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IC 
 
 9055 
 
 Bureau of Mines information Circular/1985 
 
 Corrosion of Roof Bolt Steels in Missouri 
 Lead and Iron Mine Waters 
 
 By M. M. Tilman, A. F. Jolly III, and L. A. Neumeier 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 
 751 
 
 1f/NES 75TH A^"^ 
 
 -...iiBfiraiitMwaisaiimiSRiBiMTOinnnsiftTffliHaiiiirjiiiusMMBiiiwiiiMBffliiiw*!!!* 
 
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 ^■^t,\iimi 
 
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 Information Circular 9055 
 
 A 
 
 Corrosion of Roof Bolt Steels in Missouri 
 Lead and Iron Mine Waters 
 
 By M. M. Tilman, A. F. Jolly III, and L. A. Neumeier 
 
 UNITED STATES DEPARTMENT OF THE INTERIOR 
 Donald Paul Model, Secretary 
 
 BUREAU OF MINES 
 Robert C. Horton, Director 
 
iii!iaji<«-;3' if.WitS^^iSMW 
 
 -w^ 
 
 z 
 
 ^5 
 
 
 Library of Congress Cataloging in Publication Data: 
 
 Tilman, IVl. M. (Milton M.) 
 
 Corrosion of roof bolt steels in Missouri lead and iron mine waters. 
 
 (Bureau of Mines information circular ; 9055) 
 
 Bibliography: p. 9. 
 
 Supt. of Docs, no.: I 28.27: 905 5. 
 
 1. Mine roof bolting. 2. Rock bolts — Corrosion. 3. Mine waters. 
 4, Lead mines and mining— Mi ssouri. 5. Iron mines and mining— Mis- 
 souri. I. Jolly, A. F. (A. Fletcher). II. Neumeier, L. A. III. Title. 
 IV. Scries: Information circular (United States. Bureau of Mines) ; 9055. 
 
 TN295.U4 [ TN289.31 622s[622\28] 85-600221 
 
 li 
 
5J- 
 0- 
 
 00 
 
 '^ 
 -^ CONTENTS 
 
 ^ Page 
 
 Abstract. 1 
 
 Introduction 2 
 
 Experimental procedure, 2 
 
 Results and discussion 4 
 
 Conclusions 8 
 
 References 9 
 
 ILLUSTRATIONS 
 
 1 . Example of anodic polarization plot 5 
 
 2. Example of cathodic polarization plot 5 
 
 3. Example of polarization resistance (linear polarization) plot 6 
 
 4. Example of derived electrochemical corrosion rate versus stabilization 
 
 time 6 
 
 5. Example of pitting scan showing little tendency of specimen to pit 7 
 
 6. Example of pitting scan indicating tendency of specimen to pit 7 
 
 TABLES 
 
 1. High-strength, low-alloy steel compositions 4 
 
 2. Analyses of mine waters from Missouri lead and iron mines 5 
 
 3. Electrochemically detemnined corrosion rates. 6 
 
 4. Corrosion rates determined by weight-loss method 7 
 
 5. Pitting tendency of HSLA and galvanized steels in Missouri mine waters..,. 8 
 

 UNIT OF MEASURE ABBREVIATIONS USED IN 
 
 THIS REPORT 
 
 °F 
 
 degree Fahrenheit nA/cm^ 
 
 nanoampere per square 
 centimeter 
 
 h 
 
 hour 
 
 
 
 ppm 
 
 part per million 
 
 in 
 
 inch 
 
 
 
 V 
 
 volt 
 
 min 
 
 minute 
 
 
 
 wt pet 
 
 weight percent 
 
 mL 
 
 milliliter 
 
 
 mpy 
 
 mil per year 
 
 
 aHi 
 
CORROSION OF ROOF BOLT STEELS IN MISSOURI LEAD AND IRON MINE WATERS 
 
 By M. M. Tilman, ^ A. F. Jolly lll,2and L. A. Neumeier^ 
 
 ABSTRACT 
 
 As part of ongoing research to improve mine safety, the Bureau of 
 Mines conducted research on the corrosion of friction rock stabilizer 
 steels in five Missouri lead and iron mine waters. Electrochemical cor- 
 rosion tests, including evaluation of pitting tendency, were performed 
 on two types of high-strength, low-alloy (HSLA) steels and galvanized 
 steel in four Missouri lead mine waters and one Missouri iron mine wa- 
 ter. The tests were conducted at in-mine water temperatures in both 
 air-saturated and deaerated waters. Static, weight-loss corrosion tests 
 were also conducted on HSLA steel specimens in the five Missouri mine 
 waters for 2,900-h duration at average In-mine water temperatures and 
 air-dissolved oxygen contents of 6 to 7 ppm. Corrosion rates determined 
 by the weight-loss tests were roughly comparable with rates determined 
 electrochemically in deaerated waters containing 0.3 to 0.5 ppm dis- 
 solved oxygen content. Passivation of specimen (nongalvanized) surfaces 
 in air-saturated waters resulted in very low electrochemically deter- 
 mined corrosion rates. Pitting tendency was generally higher for both 
 HSLA steels in air-saturated waters than in deaerated waters. Gal- 
 vanized steel generally exhibited higher tendency to pitting in the de- 
 aerated waters than in the aerated mine waters. 
 
