corrosion - acetic acid - 10% - 232 c - per year.pdf

ATICORROSIONCONFERENCE.COM | CORROSION SOLUTIONS® CONFERENCE 2011 PROCEEDINGS 127

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Evan HinshawGlobal vP of SalesTantaline 303 Wyman St, Suite 300Waltham, MA 02451USAE: ehinshaw@tantaline .com

Dean GambaleCEO, AmericasTantaline303 Wyman St, Suite 300Waltham, MA 02451USAE: dgambale@tantaline .com

Brian ChambersLead Engineer Technical ServicesHoneywell Corrosion Solutions11201 Greens Crossing Blvd, Suite 700 Houston, TX 77067USAT: 281-248-0705E: brian .chambers@honeywell .com

Biography

Evan Hinshaw, VP Sales at Tantaline, has been developing and promoting specialty metal products for over 20 years . He graduated from The Ohio State Engineering program with a BS in Welding Engineering and Materials Science and a MBA degree from the University of Phoenix . Evan is a registered Professional Welding Engineer in the state of Ohio, and a registered International Welding Engineer . He has contributed to several patents for welding consumables and new alloys for nickel-based consumables and refractory metals . Starting in the R&D labs at Special Metals (formerly INCO Alloys) Primary Mill Operations as well as their Welding Consumables Division, he then shifted into market development and sales as Industry Manager in Nuclear, Marine and the Chemical Processing Industries . As a Product Manager at H .C . Starck, he significantly increased the level of sales and exposure of Tantalum Mill Products and Processing capabilities into various aqueous corrosion applications for the Steel, Pharmaceutical, Chemical Processing and Oil and Gas Industries . Now as the VP of Sales at Tantaline, Evan is responsible for the Sales and Marketing in North and South America and Asia Pacific regions for Tantaline’s aftermarket products and Tantaline surface alloy services for custom parts and equipment for highly corrosive hot concentrated acidic environments .

Abstract

This paper describes the results of a laboratory study evaluating corrosion resistance of a tantalum surface alloy on stainless steel,

and multiple corrosion-resistant alloys in a laboratory simulation of two deep well acidizing environments . Acidizing is a common practice in oil production where well-stimulation acids are pumped through tubular goods into an oil reservoir in order to remove formation damage, increase porosity in the formation, and clean deposits from tubulars . These acids can cause high corrosion rates on nearly every alloy utilized in production . General and localized corrosion susceptibility of alloys 316L, Ti 6-4, Ti 6-2-4-6, C276 and a tantalum (Ta) surface alloy on 316L in high temperature mineral and organic acids was assessed . The two acidizing environments that were studied included 10% acetic acid and a mixture of 10% acetic acid and 10% hydrochloric acid with 15 psia hydrogen sulfide (H2S) at 232ºC (450ºF) . The paper also presents the possible use of tantalum surface alloys on commonly employed steels in the oilfield for improved resistance to extreme environments where nickel and titanium alloys fare poorly .

Keywords

• tantalum• stainless steel• acidizing

Introduction

A laboratory study was conducted to evaluate the corrosion resistance of multiple alloys to simulate acidizing in deep production wells . Several classes of alloys were investigated, including stainless steel (316L), nickel-based alloy (C276), titanium alloys (Ti 6-4 and Ti

Evaluation of Corrosion Resistant Alloys for Deep Well Acidizing Environments

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6-2-4-6), and 316L surface-alloyed with tantalum (Ta) . Two tests were conducted using two acidizing environments representing a mild condition (10% acetic acid) and an aggressive condition (10% hydrochloric acid — HCl, 10% acetic acid, 15 psia hydrogen sulfide — H2S); neither solution contained any corrosion inhibitor . Tests were conducted at 450ºF (232ºC) to represent the bottom-hole temperature of a deep well . Acidizing is a common practice in oil production where well-stimulation acids are pumped through tubular goods into an oil reservoir in order to remove formation damage, increase porosity in the formation, and clean deposits from tubulars . Concentrated mineral and organic acids containing corrosion inhibitors are used for acidizing; commonly used examples of these solutions include:• 10% HCl• 15% HCl• 28% HCl• 12% HCl / 3% HF• 15% HCl / 10% Acetic Acid• 10% Acetic Acid• 10% Formic Acid

