountfor the corrosion-stim ulating role of CuO , it w as postulated thatit m ay catalyze the form ation of elem ental chlorine via theD eacon reaction. The detrim ental effect of CuO in depositsleads to the speculation that copper alloying additions m ightsim ilarly im pair corrosion resistance. If this speculation issubstantiated by further studies, it m ay help explain the variableperform ance of alloy 825 (2.3% Cu), discussed later.

Corrosion inhibition by sulfur

D uring Battelle's test program to discern the effects of chlorineand sulfur com pounds on M SW incinerator corrosion, thediscovery w as m ade that additions of elem ental sulfurunexpectedly caused a substantial reduction of corrosions. Thisfinding gave rise to a com prehensive series of tests to investigatethis inhibitive effect further, first by controlled additions ofsulfur26and later by co-firing w ith sulfur-containing coals27,28.The positive results achieved w ith sulfur additions to M SWplotted as a function of S02/H CI ratios, are presented in Figure14. These studies led to the conclusion that corrosion in refuseboilers can be effectively reduced by providing sufficient sulfurto exceed an approxim ate S/Cl ratio of 430.

The explanation for the corrosion-inhibiting effect of sulfurpostulates that the m ost serious corrosion-prom oting reactionsare caused to occur harm lessly in the gas stream rather thaninside or underneath deposits. Specifically, in the presence ofsufficient SO 2in the furnace atm osphere, m etal chlorides (M CI)in the com bustion products are converted to sulfates in the gasstream , according to the reaction (11), w hich is a generalizedversion of reaction (2).

M CI + SO 2+ O 2+ H 2O M SO 4+ H Cl (11)

Figure 14 Effect of sulfur additions to raw refuse on corrosion of steels (ref. 31).

Because the H Cl is released in the gas stream rather than w ithindeposits, it does not have the opportunity to react w ith the tubem etal and participate in the cyclic corrosion sequence describedearlier.

The encouraging results from these series of tests led to alonger-term test program utilizing probes and integral tubesections located in the furnace and superheater areas of acoal-fired boiler. The objective w as to determ ine w hetherco-firing w ith up to 22% RD F could be achieved w ithout any

negative corrosion consequences33. The high sulfur coal in thesetests produced a S/Cl ratio of about 11, w hich w as expected tobe am ple for vapor phase conversion of chlorides to sulfates andhence suppression of chloride attack.

W hile co-firing M SW did not affect corrosion in the furnacearea, a 6-10 fold increase in corrosion of low alloy steels w asexperienced in the superheater area. This increased corrosionw as attributed to sulfide attack, on the rationale that the depositshad a higher sulfur content during the co-firing period thanduring coal firing alone. This explanation appears flaw ed sincesuperheater deposits in refuse boilers typically are fairly high insulfur because chlorides tend to convert to m ore stable sulfates.Consequently, the presence of sulfur-rich corrosion products perse does not disprove that the corrosion w as chloride dom inated.

To the contrary, one w ould expect to see less, not m ore, sulfur indeposits during cofiring, since the M SW /coal m ix had a 20%low er sulfur content than the coal. O n these considerations, theresults from this field test are judged inconclusive for assessingthe efficacy of sulfur in curbing chloride attack.

CO RRO SIO N-RESISTAN T ALLO YS

The relatively high chlorine content of M SW profoundlyinfluences m aterials selection for refuse boilers because carbon

and low alloy steels, the w orkhorses in regular utility boilers,possess inadequate resistance to chloride attack at elevatedtem peratures. As w ill be show n, this applies also to a largem easure to conventional austenitic stainless steels. The m aterialsof choice are high nickel-containing austenitics and especiallynickel-base alloys. Som e com m on Fe-base and N i-base alloysem ployed in w aste incinerators are listed in Table 2.

M ore recently developed alloys targeted prim arily at theincineration sector, listed in Table 3, are alloys H R16078,AC 6679, 45 T M 80, H R11N 52, H R30M 11and JH N 2411. All ofthese contain m ajor fractions of nickel for providing prim arychloride resistance, together w ith



10/14

substantial chrom ium content for protective scale form ation.Alloy 6581and look-alike alloy 625M 11are m odified versions ofalloy 625 (m inus refractory m etal additions) optim ized for w eldoverlay applications.

