Application Limits of CRA.pdf

CORROSION ENGINEERING

Corrosion Performance and Application Limitsof Corrosion-Resistant Alloys in Oilfield Service

A. Miyasaka* and H. Ogawa**

ABSTRACT

The corrosion behavior of corrosion-resistant alloys (CRA)in sour environments was investigated using a duplexstainless steel as a representative CRA. Changes incorrosion morphologies resulting from changes inenvironmental aggressiveness were elucidated. Theapplication limits of CRA were shown to be determined bywhether pitting corrosion occurred. A theory was proposedfor predicting the corrosion morphologies and, thus,determining the application limits of the CRA. The validityof prediction by this new theory was confirmed by goodagreement with results from long-term immersion tests anda field test for actual-size test pipes. Since this theory wasbased on the corrosion mechanism, it showed manyadvantages: The prediction was accurate, the results forone environment could be extended to other environments,and the prediction was conducted very quickly.

KEY WORDS: corrosion-resistant alloys, field testing,immersion testing, localized corrosion, morphology, oil andgas environments, pH, pitting corrosion, sour gas, stresscorrosion cracking

INTRODUCTION

Recently produced oil and natural gas sometimescontain a large amount of hydrogen sulfide (H2S) andcarbon dioxide (CO2). To exploit reservoirs with such

CORROSION–Vol. 51, No. 30010-9312/95/00005

© 1995, NACE I

Submitted for publication February 1994. Presented at the 12thInternational Corrosion Congress, September 1993, Houston, TX.

* Nippon Steel Corp., Nagoya Research and Development Laboratories,5-3 Tokai-machi, Tokai, Aichi, 476 Japan.

** Nippon Steel Corp., Steel Research Laboratories, 20-1 Shintomi, Futtsu,Chiba, 299-12 Japan.

corrosive and hostile environments, low-alloy tubularsteels traditionally have been used with corrosioninhibitors for corrosion prevention. Chemicalinhibition, however, has little effect in very deep wellsand is expensive for offshore wells. Thus, thedemand for oil country tubular goods (OCTG) madeof corrosion resistant-alloys (CRA) has increasedbecause their use can eliminate the need forchemical inhibition.

A great variety of CRA, from 13% chromium (Cr)martensitic stainless steel (SS) to the Cr-nickel (Ni)-molybdenum (Mo) superalloys, has been proposedfor sour service. Each CRA has its own applicationlimit for corrosion or cracking, which dependsprincipally on its alloy chemistry. The selection of aCRA with the necessary and sufficient corrosionresistance for a given environment is indispensableto ensure the structural integrity of production wells atthe least possible expenditure. This necessitatesprecise information on the critical environments foreach CRA.

Conventionally, such application limits have beendetermined experimentally by “go/no go” testmethods.1 Results by these techniques, however,depend significantly on the test conditions. Forexample, results of constant-load type and constantstrain-type stress corrosion cracking (SCC) tests areaffected by the applied stress and test duration. It isnow well known that strain rate has a remarkableinfluence on results of slow strain rate testing(SSRT). For this reason, the application ofconventional SCC test results has been confined

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FIGURE 1. Influence of HCO3– content on pH of 20 mass%

NaCl aqueous solution saturated with H2S at 333 K.

primarily to relative comparisons of corrosionresistance between CRA.

In this study, the corrosion and crackingmechanism of CRA in sour gas environments wasinvestigated. On the basis of the results, a newcriterion for rational determination of the applicationlimits of a CRA, not affected by test conditions, wasproposed.

ENVIRONMENTAL AGGRESSIVENESS

The aggressiveness of environments can becharacterized by two factors: pH and redox potential.

pH Estimation in Oilfield EnvironmentsEquation (1) was obtained for calculating the pH

of sour and sweet environments, considering thefollowing conditions:

— The dissociation equilibria of H2S, CO2, water(H2O), and bisulfate (HSO4

–);— The electric neutrality condition for aqueous

solutions; and— The mass balance of bicarbonate (HCO3

–)-and sulfate (SO4

2–)-related substances.The deduction of Equation (1) was detailed in a

previous work.2 The molar hydrogen concentration

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(mH+) was obtained as a positive solution of Equation(1), and by substituting mH+ into the definition of pH inEquation (8), the pH value could be calculatedaccording to (see List of Symbols for definitions ofvariables):

mH+4 + (X + C2 + Z + C4)mH+

3

– (C1mH2S + C3 – ZC2 – XC4 – C2C4)mH+2 (1)