Corrosion damage, even with high doses of the proper inhibitors, are expected to occur in acidizing solutions at elevated temperatures . A general rule in high temperature acidizing solutions is that corrosion rates less than 2,000 mpy (50 .8 mm/yr) are considered acceptable [1] based on the short period of time that tubulars are exposed to the acidizing solution . Organic acid solutions are occasionally used to prevent excessive formation damage or corrosion [2] . Solutions of 10% acetic acid or 10% formic acid are most commonly used for organic acidizing solutions . Studies have shown that these organic acid solutions are significantly less corrosive than mineral acids [1-4] , especially on corrosion-resistant alloys . For example, Ti Beta-C exhibits zero corrosion rates in either 10% acetic or 10% formic acid at 450ºF(232ºC) [3,4] . Corrosion inhibitors have been demonstrated to provide sufficient corrosion protection over a range of temperatures for different alloy classes used in tubular goods . Studies in inhibited mineral acids at elevated temperature include evaluation of alloys like N80 carbon steel [5,6,] 13Cr martensitic stainless steels [1,2,5,7] ,

duplex stainless steels [1,2,5,7,8] , nickel-based alloys [1,5,6] , and titanium alloys [3,4] . Limitations of corrosion inhibitors have been noted in laboratory and field studies . Field results on 25Cr duplex stainless steel tubular noted that corrosion rates at approximately 266ºF(130ºC) were an order of magnitude higher than corresponding laboratory results; this finding was indicative of decreased inhibitor efficiency in the field due to flow considerations or consumption of the inhibitor[8] . Multiple studies have also concluded that corrosion inhibitors do not provide equivalent protection between different classes of alloys [1,2,5] , e .g . carbon steel vs . duplex stainless steels, which can lead to difficulties in mitigating corrosion on tubing strings consisting of multiple alloy types . The presence of H2S, common in many wells, has also been established to interfere with corrosion inhibition by a hypothesized competition between sulfide and inhibitors on alloy surfaces, resulting in increases in corrosion rates of an order of magnitude [6] . General corrosion is the most prevalent form of attack by acidizing solutions although localized corrosion and stress corrosion

Figure 1. Results of corrosion and cracking evaluations in a variety of conditions with inhibited 15% hCl [1].



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cracking (SCC) may also occur[1-3] . While the majority of acidizing laboratory studies are conducted in the absence of H2S, those studies evaluating the effect of H2S have demonstrated a strong effect on promoting general corrosion, localized corrosion, and SCC [1,6] . Figure 1 presents one set of results from a study by Kane and Wilhelm [1] demonstrating the increase in general corrosion rates on several materials in inhibited 15% HCl upon the addition of H2S . A study by Kolts and Corey [6] resulted in SCC of multiple nickel-based alloys in inhibited acidizing conditions containing H2S; these same alloys did not exhibit cracking in the same conditions without the presence of H2S . Corrosion rates in uninhibited acidizing solutions represent a worst-case condition that may more accurately represent acidizing operations under flow or where inhibitor compounds have been consumed at shallower depths in the well . As noted earlier, corrosion rates in acidizing solutions can be high even at moderate temperatures . A study by Garber and Kantour[5] found that the corrosion rate of alloy 625 in uninhibited 10% HCl ranged from approximately 15 mpy (0 .4 mm/yr) at 104ºF (40ºC) to 300 mpy (7 .6 mm/yr) at 180ºF (82ºC) . Even corrosion-resistant titanium alloys, such as Ti Beta-C, exhibit high corrosion rates in uninhibited 10% HCl as demonstrated by a measured 584 mpy (14 .8 mm/yr) corrosion rate at 212ºF (100ºC) [3,4] . Corrosion rates increase significantly in both inhibited and uninhibited acidizing solutions with temperature . An investigation [6] at higher temperature, 350ºF (177ºC), in uninhibited 15% HCl discovered that nickel-based alloys 535, 825, and G3 all completely dissolved .

Experimental Procedure

General and localized corrosion behavior of multiple alloys exposed to two high temperature acidizing environments was assessed in this investigation . Duplicate (2) rectangular coupons of 316L, C276, Ti 6-4, Ti 6-2-4-6, and tantalum surface-alloyed 316L were exposed in each environment . The two acidizing environments that were utilized represented a mild corrosive case, 10% acetic acid, and a severe corrosive case, 10% HCl and 10% acetic acid with 15 psia H2S; neither solution contained any corrosion inhibitor .

expeRimental SetupAcidizing exposure tests were conducted under static, deaerated conditions . Due to the highly corrosive nature of the environments, an autoclave constructed of tantalum surface-alloyed 316L was utilized to prevent excessive corrosion and subsequent possible failure of the pressure vessel . All internal parts of the autoclave were constructed of either tantalum surface-alloyed 316L or alumina ceramic . Photographs of the autoclave assembly and internals are presented in Figure 2 . As demonstrated in the evaluations presented herein, the tantalum surface-alloy was critical for equipment integrity for severe acidizing experiments .