 ^Metallurgist (retired). 
 ^Metallurgist. 
 ■^Supervisory metallurgist. 
 Rolla Research Center, Bureau of Mines, Rolla, MO. 
 
..'^-^i^.'--H£:»'.:'>;'&3£!3«iui»«eB^3i!iSS^i<t^iijai^S^y^!^^S^ 
 
 INTRODUCTION 
 
 In the late 1970' s, a different concept 
 in roof-rock bolts was introduced commer- 
 cially in friction rock stabilizers. 
 Several types of the stabilizers have 
 been developed and are in commercial use. 
 They are thin-wall tubular devices which, 
 unlike point-anchor bolts, exert their 
 holding power by compressive forces act- 
 ing over the length of the stabilizer. 
 Because of their unique holding mechan- 
 ism, the stabilizers are claimed to be 
 particularly useful in softer rock such 
 as sandstone and shale. However, because 
 of the relatively thin wall, they are 
 more vulnerable to corrosion, which can 
 under certain conditions cause a serious 
 loss of strength in a relatively short 
 time. Friction rock stabilizers are nor- 
 mally not recommended for use where par- 
 ticularly long-term support is required. 
 
 The Split Set4 stabilizer has gained 
 wide acceptance in the metal mining in- 
 dustry. Over 25 million Split Set sta- 
 bilizers have been installed, primarily 
 in metal mines, not only in the United 
 States but also in approximately 30 
 foreign countries. The Split Set sta- 
 bilizer is a slotted tube 1-1/2 in or 
 larger in diameter, which is forced into 
 an undersize hole, with the result that 
 compressive forces act over the entire 
 length of the tube. The stabilizers are 
 made of steel sheet nominally about 0.1 
 in thick and are produced in various 
 lengths. Although a device has been de- 
 veloped to check for proper installation 
 of Split Set stabilizers (9^),^ no tech- 
 nique has been developed for revealing 
 loss of strength after installation, such 
 as that due to corrosion. Two types of 
 high-strength, low-alloy (HSLA) steels 
 
 are used to manufacture Split Set sta- 
 bilizers. Hot-dip-galvanized Split Set 
 stabilizers are also available. 
 
 Research was previously conducted by 
 the Bureau of Mines on the corrosion 
 resistance of Split Set stabilizers in 
 copper and uranium mine waters (11). 
 Results of the prior research indicated 
 that galvanized steel, not surprisingly, 
 was far superior to the unprotected steel 
 in general corrosion resistance. For the 
 waters evaluated, limited corrosion tests 
 indicated little tendency to pitting 
 of galvanized, steel compared to that 
 for the uncoated steel. Copper-bearing 
 HSLA steel was shown to be slightly 
 more corrosion resistant than non-copper- 
 bearing HSLA steel. Equations were de- 
 veloped relating dissolved oxygen, chlo- 
 ride, sulfate, and magnesium contents of 
 the mine waters to corrosion rates of two 
 nongalvanized HSLA steels. An equation 
 was developed relating dissolved oxygen 
 content and mine water temperature to 
 corrosion rate of galvanized steel. The 
 research indicated the need for preven- 
 tion and control of corrosion of the roof 
 support members in view of the considera- 
 ble variables involved in prediction of 
 corrosion damage. 
 
 The work with Missouri mine waters de- 
 scribed in this report is an extension of 
 the previous research on corrosion of 
 Split Set stabilizers in Western mine wa- 
 ters and is part of the Bureau's ongoing 
 program to improve mine safety. Results 
 of the work are intended to aid Mine 
 Safety and Health Administration and min- 
 ing industry personnel in better predict- 
 ing safe installation periods of friction 
 rock stabilizers. 
 
 EXPERIMENTAL PROCEDURE 
 
 The Ingersoll-Rand Corp. provided sheet 
 samples of EX-TEN-H60 and KAI-WELL-55, 
 the two high-strength, low-alloy (HSLA) 
 
 'Registered trademark of Ingersoll-Rand 
 
 Co. 
 
 ■'Underlined numbers in parentheses re- 
 fer to items in the list of references at 
 the end of this report. 
 
 steels from which Split Set stabilizers 
 are manufactured, for use in the corro- 
 sion experiments. Samples of the steels 
 were analyzed for comparison with speci- 
 fications. Microstructures of the steels 
 were shown in a previous report (11). 
 Galvanized plain-carbon steel sheet 
 (flat) , obtained from a commercial sup- 
 plier, was used for corrosion testing 
 
instead of galvanized Split Set stabiliz- 
 er steel, because galvanized Split Set 
 sheet stock was not readily available. 
 Corrosion samples cut from galvanized 
 stabilizers were incompatible with the 
 corrosion test equipment because of their 
 curvature; the specimen holder would only 
 accept flat specimens for a proper fit. 
 Attempts to flatten the galvanized stabi- 
 lizer samples damaged the galvanized sur- 
 face. The use of plain-carbon galvanized 
 steel sheet was deemed acceptable, since 
 variation in composition of the outer 
 zinc layer of galvanized coatings, if 
 present, has been indicated to be insig- 
 nificant with respect to detrimental cor- 
 rosion effects (2^, p. 712; _3, p. 646). 
 The scope of the research did not extend 
 to the complex condition in which corro- 
 sion might, with extended time, proceed 
 to penetrate the zinc coating. It should 
 be mentioned that, even in that eventual- 
 ity, the zinc continues to provide sacri- 
 ficial protection to steel until consid- 
 erable steel is exposed (2_, p. 712). 
 