Effect of alloy composition

The w ell-established role of nickel for providing outstandingcorrosion resistance in reducing-chloridizing environm entsapplies equally to oxidation-chloridation. The beneficial effect ofN i and Cr in retarding corrosion in incineration environm entsw as quantified in recent Japanese studies10,11,.52,54. Correlationsfrom these investigations are show n in Figures 15, 16 and 17.The results plotted in Figure 17 are of special interest becausethey are based on long-term , in situ exposures in three M SW

incinerators. Chrom ium is im portant for the form ation ofprotective oxides on iron- and nickel-base alloys, w hich requiresa m inim um content of about 20% Cr. Although higher Cr levelsm ay further enhance corrosion resistance, 30% Cr is a judged tobe a practical m axim um for engineering alloys to assure goodductility and w eldability.

M olybdenum appears to be highly beneficial in im proving

corrosion resistance in M SW incineration environm ents. Thestrongest evidence is the outstanding perform ance of alloy 625w eld overlay in refuse boiler w aterw all applications. Alloy 625(9% M o) w as found to be even m ore resistant than55N i-14Cr-1M o alloy in long-term field exposures10, lendingstrong support for the corrosion-suppressing effect of M o. Thebeneficial role of M o has been further verified by other field andlaboratory data11,51,54,82-84. H ow ever, high M o contents

Figure 1 6 Effect of Cr + M o content on corrosion in sim ulated M SW incinerationenvironm ent (ref. 54).

Figure 1 5Effect of N i content on corrosion in sim ulated M SW incinerationenvironm ent (ref. 5-1).


aH aynes International, Inc. bM annesm ann Edelstahlrohr G m bH . cKrupp VD M G m bH; dSum itom o M etal Industries, Ltd. eM itsubishi M aterials Corp. fSandvik AB.gD aido Steel Com pany, Ltd.

aAvesta Sheffield AB; bRolled Alloys, Inc; cH aynes International, Inc.; dM inim um ; eM axim um .


Table 2W rought alloys for high tem perature applications in M SW incinerators

Table 3Recently developed alloys for high tem perature applications in M SW incinerators


11/14

operating M SW incinerators10. Alloy 625 excels not only forrefuse boiler waterw all protection but also for superheatertubing. For that application, the corrosion rate of alloy 625 w asestim ated to be 10 to 20 tim es low er than for carbon steel86. Acom parable im provem ent factor over a low alloy steel (T-22) isshow n in Figure 18.

Seem ingly at variance w ith the excellent perform ance of alloy625 is the reported m etal loss of 0.35 m m (14 m ils) on a testsection of alloy 625 overlayed screen tubing after a 15 m onthexposure in a U S W TE plant86. N otw ithstanding these m ediocretest results, the plant w ent ahead w ith w eld overlaying the entirescreen section. Significantly, after 30 m onthsservice, the alloy625 overlay show ed no discernible attack. The m arked disparitybetw een the earlier test results and the follow -on full-scaleinstallation probably stem s from uncertainties regarding m etalloss determ inations on the original test section. These w erebased on ultrasonic thickness m easurem ents, w hich are verydifficult to perform accurately on rippled w eld deposit surfaces.

A lloy 825 is another long-established alloy in U S W TE plants,used prim arily for high tem perature superheater tubing, as notedearlier18. This M o-enhanced N i-Fe-Cr alloy has generallyperform ed w ell, but there are scattered instances w here it failedto provide satisfactory life. M ost notew orthy is the unfavorablecorrosion experience w ith alloy 825/carbon steel com posite

w aterwall tubing in a R D F incinerator20

. After as little as tw oyears, corrosion of the alloy 825 O .D . necessitated progressiverepairs by piecem eal w eld overlaying w ith alloy 625. The restoredw aterw all has now been in service for up to six years and show sno signs of corrosion87. As w ould be expected from its low er N iand higher Fe content, alloy 825 is less resistant than alloy 625, asexem plified in Figure 18. Another exam ple of the superiority ofalloy 625 w as provided by side-by-side tube shield installations ofthese m aterials in a M SW incinerator, w hich show ed substantiallyshorter life of the alloy 825 shields21.