TANTALUM SURFACE-ALLOYThe tantalum surface alloy on all equipment, accessories, and corrosion coupons was prepared using a proprietary process developed

by Tantaline [1] . The tantalum surface alloy process involves the production of a gaseous atmosphere of tantalum that grows the tantalum metal into and onto the substrate, as demonstrated in Figure 3 . Tantalum metal forms over the substrate-tantalum interface, providing the chemical and corrosion resistance properties of pure tantalum . This process occurs at nanoscale dimensions and at high temperatures creating a metallurgically bonded tantalum layer superior to traditional coatings or electroplating in its durability .

mateRialSFive different materials were evaluated in this study, namely 316L, C276, Ti 6-4, Ti 6-2-4-6, and tantalum surface-alloyed 316L . Details on the mill heat identification and elemental composition are presented in Tables 1A and 1B for all alloys except surface-alloyed 316L . The

Figure 2. Tantalum surface-treated autoclave.

Figure 3. Depth profile of Ta following Ta surface alloy treatment.




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Ta surface alloy was applied to the same heat of 316L as detailed in Tables 1A and 1B .

teSt conditionSTwo experiments were conducted in uninhibited acidizing solutions at 232ºC (450ºF) . Typically, inhibited acidizing solutions are utilized both in laboratory experiments and in the field . These inhibitor formulations are often designed for effectiveness on particular alloy classes (e .g . carbon steels, nickel alloys, etc .) as noted in the Introduction section . As the objective of this study was to both evaluate corrosion in the worst-case condition (uninhibited) and on multiple classes of alloys, no inhibitor was used in either experiment . Details of the experiments conducted are presented in Table 2 . Acidizing solutions were prepared from reagent grade glacial acetic acid and HCl . A gas cap of nitrogen (N2) pressure was used in each test in order to lessen vaporization of the acidizing solutions at test temperature . N2 gas caps were applied at room temperature prior to heating the autoclave .

pRoceduReCoupons were stamped with unique

identification numbers and affixed to a test rack made of tantalum surface-alloyed 316L all-thread, rod, and nuts; ceramic shoulder washers were utilized to prevent a galvanic couple between the tantalum and the specimen . A photograph of the coupons attached to the specimen test rack is shown in Figure 4 . The relative location of each set of coupons was noted prior to exposure to permit coupon identification if identification numbers

were illegible following exposure . The specimen test rack was inserted into the autoclave and 1L of acid solution (see Table 2) was added to the autoclave by pouring . The autoclave was then sealed and pressurized with N2 gas to ensure seal integrity . The solution was deaerated by N2 gas purge for 1 .5 hours at room temperature . Following the gas purge, the target gas environment (see Table 2) was applied to the

Table 1b. Alloy coupon heat and composition information.

Alloy HON # Heat # Composition

N Sn Co C Mn P S Si O

316L 11618 891160 0 .03 — — 0 .023 1 .84 0 .031 0 .001 0 .37 —

C276 11965 276083604 — — 1 .65 <0 .001 0 .52 0 .011 0 .004 <0 .02 —

Ti 6-4 11966 PBBSJ 0 .003 — — 0 .03 — — — — 0 .12

Ti 6-2-4-6 11967 01209 0 .005 1 .9 — 0 .011 — — — 0 .032 0 .09

Table 1A. Alloy coupon heat and composition information.

Alloy HON # Heat # Composition

Fe Ni Ti Cr Mo Al V Zr W

316L 11618 891160 balance 10 .16 — 16 .29 2 .11 — — — —

C276 11965 276083604 5 .53 balance — 15 .95 15 .48 — — — 3 .57

Ti 6-4 11966 PBBSJ 0 .17 — balance — — 6 .07 3 .88 — —

Ti 6-2-4-6 11967 01209 0 .12 — balance — 6 .0 5 .9 — 4 .4 —

Figure 4. Photograph of Ta surface-alloyed specimen test rack with coupons affixed.




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autoclave following which the autoclave was rapidly heated to 232ºC (450ºF); approximate heating time was 1 hour . Once at temperature, the exposure commenced and was continued for 8 hours . At the end of the 8 hour exposure period, the autoclave was rapidly cooled and the specimens removed; approximate time to remove the specimens was 1 .5 hours . Following exposure to the test environment, the coupons were removed from the autoclave, cleaned, photographed, and evaluated for general corrosion and localized corrosion . General corrosion was determined by weight loss analysis per ASTM G1[9] — “Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens .” Localized corrosion would have been determined per microscopical measurements as detailed in ASTM G46 [10] —

“Standard Guide for Examination and Evaluation of Pitting Corrosion” but no discrete pits were observed on any of the test specimens .

