mat condenser 5-pgu nuclearrenmaterials

8/6/2019 Mat Condenser 5-PGU NuclearRenMaterials

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The NuclearRenaissance:

Materials of Choicefor Power PlantSurface Condensers &BOP Heat Exchangers


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Educational ObjectivesOn completion of this course, students will:

The Nuclear Renaissance: Materials

of Choice for Power Plant Surface

Condensers & BOP Heat Exchangers

Amidst the clamor and increasing world demand for en-

ergy, the continued use of fossil fuels for electric power

generation has recently emerged as the bane of the indus-

try. Green power is being championed as the new fuel de

jour kid on the block. Environmentalists and other global

warming advocates are successful ly lobbying their political

agendas for cap & trade policies, carbon sequestration, N0X

and S0X

and other greenhouse gas limits. In many cases,

these eorts have resulted in the outright cancellation,

delay or unit reductions of new coal-red plants. Indeed,

the Obama Administration has tacitly noted that coal-red

power plants are not necessarily o the table they just

wont be aordable. Similarly, simple and combined cycle

gas turbine (CCGT) units, popularized during the Enron

gas bubble era, are, due to currently competitive pric-

ing, may be the only stopgap option for new base load and

peaking capacity additions. Indeed, due to its low cost, 2-3

year construction window and lower emissions vs. compet-

ing technologies, the CCGT conundrum remains as one of

the few remaining options suitable for power production.

Wind, biomass, hydro, photovoltaic, solar and other re-

newables continue to produce an increased percentage of

the power base but contribution remains politically driven,

costly, inecient and pitifully low.Enter the nuclear renaissance. Continuing market pres-

sures, generation eciencies, increasing ROI revenues and an

enviable safety record since TMI and Chernobyl has allowed

the nuclear phoenix to rise with the promise of emission-

free power. Even many of the ercest and pragmatic green

power advocates have assumed a dramatic paradigm shift

from their early anti-nuke platforms. Assuming this energy

source conceives and bears the gestated fruit of the renais-

sance, the next several years will be telling in terms of the

challenges brought forward by licensing, design, nancing,

construction and operation of a new generation of nuclear

power reactors.

Paramount among these is a new, time-tested generation

of construction materials that will be evaluated to insure a

40 - 60 operational life of the plant. Consider the problem-

atic copper materials that were chosen during the early 70s

for their high thermal conductivity, competitive cost and

ease of fabrication. Contrast these past lessons-learned to

current-day, state-of-the-art generation eet construction

standards where high performance, state-of-the-art materi-

als can emerge as the prominent industry players of choice.

The paper will examine these and other relevant aspects of

the technical and commercial supply chain that is predicted

to both challenge and reward designers and material suppli-

ers well into the next decade.

OverviewCurrently, there are 440 nuclear power reactors around theworld with 104 in the US producing some 11% of the worlds

power generation needs and 20% in the US (See Figure 1).

1. Discover the impurities that can cause the mostdamage to nuclear plant heat exchangers.

2. Learn some of the most common corrosionprocesses that occur in heat exchangers.

3. Be introduced to the materials that are consideredstate-of-the-art for heat exchanger fabrication.

4. Learn about modern technologies to minimizecorrosion in heat exchangers, and thus reduce plantcosts due to outages and maintenance repairs.


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Figure 3 The Boiling Water Reactor

Main

Steam Lines

Turbine

Generators

CondenserFeedwater

Pumps

Torus

Control Rods

Reactor

Core

Inerted Drywell

(Primary

Containment)

Reactor Building

(Secondary Containment)

Electricity

to Switch Yard

Figure 1 Current U.S. Fuel Mix Breakdown

3.0%Oil

18.6% Natural Gas

19.4% Nuclear

6.4%Nuclear

2.7%Renewables

49.9% Coal

Figure 2 The Pressurized Water Reactor

Figure 4 The CANDU Reactor

www.powergenu.com 3

Of the some 440 reactors, there are three (3) main

producers of electrical power. All are classically dened as

pressurized light water ssion reactors varying in design and

conguration (see Figures 2, 3, 4).

AdvancedReactorDesigns To compliment the signicant availability factor advances

made by the existing nuclear eets, new, Generation II &

Generation III reactor designs have been heralded as dra-

matically advancing the economics and safety of the package.

Indeed, this new generation of light water reactors oers

a highly economical and more modular design, enhanced

safety, purported minimal waste and resistance to fuel pro-

liferation. Currently, the U.S. NRC has certied a number of

reactor designs. They include the following in Table 1.

Background&HistoryMost of the worlds 440 Generation 1 nuclear power reactors

were designed and constructed employing one of the afore-

mentioned Figure 1, 2 or 3 designs. And, since most were

designed in the 1960s and 1970s, many could be considered

as nearing the end of their useful life. Indeed, operating

license extensions may have become the industry savior

allowing many plants to extend their careers well beyond

initial design limits.

Early concepts utilized during the rst generation of

nuclear power plant design employed materials that had

their DNA connected to the more mature industries. These

reference industries included chemical process, petrochemi-

cal and of course, existing oil and coal-red power plants.

Material and design standards covering general heat ex-

Table 1: Generation III Advanced Reactor Designs Current Committed COL Design Applications

Design

ABWR: Toshiba America Nuclear Energy Corporation Advanced Boiling Water Reactor design

AP1000: Reactor by Westinghouse Electric Company

EPR: U.S. Evolutionary Power Reactor by AREVA Nuclear Power

ESBWR: Economic Simplied Boiling Water Reactor by GE-Hitachi

USAPWR: U.S. Advanced Pressurized Water Reactor by Mitsubishi Heavy Industries, Ltd.



changers within these industries were transferred directly

into the heat transfer equipment within the nuclear steam

supply system (NSSS). Design codes such as the early ver-

sions of the HEI, ASME, TEMA and other governing bod-

ies were driven by design standards already in place. Steam

generators, surface condensers, feedwater heaters, MSRs,

and BOP exchanges all followed the traditional paths. It

was not until later in their operational life did problemsmanifest themselves. These problems were typically as-

sociated with improper material selection within the plant

operating envelope highlighted by the use of copper bearing

materials in the secondary side.