– (C2 – C4) (C1mH2S + C3)mH+

– C2C4(C1mH2S + C3) = 0

where

C1 = K1,H xγH2S

γ2± H2S

(2)

C2 = K1,C x γCO2

γ2± CO2

(3)

C3 =

KW

γ2± H2O

(4)

C4 = K1,S x γHSO4

–

γ2± HSO4

– (5)

X = mCO2+ mHCO3

– (6)

Z = mSO42– + mHSO4

– (7)

Thus,

pH = – log aH+

= – log gH+mH+ (8)

The physicochemical parameters required toaccount for the effect of concentrated ions on ionicactivity coefficients and mean activity coefficientswere estimated or extrapolated2 from the data forthose in sodium chloride (NaCl) aqueous solutions.3

The dissociation constants and solubility coefficientsof H2S and CO2 were estimated thermodynamicallyusing the correspondence principle4 and the principleof balance of identical-like charges,5 respectively.The estimation for physicochemical parameters alsowas detailed in a previous work.2,6 The validity of theabove approximation and estimation already hasbeen confirmed for concentrated NaCl aqueoussolutions by measuring directly the pH values usingan n-type titanium dioxide (TiO2) semiconductorelectrode up to temperatures of 473 K.6 Figure 1

CORROSION–MARCH 1995


FIGURE 2. Changes of S/H2S equilibrium potential as afunction of HCO3

– concentration.

gives an example of the typical change in pH withincreasing HCO3

– content.

Redox Potential of the EnvironmentsIn every service environment, the most noble

immersion potential (Eip) an alloy can take is theredox potential (E1) of the cathodic reaction thatcontrols corrosion of the alloy in the environment.Strictly speaking, Eip does not agree with E1, becauseEip is controlled by the balance of anodic andcathodic reactions. However, the approximation of E1

= Eip enables simple and prompt prediction with aslightly conservative estimation.

The cathodic reaction that controls corrosion andSCC of CRA in sour environments is the reduction ofelemental sulfur (S) in Equation (9).7 Then, the E1

value of this reaction, and approximately Eip ofpassive alloys, can be calculated using Equation(10).8 In Equation (10), the pH value can be obtainedby the procedure introduced in the previous section,and H2S activity can be calculated thermodynamicallyas:6

S + 2H+ + 2e– = H2S (9)

E1 = ET0 – 2.303RT

Fx pH – 2.303RT

2Fx log aH2S (10)

Figure 2 shows an example of the influence ofHCO3

– concentration on E1 of Reaction (9) at varioustemperatures. The presence of HCO3

– moved E1 ofReaction (9) in the less noble direction. This meantthat the aggressiveness of the environment wasmitigated with increasing HCO3

–.

EXPERIMENTAL PROCEDURE

Test MaterialsA 20-mm-thick plate of UNS S31803(1) was used

as a representative CRA for oil and gas production. Itwas solution heat treated at 1,323 K for 300 s andthen water quenched. The steel was used in as-solution treated and cold-rolled conditions. The totalreduction in thickness in the cold-rolled samples was20%. The major chemical composition of the teststeel was 0.019% carbon (C)-0.43% silicon (Si)-1.78% manganese (Mn)-21.4% Cr-5.3% Ni-2.78%Mo-0.146% nitrogen (N)-balance iron (Fe).

Test ProcedureElectrochemical Measurements — The critical

pitting potential (Vc´) and depassivation pH (pHd)

CORROSION–Vol. 51, No. 3

(1) UNS numbers are listed in Metals and Alloys in the Unified NumberingSystem, published by the Society of Automotive Engineers (SAE) andcosponsored by ASTM.

were measured. Test coupons 3 mm thick, 15 mmwide, and 20 mm long were machined from themiddle of the wall. They were degreased in acetone,polished with 320-grit paper, and coated with Siresin, leaving an area 1 cm by 1 cm formeasurements. Just before being immersed in testsolutions, the specimens were pickled in 50% sulfuricacid (H2SO4) at 333 K to remove the air-formed film.

