03 inl seminar_scc in low temperature environments (52)_ pc

Stress Corrosion Cracking in low temperature environments

Pierre Combrade INL Seminar on SCC in LWRs

Idaho Falls, Idaho, USA, March 19th 20th, 2013 INL SCC 3

Introduction

In addition to the primary coolant circuits, which are exposed mainly to well controlled aqueous environments, austenitic stainless steels are used in many auxiliary circuits where contaminants and oxygen may occasionally be present. The most widespread and most dangerous contaminants are obviously chloride ions although other contaminants like sulphur species may also be of concern. This presentation will address mainly contamination by chlorides. Other SCC phenomena possibly relevant to LWRs will also be briefly mentioned.

2

INL SCC 2013, Pierre Combrade

SUMMARY

Low temperature ( 250 C) stress corrosion cracking of Stainless Steels:

Generalities Stress corrosion cracking in chloride environments:

Field experience from LWRs General phenomenology Stress corrosion cracking in very dilute environments

External Surface Stress Corrosion Cracking: Field experience Atmospheric Stress Corrosion Cracking Corrosion under Insulation (CUI)

Other low temperature stainless steel SCC phenomena: Sensitised Stainless Steels

3


SCC of Austenitic SSs Main environments promoting SCC of non-sensitised austenitic SSs:

Chloride solutions Caustic environments:

Aerated, deaerated, hydrogenated Intergranular and/or transgranular cracking A general rule is to not use austenitic SSs in caustic environments above 50/60 C

H2S + Chloride: oil industry

SCC of sensitised austenitic SSs:

BWR environments (see F.P. Ford presentations)

Reactive sulphur species (Polythionates, thiosulfates, )

After Combrade

Example of IGSCC of austenitic SS in 50% NaOH solution at 200 C

4


Chloride SCC: field experience in LWRs In PWRs, 85 % of SCC events of SS in the PWR primary circuit are due to contamination in occluded regions (blue bars in the figure):

Main affected zones: Canopy seals, CRDM housings, Valve drain lines Only 15 % occurred in the nominal flowing environment (red bars in the figure)

After Ilevbare

5


Chloride SCC: field experience in LWRs In occluded conditions, contamination of PWR primary water, when identified, is mainly by chloride and sulphur species

After Ilevbare

6


SS SCC Field Experience in German NPPs

TGSCC is a recurrent but not critical problem: ~35 events in PWRs and ~40 events in BWRs between 1974 and 2005

SICC = Strain Induced Corrosion Cracking (Low Alloy Steel), MIC = Microbially Induced Corrosion (mostly Stainless Steels),

FAC = Flow Assisted Corrosion (Carbon Steel with low residual Cr, Cu, Ni, Mo concentrations)

After Jendrich et al

7


SS SCC Field Experience in German NPPs

TGSCC events do not become more frequent with time: TGSCC is, therefore, not a problem of plant ageing

After Jendrich et al

8


TG-SCC: Field experience in LWRs Dead legs between isolation valves (PWR):

Stagnant water, elevated temperature (> 200 C) Possible two phase environment with evaporation and concentration of solutes near

waterline

TGSCC of non sensitised Type 316 (L) and cast stainless steels

Attributed to (chloride + oxygen) and concentrated boric acid

Residual Heat Removal System

Valve Water level during shutdown periods

Primary piping

Two phase environment With trapped air

Residual Heat Removal System Primary piping

Air transfer through open valve during filling

After Economou et al.

During shutdown periods After filling primary circuit

After Berge et al.

9


Valve housing: Stagnant conditions TGSCC of Type 321 stainless steel

TG-SCC: Field experience in LWRs

After Kilian et al.

10


TG-SCC: Field experience in LWRs Valves:

TG-cracks near the gland packing and leakage outlet areas Contamination comes from an old (now discontinued) gland packing material:

New specifications limit the soluble chloride in packing materials Note the cracks concentrated in the cold worked surface layer

From Httner & Kilian

11


Chloride SCC: field experience in LWRs Canopy seals:

Welded Canopy seals ensure the leak tightness of threaded joints between the top of the vessel head penetrations (Type 304L SS) and the CRDM housings (Type 304 SS).