 A Swellex6 bolt, another type of fric- 
 tion rock stabilizer, was provided by 
 personnel at a western mine. A section 
 of the bolt was flattened, corrosion sam- 
 ples punched, and the steel analyzed. 
 
 Five-gallon water samples were obtained 
 from four Missouri lead mines and one 
 Missouri iron mine. The lead mines were 
 the Fletcher Mine, Indian Creek Mine, and 
 St. Joe #28 Mine, of St. Joe Lead Co., 
 and the Magmont Mine, of Cominco Ameri- 
 can/Dresser Industries. The iron mine 
 was the Pea Ridge Mine of Pea Ridge Iron 
 Ore Co. Mine water temperatures were 
 measured at the sampling site. The sam- 
 ples were analyzed for common elements, 
 and the pH values were measured. The 
 Langelier (saturation) indices, which 
 indicate the relative tendency for CaC03 
 to precipitate from water and form a 
 protective deposit, were calculated using 
 the values for the total dissolved 
 solids, calcium and HCO3 contents, and pH 
 and temperature. Corrosion rates of EX- 
 TEN-H60 and KAI-WELL-55 steels were mea- 
 sured by both electrochemical and weight- 
 loss methods in all five mine waters. 
 Corrosion rates of galvanized steel were 
 
 ^Registered trademark of Atlas Copco. 
 
 measured in the five mine waters by 
 electrochemical methods only. Corrosion 
 rates of the Swellex steel were measured 
 electrochemically in air-saturated and 
 deaerated water from the St. Joe #28 lead 
 mine. 
 
 A commercial corrosion measurement sys- 
 tem (10) , consisting of a corrosion cell 
 and microprocessor unit, was used to ob- 
 tain "instantaneous" corrosion rates. In 
 operation, the corrosion cell containing 
 test solution, specimen, counter elec- 
 trodes, and standard calomel reference 
 electrode is immersed in a controlled- 
 temperature water bath. The micropro- 
 cessor unit, correctly programmed and 
 with appropriate operator skill, calcu- 
 lates corrosion rates based on the corro- 
 sion current. Tafel constants obtained 
 in anodic and cathodic polarization plots 
 are used in a subsequent polarization re- 
 sistance plot to calculate the general 
 corrosion rate. A more detailed discus- 
 sion of the electrochemical test equip- 
 ment and technique may be found in a pre- 
 vious Bureau report (11). Discussions of 
 electrochemical measurement of corrosion 
 rates are found in several references (_1^, 
 4, 6, 8). Corrosion rates were deter- 
 mined electrochemically in both helium- 
 degassed (deaerated) and air-saturated 
 (aerated) mine waters at the measured in- 
 mine water temperature. 
 
 In addition to corrosion rate deter- 
 minations, pitting susceptibility scans 
 were run on each steel in all except one 
 mine water. The pitting scans were run 
 in both deaerated and air-saturated wa- 
 ters at the in-mine water temperature. 
 
 Test specimens of the HSLA steels were 
 ground over 600-grit SiC abrasive paper, 
 ultrasonically cleaned in ethanol, and 
 dried in a warm air blast. Galvanized 
 specimens were prepared with the same 
 procedure, except that grinding was omit- 
 ted. After immersion in deaerated test 
 solutions, the specimens were electrolyt- 
 ically cleaned by operating the cell with 
 the specimen as cathode [-1.0 V vs stan- 
 dard calomel electrode (SCE)] for 1 rain 
 immediately preceding the test run. Spe- 
 cimens tested in aerated waters were not 
 electrolytically cleaned because of the 
 resulting instability of the open circuit 
 potential (Ecorr)- ^ series of test runs 
 
was made with EX-TEN-H60 steel in Magmont 
 water to determine variation of the open 
 circuit cell potential (corrosion poten- 
 tial) and corrosion rate, the latter as a 
 function of the time interval in which 
 the specimen was in solution prior to 
 initiation of linear polarization tests. 
 