Potentiodynamic experiments were conducted ata scan rate of 10 mV/min. The potential scan wasmade from the spontaneous potential in the nobledirection. The potential corresponding to the currentdensity of 100 µA/cm2 was adopted as Vc´.

For measuring pHd, specimens were immersed intest solutions of various pH values, which wereadjusted before immersion. Potential changes weremonitored continuously for 8.64 x 104 s. The pHd

value was the pH at which Eip shifted in the nobledirection on the potential-pH diagram.9

Immersion Tests — The relationship betweenenvironmental conditions and corrosion morphologieswas examined by immersion testing. The testcoupons were 2 mm thick, 15 mm wide, and 20 mmlong. They were degreased in acetone and polishedwith 320-grit paper just before the tests. Atmosphericpressure tests were performed in glass vessels,whereas high-pressure tests and high-temperature

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FIGURE 3. Influence of temperature and PH2S on Vc´.

FIGURE 4. Influence of temperature and PH2S on pHd.

tests (> 373 K) were conducted in high-pressureautoclaves. Test duration usually was 1.21 x 106 s.Tests for 1.56 x 107 s also were carried out when thecorrosion morphologies were marginal. After sampleimmersion, corrosion morphologies were determinedby visual and opto-microscopic observations. Theywere classified into three types: no attack (N), pitting(L), and general corrosion (G).

SCC Tests — SSRT and four-point, bent-beamtests were performed. The bent-beam test was donefor cold-rolled materials, according to ASTMStandard G 39-79.10 Specimens 2 mm thick, 10 mmwide, and 65 mm long were sampled lengthwise from

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the middle of the wall. Stress equal to 0.2% offsetproof stress was applied in the rolling direction. Testduration was 1.21 x 106 s. SSRT specimens withgauge sections 4 mm in diam and 20 mm long weresampled in the rolling direction from the as-solutiontreated material. SSRT were conducted at a nominalstrain rate of 2.0 x 10–6/s until failure.

The reduction-in-area ratio (RAR = RAenv/RAinert)and elongation ratio (ELenv/ELinert) were used toexpress the SSRT results, where RAenv and RAinert arethe reductions in area in the test environments and inan inert environment, and ELenv and ELinert areelongations in the test environments and in an inertenvironment, respectively. Dry nitrogen gas (N2,5 MPa) was used as an inert environment to obtainthe baseline data for SSRT. Without aqueous solu-tions, corrosion did not take place. Scanning electronmicroscopy (SEM) of fracture surfaces and crosssections was conducted as necessary for both typesof SCC tests to determine the occurrence of SCC.

Test EnvironmentsDeaerated aqueous solutions that contained

20 mass% (4.28 mol/kg H2O) NaCl and that were inequilibrium with H2S at the scheduled pressure wereselected as the test solutions. For examining theinfluence of anions, sodium bicarbonate (NaHCO3) orsodium sulfate (Na2SO4), ranging from 10–4 mol/kg to10–1 mol/kg, was added to the solutions. Ion-exchanged and distilled pure water and analytical-grade chemicals were used to prepare the testsolutions. All the tests were performed at tempera-tures ranging from 298 K to 523 K. H2S partialpressure (PH2S) was varied between 0.001 MPa and4 MPa.

RESULTS AND DISCUSSION

Electrochemical MeasurementsFigure 3 shows the influence of temperature and

PH2S on Vc´. Vc´ shifted in the less noble direction witha temperature rise from 333 K to 373 K. The furthertemperature rise resulted in a slight decrease of Vc´.Vc´ took a less noble value with increasing PH2S. Theeffects of temperature and PH2S on pHd are given inFigure 4. The pHd value increased with thetemperature and PH2S. These results indicated thatthe passivation capability of the CRA decreased(i.e., the passive film became unstable) at hightemperature and under high PH2S.