This conventional wisdom drove the material selection

process for the secondary or steam and raw water side materi-

als for the Generation 1 NSSS. Copper and copper-alloys were

typically chosen for their high thermal conductivity, ease of

fabrication and competitive cost. Selection and use of these

and other materials proved to be less than adequate causing

costly repairs and replacements over the years. Many of theworlds eet of nuclear units, and in particularly in the US, have

replaced their entire secondary side cadre of materials due to

a number of maladies that have eected plant performance.

Denting (a phenomenon of copper pick up and transport

from mainly the feedwater heater system and, to a lesser

extent, the main surface condensers and other cycle heat

exchangers) has been particularly problematic resulting in

the replacement of plant steam generators, turbine blades

and secondary side equipment such as surface condenser

and regenerative feedwater heater tube materials. Addi-

tional and unforeseen corrosion activities have also greatly

reduced the operating life of many secondary side systems

requiring signicant modication and cost to mitigate the

issues. These issues will be addressed later in the paper.

It is clear that there are signicant lessons to be learned

in the material application of the latest generation of nuclear

plants. Based upon the success of license extensions, power

uprates, etc. the existing nuclear eet has demonstrated

dramatic success in metallurgical upgrades over the past

20 years. These lessons learned can provide a successful

pathway for material upgrades for BOP/secondary side heat

exchanges within the NSSS loop.

HighPurityWater

Water chemistry is strictly controlled in NSSS systems.Protection of this working uid is essential and continu-

ously monitored as a vital organ of the plant water system.

Having noted this, extreme care must be exercised in the

selection of appropriate materials that come in contact with

this water and systems must be put in place to prevent the

intrusion of unwanted elements.

In support of this requirement, all NSSS manufactur-

ers have provided guidelines relating to high feedwater/

condensate water purity. Paramount on the purity level is

the control of dissolved oxygen, reducing conductivity and,

possibly the most important is maintaining an exceedinglylow level of chlorides (Table 2). Of equal importance is the

limitation of the noted corrosion products to very low levels.

It bears noting at this point in the paper that the larg-

est single source of potentially corrosive product ingress

is the surface condenser. Assured protection against these

intrusions must be considered in the equipment designs to

prevent a reoccurrence of past catastrophic failures within

the CIRH2O, air removal and condensate systems.

MoreonWaterPurityWhile feedwater heaters and other power plant heat exchang-

ers can be bypassed, a power plant cannot operate without the

full or partial availability of the surface condenser. As noted

above, the power plant surface condenser is also the largest

potential single source of corrosive product ingress. Within

this context, condensate contamination may be the single larg-

est operational malady. Since the circulating water (CIRH2O)

Table 2: Steam Turbine Feedwater/Condensate Purity Requirements (*) 1 (PARTIAL)

WaterQualityParameters TypicallyReported ValueAnd/OrRange

Dissolved Oxygen ppb (mg/L) 10 - 20

Conductivity mmhos/cm (S/cm) 0.3 0.5

Chlorides ppb as CL 1 - 5

Silica ppb as Si02 10 - 50

Sulfate ppb as S04


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source may be from the ocean, fresh

water lakes, rivers, cooling towers and

in more increasing numbers, gray water

or treated sewage euent, it become

absolutely imperative that this device

be aorded all possible protection. Gray

water is particularly troubling as this

medium can produce not only a toxicenvironment if not treated properly

but can become a breeding ground for

organic buildup due to high blowdown

levels, producing a MIC-friendly envi-

ronment (Table 3). This below graphic

identies a typical gray water environ-

ment with specic areas of concern.

Should gray water be considered or

suspected to be present, the appropriate

experts should be consulted.

MoreonCorrosionOther areas of concern that should

be investigated when evaluating the

circulating water would include some

of the following corrodent activities

characterized from the traditional to

the more exotic (Table 4). It is not

the intent of this paper to discuss the

many corrosion activities that can

occur within a power plant circuit.

Rather, these possible maladies are

noted and should be addressed care-

fully when selecting construction

materials for heat exchangers.

CandidateMaterialsShould the nuclear phoenix arise to

renaissance maturity and currently

planned programs are fully implanted,

there exists a wide selection of tubing

materials available in the marketplace

that may, on the surface, appear suitable

and cost eective for the application

within surface condenser and secondary

side BOP heat exchangers (Table 5).

However, as a cautionary note, this

author is compelled to strongly sug-

gest that nothing short of an opera-

tional 90%+ capacity factor coupled

with a 40-60 year expected equipment

service life will be acceptable. These

commercial and operational severe-service requirements will indeed, pre-

clude the use of most of these material

options. As a result, this paper will

focus attention on selected candidate

materials that have demonstrated a

high level of worthiness and suitabil-

ity. Those materials would include Gr.

2 titanium and the family of super-

stainless alloy tubing materials.

Due to its now-approaching 40 years

of corrosion-free service9 in condenser

applications and demonstrated im-

munity to general and localized attack,

titanium has been and continues to be

the preferred material for sea water and

brackish water-cooled heat exchanger

tubing. However, given the signicant

excursions in titanium pricing and

availability over the past several years,

engineering companies and end-users

have shown an increasing interest in

more cost-eective alternative solutions

using highly alloyed stainless steels.These high performance stainless

alloys demonstrate a much improved

corrosion resistance over past gen-

Table 4: Corrosion Activities

Oxidizing Neutral

& Inhibited Conditions

Chlorides

Steam Droplet Erosion (Nuclear)

Inlet Erosion/Corrosion

Crevice & Underdeposit Corrosion

Ammonia

Galvanic (I-C)

Suspended Solids Erosion (I.E. Sand)

Calcium Carbonate

MIC

Manganese

Grey Water (Impaired Efuent)

Hydrogen Embrittlement

Biocidal Growth Fouling

Table 3: Typical Gray/Impaired or Treated Efuent Water Analysis 6

ParameterEfuent

(mg/l)HeavyMetals(total) Efuent(mg/l)

Fecal Coliform 13 Aluminum 0.15

Fecal Coliform 7 Antimony



erations while maintaining a modest increase in premium

pricing when compared to conventional stainless steels.