 Total immersion, weight-loss determin- 
 ation of corrosion rates from static 
 tests was based on ASTM Standard G31-72, 
 "Laboratory Immersion Corrosion Testing 
 of Metals" (_5 ) . Specimens of EX-TEN- 
 H60 and KAI-WELL-55 steels were machined 
 from sheet stock to approximately 1 in 
 square, and a 0.082-in-diam hole was 
 drilled in each specimen for suspension 
 in the test solution. The specimens were 
 ground over 120-grit SiC paper, dimen- 
 sions were measured, and surface areas 
 calculated. They were then ultrasonical- 
 ly cleaned in ethanol and weighed. Two 
 specimens of each steel were suspended 
 with nylon line in each mine water. The 
 four lead mine waters were contained in 
 
 1,000-mL beakers immersed in a constant- 
 temperature bath at 62° ±0.5° F. The tem- 
 perature of 62° F was the average temper- 
 ature of the lead mine waters , which 
 ranged from 61° to 64° F. The beaker 
 containing the iron mine water was im- 
 mersed in a separate constant-temperature 
 bath, which was maintained at 80°±0.5° F, 
 the in-mine water temperature. Test so- 
 lution temperatures were monitored daily. 
 Dissolved oxygen contents were measured 
 daily for the first few days and weekly 
 thereafter for the duration of the test. 
 No attempt was made to control dissolved 
 oxygen content. The beakers were covered 
 loosely to permit access of air. The 
 total-immersion tests were terminated at 
 2,900 h. The specimens were rinsed and 
 scrubbed with a bristle brush under run- 
 ning water to remove loosely adherent 
 corrosion products, dried in a warm air 
 blast, and weighed. Corrosion rates were 
 calculated from weight losses. 
 
 RESULTS AND DISCUSSION 
 
 Results of chemical analyses of the 
 HSLA steels used for the manufacture of 
 Split Sets are shown in table 1. The EX- 
 TEN-H60 composition was within specifica- 
 tions (12). No analysis was performed 
 for the nonspecified elements of sulfur, 
 phosphorus, and copper, nor for nitrogen. 
 The composition of KAI-WELL-55 steel 
 was within specifications (7) for those 
 
 elements for which analyses were per- 
 formed. No analyses were conducted on 
 KAI-WELL-55 steel for the specified minor 
 elements of sulfur and phosphorus. Re- 
 sults of analysis of the Swellex steel, 
 in weight-percent, are as follows: C, 
 0.06; Mn, 0.24; Si, <0.05; S, 0,02; P, 
 <0,01; and balance Fe. 
 
 TABLE 1. - High-strength, low-alloy steel compositions, weight percent 
 
 Element 
 
 EX-TEN-H60 
 
 KAI-WELL-55 
 
 
 Specification' 
 
 Analysis 
 
 Specif ication^ 
 
 Analysis 
 
 C 
 
 Max 0.25 
 
 0) 
 NS 
 
 Max 1.35 
 
 Max .012 
 
 NS 
 
 NS 
 
 NS 
 
 (^) 
 
 0.23 
 
 .01 
 
 NA 
 
 1.22 
 
 NA 
 
 NA 
 
 NA 
 
 <.02 
 
 .01 
 
 0.2 -0.3 
 
 NS 
 
 Min .20 
 
 .85-1.30 
 
 NS 
 
 Max .05 
 
 Max .05 
 
 Max .12 
 
 NS 
 
 0.3 
 
 Cb 
 
 NA 
 
 Cu 
 
 32 
 
 Mn 
 
 1 . 12 
 
 N 
 
 NA 
 
 P 
 
 NA 
 
 S 
 
 NA 
 
 Si 
 
 <.02 
 
 NA 
 
 V 
 
 
 NA Not analyzed. 
 NS Not specified. 
 'Woldman (12), p. 435. 
 
 ^Ingersoll-Rand Co. (_7 ) . 
 
 ^Specification minimum 0.02 wt pet Cb + V, 
 
Analyses of mine waters are shown in 
 table 2. All of the waters were somewhat 
 basic, with pH values of 8.0 or 8.1. 
 Calculated Langelier indices of -0.2 to 
 +0.5 indicate little tendency toward car- 
 bonate precipitation for any of the five 
 mine waters. The Pea Ridge water con- 
 tains relatively large amounts of Na"*", 
 S04"2, and HC03~ ions, as reflected in 
 the large amount of total dissolved sol- 
 ids. The Magmont and Indian Creek waters 
 are much higher in CI" ion content than 
 the other waters, and the Magmont water 
 is also relatively high in HC03~ ion con- 
 tent. All of the waters analyzed low in 
 iron contents, <0.1 ppm Fe. 
 
 Shown in figures 1 and 2 are exam- 
 ples of anodic and cathodic polarization 
 plots, respectively, from which Tafel 
 constants (slopes) are calculated. The 
 plots were generated from a deaerated 
 lead mine water and Split Set steel sam- 
 ples. Corrosion current and subsequently 
 general corrosion rate are calculated 
 from the slope of a polarization resist- 
 ance (linear polarization) plot and the 
 Tafel constants. An example of a pol- 
 arization resistance plot obtained with 
 deaerated lead mine water and a Split Set 
 steel sample is shown in figure 3. 
 