Austeni tic stainless steel

Austenitic stainless steels gave fairly good service in early W TEplants, m any of w hich operated w ith relatively m ild conditions.W ith accum ulating plant experience, it becam e increasingly clearthat the perform ance of stainless steels proved unreliable, andthat stainlesses m ay offer only little, if any, im provem ent overordinary boiler tube steels14,20,38,45,51,88,89.In several instances, Type304 S.S. com posite tube test panels had to be taken



Figure 17 Effect of alloy com position on corrosion in operating M SWincinerators (ref. 11).

(over about 15% ) can be counterproductive in oxidizing-chloridizing environm ents, especially at elevated tem per-atures60,61. The concern is form ation of m olybdenum chlorides

or oxychlorides and consequent risk of form ing m oltencorrosion products.An interesting and unexplained M o effect w as discovered

during the developm ent of alloy H R11N 52. It w as found thatdevelopm ental alloys w ith M o contents of 3% or higher sufferedfrom a new ly discovered form of high tem perature stresscorrosion cracking, w hile com positions w ith very sm all or noM o content sustained intergranular attack. These findingsaccount for Sum itom o optim izing the M o content of alloysH R11N and H R30M at 1% M o11,52. Effective suppression ofintergranular attack in both of these alloys is achieved byadditions of about 0.15% nitrogen.

The effect of silicon appears to be variable. W hile Si additionsenhance the protectiveness of oxide scales and decrease the

form ation of volatile m etal chlorides85

, Si is reported to bedetrim ental in reducing-chloridizing environm ents84. Cobalt isconsidered beneficial for im proving chloridation resistance, butto a far lesser extent than N i. Cobalt m ay possibly be detrim entalat tem peratures above 740C (1364F) w hich is the m elting pointof CoC1273 Alum inum , sim ilar to silicon, enhances theeffectiveness of protective oxides, and has been show n toim prove corrosion resistance in reducing chloridizingenvironm ents61.

Figure 1 8Corrosion of test tubes in an RD F incinerator (ref 45).

High-nickel alloy

Based on extensive test data and service experience, alloyscontaining large fractions of nickel have dem onstrated

outstanding corrosion resistance in M SW incinerationenvironm ents. Am ong these, N i-Cr-M o alloy 625 has establisheditself by far as the m ost w idely used m aterial for effectivecorrosion protection in refuse boilers, prim arily in the form ofw eld overlay on w aterwalls. There is broad consensus thatw astage rate of alloy 625 is less than 0.25 m m yr1(10 m py) andthat it outperform s carbon and low alloy steels by at least a factorof 10. For instance, in an exceptionally severe RD F boilerexposure w here the carbon steel corrosion rate w as 180 m py,alloy 625 corroded at less than 3 m py47. The outstandingperform ance of alloy 625 w as verified in an extensive fieldevaluation encom passing several


12/14


out of service due to excessive corrosion. Even m ore highlyalloyed stainless grades m ay fare badly. In one instance, aniobium -enhanced version of 25C r-20N i S.S. (H R-3C) corrodedfaster than Type 304 S.S., as show n in Figure 18. It isconjectured that the poor show ing of the H R-3C m ay possiblybe related to the very high volatility of niobium chloride.

The presence of FeC12 appears to be especially detrim ental tostainless steels. In laboratory tests w ith chloride-rich saltm ixtures, com positions containing FeC12or PbC 12proved to beextrem ely aggressive38. Salt m ixtures containing either one ofthese m etal chlorides attacked Type 304L S.S. m ore severely than

carbon steel. These experim ents led to the conclusion thatm ixtures of N aC I + K CI, previously thought to be noncorrosiveto refuse boiler steam generating tubes, can becom e highlycorrosive w hen m ixed w ith FeC12present as a corrosion prod-uct. The aggressiveness of FeC12is apparent also from Figure 13,w hich sim ilarly show s higher corrosion rates of Type 304L S.S.than for carbon steel in iron chloride containing salt m ixtures.

An additional shortcom ing of 300 Series stainless steels istheir susceptibility to chloride-induced pitting and stresscorrosion cracking during dow ntim e. The risk of such attack bym oist tube deposits w as identified as a potential problem areaw hen W TE plants first cam e onto the scene. The W TE sector isslow in accepting that the perform ance of stainless steels inrefuse boilers varies w idely and therefore are a questionable

choice for dependable corrosion resistance. N onetheless, m anyM SW incinerator operators continue to em ploy stainless steels,partly on the basis that they do perform fairly w ell in som eplants, and partly on reluctance to upgrade to costliercorrosion-resistant alloys.