The influence of SO42– and HCO3

– concentrationson Vc´ is shown in Figure 5. It was evident that SO4

2–

raised Vc´ when the molar ratio of SO42– to chloride

ion (Cl–) was ≈ > 0.5.HCO3

– did not affect Vc´ up to mHCO3–/mCl– = 1. A

similar tendency for the effect of anions was



FIGURE 5. Effect of SO42– and HCO3

– contents on Vc´.

FIGURE 6. Relationship between corrosion morphologies andenvironmental conditions.

observed for 5% NaCl (0.90 mol/kg) aqueoussolutions. The above-mentioned influence of SO4

2–

for raising Vc´ was similar to that in neutral Cl–-containing aqueous solutions.11-12 SO4

2– inhibitedpitting also in H2S-containing brine, when SO4

2–

concentration was sufficiently great compared to thatof Cl–. This presumably was because of SO4

2– and Cl–

migration into pits, which decreased the Cl–

concentration in a pit.

Immersion TestsThe relationship between the corrosion

morphologies and the environmental conditions in theimmersion tests is shown in Figure 6. At low tempera-ture and low PH2S, the alloy underwent no attack (N).The corrosion morphology changed to localizedcorrosion (L) with a temperature rise and an increasein PH2S and finally exhibited general corrosion (G).Results in Figure 6 for PH2S of 0.05 MPa and 0.5 MPaand temperature of 333 K and 423 K are from1.56 x 107 s of immersion. At PH2S of 0.5 MPa and at423 K (Point A in Figure 6), the corrosion morphologyinitially was determined as localized corrosion after1.21 x 106 s of immersion, whereas it was determinedto be general corrosion after 1.56 x 107 s. The quasi-pitting after 1.21 x 106 s was attributed to incompletedissolution of the air-formed film within that limitedtime of 1.21 x 106 s. At Point B in Figure 6, thecorrosion morphology was marginal between noattack and localized corrosion after 1.21 x 106 s, but itchanged to complete pitting (L) after 1.56 x 107 s.

It was obvious from these results that the resultsof conventional immersion-type tests1 were affectedsignificantly by test duration. No changes in corrosionmorphology as a result of prolonging test durationwere observed at Points C and D.

SCC TestsFigures 7 and 8 show SCC test results for four-

point, bent-beam tests and SSRT, respectively. In thefour-point, bent-beam tests, the SCC-to-no SCCboundary was found between PH2S of 0.01 MPa and0.03 MPa. The influence of temperature and PH2S wasconsiderable in SSRT. Also in this case, thetransition from no SCC to SCC was observed at PH2S

of ≈ 0.03 MPa. These critical PH2S values were slightlygreater than those previously reported.13-14

Visual and opto-microscopic examination forcracking morphology revealed that cracks initiatedat pits and propagated by connecting pits whenPH2S was small.15 At higher PH2S values, SCC cracksinitiated directly at the metal surface without pitting.

Figure 9 shows the influence of HCO3– concen-

tration on RAR. RAR remained unchanged up to aHCO3

– concentration of 10–2 mol/kg. At mHCO3– of

0.1 mol/kg, RAR reached approximately unity, and no


SCC was observed by SEM on the fracture surface.The failure was caused completely by ductilefracture. This mitigation of SCC susceptibility byHCO3

– was attributed to the increase in pH and theresultant shift of E1 in the less noble direction, as wasexpected from Figures 1 and 2, because HCO3

–

buffered and raised the pH of the solution.

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FIGURE 7. Four-point, bent-beam SCC test results (F = failed,NF = not failed). FIGURE 8. Elongation ratio obtained by SSRT.

Such an SCC mitigation effect was not observedin the case of SO4

2– up to a concentration of 10–1 mol/kg. This was because the pH buffering effect of SO4

2–

was much smaller than that of HCO3–.2 The SO4

2–

concentration of 10–1 mol/kg was not sufficient toprevent pitting or SCC, as was expected from resultsin Figure 5.