 Results of the series of electrochemi- 
 cal tests to determine effects on the 
 apparent corrosion rate of specimen sta- 
 bilization times are shown in figure 4. 
 Apparent corrosion rates of specimens 
 in either electrolytically cleaned or 
 abraded only (600-grit SiC paper and 
 ultrasonically cleaned in ethanol) con- 
 ditions stabilized quickly in deaerated 
 water. Apparent corrosion rates of 
 abraded specimens also stabilized quickly 
 in air-saturated water. However, elec- 
 trolytic cleaning of specimens tested in 
 
 CURRENT, nA/cm^ 
 
 FIGURE 1.- Example of anodic polarization plot. 
 Deaerated lead mine water and HSLA steel. 
 
 . -.80 h 
 
 z 
 
 o 
 
 a. -.90 - 
 
 1 
 
 1 
 
 
 1 
 
 
 
 
 ~ 
 
 
 
 
 - 
 
 1 
 
 1 
 
 
 NX 
 
 1 
 
 
 10' 
 
 10= 
 
 CURRENT, nA/cm^ 
 
 FIGURE 2. • Example of cathodic polarization plot. 
 Deaerated lead mine water and HSLA steel. 
 
 air-saturated water resulted in very un- 
 stable apparent rates for the first few 
 minutes of immersion. Corrosion rates 
 were relatively stable in all cases after 
 immersion for ~4 min. Corrosion rates 
 reported in table 3 for electropolished 
 specimens in air-saturated waters were 
 obtained with specimens that had been 
 cleaned by abrasion only. All other 
 
 TABLE 2. - Analyses 
 
 of mine 
 
 waters 
 
 from 
 
 Missouri le 
 
 ad and iron 
 
 mines 
 
 
 Contents, ppm 
 
 pH 
 
 
 Mine 
 
 Cations 
 
 Anions 
 
 Total 
 dissolved 
 solids 
 
 Langelier 
 
 
 Ca 
 
 K 
 
 Mg 
 
 NA 
 
 CI 
 
 HCO3 
 
 SO4 
 
 index 
 
 Fletcher 
 
 13 
 33 
 22 
 18 
 16 
 
 0.8 
 5.4 
 .5 
 2,0 
 3,8 
 
 22 
 21 
 26 
 19 
 16 
 
 3.4 
 39 
 
 1.3 
 12 
 198 
 
 24 
 
 105 
 
 105 
 
 26 
 
 29 
 
 194 
 226 
 269 
 213 
 255 
 
 86 
 
 26 
 
 62 
 
 101 
 
 127 
 
 265 
 451 
 438 
 321 
 565 
 
 8.1 
 8,1 
 8.0 
 8,0 
 8,0 
 
 -0.2 
 
 Indian Creek 
 
 +,5 
 
 Magmont 
 
 St. Joe #28 
 
 Pea Ridge ' 
 
 + .2 
 +.3 
 + .4 
 
 'iron mine; others lead mines. 
 
..;.-:t-i ^i?EH:::5g5JU?ii3iS?H^Mii^Sia^il 
 
 -0.68 
 
 -.70 - 
 
 -.72- 
 
 -.74 
 
 -10 
 
 CURRENT, nA/cm^ 
 
 FIGURE 3. - Example of polarization resistance 
 (linear polarization) plot. Deaerated lead mine wa- 
 ter and HSLA steel. 
 
 rates were determined on specimens that 
 had been electrolytically cleaned. 
 
 Results of electrochemical corrosion 
 tests, shown in table 3 (standard devia- 
 tion denoted by sjoabol a), indicate that 
 KAI-WELL-55 steel exhibits, on the aver- 
 age, slightly lower corrosion rates than 
 EX-TEN-H60. Such a difference was also 
 observed in corrosion studies of these 
 
 KEY 
 
 soturoted water 
 
 Deaerated water 
 
 Electrolytically 
 
 • Electrolytically 
 
 cleaned 
 
 cleaned 
 
 Abroded 
 
 ■ Abraded 
 
 TIME , min 
 
 FIGURE 4. - Exampleof derived electrochemical 
 corrosion rate versus stabilization time for EX- 
 TEN-H60 steel in a lead mine water. 
 
 steels in western copper and uranium mine 
 waters (11). Galvanized steel exhibited 
 much lower rates in deaerated waters than 
 either of the two HSLA steels. In aer- 
 ated waters, however, passivation of both 
 EX-TEN-H60 and KAI-WELL-55 resulted in 
 much lower rates than those of galvanized 
 steel, except in the Pea Ridge water. 
 Passivation was observed only in certain 
 electrochemical tests and was not evident 
 in the gravimetric tests. It may there- 
 fore not be a significant factor for the 
 longer term exposure of installed roof 
 bolts. Rates of 17.6 and 11.6 mpy for 
 EX-TEN-H60 and KAI-WELL-55, respectively, 
 in aerated Pea Ridge water were the high- 
 est observed. Also, rates for the two 
 steels in deaerated water from this iron 
 
 TABLE 3. - Electrochemically determined corrosion rates 
 
 Mine water 
 
 Test 
 
 solution 
 
 temperature. 
 