Results

Measured corrosion rates from the two experiments were substantially different . Corrosion rates in the 10% acetic acid at 232ºC (450ºF) were considered mild with 316L exhibiting the highest corrosion rate — 242 mpy (6 .1 mm/yr) . Corrosion rates in the 10% HCl / 10% acetic acid with H2S environment were extremely high for all alloys except Ta surface-alloyed 316L; 316L, Ti 6-4, and Ti 6-2-4-6 coupons were each completely dissolved during the 8 hour exposure .

ReSultS of teSt #1: 10% acetic acid at 232ºc (450ºf)As expected based on previous investigations in organic acidizing solutions at high temperature [1-4] , the corrosion rates in 10% acetic acid at 232ºC (450ºF) ranged from non-existent to moderate for the alloys evaluated . Tantalum surface-alloyed 316L and Ti 6-2-4-6 each exhibited zero corrosion rates . 316L corrosion was measured at 242 mpy (6 .1 mm/yr) while corrosion rates on C276 and Ti 6-4 were 11 .9 mpy (0 .3 mm/yr) and 2 .2 mpy (0 .1 mm/yr), respectively . All alloys exhibited corrosion rates well below the acceptability criteria of 2,000 mpy . The results are detailed in Table 3 and photographs of the post-exposure coupons are presented in Figure 5 .

Table 3. Corrosion rates for alloy coupons exposed to 10% acetic acid at 232ºC (450ºF).

Material Weight-loss Over 8 Hour Exposure

Corrosion Rate Average Corrosion Rate

316L 30 .6 mg 193 mpy (4 .9 mm/yr) 242 mpy (6 .1 mm/yr)

45 .8 mg 291 mpy (7 .4 mm/yr)

C276 2 .1 mg 12 .2 mpy (0 .3 mm/yr) 11 .9 mpy (0 .3 mm/yr)

2 .0 mg 11 .6 mpy (0 .3 mm/yr)

Ti 6-4 0 .3 mg 3 .3 mpy (0 .1 mm/yr) 2 .2 mpy (0 .1 mm/yr)

0 .1 mg 1 .1 mpy (0 .0 mm/yr)

Ti 6-2-4-6 None (0 .0 mg) Zero Zero

None (-0 .1 mg) Zero

Ta surface-alloyed 316L None (-0 .3 mg) Zero Zero


Table 2. Experimental conditions for corrosion evaluation in acidizing solutions.

Test Alloys Number of Coupons in Liquid

Solution Concentration

Temperature Pressure Duration

1 316C276Ti 6-4Ti 6-2-4-6Ta=surface316L

2 per day 10% Acetic Acid 450ºF (232ºC) 35 psi N2 applied at 70ºF (21ºC)

8 hours

2 10% Acetic Acid10% HCl

15 psia H2S at 450ºF (232ºC),140 psi N2 at 70ºF (21ºC)




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ReSultS of teSt #2: 10% hcl / 10% acetic acid / 15 pSia h2S at 450ºf(232ºc)The corrosion rates in 10% HCl / 10% acetic acid / 15 psia H2S at 450ºF (232ºC) were extremely high for the alloys evaluated except tantalum surface-alloyed 316L . Tantalum surface-alloyed 316L coupons exhibited zero corrosion rates and were noted as displaying a blue tint due to plating of metallic ions from solution during the exposure . 316L, Ti 6-4, and Ti 6-2-4-6 coupons were all completely dissolved during the 8 hour exposure (see Figure 6), translating to minimum corrosion rates in the range of 16"/yr (406 mm/yr) to 41"/yr (1,049 mm/yr) . C276 coupons displayed an extreme amount of attack and corrosion rate was measured at 21"/yr (531 mm/yr), well beyond the acceptability criteria of 2,000 mpy . The results are detailed in Table 4 and photographs of the post-exposure coupons are presented in Figure 7 . The performance of the tantalum surface-alloyed coupons, autoclave, and wetted accessories successfully demonstrated the corrosion protection provided by the surface treatment process in the highly aggressive environments tested . Inspection of the coupons, autoclaves, and accessories found no indications of localized attack, blistering, or other damage to the tantalum surface alloy or underlying substrate .

Conclusion

Based on the laboratory evaluation described herein, the following conclusions can be made:• 316L, C276, Ti 6-4, Ti 6-2-4-6 and

Figure 6. Specimen “tree” following exposure to 10% hCl, 10% acetic acid, 15 psia h2S at 232ºC (450ºF).