A 2 mm thick TIG weld is made with Type 308 L SS.

TGSCC of Type 304 SS base metal has occurred at 150/200 C, in several plants, independently of any welding defects, but often in conjunction with small pits.

Analyses of water trapped in Canopy seals have shown few impurities:

Cl- usually < 1 mg/L SO42- up to a few mg/l Air can be trapped in the Canopy seal during filling of the primary circuit

Cause of TGSCC not really clear

12


SUMMARY

Low temperature ( 250 C) stress corrosion cracking of Stainless Steels:



External Stress Corrosion Cracking: Field experience Atmospheric Stress Corrosion Cracking Corrosion under Insulation (CUI)

Other low temperature stainless steel SCC phenomena: Sensitised Stainless Steels

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Chloride SCC: general phenomenology Cracking occurs when corrosion potential exceeds a critical value:

Often close to the pitting potential Cracks are generally transgranular

Transgranular cracking of Type 304 SS

in 100 mg/L chloride, aerated solution at 200 C

After Combrade Critical potential for SCC

Af ter Poznanski & Duquette

Effect of applied potential on time to failure and reduction in rupture surface area of specimens continuously strained

in 100 mg/L chloride + 100 mg/L sulphate solution at 200 C

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Chloride SCC: critical potential In concentrated, moderately acidic, solutions, no oxidising species other than water are required for cracking to occur:

Example: boiling MgCl2 solutions used in standard SCC tests In near neutral, dilute chloride solutions, an oxidising species other than water is required for SCC to occur:

i.e. no chloride SCC in near neutral deaerated water Critical potential decreases with increasing chloride concentration the higher the chloride content, the lower the oxygen concentration required for SCC

Note the deleterious effect of sensitisation

0.01

0.1

1

10

100

1000

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0.01 0.1 1 10 100 1000 10000 100000

Chloride (mg/kg)

Oxy

gen

(m

g/kg

)

tentative threshold for SCC at 260-300 C from

re-analyzed Gordon review

SCC

No SCC From Speidel re-analyzed

Caution: these figures must be considered as showing trends rather than precise data

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Chloride SCC: temperature In near neutral, dilute solutions containing mainly sodium chloride, it is generally considered that SCC cannot occur below 50/60 C:

The value given in the literature is often 60 C

In very concentrated acidic environments (NaCl + HCl, HCl, HCl + H2SO4), SCC can occur at room temperature Atmospheric SCC may also occur at room temperature, e.g.

Marine environments Swimming pool environments:

role of volatile monochloramines to transport chlorine from pool water to roof

0

50

100

150

200

250

300

0.1 1 10 100 1000 10000 100000

chloride (mg/kg)

tem

per

atu

re

( C

)Oberndorfer et al. - near neutral Cl- solutions - 321 SS

McIntyre - review - full immersion McIntyre - review - all data

Truman - NaCl, pH 7 - 304 SSHerbsleb & Pfeiffer - Ca Cl2 solutions - 304 SS

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Chloride SCC: effect of SS composition Major effect of nickel:

Ni content above ~ 30 to 40 % tends to inhibit SCC of austenitic alloys: By increasing the critical potential for SCC Alloy 800 is practically immune in most dilute chloride environments

42% boiling MgCl2 solution After Copson

Effect of Ni content on the corrosion potential and on the critical cracking potential

for 20 % Cr SSs in MgCl2 solution at 130 C After Lee and Uhlig

22 % NaCl at 105 C After Speidel

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Chloride SCC: effect of SS composition Effect of Cr not well characterized:

Seems to be a maximum in susceptibility to chloride SCC for Cr ~20 % to 25 % but inhibition for higher values

Mo also increases resistance to SCC: This point has been controversial

Residual elements: S is detrimental because it decreases

the resistance to localised corrosion: Role of MnS inclusions

Warning: many results in the literature were obtained in conventional boiling MgCl2 solutions that promote cracking in very short times. They are not necessarily representative of parametric effects in near-neutral environments:

e.g. Si is very beneficial in MgCl2 solution but has no major effect in dilute near-neutral chloride solutions