 Oxygen 
 content, ' 
 ppm 
 
 Corrosion rate,^ mpy 
 
 EX-TEN-H60 
 
 Av 
 
 KAI-WELL-55 
 
 Av 
 
 a 
 
 Galvanized 
 
 Av 
 
 Fletcher, . . . , 
 Indian Creek, 
 
 Magmont , 
 
 St. Joe #283, 
 Pea Ridge*.., 
 
 63 
 63 
 62 
 62 
 61 
 61 
 64 
 64 
 80 
 80 
 
 0.4 
 9.4 
 
 .5 
 9.4 
 
 .4 
 9.6 
 
 .5 
 9.3 
 
 .3 
 7.5 
 
 2.7 
 
 .3 
 1.6 
 
 .2 
 1.8 
 
 .2 
 1.6 
 
 .4 
 
 2.8 
 
 17.6 
 
 0.7 
 
 .1 
 
 .2 
 
 .05 
 
 .3 
 
 .1 
 
 .4 
 
 .1 
 
 .3 
 6.1 
 
 1.4 
 
 .2 
 1.5 
 
 .4 
 1.6 
 
 .1 
 1.4 
 
 .2 
 
 2.1 
 
 11.6 
 
 0.2 
 
 .02 
 
 .2 
 
 .02 
 
 .2 
 
 .04 
 
 .4 
 
 .02 
 
 .1 
 3.3 
 
 0.5 
 2.3 
 
 .3 
 3.8 
 
 .5 
 1.6 
 
 .6 
 2.3 
 
 .4 
 1.6 
 
 0.1 
 .8 
 .05 
 .5 
 .1 
 .2 
 .1 
 .9 
 .1 
 .4 
 
 'Higher values are aerated; those at 0.5 ppm or less are deaerated. 
 ^o is standard deviation. 
 
 ^For same conditions, indicated rates for Swellex steel were 0.1 mpy (deaerated) 
 and 0.2 mpy (aerated). 
 
 *Iron mine; others lead mines. 
 
- 
 
 1 
 
 1 I 
 
 1 1 
 
 1 
 
 
 ^ 
 
 ^"^y^-V 
 
 / _ 
 
 - 
 
 
 
 - 
 
 E corr^ 
 
 1 1 
 
 1 1 
 
 1 
 
 10^ 10" 10° 
 
 CURRENT, nA/cm^ 
 
 FIGURE 5. - Example of pitting scan showing 
 little tendency of specimen to pit. 
 
 1 
 
 III! 
 
 I 
 
 - 
 
 Ec— (^ / 
 
 - 
 
 E corr N^ 
 
 ~.=^^ ^/>*^ 
 
 1 
 
 
 ' ~-- -^ — — 
 
 1 
 
 1 1 1 1 
 
 10^ 10^ 
 
 CURRENT, nA/cm 
 
 0= 10" 
 
 2 
 
 FIGURE 6. - Example of pitting scan indicating 
 tendency of specimen to pit. 
 
 mine were higher than rates obtained in 
 the deaerated waters from the lead mines. 
 
 Limited electrochemical tests on Swell- 
 ex bolt steel resulted in indicated cor- 
 rosion rates lower than those obtained 
 with EX-TEN-H60 or KAI-WELL-55 steels. 
 In deaerated St. Joe #28 water, a rate 
 of 0.1 mpy (a = 0.02) was observed with 
 Swellex steel compared with rates of 1.6 
 and 1.4 mpy for EX-TEN-H60 and KAI-WELL- 
 55 steels, respectively, in the same wa- 
 ter. Similarly, in aerated St. Joe #28 
 water, a rate of 0.2 mpy (a = 0.03) was 
 obtained for Swellex steel compared with 
 rates of 0.4 and 0.2 mpy for EX-TEN- H60 
 and KAI-WELL-55, respectively. 
 
 Corrosion rates determined by the long- 
 term, static weight-loss method are shown 
 in table 4. The slightly lower electro- 
 chemical corrosion rates of KAI-WELL-55 
 steel compared with those of EX-TEN-H60 
 steel were not evident in the weight-loss 
 tests except in Pea Ridge water, where 
 KAI-WELL-55 steel averaged 1.6 mpy and 
 
 EX-TEN-H60 averaged 2.3 mpy. The highest 
 rate observed in the weight-loss tests 
 was 2.8 mpy for KAI-WELL-55 steel in 
 Fletcher water. Corrosion rates deter- 
 mined with weight-loss tests in waters 
 containing from 6.3 to 7.2 ppm dissolved 
 oxygen (from air dissolution) were com- 
 parable with electrochemically determined 
 rates in deaerated mine waters containing 
 only 0.3 to 0.5 ppm dissolved oxygen. 
 Apparently, rates determined electrochem- 
 ically in deaerated waters are somewhat 
 more indicative of long-term corrosion 
 rates than those electrochemical rates 
 obtained in air-saturated waters. Pas- 
 sivation was not evident in the static 
 tests, although it may have been a tran- 
 sient occurrence early in the tests on 
 relatively clean surfaces before substan- 
 tial rust products began to form. 
 