Given the lessons learned from Generation 1 designs, this

paper will examine the relevant characteristics of both the

titanium and super-stainless alloys for application into the

new Generation of nuclear power plants.

MechanicalPropertiesTable(s) 6 & 8 will enable the reader to compare the chemi-

cal & mechanical properties of titanium with three super al-

loy alternatives which have been developed for the market:

They include UNS S31254 super austenitic alloy and UNS

S44735 and UNS S44660 super-ferritic alloys.

HeatTransferPropertiesTable 7 identies the thermal conductivity of the three com-

peting super alloys under consideration and cp (commer-

cially pure) titanium. Al l three super alloys have reasonable

thermal performance in steam condensers, especially when

used in thin-wall conditions. Titanium, due to its improved

thermal conductivity, performs somewhat better than the

stainless alloys. However, the thermal performance all four

Table 5: Surface Condenser & BOP Exchanger Candidate Material Options (Partial List - Values May Vary)

Material Spec( AS TM) UNSNo. TubeCondition MinYield(ksi)ThermalCond

BTU/hr-FModulus106ksi

DensityLB/in3

Titanium Gr. 1 B-338 R50250 Wld/Smls 25 12.68 15.5 .163



TP304L A249 S30403 Wld 25 8.6 28.3 .29

TP304N A249 S30451 Wld 35 8.6 28.3 .29

TP316L A249 S31603 Wld 25 8.6 28.3 .29

TP317L A249 S31703 Wld 30 8.6 28.3 .28

AL2003 A240 S32003 Wld 70 10 30.5 .279

LDX2101 A240 S32101 Wld 70 9.2 29 .28

TP439 A268 S43035 Wld/Smls 30 12.3 29 .28

2205 A789 S32205 Wld 65 11 27.5 .285

2507 A789 S32750 Wld 80 8.7 29 .28

904L B674 N08904 Wld 31 8.8 28 .287

254SMO B676 S31254 Wld 45 ~ 8 29 .287

AL6XN B676 N08367 Wld 45 7.9 27 .29

SeaCure A268 S44660 Wld 65 9.8 31 .28

AL29-4C A268 S44735 Wld 60 9.8 29 .28

Inh Admiralty B111/B543 C44300/400/50 Smls 15 64 16.0 .308

Al Brass B111/B543 C68700 Wld/Smls 18 58 16.0 .301

Al Bronze B111/B543 C60800 Wld/Smls 18 46 17.5 .301

CuNi 70/30 B111/B543 C71500 Wld/Smls 18 17 22.0 .323

CuNi 90/10 B111/B543 C70600 Smls 15 26 18.0 .323

Ars Copper B111/B543 C14200 Smls ~15 112 17.0 .323Copper Iron B111/B543 C19400 Smls ~15 150 17.5 .317

Carbon Steel A-179 Smls 24.3 @ 400 27.5 29.5 .283

Carbon Steel A-214 Wld 24.3 @ 400 27.5 29.5 .283

Table 6: Typical Chemical Requirements (%) According to ASTM

UNSNo.YieldStrength

(0.2%)MPa(ksi)UltimateTensile

StrengthMPa(ksi)Elongation%

YoungsModulusGPa(ksix103)

MaxHardnessBHN

R50400 Titanium 275 (40) 345 (50) 20 107 (15.5) 180

S31254 NiCr Aust 310 (45) 675 (98) 35 200 (29) 210S44735 AL29-4C 415 (60) 515 (75) 18 200 (29) 241

S44660 Sea Cure 450 (65) 585 (85) 20 217 (31.5) 241



candidate materials is decidedly less than that of the copper

alloys.

Experience within the power generation industry has

demonstrated that thermal conductivity is only a small

contributor to overall heat transfer. Steam and water-side

lm and fouling coecients have a more signicant inu-

ence. Rather, the heat transfer performance is more closely

linked to the corrosion resistance of the tubing material. Analloy surface that exhibits low corrosion rates in the heat ex-

changer environment while remaining relatively clean can

provide excellent heat transfer performance over the service

life of the heat exchanger.

MechanicalPropertiesErosionResistance The four materials under investigation demonstrate excel-

lent resistance to suspended solids (sand) erosion, steam side

droplet impingement, cavitation, turbulence and high velocity

ow including mechanical damage as a result of ow-assisted

corrosion (FAC). Superior mechanical strength associated with

these alloys is the principal reason for their excellent resistance

to this type of attack (see Table 8). A further review of suggests

UNS S44735 and UNS S44660 exhibit very high mechanical

properties and are particularly erosion-resistant. .

Two types of erosion can commonly cause potential

problems for condenser applications.

ID erosion and/or cavitation caused by the

circulating water (CIRH2O) scouring or

collapsing a vena contracta bubble.

OD erosion can be caused by localized

steam droplet impingement erosion.

ID erosion is typically caused by high water velocities

as a result of partial blockage by debris or micro- or macro-

biological activity. Published literature has suggested that

both titanium and the family of super- stainless steels have

demonstrated an ability to safely accommodate sea water

or brackish water owing at velocities up to 30 m/s (~100/

sec). In many cases, these numbers carry little signicance

as condenser tube velocities rarely get above 7-10/sec.

It is of interest however that in 1970, Imperial Metals

(see Table 8 Reference) performed actual erosion tests us-

ing Gr. 2 titanium in various unltered sea water locations

around the world. The locations varied as did the salinityand suspended solids concentration levels. The reader will

note that the erosion rates for each of the test cases are very

low and in most cases defy accurate measurement.

Published literature again suggests that titanium is

considered one of the best cavitation-resistant materials

available for seawater service. UNS S31254, UNS S44735 and

UNS S44660 super-alloys a lso demonstrate an outstanding

resistance to cavitation, turbulence and high velocity ow

thanks to their high mechanical strengths.