Effect of Mo concentration on KI-SCC of 18 % SS in 22 % NaCl solutions at 105 C

After Speidel

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Chloride SCC: effect of stress

Threshold stress / stress intensity for cracking: No precise data in the literature In conventional MgCl2 solutions at 154 C:

threshold stress for initiation can be as low as 75 to 120 MPa KI-SCC values as low as 4 MPam have been reported

Crack propagation: Plateau behaviour for KI > KI-SCC Crack velocity increases

with temperature: Results below are consistent with an apparent activation energy ~ 75 kJ/mole

After Speidel

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SCC in very dilute chloride + sulphate solutions At 200 C in very dilute solutions in the presence of dissolved oxygen:

SCC of Type 304 SS occurs when the chloride concentration exceeds ~5 to 10 mg/L However, the simultaneous presence of comparable low concentrations of chloride

and sulphate ions (~ mg/l) may cause TGSCC of Type 304 SS in very short times with the cracks very often initiating from small pits.

This effect of sulphate ions is quite different to that observed in more concentrated environments where sulphate tends to retard chloride SCC. Although available water analyses from canopy seals do not exactly fall in the SCC zone, this synergism between Cl- and SO4 possibly accounts for the observed SCC

After Couvant et al.

Crack initiated at a small pit in 1 mg/L chloride + 1 mg/L

sulphate, aerated solution at 200 C

After Combrade.

0.01

0.1

1

10

100

0.01 0.1 1 10 100Chloride (g/g)

Sulfa

te

(g/

g)

Srie1

Srie2

Srie8

Srie9

Srie10

Srie11

Srie12

O2 from 0.5 to 10 g/g - No crack

O2 from 0.5 to 10 g/g - Cracks

O2 ~1300 g/g or E ~204 mV/Ag/Cl - No crack

O2 ~1300 g/g or E ~204 mV/Ag/Cl - Cracks

Deaerated - Shallow cracks

Dearated - No cracksAnalyses of Canopy seal environments

tentative threshold for aerated environments

tentative threshold for deaerated conditions

Possible cracking under dynamic loading

Possible cracking under static loading

No cracking

Tentative thresholds for SCC in aerated and deaerated PWR primary water contaminated by low concentrations of chloride and sulphate ions at 200 C

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Mechanism of chloride TG-SCC Initiation:

Cracks seems to initiate only in acidic and chloride-rich environments present either in bulk solutions or in local environments created by localised corrosion.

Propagation: Environment in cracks is generally considered to be acidic and Cl-rich

due to local hydrolysis of cations produced by dissolution and to potential gradients that causes electro- migration of chloride ions into cracks.

However, the environment is not aggressive enough to inhibit passivation and cause general corrosion of crack flanks.

Galvanic current in the liquid

Na+

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Mechanism of chloride TG-SCC Cracking mechanisms:

Not really known Slip dissolution has been considered by many authors:

Can give reasonable predictions of crack propagation rates Not really consistent with:

Very brittle appearance of crack surfaces with very accurate matching of opposite faces

Acoustic emissions Film-induced cleavage (Newman):

The formation of nano-porous de-alloyed layers has not been clearly observed in chloride solutions

Hydrogen based mechanisms: Hydrogen is clearly formed in cracks and in pit precursors due to low local pH and potential Hydrogen is claimed to play a role by CEPM but both hydrogen-dislocation interactions and weakening of atomic bonds are hardly consistent with an accelerating effect of temperature on SCC

Why not a vacancy related mechanism ??

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SUMMARY

Low temperature stress corrosion cracking of Stainless Steels: Generalities Stress corrosion cracking in chloride environments:



Other low temperature stainless steel SCC phenomena:

Sensitised Stainless Steels

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External corrosion and stress corrosion External corrosion is not caused by process environments but by those that occur on the external surfaces of installations.

It is characterized either by surface pitting or SCC, or a combination of both.