Composites and coatings

Co-extruded com posite Type 304 S.S./C.S. w aterw all tubingperform ed w ell in several Sw edish W TE plants86, but theseoperated w ith quite m ild steam conditions unrepresentative of

m odern higher tem perature units. In the U S, the singlelarge-scale com m ercial application of com posite tubing w as inthe aforem entioned RD F plant w here co-extruded alloy 825/C.S.w aterw all tubing failed to provide adequate life87. The superiorperform ance of Alloy 625 prom pted several attem pts to producecoextruded Alloy 625/C.S. com posite tubing on a com m ercialscale, but this effort proved unsuccessful due to the largestrength differential. Difficulties in m anufacturing alloy 625com posite tubing by co-extrusion have fostered the developm entof novel techniques for producing N i-Cr-M o alloy com positesthat offer alternatives to conventional overlay deposition by G asM etal Arc W elding (G M A W ). Recent developm ents aim edlargely at the W TE sector include liquid atom ized m etal deposi-tion of alloy 6581, plasm a pow der weld deposition of alloys C-276and alloy 625M 11, and helical rolling of alloy C -2211.

Boiler vendor and plant operators have experim ented w ith aw ide range of m etallic coatings in the hope of finding acost-effective m ethod for extending the life of refuse boilertubing, prim arily for waterw all panels45,47,49,55,82,91,92. The successof these test installations has varied greatly. Som e field trialsindicated unsatisfactory coating perform ance and life, w hileothers produced fair to good results. In general, coatings need tobe renewed on an


AREA S FO R FU RTH ER R& D

There are several areas w here further R& D could beproductively focused to attain a fuller understanding ofchloride-induced corrosion in M SW incineration, and to advancethe developm ent of corrosion-resistant m aterials.Corrosion-related issues m eriting further elucidation are listedbelow .

M echanism by w hich chlorides perm eate protectiveoxide scales.

Characterization of the corrosive environm ent and ashdeposits.

Corrosion inhibitive effect of sulfur species. M echanism of high tem perature stress corrosion

cracking and intergranular attack. Effect alloying additions of m olybdenum and copper

on corrosion behavior. Synergism betw een corrosion and abrasive/erosive w ear.

To gain further insights into corrosion m echanism s andm anifestations, various novel approaches are being exploited.Am ong these are electrochem ical techniques based on A .C.im pedance94,95 and potentiodynam ic polarization96, electronm icroscopy25and calorim etry56.

Continuing w ork effort should additionally be directed atdeveloping new and im proved corrosion-resistant m aterials. Thisincludes not only alloys optim ized for refuse boiler applications,but also cost-effective com posites and coatings. To support thecorrosion research and m aterials developm ent effort, m oreintensive m onitoring and data collection/dissem ination is neededto precisely characterize the corrosive environm ents and toevaluate m aterials perform ance. All of these endeavors are beingsystem atically pursued in the aforem entioned N ED O Programon developing high-efficiency W TE technology10,11. Furtherprogress tow ard that objective could be achieved if a sim ilarcollaborative developm ent program w ould be instituted in theW estern hem isphere.

A CK N O W LED G M EN T

Support from the N ickel D evelopm ent Institute for preparationof this paper is gratefully acknow ledged. The author also w ishesto express his appreciation to D r. I.G . W right for his review andhelpful com m ents.

REFERENCES

1 Cutter, A. J. B., Halstead, W. D., Laxton, J. W. and Stevens, C. G.Trans. ASME, J.Engg. for Power, 307-312 (1971).

2 James, P. J. and Pinder, L. W. Paper No. 133,CORROSION/97,NACE International, Houston, TX (1997).

annual basis because they spall off or are consum ed13. G oodresults are reported w ith a heavy-body fused coating consistingof tungsten carbide in a high-nickel braze m atrix49. A highlyprom ising developm ent is a therm al spray applied dual-layerAl/80N i20Cr coating, reported to have m aintained excellentdurability for over three years55. The outer alum inum layer isclaim ed to function in a sacrificial m anner to provide cathodicprotection for the underlying alloy layer during dow ntim e. Thiscoating system has now been applied at seven Japanese W TEplants, m ost recently by high velocity oxygen fuel (H VO F)spraying93.