Steam droplet erosion is the second type of erosion dam-

age experienced with condenser tubing. Erosion can typi-

cally take place immediately below the exhaust hood, in the

steam lanes and/or along the bundle to shell clearance. The

problem mainly occurs during winter periods when the con-

denser cooling water temperature is low. If the CIRH2O

is not throttled at these low temperatures, condenser back-

pressure will follow the reduced temperature curve greatly

increasing the velocity of wet steam entering the condenser.

The phenomenon can ultimately result in a turbine choke

ow condition that accelerates condensed water particles

(droplets) in the exhaust steam. This impinging action even-

tually removes the metal oxide and metal. Should the condi-

tion continue unabated, perforation of the tube eventually

takes place.

Resistance to this erosion phenomenon can be linked

directly to the metal hardness. Higher hardness provides

increased erosion resistance. UNS S44735 and UNS S44660

are therefore particularly resistant to this kind of erosion

damage, with a slightly better behavior than UNS S31254

and Titanium Gr. 2. Thanks to these high mechanical prop-

erties, UNS S44735 and UNS S44660 are particularly suited

as erosion-resistant materials.

Pitting&CreviceCorrosionResistance

Titanium is known to oer an exceptional resistance to cor-rosion because of its naturally forming protective oxide lm

layer. This lm layer, which increases over time, provides

immunity to general and localized attack in power plant

Table 7: Thermal Conductivity of Candidate Alloys

UNSNo.Conductivity

KW/(moC)[[BTU/hrftoF)

R50400 (Titanium) 22 [13] (@ 20oC/68oF)

S31254 (NiCr Austenitic) 13.5 [8] (@ 20oC/68oF)

S44735 (AL29-4C) 17 [10] (@ 20oC/68oF)

S44660 (Sea Cure) 15.9 [9] (@ 20oC/68oF)

Table 8: Erosion Of Unalloyed Titanium In Seawater Locations

LocationFlowRate

Ft/sec(m/sec)

Duration

MonthsGr2Titanium

Brixham Sea 32.9 (9.8) 12



surface condenser applications where high chloride and

brackish water conditions exist. Grade 2 cp titanium has

operated nearly 40 years in condenser power plant service

without one reported corrosion incident 9.

UNS S31254, S44735 and S44660 are highly alloyed

stainless steels designed to resist mainly pitting and crevicecorrosion but also stress corrosion cracking in saline envi-

ronments. Their performance can also be linked to their

oxide lm layer. A considerable upturn over the past 10

years in the usage of the super stainless materials has sug-

gested these materials provide good resistance to the pitting

and SCC maladies within their operational temperature and

concentration limits.

It is necessary however to take several precautionary

measures when considering the super stainless family.

These measures include keeping the tubes clean and free

from ID build-up that may promote an underdeposit pitting

event. In addition, it is not recommend that heavily chlo-

rinated waters be left in the tube for any extended period

of time. A fresh water ush is recommended for extended

layup periods.

CorrosionResistanceMeasurementsUsingEmpiricalDataCertain corrosion resistance measurements are commonly

used in order to assess the resistance of stainless steels to lo-

calized corrosion phenomena. Table 9 provides the average,

minimum and maximum values for the Pitting Resistance

Equivalent Number (PREN), the Critical Pitting Tempera-

ture (CPT) and the Critical Crevice Temperature (CCT)

of the three super stainless alloys under investigation, ac-

cording to the chemical composition range as indicated in

ASTM standards.

Attention is to be paid not only to the average values

but also to the minimum values PREN, CPT and CCT can

reach due to the tolerances of the dierent chemical com-

ponents of the three super alloys under investigation. The

empirical values of PREN, CPT and CCT are typically ac-

cepted benchmarks within industry and employed as toolsto estimate the pitting and crevice corrosion resistance of

conventional stainless steel grades. Unfortunately, these

calculated values are not suciently accurate to legitimately

compare the family of highly alloyed stainless - one against

the other. Corrosion investigations performed on super

stainless alloys used in sea water applications require both

electrochemical and conventional ASTM tests, which will

enable the investigator to have a better overview of the ma-

terials performance.

ASTMG48Test:Pitting&CreviceCorrosionAssessmentMethodA&B

ASTM G48 standard Method A and Method B tests were

conducted on superferritic stainless materials, UNS S44735

and S44660. Weight loss leading to the corrosion rate and

visual/optical examination of the specimens after testing

allow assessment of the susceptibility to localized corro-

sion. According to the ASTM G48 Method A, samples were

immersed into an iron chloride solution at 50C during 24

hours (pH 0.5). Both

UNS S44735 and S44660 materials showed a low suscep-

tibility to pitting corrosion without any trace of pits and low

corrosion rates (4 mpy for UNS S44660 and 3 mpy for

UNS S44735).

Following the procedure requirements of ASTM G48

Method B, samples were immersed in an iron chloride solu-

tion at 50C for 24 hours (pH 1.08). Two TFE-uorocarbon

blocks were fastened to the test specimens in order to

reproduce calibrated deposits where crevice corrosion

susceptibility could initiate. Both UNS S44660 and S44735

materials showed a low susceptibility to crevice corrosion

(no sign of crevice corrosion).

ElectrochemicalInvestigation The drawback to the ASTM G48 testing method is of

course the use of an articial medium to test the materials in

question. This medium may not accurately represent actual

performance in a seawater or brackish water service envi-

ronment. Therefore, electrochemical tests were performed

using articial sea water as a reference; i.e. the tness-for-

purpose environment according to the medium in contactwith materials in heat exchangers. The investigations were

carried out on welded tube samples of 25.4 mm OD 0.7 mm

WT at 50C, in two testing solutions:

Table 9: PREN, CPT and CCT of UNS S31254, S44735 and S44660

PREN CPT(C) CCT(C)

UNSN Average Min. Max. Average Min. Max. Average Min. Max.