External Stress Corrosion Cracking (ESCC) is usually a slow phenomenon that often takes years to produce significant damage:

Atmospheric stress corrosion (without thermal insulation): Typically on weld HAZs and/or cold worked materials More frequently IG than TG because it is often related to sensitisation Occurs mainly at or near ambient temperature

Corrosion Under Insulation (CUI): SCC is generally TransGranular and not related to sensitisation Usually in the range 50/150 C with no marked effect of temperature in this range Chloride may come from the insulating material or from external sources, usually rainwater, fog condensate, wash water, firewater,

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Chloride ESCC of stainless steels - field experience in LWRs

Surface contamination: Thermocouple sheaths in a LWR primary circuit:

Chloride contamination + air trapped in the thermowell dead leg, and an elevated temperature > 250 C TGSCC in a few days Remedy = surface cleaning at the end of fabrication

Residues of glues, lubricants, adhesive tape,

Leaking line

Cracks on the OD of a Type 304 SS CRD withdrawal line due to polyvinyl Dymo tape stuck on during fabrication. Time of service ~30 years. Cracking is thought to have occurred during shutdown periods at

temperatures below 100 C when a condensed liquid film could form on the surfaces.

Trace of crack on OD

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Chloride ESCC of stainless steels - field experience in LWRs

Atmospheric SCC has been reported at the Koeberg PWR units: Numerous externally initiated cracks, some through-wall, were observed

on seam welded Type 304 L piping of safety related systems, the refuelling storage water tanks, and cast valves of both units

Cracking was almost exclusively initiated from surface pits, (see below) The tanks, piping and valves were manufactured from Type 304L SS

The systems concerned typically operated for > 10 years, below 50C with no insulation.

Pitting and TG cracks on the outer surfaces of Type 304L SS equipment at Koeberg

After Basson & Wicker

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Atmospheric Corrosion - Background Severity of atmospheric corrosion depends on many factors:

Geographic location Moisture content, time of wetness, and alternating wet and dry periods:

Dry-out leads to very high concentrations of contaminants on surfaces Temperature Airborne contaminants:

Chlorides, which are the most damaging species for SSs Sulphur species Carbon dioxide

Solar radiation

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Atmospheric Corrosion - Background Atmospheres are usually classified as follows (in order mild to aggressive):

Rural atmospheres Urban atmospheres Industrial atmospheres Marine atmospheres:

which are far more severe than all the others; whose severity depends on temperature, proximity to the ocean, elevation above sea level, sunlight, prevailing winds and wave action, and whether a component is sheltered or not (i.e. rain water washing possible or not)

28


2004 monthly chloride accumulation at Kure Beach, NC, USA, in mg/m2/day

After Gordon et al

Atmospheric Corrosion - Background For SSs, chlorides are the most deleterious species Near the seaside, rain water or fog may contain several mg/kg of chloride and deposition of chloride on surfaces can be very significant

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Atmospheric Corrosion - Background Modelling dry-out of surfaces by evaporation shows that the chloride concentration mainly depends on the [H+]/[Cl-] ratio of the of rain, cloud or fog moisture:

[H+]/[Cl-] > 1 low chloride, acidic liquid films that are not harmful to SSs [H+]/[Cl-] < 1 high chloride liquid film, which can cause localised

corrosion and/or SCC. Most marine atmospheres fall in this category.

Plot of maximum Cl- concentration in evaporated solutions as a function of the [H+]/[Cl-]ratio (after Gordon)

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Uniform and Localised Atmospheric Corrosion

General corrosion of stainless steel is negligible in all atmospheres for alloys with Cr contents in excess of ~15 %:

Corrosion rate of Type 3XX series SSs < 25 nm/year after 26 years of exposure to a severe marine atmosphere (Kure Beach, North Carolina)

Stainless steels may suffer staining and pitting in industrial and marine atmospheres, particularly on rough surfaces

After Johnson & Pavlik

31


Atmospheric Stress Corrosion Cracking Field experience outside the nuclear industry:

Typically, but not exclusively, on weld HAZs and/or cold worked materials More frequently IG than TG because it is often related to sensitisation:

IG related to sensitisation TG favoured by localised corrosion, particularly crevice corrosion

Note that atmospheric corrosion and, in particular, SCC is a concern for SS canisters of radioactive wastes studies are in progress

After Toshima et al

After Toshima et al

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Atmospheric Stress Corrosion Cracking Parametric Effects

All parametric effects presented in the following slides have been obtained from laboratory studies with:

controlled amounts of chloride contamination deposited on surfaces: thus, the results can be used to determine acceptable levels of surface contamination

specimens subjected to controlled tensile stress exposed to controlled RH and temperature atmospheres

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A-SCC and Relative Humidity (RH) A-SCC occurs in a limited range of relative humidity:

Very low RH No electrolyte film Very high RH Too low chloride concentration in liquid surface films:

According to Fairweather & Tice, increasing the RH is a safer way to avoid A-SCC than reducing RH.

After Shoji & Ohnaka

34


A-SCC and Relative Humidity (RH) Range of critical RH depends on temperature and the chemical composition of chloride salts:

Max SCC occurs at RH close to saturation RH (Psat) of the chloride salt contaminant, i.e. at the RH that causes the most concentrated surface film

Salts promoting SCC at room temperature are:

MgCl2 (and seawater due to the presence of MgCl2) CaCl2 ZnCl2


25 C 50 C 70 C Chloride Psat RHmax RHrange Psat RHmax RHrange Psat RHmax RHrange

NaCl 75 no SCC no

SCC 75 no

SCC no

SCC 75 60 45-60

M gCl2 33 30 25-50 30 30 20-50 28 30 20-80

CaCl2 31 20 15-50 17 20 20-50 18 20 10-80

ZnCl2 10 10 5-25 10 10 10-40 Und 10 10-40

LiCl 11 n t n t 10 10 n t 11 10 No data Synthetic seawater n k 30 30-50 n k 30 20-50 n k 30 20-80

35


A-SCC and Chloride Surface Concentration

A critical chloride concentration in the surface liquid film is required for atmospheric SCC to occur:

Chloride concentration of the surface film appears to be more important than pH or the identity of the cation (except for the fact that the cation identity determines the maximum chloride solubility of the surface films):

Only chloride salts that give very concentrated liquid films produce A-SCC at room temperature:

NaCl films are not concentrated enough to promote SCC at room temperature

Crack propagation rate increases with increasing chloride concentration of surface films:

Too low pH values of surface films are suspected to reduce crack propagation rates (see ZnCl2 vs. LiCl)

SCC may occur in concentrated solutions of salts at

the same temperature as in atmospheric exposure, Both A-SCC and SCC in bulk solutions occur near 50 to 60 C for NaCl SCC is possible in MgCl2 bulk solutions at 30 C


36


A-SCC Initiation Initiation of cracks occurs very frequently from pits, but not always:

Warning - Cracks can develop on visually clean surfaces and can be missed by visual examination (Fairweather et al)

Laboratory tests show that initiation occurs after relatively short exposure times, i.e. weeks or a few months Field experience shows that A-SCC usually requires much longer times This means that the lifetimes of components subject to atmospheric corrosion are controlled by the time required to obtain the critical surface contamination and/or the time during which these critical surface conditions prevail:

In particular, surface contamination of non sheltered components can be periodically washed away by rain and thereby retard or avoid A-SCC


37


A-SCC Other Influencing Parameters Sensitisation increases susceptibility to A-SCC and promotes IGSCC Temperature:

Increasing temperature increases susceptibility to A-SCC: SCC can occur in more dilute solutions when temperature increases

salts that are unable to propagate SCC at RT may promote cracking at higher temperatures

e.g. NaCl promotes SCC at temperatures > 50/60 C Increasing temperature decreases initiation times and increases propagation rates

Stress: Very low stresses can promote A-SCC

Surface condition:

Roughness and dust favour crack initiation Surface cold work and residual tensile stresses

favour crack initiation Importance of good surface finish and cleanliness

After Tani et al

38


Corrosion under insulation (CUI) - field experience

Very widespread phenomenon in the chemical industry: Example of SCC under insulation of a Type 304 L vessel undergoing

thermal cycles from < 0 to + 80 C shown below. TG Cracks occurred both on base metal and welds