13/14


3 W eight, 1. G ., Km nsC. H . H . and N agarajan, V.Boiler Tube Failures inMSW/RUB Incineration/Co-Firing, EPRI Report 7R-103658, Palo

Alto, CA, D ecem ber 1994.4 K rause, H . H . Paper N o. 200, CO RR O SIO N /93, N AC E International,

H ouston, TX (1993).5 K rause, H . H . and W right, 1. G .Materials Performance, 35 (1), 46-53

(1996).6 Bryers, R. W . In: R. W . Bryers, ed.Incinerating Municipal and

Industrial Waste, pp. IX-XII. H em isphere Publishing Corp.W ashington, D .C. (1991).

7 M iller, P. D .et al. Corrosion Studies in Municipal Incinerators.Battelle Report to Environm ental Protection Agency, EPA ReportSW -72-3-3 (1972).

8 Vaughan, D . A., K rause, H . H . and Boyd, W . K.MaterialsPerformance, 14 (5) 16-24 (1975).

9 O utlook of W aste Pow er G eneration in Japan and N ED O Project,Alcohol and Biom ass Energy Departm ent, N ED O , Japan (1992).

10 K aw ahara, Y., H agiw ara, H ., N akam ura, M ., Shibuya, E. and Y ukaw a, K.,Paper N o. 564,CORROSIONl95, N A C E International, H ouston, TX (1995).

11 K aw ahara, Y., N akam ura, M ., Tsuboi, H . and Yukaw a, K., Paper N o.165, CO RRO SIO N /97, N AC E International, H ouston, TX (1997).

12 Stoltz S. C. and Kitto, J. B. (eds)Steam, Babcock & W ilcoxCom pany, Barberton, O H , 1992, p. 27/1-27/21.

13 W right, 1. G . and K rause, H . H .,Assessment of Factors Affecting Boiler TubeLifetime in Waste-Fired Steam Generators: New Opportunities for Research

and Development, N ational Renew able Energy Laboratory ReportN REL/TP-430-21480, (1996).

14 Sorell, G . and Schillm oller, C. M . In: K. N atesan and D . J. Tillack (eds)Heat-Resistant Materials, pp. 623-644. ASM International, M aterials Park,O H (1991).

15 Strach, L. In: G . Y. Lai and G . Sorell (eds),Materials Performance in WasteIncineration Systems, pp. 8/1-8/10. N A CE, H ouston, TX (1992).

16 Strach, L. and W asyluk, D .T. Materials Performance, 32 (12) 28-34(1993).

17 H ulsizer, P. N . In: G . Y. Lai and G . Sorell (eds),Materials Performance inWaste Incineration Systems, pp. 11/1-11/14. N A C E H ouston, TX (1992).

18 Sm ith, G . D . and Lipscom b, W . G . In: G .Y . Lai and G . Sorell (eds),Materials Performance in Waste Incineration Systems, pp.

29/1-29/15. N AC E, H ouston, TX (1992).19 G ibbs, D . R., Blue, J. D . and H epp, M .P. Proc. 1988 National Waste

Processing Conf., pp. 93-99. ASM E, N ew York, N Y (1988).20 Burnham , D . E., G ibbs, D . R., G ittinger, J. S. and Johnson, H . E.EPRI

Conference on Municipal Waste as a Utility Fuel, Springfield, M A (1989).21 Stanko, G . J., Blough, J. L. and M ontrone, E. D . In: R. W . Bryers,Incinerating

Municipal and Industrial Waste, pp. 261-278. H em isphere Publishing C orp.W ashington, D .C. (1991).

22 Licata, A. J., Terracciano L. A., H erbert, R. W . and Kaiser, U . In: G . Y. Lai andG . Sorell, Materials Performance in Waste Incineration Systems, pp.

5/1-5/9. N AC E, H ouston, TX (1992).23 Sorell, G . Paper N o. 212, CO RRO SIO N /93, N AC E International,

H ouston, TX (1993).24 Brobjorg J. N . and K rause, H . H . In: R. W . Bryers (ed.),Incinerating

Municipal and Industrial Waste, pp. 321-341. H em isphere Publishing Corp.,W ashington, D .C., (1991).