S31254 44.1 42.2 46.0 63.4 59.1 67.6 32.8 28.9 36.6

S44735 42.2 39.9 44.6 61.1 56.4 65.9 41.4 36.0 46.9

S44660 38.4 34.9 41.8 51.9 44.3 59.4 30.4 21.8 39.0PREN = (%Cr) + (3.3 %Mo) + (16 %N) (Herbsled 1982)

CPT (C) = (2.5 %Cr) + (7.6 %Mo) + (31.9 %N) - 41.0 (G-48)

CCT (C) = (3.2 %Cr) + (7.6 %Mo) + (10.5 %N) - 81.0 (G-48)


9/15

Figure 6 Testing Assembly Used for Electrochemical Tests

Counter Electrode

Ref. Electrode (SCE)

Electrochemical Cell

Working Electrode

Figure 7 Polarization Curves & Electrochemical Parameters* of Materials Tested in Sea Water

100.0 mA

10.00 mA

1.000 mA

100.0 A

*critical current density (Jc), Corrosion Potential Ecorr & Passivation Current Density (Jp)

lm(

A) 10.00 A

1.000 A

100.0 pA-2.000 V

Vf (V vs. Ref.)

-1.000 V 0.000 V 1.000 V 2.000 V

100.0 nA

10.00 nA

1.000 nA

CURVE (254 SMO TTh 1200C - cordon de soudure - TEST1.DTA)

CURVE (SEA CURE - cordon de soudure - TEST1.DTA)

CURVE (29-4C - cordon de soudure - TEST1.DTA)

CURVE (TITANE VALTIMET 25x0.5 cle V382464-Pol - TEST1.DTA)

Jc (A.cm-2) Ecorr (mV/SCE) Jp (A.cm-2)

UNS S31254 6.2 -660 4.8

UNS S44660 4.1 -582 4.1

UNS S44735 2.7 -350 2

Titanium Grade 2 1.3 -80 1.5

Ti-Gr.2 > UNS S44735 > UNS S31254 > S44660

www.powergenu.com 9

Articial seawater based on ASTM D-1141 (pH = 7.5)

representing typical in-plant service conditions.

Chloride solution composed of 100 g/L NaCl

(pH = 5.8), representing more severe conditions

(higher chloride content and lower pH) in order

to more clearly distinguish the materials.

Figure 6 (See Attachment), identies the electrochemi-

cal testing apparatus employed to develop polarizationcurves referenced in the following paragraph. Simply

stated, samples were mounted in a Teon resin cylinder

representing the working electrode. The two testing solu-

tions identied in the previous paragraph were employed,

temperatures were xed and a testing electrode measured

the corrosion potential of the material. The electrochemical

recording was carried out in a glass cell, with a Saturated

Calomel Electrode (SCE) immersed in the solution with a

KCI saturated solution.

Polarization tests performed in an articial seawater

environment (Figure 7 See Attachment) then result in a

ranking in terms of nobleness of the materials. According

to current densities (both critical related to dissolution peak

and passivation stage), this same ranking can be applied

to the corrosion resistance properties of the alloys. These

rankings are identied below and, left to right, rank from

the rated highest corrosion resistance to the lowest.

In addition to the polarization tests, electrochemical

tests were performed on the three super-stainless candidates

using 100 g/L NaCl solution (Table 10). This additional test-

ing appears to conrm the superior corrosion resistance of

UNS S44735 over UNS S44660 and S31254.

Cyclic polarization curves measure the pitting potential

in 1M NaCl solution according to ASTM Standard G61 (pH

3 - 50C). The results (Table 11) are conclusive and lead to the

same stainless ranking as identied in the electrochemical

tests identied in Table 10.

Figure 10: Electrochemical Parameters of Materials Tested in 100 g/l

NaCl Solution

100g/LNaClsolution

Jc(A.cm-2) Ecorr(mV/SCE) Jp(A.cm-2)

UNSS44735 2.7 -340 2.2

UNSS31254 2.9 -562 2.7

UNSS44660 7.1 -510 4

Legend

Ecorr = Corrosion (open-circuit) Potential

Jc = Critical Current Densities

Jp = Passivation Current Densities

Note: The higher Ecorr and the lower Jc & Jp, the more

corrosion resistance the alloy.

Figure 11: Pitting Potentials of Materials in 1M Solution @ pH 3.0

UNSS31254 UNSS44735 UNSS44660

Ep1(mV/SCE) 921 963 884

Ep2(mV/SCE) 934 971 875

Average(mV/SCE) 927.5 967 879.5

Std.Dev.(mV/SCE) 9 6 6

UNS S44735 > UNS S31254 > UNS S44660


10/15

Figure 8 Polarization Curves & Electrochemical Parameters of Samples Tested in Articial Reference Seawater

100.0 mA

10.00 mA

1.000 mA

100.0 A

lm(

A) 10.00 A

1.000 A

100.0 pA

-2.000 V

Vf (V vs. Ref.)

-1.000 V 0.000 V 1.000 V 2.000 V

100.0 nA

10.00 nA

1.000 nA

Jc (A.cm-2) Ecorr (mV/SCE) Jp (A.cm-2)

1 2

5

6.5

-355

5.5-435.5

6-492

900-H2/1650F

900-Air/1650F

As received

10 www.powergenu.com

InuenceofHeatTreatmentonCorrosionResistance21Investigations were carried out on UNS S44735 (Allegheny

Ludlum AL29-4C Superferritic) material to assess the impact

of various heat treatment (HT) processes which are used dur-

ing the tube manufacturing operation. Electrochemical and

conventional ASTM tests were performed on three dierent

tube surface conditions in accordance with two (2), commer-cially available heat treatment processes. These processes

would include the following three conditions.