DETERMINATION OF APPLICATION LIMITS

Prediction of Transitionfrom No Attack to Pitting

It has been understood generally that Vc

corresponds to the critical potential above whichmacroscopic pitting takes place.16-17 The pit embryocontinues to grow at potentials more noble than Vc,but it stops propagating when the potential is lessnoble than Vc. Therefore, if the potential of a givenalloy (Eip) in a given environment is known, theoccurrence of pitting can be predicted by comparingVc with Eip. Thus, the following criteria predict thecritical environments for the occurrence of pitting:

— Vc < E1: macroscopic pits propagate; or— Vc > E1: macroscopic pitting does not occur.Vc can be obtained by electrochemical

measurements. E1 can be calculated thermodynam-ically using Equation (10). The predicted boundary forthe transition from no attack to pitting is given as lineA in Figure 10.

Prediction of Transitionfrom Pitting to General Corrosion

pHd is defined as a critical pH value for an alloyto exhibit passive-to-depassive or depassive-to-

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passive transition. Therefore, if the pH value of agiven environment is known, it is possible todetermine whether the alloy can be passive in theenvironment. If the alloy cannot be passive, thepassive film will not form on the alloy surface so thatthe corrosion morphology must be general corrosion(active dissolution). The corrosion morphology in asituation where the alloy is passive should be noattack or pitting. Since the passive film is quiteunstable in the vicinity of passive-to-active transition,the critical environments for the transition shouldcoincide with the boundary between pitting andgeneral corrosion. Therefore, the critical environ-ments for general corrosion of an alloy can bepredicted by comparing pH of the environments withpHd of the alloy as:

— pH < pHd: the alloy will undergo generalcorrosion; or

— pH > pHd: the alloy will exhibit pitting or noattack.

The pHd values can be obtained by electrochemi-cal measurements. The pH values can be calculatedthermodynamically as in the previous section.2 Thepredicted boundary for the transition from pitting togeneral corrosion also is given as line B in Figure 10,in which the critical environment is a locus of thenode of the equi-pH lines and the equi-pHd lines.9

Comparison of Electrochemical PredictionWith Experimental Results

Figure 10 compares the electrochemicallypredicted transitions of corrosion morphologies withthe long-term immersion test results. Here, theboundary A is the electrochemical prediction for the



FIGURE 9. Influence of coexisting anion contents on RARobtained by SSRT.

FIGURE 10. Comparison of predictions for the no attack-to-pitting and pitting-to-general corrosion transitions with theexperimental results.

no attack-to-pitting transition, and the boundary B isthe prediction for the pitting-to-general corrosiontransition. The letters in circles indicate the corrosionmorphologies determined in the immersion tests. It isobvious from the figure that the electrochemicallypredicted transitions of corrosion morphologies werein good agreement with experimental results. Thisstrongly validated the proposed criteria.

Prediction of Transition from No SCCto SCC

In Figure 10, the no SCC-to-SCC boundary Cdetermined empirically in the previous section also isshown. Boundary C is fairly close to the criticalenvironments for pitting. Considering that SCC insour environments initiates at pits, the two bounda-ries were expected to coincide with each other after asufficiently long time.7,15 By substituting transition A(no attack-to-pitting) for transition C (no SCC-to-SCC), transition C also could be predicted byelectrochemical techniques.

Application of the Proposed TechniqueThe electrochemical prediction of corrosion

morphology proposed in this paper has the followingadvantages:

— The predicted results are not dependent ontest duration;

— The corrosion morphology can be predictedtheoretically on the basis of the corrosionmechanism;

— There is a possibility that the performance ofalloys for the lifetime of oil and gas wells can bepredicted; and

— Each measurement takes a very short time.In addition to the above advantages, the

proposed technique has other unique characteristics.The corrosion morphology in environmentscontaining both H2S and CO2 can be predicted byusing the results obtained in CO2-free conditions. Or,the influence of anions such as HCO3

– and SO42– can

be taken into account without repeating the corrosionand SCC tests. This is because the technique isbased on the corrosion mechanism. Conventionaltechniques require that tests be repeated when theenvironmental constituents are changed. However,the present technique easily predicts the corrosionmorphology even with the existence of CO2 and/orHCO3

–, since CO2 or HCO3– do not affect Vc´ or pHd of

CRA in sour environments.9

CO2 only reduces pH of the environment, and thepH of a sour environment shifts to a smaller valuewith increasing CO2 pressure. This slightly raises E1,as was shown in Equation (10). Because Vc´ isindependent of pH in acidic environments,18 Vc´values obtained in CO2-free conditions stand also for


CO2-containing environments. Figure 11 shows thecalculated results for the change in the no attack-to-pitting transition as a function of CO2 partial pressure(PCO2). The no-attack region shrank with an increasein PCO2.