Chloride is thought to have come from insulating materials Chloride-rich condensed film may form during cooling Remedy = low chloride insulating material and cathodic protection by

wrapping Al foils around the vessel

From Combrade

39


Corrosion under insulation (CUI) - field experience

In LWRs: no recent open literature reports of CUI

In the early 60s, SCC under insulation occurred during initial hot

functional tests of the Nuclear Merchant Ship Savannah, due to wetted chloride containing insulation

The remedies were to clean all surfaces, to replace the insulation by a lower chloride product inhibited with 20 % sodium silicate, and to seal the insulation in order to prevent water ingress. Wrapping with Al foil was considered but not applied

40


Chloride SCC: Mitigation of CUI Selection of an appropriate insulation material:

Several standards are available, e.g. NRC Regulatory Guide 1-36

Limited level of leachable chloride (ASTM C-795) or chloride+ fluoride (NRC, and MIL I-24244)

Presence of inhibiting salts, i.e. sodium silicate

Limited pH range of leaching solution (7 to 11.7 for ASTM C 795)

Limitations of this approach:

These standards are based on old results (1967) that may be somewhat optimistic according to more recent data

These standards implicitly assume that no additional contamination will be added by an external source:

Rain water, for example, may bring much more chloride than that which is contained in the insulation In addition, external water may wash inhibitors out of the insulation

41


Chloride SCC: Mitigation of SCC under insulation

Other countermeasures: Seal the insulation to avoid ingress of external water Use coatings to prevent contact of metallic surfaces with water Use cathodic protection:

Use Al containing paints or foil coating: Wrapping the surfaces with Al foil has proven to be effective even

when the Al foil is heavily corroded Avoid Zn because of the possibility of liquid metal embrittlement of SSs by molten Zn in case of fire Very rapid IG cracking

42


SUMMARY Low temperature ( 250 C) stress corrosion cracking of Stainless Steels:




Other low temperature stainless steel SCC phenomena:

Sensitised Stainless Steels

43


IG-SCC of sensitised austenitic Alloys in solutions with reactive sulfur species

Field experience: IG-SCC of sensitised Stainless Steel occurs mainly in oil industry;

e.g. in desulfurising units during shut down if the atmosphere is not safely deaerated

In LWR reactors, reactive sulphur species may be present due to accidental ingress of resins that are thermally decomposed:

IG-SCC of sensitized Alloy 600 in CRDM nozzle occurred at Zorita Alloy 800 SG Tubes ???

44


IG SCC of sensitized austenitic Alloys in solutions with reactive sulphur species Phenomenology:

IG-SCC occurs in: Polythionate solutions tetrathionate is the most aggressive species Thiosulphate solutions To a lesser extent, sulphite solutions

IG-SCC is clearly due to sensitisation, i.e. Grain Boundary Cr-depletion, due to heating in the 500-800 C range by nearby welding, stress relieving , ....

After Hosoya et al.

45


IG SCC of sensitised austenitic Alloys in solutions with reactive sulphur species Phenomenology:

IG-SCC occurs similarly on sensitised Stainless Steels and Ni-base alloys It occurs at room temperature and is accelerated by higher temperatures It occurs in a limited range of potential that includes the free corrosion

potential in aerated solutions

After Macdonald et al. After Hosoya et al.

46



Susceptibility to IG-SCC increases with the concentration of polythionate (or thiosulphate)

After Hosoya et al. After Macdonald et al.

47



Crack morphology changes from IG-SCC to IGA depending on pH and potential

After Matshushima

After Hosoya et al.