Condition 1: As Received: UNS S44735 (AL29-4C) strip

tested without any additional heat treatment other

than the one performed during the strip production

Condition 2: Open-air anneal - UNS S44735 (AL29-

4C Superferritic) annealed @ 900C/1650+F and

pickled & passivated to remove residual oxidation

due to the oxidizing environment during the heat

treatment process (representative of welded tubes

which are open-air annealed and pickled)

Condition 3: Bright anneal - UNS S44735 (AL29-4C

Superferritic) annealed @ 900C/1650+F under

hydrogen protective atmosphere (representative

of welded tubes which are bright annealed)

ElectrochemicalInvestigationPolarization tests again performed in articial seawater (Fig-

ure 8) demonstrate that the heat treatment under a protective

atmosphere provides improved corrosion behavior vs. either

the As Received or the Open Air Annealed specimens.

The polarization curve of the Open Air specimen, even if it

has been cleaned from residual oxidation in an acidic solution,

shows a small increase of the passivation stage conventionally

correlated to a small susceptibility to crevice corrosion which

might be generated under remaining oxidized area.

Electrochemical tests performed using a 100 g/L NaCl

solution will similarly allow ranking of the three heat treat-ment conditions of the UNS S44735 material when tested in

100 g/L NaCl solution:

The use of corrosion rate assessment (Table 12) and pit-

ting potential values (Table 13) also point to a better corro-

sion resistance of UNS S44735 material when heat treated

under hydrogen/ protective atmosphere.

Table 12: Corrosion Rate (C.R.) of Materials Under Investigation in Articial Reference Sea Water

H2BrightAnneal900C/1650F OpenAir(Pickel)900C/1650F AsreceivedNoPostWeldHT

Test1 Test2 Test1 Test2 Test1 Test2

0.1681 0.1784 0.3579 0.1623 0.2672 -

0.1719 0.1748 0.3826 0.2031 0.2781 -

0.162 0.1857 0.368 0.1684 0.2678 -

0.1775 0.1701 0.3603 0.1591 0.239 -C.R.(mmpy) 0.174 0.270 0.263

Std. Dev. (mmpy) 0.007 0.105 0.017

Table 13: Pitting Potential of Materials in 1M NaCl Solution @ pH 3.0

H2BrightAnneal

900C/1650F

OpenAir(Pickel)

900C/1650F

AsreceivedNoPostWeldHT

Ep1(mV/SCE) 963 808 936

Ep2(mV/SCE) 971 842 936

Average(mV/SCE) 967 825 936

Std.Dev.(mV/SCE) 6 24 0

Bright Anneal (900-H2)/1650F >Open Air Anneal

(900-Air/1650F) > As Received



ASTMG48Pitting&CreviceCorrosionAssessment ASTM G48 pitting and crevice corrosion tests also con-

rm that heat treatment under a hydrogen (or) protective

atmosphere demonstrates better corrosion resistance than

either the Open Air Anneal (900-Air/1650F) or the As

Received (Table 11 See Attached). Furthermore, the

Open Air Annealed (900-Air/1650F) UNS S44735 speci-

men showed a very high susceptibility to crevice corrosion

apparently due to a residual oxidation contamination fol-

lowing the heat treatment and acid pickling process. See

Figures 9, 10, 11 Attached)

Table 14 summarizes the ASTM G-48 Method(s) A&B

test results identifying weight loss corrosion in each of the

three tube conditions tested.

The ASTM G-48 pitting and corrosion tests can be gen-

eralized to all stainless steels concluding that welded tubes

which are bright-annealed during the production process

demonstrate a better corrosion resistance than the ones

which are open air-annealed then pickled.

ConclusionCurrent market conditions coupled with the possible emer-

gence renaissance of new nuclear units have encouraged

engineering companies, fabricators and end-users alike to

consider all material options for surface condensers and BOP

exchangers including the super stainless alloy materials as

alternates to cp Gr. 2 titanium. Of particular interest is their

long-term performance history in sea water, brackish water

or polluted water conditions were the control of condenser

condensate and reactor feedwater chemistry is of paramount

importance. Electrochemical and ASTM standardized corro-sion investigations on welded tube portions presented in this

paper have shown that UNS S31254, S44735 and S44660 are

three super stainless alloys potentially suitable for seawater

service with S44737 demonstrating the best performance. It

is also clear that titanium remains the best technical solu-

tion combining reasonable heat transfer characteristics with

general corrosion immunity. Its superiority and corrosion-

free record is well documented for 409 years particularly for

industries such as power generation and desalination

The reader should clearly understand however that the

family of super stainless steels examined perform well up to

certain tested concentration and temperature limits. It can

also be stated that research has demonstrated that titanium

provides not only corrosion immunity at classic equipment

operating levels but provides this immunity at signicant in-

creases in both temperature and concentration. For instance,

at typical sea water concentration and equipment operating

temperatures, (3.5% sea water @ 120F/49C), Figure 11 dem-

onstrates titaniums general corrosion immunity in actual sea

and brackish water environments even up to elevated tem-

peratures in excess of 120oC/248oF. However, certain sea

water-cooled cooling towers and canals can, through cycle

concentration and recirculation, increase chloride and con-

ductivity concentration limits signicantly anywhere from

1.3 to 2X normal levels. If we again refer to Figure 11, titanium

remains completely immune to chloride attack even when

approaching concentrations of 6X normal and temperatures

approaching 80oC/176oF well below the operating metal

temperature of a surface condenser. For more severe applica-

tions such as brine concentrators and salt evaporators, alloyed

titanium should be considered. In addition, titanium can be

utilized in very thin-wall gauges (down to 0.4mm/0.016)

enabling savings in both rst cost and weight.