 Typical pitting scans of the HSLA and 
 galvanized steels are shown in figures 5 
 and 6. Figure 5 is a scan indicating 
 little tendency of the specimen to pit. 
 
 TABLE 4. - Corrosion rates determined by weight-loss method 
 
 
 Test 
 
 solution 
 
 temperature, 
 
 °F 
 
 Oxygen 
 
 content , 
 
 ppm 
 
 Corrosion 
 
 rate, mpy 
 
 Mine water 
 
 EX-TEN-H60 
 
 KAI-WELL-55 
 
 
 Av 
 
 a 
 
 Av 
 
 a 
 
 Fletcher 
 
 Indian Creek. . . . 
 Magmont 
 
 62 
 62 
 62 
 62 
 80 
 
 6.3 
 6.4 
 7.2 
 6.7 
 6.6 
 
 2.1 
 2.4 
 1.8 
 2.6 
 2.3 
 
 0.2 
 .3 
 .3 
 .3 
 .4 
 
 2.8 
 2.7 
 1.6 
 2.3 
 1.6 
 
 0.5 
 .2 
 .8 
 
 St. Joe #28 
 
 Pea Ridge! 
 
 .2 
 .04 
 
 ^Iron mine; others lead mines, 
 
.-.:..r^^--^.~.:^.i<''^:r^.fr:v?.^i^^^^^ 
 
 TABLE 5. - Pitting tendency of HSLA and galvanized steels 
 in Missouri mine waters 
 
 Mine 
 
 EX-TEN-H60 KAI-WELL-55 Galvanized 
 
 PITTING TENDENCY— DEAERATED 
 
 Fletcher. . . . , 
 Indian Creek, 
 
 Magmont , 
 
 St. Joe #28.. 
 Pea Ridge 1 , , . 
 
 PITTING TENDENCY— AERATED 
 
 Fletcher. . . . , 
 Indian Creek, 
 
 Magmont 
 
 St. Joe #28.. 
 Pea Ridge ^ . . , 
 
 ND Not determined. Mod Moderate, 
 'iron mine; others lead mines. 
 
 If the protection potential (Ep) is more 
 positive than the corrosion potential 
 (E^Q^^), as it is in figure 5, pitting 
 becomes less likely to occur (4^, 6^) as E- 
 becomes more positive relative to E^q^j.. 
 Ej.Qj.j. is the open-circuit potential. The 
 protection potential E is defined as the 
 potential at which the hysteresis loop of 
 the pitting scan is completed and below 
 which (E more negative) pits will not 
 initiate. Figure 6 is a typical plot in 
 which the protection potential is more 
 negative than the corrosion potential and 
 pitting of the specimen is indicated. 
 The pitting potential (E^,, also referred 
 to as the critical potential) has also 
 been used as an indication of pitting 
 tendency, but the protection potential is 
 more reproducible and is now considered a 
 more reliable indicator (6), The pitting 
 potential is defined as the potential at 
 which the current increases rapidly and 
 above which (E more positive) pits will 
 initiate and grow. Research has been 
 done (8^) which indicates that, when pit 
 initiation time is considered, E^, = E . 
 
 Results of the evaluation of pitting 
 scans are shown in table 5. Pitting 
 
 tendency was evaluated on the basis of 
 difference between E^^^^ and E . If Ep 
 was more negative than E^^^^, pitting 
 tendency was rated as high. When Ep 
 was somewhat more positive than E^^^^, 
 but the difference between E^^^^ and Ep 
 remained in the range to 0.1 V, the 
 pitting tendency was arbitrarily rated 
 as moderate. Similarly, with Ep more 
 positive than E^.^^^, a difference be- 
 tween E^Qpp and Ep greater than 0.1 V was 
 rated as an indication of low tendency 
 to pit. 
 
 Moderate to high pitting tendency is 
 indicated for both HSLA steels in all of 
 the air-saturated waters. Passivation of 
 the steels in air-saturated waters during 
 electrochemical testing also indicates a 
 probable tendency to pitting, since this 
 is a common occurrence on metals that 
 passivate. A high tendency to pitting is 
 indicated for galvanized steel in the de- 
 aerated waters, as well as aerated Indian 
 Creek and Pea Ridge water. Evaluation of 
 the scans indicates a high pitting ten- 
 dency for both HSLA steels and galvanized 
 steel in Pea Ridge water in aerated and 
 deaerated conditions. 
 
 CONCLUSIONS 
 
 Based on results of total-immersion, 
 weight-loss corrosion tests, there is 
 little difference in corrosion rates be- 
 tween EX-TEN-H60 and KAI-WELL-55 steels 
 in Missouri lead and iron mine waters. 
 Slightly lower rates were observed for 
 
 copper-bearing KAI-WELL-55 steel than for 
 EX-TEN-H60 in electrochemical tests. 
 
 Galvanized steel exhibits much lower 
 rates in electrochemical tests in de- 
 aerated water (<0.5 ppm dissolved oxygen) 
 than either of the HSLA steels. 
 