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FIGURE 11. Change in no attack-to-pitting transition boundaryas a function of PCO2.

FIGURE 12. Influence of PCO2 on passive-to-active transitionboundary.

FIGURE 13. Shift of no attack-to-pitting boundary with increasingHCO3

– content and PCO2 of 10 MPa.

Similarly, the influence of PCO2 on the pitting-to-general corrosion boundary was calculated. pHd

values obtained in CO2-free conditions also areapplicable to CO2-containing environments becauseCO2 does not affect the pHd of CRA.9 An increase inPCO2 enlarged the general corrosion area toward thelower temperature and lower PH2S region, as shown inFigure 12.

The influence of HCO3– was examined by

calculation with the same procedure. Figure 13

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shows how the no attack-to-pitting boundary wasexpanded to the high-temperature and high-H2Spressure region with increasing amounts of HCO3

–.

FIELD TESTS

To confirm the accuracy and applicability of theproposed technique for predicting the applicationlimits of CRA, the two field tests were performed inthe Commonwealth of Independent States (C.I.S.,formerly the U.S.S.R.). One was for a double-wallpipe, with the liner material of type 316L SS (UNSS31603) and UNS N06625 alloy.19 The pipes wereexposed to the actual produced fluid from the naturalsour gas reservoir, which had a total pressure of10 MPa and contained 7.20 vol% CO2, 4.98 vol%H2S, and 0.28 vol% N2. Before the test, it wasexpected that type 316L SS would exhibit pitting inthis field condition but that UNS N06625 alloy wouldnot. After a 6-month test, detailed examination of theliner material revealed that the laboratory predictionwas completely in agreement with the field testresults.19

Another test was conducted in the Astrakhan gasfield in the C.I.S. for solid (mono-wall) and double-wall pipe consisting of 22% Cr-25% Ni-4% Mo-balance Fe in 5% NaCl + 0.5% acetic acid(CH3COOH) aqueous solution in equilibrium with1.5 MPa H2S plus 0.9 MPa CO2.20 Before the test, itwas considered that the alloy would not undergo anypitting or cracking in the test environment. This wascertified by detailed observation of the materialstested after the field test. In addition to the full-ringtest, the C-ring test specimens of duplex SS (UNS



S31803), both with and without a V-shaped notch atthe maximum stressed portion, were tested in thesame test condition. The laboratory predictions forSCC of these steels were confirmed by visualobservation of the specimens after the test.

CONCLUSIONS

❖ The corrosion behavior of CRA in sour environ-ments was investigated extensively using a duplexSS as a representative CRA. Electrochemicaltechniques to predict the corrosion morphology ofCRA were proposed.❖ Since the proposed technique was based on thecorrosion mechanism, it produced accurate predic-tions that were unaffected by the test conditions.Thus, it enabled the rational determination ofapplication limits of CRA.❖ Validity of the predictions was confirmed by goodagreement with long-term laboratory tests and fieldtests using full-scale sections of CRA pipes.

ACKNOWLEDGMENTS

The authors acknowledge the assistance ofNippon Steel Corp. and K. Denpo, formerly of NipponSteel.

LIST OF SYMBOLS

ai activity of chemical iET

0 equilibrium potential at temperature TF Faraday constantKH,i solubility constant of chemical i (mol/L/atm)K1,i first dissociation constant of chemical i

(C = CO2, H = H2S, S = SO42–, and w = H2O)

mi molar concentration of chemical iPG partial pressure of gas G


R gas constant (8.314 J/K/mol)T Temperature (K)gi activity coefficient of chemical ig± i mean activity coefficient of chemical i

REFERENCES

1. A. Ikeda, T. Kudo, Y. Okada, S. Mukai, F. Terasaki, “CorrosionBehaviors of High-Alloy Oil Country Tubular Goods for Deep Sour GasWells,” CORROSION/84, paper no. 206 (Houston, TX: NACE, 1984).