The paper also presented a variety of corrosion mea-surement tools for evaluating welded stainless steel tubing

including PREN, electrochemical assessment and ASTM

standardized test investigations. These tests have demon-

Table 14: Weight Loss Corrosion of Samples Under Investigation (ASTM G-48 Method A & B)

ASTMG48MethodA ASTMG48MethodB ASTMG48MethodB

Materials CorrosionRate(mpy) CorrosionRate(mpy) CreviceSpots(ArbitraryUnits)

H2BrightAnneal900C/1650F 2 12 No

OpenAir(Pickle)900C/1650F 7 7842 10/20

NoPostWeldHT 5 5 No

Table 15: Weight Loss Corrosion Samples Investigation (ASTM G48 Method(s) A&B

Materials L(mm) L(mm) (mm) E(mm) Area(cm2) T(C) Time(h)Lossof

Weight(g)Corrosion

Rate(mpy)

H2BrightAnneal900C/1650F 50.89 - 24.86 0.77 79.49 50 24 0.0005 3

H2BrightAnneal900C/1650F(secondtest)

51.70 - 25.07 0.70 40.72 50 24 0.0002 2

OpenAir(Pickle)900C/1650F 69.60 10.44 - 0.67 7.266 50 24 0.0001 7

AsreceivedNoPostWeldHT 69.90 13.22 - 0.68 9.240 50 24 0.0001 5


12/15

Figure 11 Inuence of Temperature, Concentration, and pH on Crevice

Corrosion and Pitting Corrosion Propensity of Commercially Pure

Titanium in Sea Water and NaCl Brines

Typical CondenserOperating Point

12 www.powergenu.com

strated that super alloys, UNS S31254, S44735 and S44660

can be, within limitations, considered for use in brackish

and sea water service. These same data have also demon-

strated that the bright annealed, super stainless UNS

S44735 provides better corrosion resistance than either al-

loys S31254 or S44660 (open air annealed and pickled). With

15-25 years of service in both the US and Europe, the use of

super stainless can be considered for use in aggressive water

service conditions.

Having noted the favorable super stainless corrosion

data resulting from the electrochemical assessment and

ASTM investigations, certain precautionary measures must

be identied when considering their use.

To resist the possibil ity of underdeposit pitting attack,

tubes must be kept clean either through the use of

an on-line system or regular maintenance cleaning. In

particular, organic buildup on the tube ID can reduce

the corrosion resistance of the material introducing

the possibility of MIC or pitting. Remember that

excessive chlorine usage to mitigate bio-fouling may

in fact, reduce the pitting resistance of the material.

In addition, a fresh water ush of the condenser is

highly recommended during o-line conditions.

Stagnant water or highly chlorinated water left to

evaporate in the tube may induce a corrosion cell

ultimately causing a thru-wall condition failure.

The family of super stainless steels examined are

limited to the temperature and concentration limitsA nal cautionary note should be added for the reader:

The selection of a tube material for the condenser or BOP

heat exchanger may indeed be appropriate for current and/

or even anticipated operating conditions. However, there is

no guarantee that in the future, these conditions may dra-

matically change where the cooling water could conceivably

morph from benign to aggressive. There is also no guaran-

tee that the cooling water source may change from pond to

tower, from lake to tower or to a highly polluted source such

as sewage euent or other highly impaired water source.

Final evaluation and selection of these critical materialsmust consider these worst-case scenarios.

References

11. General Electric Infra Energy Company: ESBWR FeedwaterWater Quality, Wilmington, NC Jack Noonan & UltrapureWater, October, 2007

2. EIA Energy Information Association & CERA Cambridge Energy Research Associates.

3. Nuclear Tourist Website & UtiliPoint International

4. Power Magazine Issues April & May, 2007 & PowerEngineering July, 2007

5. ITA 2007 TITANIUM - THE MATERIAL OF CHOICEFOR THE NUCLEAR RENAISSANCE, Schumerth

6. ASME Paper _ IJPGC 2006 Electric Power Conference,Paper No: PWR2006-88115 GRAY & IMPAIRED WATERCOOLING IN SURFACE CONDENSERS AND HEATEXCHANGERS

7. Valtimet & EPRI Seminar: A Tube Material Selection& Design Seminar for Condenser & Heat Exchanger

Applications.

8. Titanium Heat Exchangers for Serv ice in Sea Water, Brine& Other Natural Aqueous Environments TechnicalInformation Bulletin Imperial Metal Industries Ltd.,Witton UK Multiple authors, 1970.

9. NRG Arthur Kill Power Station

10. ValBrite TM is a trademark of Valtimet

11. Titanium & Super Stainless Steel Welded Tubing Solutionsfor Seawater Cooled Heat Exchangers IDA WorldCongress-Maspalomas, Gran Canaria Spain October 21-26,2007 REF: MP07-021, Richaud-Miner, Gerard, Marchebois

12. ASME Standardization News July, 2007 Nuclear PowerGeneration

13. Fortune Magazine August, 2007

14. Forty (40) years of PowerGen experience by the authorMiscellaneous Contributing References

15. D. Vuillaume, VALLOUREC, Tube Materials for ModernFossil Fuel and Nuclear Steam Condensers, August 1985

16. Valtimet Titanium Tubing Design & Fabrication Handbook

17. Ivan A. Franson, Selection of Stainless Steel for Steam

Surface Condenser Applications - 85-JPGC-Pwr-15 ASME/IEEE Power Generation Conference, 1985



18. Plymouth Tube Co SEA-CURE Superferritic Stainless Steel(UNS S44660) Alloy Application & Data

19. Donald M. McCue, David K. Peacock, Titanium MetalsCorporation, The Application of Titanium for Power PlantSurface Condensers

20. H. Marchebois, C.E.V., Technica l report 2006- COR-06045Comparison of Highly A lloyed Stainless Steels for Sea Water

Applications: UNS S31254 vs. UNS S44735 vs. UNS S44660,

August 2006

21. H. Marchebois, C.E.V., Technical report 2006- COR-06044Inuence of Heat Treatment of UNS Ferritic StainlessSteel on Corrosion Resistance for Sea Water Applications,October, 2006

Acknowledgements:

This course is based on the presentation The Nuclear Renaissance:Materials of Choice for Power Plant Surface Condensers& BOP Heat Exchangers by Dennis Schumerth, Directorof Business Development, Valtimet, Inc., at NUCLEAR

POWER International 2009. The presenters acknowledgedthe technical contributions made by Valtimet to the approachmethod sections of this paper.