25 K alm anovitch, D . P. and Steadm an, E. N .International Joint PowerConf., Phoenix, A Z, O ctober (1994).

26 K rause, H . H ., Vaughan, D . A. and Boyd, W . K.Trans. ASME J.Engg. Power, 97, 44"52 (1975).

27 K rause, H . H ., Vaughan, D . A. and Boyd, W . K.Trans. ASME, J.Engg. Power, 98, (3) 369-374 (1976).

28 K rause, H . H ., Vaughan, D . A., Cover, P. W ., Boyd, W . K. and O beracker, D .A.Trans. ASME, J. Engg. Power, 99 (3) 449-459 (1977).

29 Vaughan, D . A., K rause, H . H . and B oyd, W . K . In: R. W . Bryers, (ed.),Ash Deposits and Corrosion Due to Impurities in Combustion Gases,

H em isphere Publishing Corp. W ashington, D .C. pp. 455-472 (1977).

30 K rause, H . H . In: M . F. Rothm an, (ed.)High Temperature Corrosion inEnergy Systems, pp. 83-102. The M etallurgical Society of A IM E, W arrendale,PA. (1985).

31 K rause, H . H . Paper N o. 242, CO RRO SIO N /91, N A C E International,H ouston, TX (1991).

32 K rause, H . H . In: R. W . Bryers (ed.),Incinerating Municipal and IndustrialWaste, pp. 145-159. In: R. W . Bryers, (ed.), H em isphere Publishing Corp.,W ashington, D .C. (1991).

33 K rause, H . H . and Stropki, J. T. In: G . Y. Lai and G . Sorell, (eds),MaterialsPerformance in Waste Incineration Systems. pp. 2/I ?/18. N AC E. H ouston,TX, (1992).

3.1 W eight. 1. G .. N agarajan, V. and K rause. 11. H . Paper No. 21U ,CO RRO SIO N /93, N AC E International, H ouston, TX (1993).

35 W right, 1. G ., K rause, H . H . and D ooley, R. B. Paper No. 562,CO RRO SIO N /95, N AC E International, H ouston, TX (1995).

36 K rause, H . H . and W right, I. G .Materials Performance, 5(1), pp.46-54 (1996).

37 Bam a, J. L., Blue, J. D . and D aniel, P. L. Paper No. PG TP-85-40.ASME J2thBiennial National Waste Processing Conf., D enver, CO , (1986).

38 D aniel, P. L., Paul, L. D . and Barna, J. L.Materials Performance, 27,(5), pp. 22-27 (1988).

39 D aniel, P. L. In: A. V. Levy (ed.),Corrosion-Erosion-Wear ef Materials atElevated Temperatures, pp. 1/1-1/10. N A C E, H ouston. TX, (I 991).

40 Paul, L. D . and D aniel, P. L. Paper N o. 216, CO RRO SIO N /93, N AC EInternational, H ouston, TX (1993).

41 K ung, S. C., D aniel, P. L. and Seeley, R. R. Paper No. 165,CO RRO SIO N /96, N AC E International, H ouston, TX (1996).

42 Bryers, R. W . and Kerekes, Z. Paper 68-W A /CD -4, ASM E M eeting,N ew York, N Y, (1968).

43 Bryers, R. W . and Kerekes, Z., Paper 46-b, AIChE M eeting, AtlanticCity, NJ, (1971).

44 Kerekes, Z. E., Bryers, R. W . and Sauer, A. R. In: R. W . Bryers, (ed.),Ash Deposits and Corrosion Due to Impurities in Combustion Gases,

pp. 455-472. H em isphere Publishing Corp., W ashington, D .C., (t 977).45 Blough, J. L., Stanko, G . J., Bakker, W . T. and Steinbeck, T. In: K . N atesan,

P. G anesan and G . Lai (eds),Heat-Resistant Materials 11, pp. 645-652.A SM International, M aterials Park, O H , (1995).

46 Plum ley, A. L., Roczniak, W . R. and Lew is, E. C. In: R.W . Bryers, (ed.), p.373-404. Incinerating Municipal and Industrial Waste, H em ispherePublishing Corp., W ashington, D .C. (1991).

47 Plum ley, A. L., Roczniak, W . R. and Lew is, C. E. In: G . Y. Lai and G . Sorell,(eds),Materials Performance in Waste Incineration Systems, pp. 7/1 to

7/25. N A C E, Houston, TX, (1992).48 Plum ley, A. L., Roczniak, W .R. and B acchi, J.A. Paper N o. 220,

CO RR O SIO N /93, N AC E, H ouston, TX (1993).49 Plum ley, A. L., Kerber, G . and H errm ann, W . In: R.W . Bryers, (ed.),

Incinerating Municipal and Industrial Waste, pp. 25-46. H em ispherePublishing Corp., W ashington, D .C. (1991).