48


IG SCC of sensitised austenitic alloys in reactive sulphur species solutions

Mechanism of cracking: Probably the so-called Stress-Assisted InterGranular Cracking

mechanism: Intergranular corrosion oxidises grain boundaries Stress causes cracking (or opening of pores) of GB oxides and increases grain boundary oxidation rates

Adsorption on metal surfaces of reactive sulphur species enhances dissolution (oxidation) rates

49


Conclusions In LWRs, corrosion of austenitic Stainless Steels by contaminated environments is not a severe problem but it keeps recurring. Chloride ions are by far the most dangerous contaminant although sulphur ions may also be of concern:

Fluoride is rarely mentioned, which can come from welding and soldering fluxes. To our knowledge, no recent corrosion due to fluoride has been reported in LWRs.

Pitting and crevice corrosion are rarely a problem per se but they can lead to SCC. SCC due to contaminants in the main primary circuits is unlikely except:

in the case of sensitized SSs (and Ni base alloys) in the presence of reactive sulphur species (typically polythionates) that can cause rapid IGSCC at ambient temperature,

in occluded regions of the primary circuit where oxygen, chloride (and sulphate) ions may be present, at least temporarily, at temperatures above 100 C.

50


Conclusions

Other SCC events in austenitic stainless steels are not frequent but when they occur, they are due to:

Surface contamination during fabrication External corrosion in marine atmospheres

To our knowledge, no corrosion of SS under insulation has been openly reported recently in LWRs

51


Recommendations to prevent corrosion of stainless steels

Material: Avoid sensitisation Avoid excessive cold work (Hv > ~300) that can enhance many corrosion

processes, and particularly SCC Surface condition:

Limit surface cold work and geometrical defects due to machining or finishing processes

At the end of fabrication, pickle surfaces to eliminate deleterious inclusions, surface Cr- and Mo-depletions, and contamination. Then passivate to build up a robust passive layer in a non-contaminated environment

Keep surfaces clean: specify maximum allowable surface contamination: There is no universal criterion but < 1 mg/m2 has been used although very difficult to achieve at coastal locations

Use qualified insulating materials and prevent, as much as possible, access of external water into the insulating material

52


Stress Corrosion Cracking in low temperature environmentsIntroductionSUMMARYSCC of Austenitic SSsChloride SCC: field experience in LWRsChloride SCC: field experience in LWRsSS SCC Field Experience in German NPPsSS SCC Field Experience in German NPPsTG-SCC: Field experience in LWRsTG-SCC: Field experience in LWRsTG-SCC: Field experience in LWRsChloride SCC: field experience in LWRsSUMMARYChloride SCC: general phenomenologyChloride SCC: critical potentialChloride SCC: temperatureChloride SCC: effect of SS compositionChloride SCC: effect of SS compositionChloride SCC: effect of stressSCC in very dilute chloride + sulphate solutionsMechanism of chloride TG-SCCMechanism of chloride TG-SCCSUMMARYExternal corrosion and stress corrosionChloride ESCC of stainless steels - field experience in LWRsChloride ESCC of stainless steels - field experience in LWRsAtmospheric Corrosion - BackgroundAtmospheric Corrosion - BackgroundAtmospheric Corrosion - BackgroundAtmospheric Corrosion - BackgroundUniform and Localised Atmospheric CorrosionAtmospheric Stress Corrosion CrackingAtmospheric Stress Corrosion Cracking Parametric EffectsA-SCC and Relative Humidity (RH)A-SCC and Relative Humidity (RH)A-SCC and Chloride Surface ConcentrationA-SCC InitiationA-SCC Other Influencing ParametersCorrosion under insulation (CUI) - field experienceCorrosion under insulation (CUI) - field experienceChloride SCC: Mitigation of CUIChloride SCC: Mitigation of SCC under insulationSUMMARYIG-SCC of sensitised austenitic Alloys in solutions with reactive sulfur speciesIG SCC of sensitized austenitic Alloys in solutions with reactive sulphur speciesIG SCC of sensitised austenitic Alloys in solutions with reactive sulphur speciesIG SCC of sensitised austenitic Alloys in solutions with reactive sulphur speciesIG SCC of sensitised austenitic Alloys in solutions with reactive sulphur speciesIG SCC of sensitised austenitic alloys in reactive sulphur species solutionsConclusionsConclusionsRecommendations to prevent corrosion of stainless steels

03 inl seminar_scc in low temperature environments (52)_ pc

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