Questions

OnlineCompletionUse this page to review the questions and choose your answers. Return to www.powergenu.com and sign in. If you have not previously purchased the program

select it from the Online Courses listing and complete the online purchase. Once purchased the exam will be added to your User History page where a Take

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1. How many nuclear power plant

reactors currently operatein the United States?

a. 84.

b. 94.

c. 104.

2. In the boiling water reactor (PWR)

shown in Figure 1, the steam pro-

duced in the reactor is sent directly

to the turbine. Thus, this steam

and its condensate are slightly

radioactive. True or false, the

pressurized water reactor (PWR)

has two loops such that the turbine

and condenser do not directly

process the radioactive steam?

a. True.b. False.

3. What is a critical aspect

in minimizing corrosion

within heat exchangers?

a. Producing and maintaining

high purity water.

b. Installing expensive infrared

monitoring equipment.

c. Regularly shutting down the

equipment for mechanical cleaning.

4. Three critical high-purity water

chemistry issues are control of

dissolved oxygen, control of

conductivity, and maintaining a

very low level of what impurity?

a. Chromium.

b. Molybdenum.

c. Chloride.

5. What is typically the single

largest source of contaminantingress to condensate?

a. The condenser.

b. The nuclear reactor.

c. The turbine.

6. Which of the following metals

will most often show up as

corrosion products in a nuclear

condensate/feedwater system?

a. Copper (Cu).

b. Cobalt (Co).

c. Zinc (Zn).

d. Iron (Fe).

e. All of the above.

7. Table 4 outlines the most common

corrosion mechanisms that canaect condenser tube mate-

rial. Would you expect that MIC

(microbiologically inuenced cor-

rosion) and other microbiological

inuences on the waterside of the

condenser tubes could be one of the

most problematic of the corrosion

mechanisms, and thus requiresproper cooling water treatment?

a. Yes.

b. No.

8. What has been a popular material

for condenser tubing in seawater

and brackish water for 40 years?

a. Tantalum.b. Titanium.

c. Zirconium.

d. Palladium.

9. Due to cost concerns regarding

the metal from question 8, what

material is becoming more popular

as a replacement in seawater and

brackish water applications?

a. Tantalum.

b. Zirconium.

c. Highly-a lloyed stainless steels.

10. One of the three steels outlined

in the paper is known as an

austenitic stainless steel. The

term austenite refers to a

particular crystal lattice. What

are the other two steels?

a. Martensitic.

b. Pearlitic.c. Ferritic.

11. Many condenser and heat exchang-

ers installed during the middle of

the last century utilized copper alloy

tube material, due to the high heat

transfer property of copper. The

paper points out that titanium andstainless steels have a much lower

thermal conductivity, but that this

is only a small contributor to overall

heat transfer. What does the paper

say is much more inuential regard-

ing heat transfer [or lack thereof]?

a. Steam and water-side lm

and fouling coecients.

b. Steam ow to the condenser.

c. Cooling water ow rate.


15/15

Questions

OnlineCompletionUse this page to review the questions and choose your answers. Return to www.powergenu.com and sign in. If you have not previously purchased the program

select it from the Online Courses listing and complete the online purchase. Once purchased the exam will be added to your User History page where a Take

Exam link will be provided. Click on the Take Exam link, complete all the program questions and submit your answers. An immediate grade report will be

provided and upon receiving a passing grade (70%) your Certicate of Completion will be provided immediately for viewing and/or printing. Certicates of

Completion can be viewed and/or printed anytime in the future by returning to www.powergenu.com, sign in and return to your User History Page.

12. For the principal materials

outlined in the paper, what is

a mechanically-induced, ow-

related corrosion process on the

water-side that they resist well?

a. Solid metal impact.

b. Macrofouling.

c. Erosion.

13. What is the name for the

mechanical corrosion process

that can occur on topmost

condenser tubes on the steam-side

below the turbine exhaust?

a. Sonic velocity corrosion.

b. Steam droplet erosion.

c. Steam expansion erosion.

14. Titanium and stainless steels are

corrosion resistant due to formation

of an oxide layer that covers the

metal surface. Before these new

developments of stainless steel,

stainless steels could not be utilized

in high chloride waters because

chloride would penetrate the

oxide lm and cause pitting. Even

though the new stainless steels are

much more resistant to pitting,

what does the paper say is necessary

to prevent this type of corrosion?

a. Keep the tubes clean and free from

ID buildup that may promote an

under-deposit pitting event.

b. Install extremely thick-walled tubes.

c. Consider switching to a dierent

cooling water source.

15. Even though the new stainless

steels are much more resistant to

chloride attack, what water-side

procedure is recommended if

the condenser will be out of

service for an extended period?

a. Complete drain and dry ing

with portable heaters.

b. A fresh water ush.

c. Shoot the condenser tubes with

water-absorbing brushes.

16. What does the acronym

PREN stand for?

a. Polarization resistance

equivalent number.

b. Penetration resistance

equivalent number.

c. Pitting resistance equivalent number.

d. None of the above.

17. What chemical solution

is utilized for the ASTM

G48 Test for corrosion?

a. Zinc chloride.

b. Iron chloride.

c. Sodium chloride.

18. Why does the author conclude that

this test may not be accurate?

a. The chemical solution is

much too aggressive.

b. The chemical solution does not

represent real-world conditions.

c. The chemical solution is too

dicult to synthesize.

19. Which of the three super

stainless steels was shown to

have the most corrosion

resistance, as listed on page 13?

a. S44735.

b. S44660.

c. S31254.

20. Many metals for a wide

variety of applications are given

additional mechanical or heat

treatment (annealing) after

fabrication to improve corrosion

resistance and relieve stresses

within the metal structure. Three

conditions are outlined on page

14. Which most improved the

corrosion resistance of S44735?

a. Anneal ing in open air and

then pickling/passivating.

b. Anneal ing under a hydrogen

protective atmosphere.

c. No additional treatment at all,

as the initial fabr ication puts the

metal in pristine condition.

mat condenser 5-pgu nuclearrenmaterials

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