50 O tsuka, N . and Kudo, T. In: Y. Saito, B. O nay and T. M aruyam a, (eds),HighTemperature Corrosion of Advanced Materials and Protective Coatings,

pp. 205-21 1. Elsevier Science Publishers, N orthH olland, (1992).51 O tsuka, N ., N atori, A., Kudo, T. and T. Im oto, Paper No. 289, CO R

RO SIO N /93, N AC E International, H ouston, TX (1993).52 O tsuka, N . N atori, A. Kudo, T. and Im oto, T. Paper N o. 401, CO R

RO SIO N /94, N AC E International, H ouston, TX (1994).53 N akagaw a, K. and Isozaki, T. Paper N o. 177, CO RRO SIO N /94,

N A C E International, H ouston, TX (1994).54 O tsuka, N ., N akagawa, K., Kaw ahara, Y. Tsukaue, Y, Yam om oto, A. and

Yukawa, K ., Paper N o. 565, CO RRO SIO N /95, N AC E International,

H ouston, TX (1995).55 K awahara, Y. and Kira, M ., Paper N o. 563, CO RRO SIO N /95, N A C E

International, H ouston, TX (1995).56 O tsuka, N ., N akagawa, K., Tsukaue, Y., Kaw ahara, Y. and Y ukaw a, K., Paper

N o. 157, CO RRO SIO N /97, N AC E International, H ouston, TX (1997).57 G rabke, H . J., Reese, E. and Spiegel,M. Corrosion Science, 37, (3),

pp. 1023-1043 (1995).58 G rabke, H . J. In: R. W . Bryers, (ed.),Incinerating Municipal and Industrial

Waste, pp. 161-176. Hem isphere Publishing Corp., W ashington, D .C. (1991).59 Reese, E. and G rabke, H . J.,Werkstoffe and Korrosion, 43, 547-557.

(1992).60 Elliott, P., Ansari, A. A., Prescott, R. and Rothm an, M . F. Paper No.

13, CO RRO SIO N /85, N AC E, H ouston, TX (1985).61 O h, J. M ., M cN allan, M . J., Lai, G . Y. and Rothm an, M . F.

Metallurgical Transactions A, 17A, 1087-1092 (1986).62 M cN allan, M . J. Paper 626, CO RRO SIO N /94, N AC E International,

H ouston, TX (1994).

63 Stott, F. H ., Prescott, R. and Elliott, P.Werkstoffe and Korrosion, 39,pp. 401-405. (1988),

64 D aniel, P. L. and Rapp, R. A. In: M . G . Fontana and R. W . Staehle, (eds),Advances in Corrosion Science and Technology, pp. 55-173. Vol. 5,Plenum Press, New York, N Y, (1976).

65 Reid, W . T.External Corrosion and Deposits - Boilers and Gas Turbines,Am erican Elsevier Publishing C om p., N ew York, N Y, (1971), pp. 104-1 10.

66 Slusser. J. W ., D ean, S. W ., W atkins, W . R. and G off, S. P. Paper No.217, CO RR O SIO N /93, N AC E, H ouston,TX (1993).



14/14


07 Sm ilh. (i. I).. tiM ICIJn 1'. M K I Shoem aker. I.. I':. Paper No. 280_ C O RRO SIO N /90, N A C E, llouston, TX (1990).

68 Bakker, W . T. and Perkins, R. A. In: A. V. Levy, (ed.), Corrosion-Erosion-W earof M aterials at Elevated Tem peratures, pp. 2-1 to 2-29. N A C EInternational, (1991).

69 Lai, G . Y. H igh-Tem perature Corrosion of Engineering Alloys, pp.85-115. ASM International, M aterials Park, O H , (1990).

70 Fassler, K ., Leib, M . and Spahn, H . M itteilung der VG B, 48, (2),126-139 (1968).

71 Rapp, R. A. Corrosion, 42, (10), 568-577. (1986).72 Barham , D . and Tran, H . N . Canadian Institute of M ining Bulletin, 64,

(947,) 151-154. (1991).73 Barnes, J. J. Paper N o. 446, CO RRO SIO N /96, N A C E International,

H ouston, TX, (1996).