Missing 316L Coupons

C276

Ta-surface 316LMissing Ti Coupons

Figure 5. Photographs of coupons following exposure to 10% acetic acid at 232ºC (450ºF). Left to right: 316L, C276, Ti 6-4, Ti 6-2-4-6, Ta surface-alloyed 316L.

Figure 7. Coupons following exposure to 10% hCl, 10% acetic acid, 15 psia h2S at 232ºC (450ºF). Left to right: C276, Ta surface-alloyed 316L.




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tantalum surface-alloyed 316L are all acceptable for use in 10% acetic acid solution at 450ºF (232ºC) based on an acceptance criteria of corrosion rates less than 2,000 mpy .

• 316L, C276, Ti 6-4, and Ti 6-2-4-6 are not acceptable for use in 10% HCl / 10% acetic acid / 15 psia H2S at 450ºF (232ºC) . Corrosion rates significantly exceeded the 2,000 mpy acceptance criteria and most coupons were completely dissolved .

• Ta surface-alloyed 316L material exhibited zero corrosion rate in highly acidic solutions, including conditions containing H2S, at high temperatures .

References

1. R .D . Kane and S .M . Wilhelm, “Compatibility of Stainless and Nickel Base Alloys in Acidizing Environments”, CORROSION/89, paper no . 89481, Houston, TX, NACE International, 1986 .

2. M .L . Walker, J .M . Cassidy, K .R . Lancaster, and T .H . McCoy, “Acid Inhibition of CRAs: A Review”, CORROSION/94, paper no . 94019, Houston, TX: NACE International, 1994 .

3. D .R . Klink and R .W . Schutz, “Engineering Incentives for Utilizing Ti-3Al-8V-6Cr-4Zr-4Mo Alloy Tubulars in Highly Aggressive Deep Sour Wells,” CORROSION/92, paper no . 92063, Houston, TX, NACE International, 1992 .

4. R .D . Kane, B . Craig, and A . Venkatesh, “Titanium Alloys for Oil and Gas Service: A Review”, CORROSION/09, paper no . 09078, Houston, TX, NACE International, 2009 .

5. J .D . Garber and M . Kantour, “How High-Alloy Tubulars React in Acidizing Environments”, Petroleum Engineer International, July 1984, p 60 .

6. J . Kolts and S .M . Corey, “Corrosion and Stress Corrosion Cracking of High-Performance Alloys in Simulated Acidizing Environments to 175ºC (350

ºF)”, CORROSION/84, paper no . 84217, Houston, TX, NACE International, 1984 .

7. M .L . Walker and T .H . McCoy, “Effect and Inhibition of Stimulation Acids on Corrosion Resistant Alloys”, CORROSION/86, paper no . 86154, Houston, TX, NACE International, 1986 .

8. T . Cheldi, I . Obracaj, A . Cigada, M . Cabrini, B . Vicentini, and G . Rondelli, “Duplex Stainless Steel Corrosion Behavior During Acidification: Laboratory Versus Field Test Results,” CORROSION/95, paper no . 95073, Houston, TX, NACE International, 1995 .

9. ASTM G1, “Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens”, West Conshohocken, PA, ASTM .

10. ASTM G46, “Standard Guide for Examination and Evaluation of Pitting Corrosion”, West Conshohocken, PA, ASTM .

n n n

Table 4. Corrosion rates for alloy coupons exposed to 10% hCl, 10% acetic acid, 15 psia h2S at 232ºC (450ºF).

Material Weight-loss Over 8 Hour Exposure

Corrosion Rate Average Corrosion Rate

316L Dissolved >5,787 mg Dissolved >36,506 mpy (>927 mm/yr) Dissolved >36,517 mpy (>928 mm/yr)

Dissolved >5,747 mg Dissolved >36,517 mpy (>928 mm/yr)

C276 3,604 mg 20,901 mpy (531 mm/yr) 20,897 mpy (531 mm/yr)

3,589 mg 20,893 mpy (531 mm/yr)

Ti 6-4 Dissolved >3,733 mg Dissolved >41,341 mpy (>1,050 mm/yr) Dissolved >41,341 mpy (>1,050 mm/yr)

Dissolved >3,718 mg Dissolved >41,312 mpy (>1,049 mm/yr)

Ti 6-2-4-6 Dissolved >1,260 mg Dissolved >16,289 mpy (>414 mm/yr) Dissolved >16,289 mpy (>414 mm/yr)

Dissolved >1,259 mg Dissolved >16,231 mpy (>412 mm/yr)

Ta surface-alloyed 316L None (-1 .7 mg) Zero Zero



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