2. A. Miyasaka, “Thermodynamic Estimation of pH of Sour and SweetEnvironments as Influenced by the Effects of Anions and Cations,”CORROSION/92, paper no. 5 (Houston, TX: NACE, 1992).

3. M. Takahashi, Boshoku Gijutsu 23 (1974): p. 625.4. C.M. Criss, J.W. Cobble, J. Amer. Chem. Soc. 86 (1964): p. 5,385.5. J.W. Cobble, R.C. Murray Jr., P.J. Turner, K. Chen, “High-Temperature

Thermodynamic Data for Species in Aqueous Solution,” EPRI NP-2400Project 1167-1 Final Report (Palo Alto, CA: Electric Power ResearchInstitute, 1982), p. 4-13.

6. A. Miyasaka, K. Denpo, H. Ogawa, ISlJ lnt. 29 (1989): p. 85.7. A. Miyasaka, K. Denpo, H. Ogawa, Corrosion 45 (1989): p. 771.8. R.J. Biernat, R.G. Robins, Electrochim. Acta 14 (1969): p. 809.9. A. Miyasaka, K. Denpo, H. Ogawa, ISlJ lnt. 31 (1991): p. 194.

10. ASTM Standard G 39-79, “Practice for Preparation and Use of Bent-Beam Stress-Corrosion Test Specimens” (Philadelphia, PA: ASTM,1979).

11. H.H. Uhlig, J. Electrochem. Soc. 108 (1961): p. 327.12. H. Ogawa, I. Itoh, U. Nakata, Y. Hosoi, H. Okada, Tetsu-to-Hagane 63

(1977): p. 605.13. J. Sakai, I. Matsushima, Y. Kanemura, M. Tanimura, T. Osuka, “Effects

of Metallurgical Factors on Service Performance of Duplex StainlessSteel for Deep Sour Gas Wells,” Proc. 1982 ASM Metals Congress,paper no. 8201-012 (Metals Park, OH: ASM, 1982).

14. A. Ikeda, S. Mukai, M. Ueda, “Prevention of CO2 Corrosion of LinePipe and Oil Country Tubular Goods,” CORROSION/84, paper no. 289(Houston, TX: NACE, 1984).

15. A. Miyasaka, “Critical Stress for SCC of Corrosion-Resistant Alloy inSour Environments,” CORROSION/89, paper no. 5 (Houston, TX:NACE, 1989).

16. Y. Hisamatsu, Boshoku Gijutsu 21 (1972): p. 504.17. Z. Szklarska-Smialowska, Pitting Corrosion of Metals (Houston, TX:

NACE, 1986), p. 40.18. H.P. Leckie, H.H. Uhlig, J. Electrochem. Soc. 121 (1974): p. 1,137.19. H. Ogawa, Y. Murakami, K. Katayama, E. Gutman, “Prediction Method

of Pitting Corrosion Nucleation on High-Alloy Line Pipe in the SourEnvironments and Its Verification by the Field Test,” Proc. 11th Int.Corros. Cong., April 1990 (Florence, Italy: ICC, 1990), p. 4,463.

20. A. Miyasaka, A. Asahi, E. Tsuru, Y. Takano, A.F. Svetlichkin, V.P.Yakovlev, V.A. Tskhaj, “Full-Scale Evaluation of OCTG and Line Pipesin High-Pressure Sour Environments,” CORROSION/92, paper no. 38(Houston, TX: NACE, 1992).

CORROSION/96 CALL FOR PAPERS

A symposium titled Corrosionin Gas Treating is planned forCORROSION/96 by NACEInternational Task Group T-5-2on Gas Treating SystemsCorrosion Minimization. Thissymposium will cover such topicsas environmental regulationsrequiring acid gas removal

systems to have higher reliabilityand enhanced performance; howcorrosion can negatively affectboth unit reliability and quality ofgas treatment; case studies; anda panel discussion.

Papers containing informa-tion on these topics are beingsought. Prospective authors

should contact symposiumChairman John McCullough,Proton Technology Inc., 176Amsterdam Ave., Hawthorne,NY, 10532 (phone 914/769-8406)by May 1.

CORROSION/96 is plannedfor March 24 to 29, 1996, inDenver, Colorado.

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Application Limits of CRA.pdf