Passivation effects observed in elec- 
 trochemical tests in air-saturated (>9.3 
 ppm dissolved oxygen) lead mine waters 
 resulted in very low rates of 0.4 mpy 
 or less for both HSLA steels. Passiva- 
 tion probably does not occur in bolt- 
 rock contact areas of installed stabiliz- 
 ers , owing to lack of oxygen. It may 
 occur on bolt surfaces exposed to am- 
 ple air and moisture; but, if it occurs 
 on installed stabilizer surfaces, this 
 may be a transient effect for relatively 
 clean surfaces as opposed to rusting 
 surfaces. In the electrochemical tests, 
 passivation was not observed on either 
 of the HSLA steels in the iron mine wa- 
 ter. Passivation was also not evident 
 for the two HSLA steels in any of the 
 waters for the total-immersion condi- 
 tions of atmospheric oxygen dissolution, 
 although it may have occurred to some 
 extent early in these weight-loss tests 
 
 when the surfaces were relatively free of 
 rust products. 
 
 Corrosion rates determined by the long- 
 term weight-loss tests in water at at- 
 mospheric oxygen saturation are more com- 
 parable with rates determined electro- 
 chemically in deaerated water than with 
 electrochemically determined rates in 
 air-saturated water. 
 
 Limited electrochemical tests on Swell- 
 ex stabilizer steel indicated corrosion 
 rates generally of the same order of mag- 
 nitude as those obtained with the HSLA 
 steels used for Split Set stabilizers. 
 
 Moderate to high pitting tendency was 
 observed for both HSLA steels in all air- 
 saturated mine waters. Galvanized steel 
 exhibited a high tendency to pit in all 
 deaerated waters. Pitting tendency was 
 high for both of the HSLA steels and the 
 galvanized steel in either the deaerated 
 or air-saturated iron mine water. 
 
 REFERENCES 
 
 1. Ailor, W. H. Handbook on Corrosion 
 Testing and Evaluation. Wiley, 1971, 873 
 pp. 
 
 2. American Society for Metals. Met- 
 als Handbook. Cleveland, OH, 1948, 1,332 
 pp. 
 
 3. . Metals Handbook. Proper- 
 ties and Selection: Nonferrous Alloys 
 and Pure Metals. Metals Park, OH, 9th 
 ed. , V. 2, 1979, 855 pp. 
 
 4. American Society for Testing and 
 Materials. Standard Practice for Con- 
 ducting Cyclic Potentiodynamic Polariza- 
 tion Measurements for Localized Corro- 
 sion. ANSI/ASTM G61-78 in 1982 Annual 
 Book of ASTM Standards: Part 10, Met- 
 als - Physical, Mechanical, Corrosion 
 Testing. Philadelphia, PA, 1982, pp. 
 1,124-1,129. 
 
 5. Standard Recommended Practice for 
 Laboratory Immersion Corrosion Testing 
 of Metals. 031-72 in 1982 ASTM Stan- 
 dards: Part 10, Metals - Physical, Me- 
 chanical, Corrosion Testing, Philadel- 
 phia, PA, 1982, pp. 959-970. 
 
 6. Baboian, R. , and G. S. Haynes. 
 Cyclic Polarization Measurements - Exper- 
 imental Procedure and Evaluation of Test 
 Data. Ch. in Electrochemical Corrosion 
 Testing, STP 727, ed. by F. Mansfeld and 
 U. Bertocci, ASTM, 1981, pp. 274-282. 
 
 irU.S CPO: 1985-605-017/20,126 
 
 7. Ingersoll-Rand Co. research staff. 
 Private communication, July 1981; availa- 
 ble upon request from M. M, Tilman, Bu- 
 Mines, Rolla, MO. 
 
 8. Kruger, J. New Approaches to the 
 Study of Localized Corrosion. Ch. in 
 Electrochemical Techniques for Corrosion, 
 ed, by R. Baboian, Nat, Assoc, Corrosion 
 Eng,, Katy, TX, 1977, pp, 35-41, 
 
 9. Lusignea, R, , J, Felleman, and G, 
 Kirby, Development of a Nondestructive 
 Test Device for Friction Rock Supports 
 (contract H0202030, Foster-Miller, Inc.). 
 BuMines OFR 165-83, 1983, 135 pp.; NTIS 
 PB 83-257519. 
 
 10. Peterson, W. M. , and H. Siegerman, 
 A Microprocessor-Based Corrosion Mea- 
 surement System, Ch, in Electrochemi- 
 cal Corrosion Testing, STP 727, ed. by 
 F. Mansfeld and U. Bertocci. ASTM, 1981, 
 pp. 390-406. 
 
 11. Tilman, M. M. , A, F, Jolly III, 
 and L, A, Neumeier, Corrosion of Fric- 
 tion Rock Stabilizers in Selected Uranium 
 and Copper Mine Waters, BuMines RI 8904, 
 1984, 23 pp, 
 
 12. Woldman, N, E., and R. C. Gibbons, 
 Engineering Alloys, Van Nostrand Rein- 
 hold, 5th ed., 1973, 1,427 pp. 
 
 INT.-BU.OF MINES,PGH.,P A. 2 8 139 
 
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