74 Sm ith, G . D . and G anesan, P. In: K . N atesan, P. G anesan and G .Y. Lai,(eds), H eat-Resistant M aterials 17, pp. 631-636. ASM International, M aterialsPark, O H , (1995).

75 G anesan, P., Sm ith, G . D . and Shoem aker, L. E. In: G . Y. Lai and G . Sorell(eds) M aterials Perform ance in W aste Incineration System s, pp. 33-1 to33-10. N A C E, Houston, TX (1992).

76 W hitlow , G . A., G allagher, P. J. and Lee, S. Y. In: G . Y. Lai and G . Sorell(eds) M aterials Perform ance in W aste Incineration System s, pp. 6-1 to 6-15.N A C E, H ouston, TX (1992).

77 U npublished inform ation from Ishikawajim a-Harim a H eavy Industries(M arch 1997).

78 Antony, C. M ., Srivastava, S. K. and Lai, G . Y. In: K. N atesan and D . J.Tillack, (eds), H eat-Resistant M aterials, pp. 667-673. ASM International,M aterials Park, O H , (1991).

79 Bendick, W ., Lindem ann, J. and Schendler, W . Stainless Steel Europe,38-43. (1991).

80 Agarw al, D . C., Brill, U . and Klow er, J. Paper N o. 566, CO RRO

SIO N /95, N AC E International, H ouston, TX (1995).81 W ilson, A. Forsberg, U . and N oble, J. Paper N o. 153, CO RRO

SIO N /97, N AC E International. H ouston. TX (1997).

82 I lagLhlom . 1:. and N\ lol 1. I.. Prm. th~rr rr Irk nrr rrl l'ni r r Enghwerutg, pp.1617-1628. Kluw er Academ ic Publishers, D ordrecht, The Netherlands,(1994).

83 N ylof, L. and Haggblom , E. Paper N o. 154, CO RR O SIO N /97, N A C EInternational, H ouston, TX (1997).

84 Brill, U ., Kl6w er, J. and Agarw al, D . C., Paper No. 439, CO RROSIO N /96, N AC E International, H ouston, TX (1996).

85 Brill, U ., K ldw er, J., M aassen, E., Richter, H ., Schw enk, W . and J.Venkatesw arlu, In: Coutsouvadis et al., (eds), M aterials for Advanced Pow erEngineering, pp. 1585-1596. K luw er Academ ic Publishers, D ordrecht, TheN etherlands, (1994).

86 Private com m unication from O gden-M artin Projects (February 1997).87 Private com m unication from Babcock & W ilcox (February 1997).88 Tracy, R. A. and Perry, D . A. In: G . Y. Lai and G . Sorell, (eds), M aterials

Perform ance in W aste Incineration System s, pp. 9/1-9/9. N A C E, H ouston,TX, (1992).

89 M eadow croft, D . B. In: Coutsouradis et al., (eds) M aterials for AdvancedPow er Engineering pp. 1413-1430. K luw er Academ ic Publishers, D ordrecht,The N etherlands, (1994).

90 O delstam , T., Berglund, G , and N ylof, L. In: R.W . Bryers, (ed.), IncineratingM unicipal and Industrial W aste, pp. 279-298. H em isphere Publishing C orp.W ashington, D .C. (1991).

91 D eVincentis, D . M ., G off, S. P., Slusser, J. W ., Zurecki, Z. and Rooney, J. T.Paper N o. 198, CO RRO SIO N /93, N ACE, Houston, TX (1993).

92 K rause, H . H . Paper N o. 140, CO RR O SIO N /92, N AC E H ouston, TX(1992).

93 K aw ahara, Y. and K ira, M . Corrosion, 3, (3), 241-251 (1997).94 N ishikata, A., N um ata, H . and Tsuru, T. M aterials Science and

Engineering, A 146, 15-31 (1991).95 M atsunaga, Y. and Nakagaw a, K. Paper N o. 163, CO RRO SIO N /97,

N A C E International, H ouston, TX (1997).

96 N akagaw a, K , M atsunaga, Y. and Yukawa, K. Paper N o. 164, CO RRO SIO N /97, N AC E International, H ouston, TX (1997).

Documents

TheRoleofChlorineinHigh TemperatureCorrosioninWaste to EnergyPlants 14045