1、STP-NU-068CORROSION OF A193 GRADE B7BOLT MATERIAL IN BWR SODIUM PENTABORATE SOLUTIONSSTP-NU-068 CORROSION OF A193 GRADE B7 BOLT MATERIAL IN BWR SODIUM PENTABORATE SOLUTIONS Prepared by: S. G. Sawochka M. R. Miller M. A. Leonard NWT Corporation Date of Issuance: March 14, 2014 This report was prepare
2、d as an account of work sponsored by ASME Nuclear Codes shiny surface N/A No visible corrosion; shiny surface C1010 1 C1010 Small of regions of oxide discoloration on bottom 10% of front side C1010 Front Slight increase in number of oxide nodules on bottom 10% of front side. No nodules on back side
3、C4140 7 N/A No visible corrosion C4140 Back Limited number of oxide nodules on bottom of back side C4140 8 C4140 Back Limited regions of oxide discoloration on bottom back side C4140 Back and Front Limited oxide nodules on bottom 10% of front side. Limited oxide nodules on bottom 40% of back side C4
4、140 9 N/A No visible corrosion; shiny surface C4140 Back No visible corrosion; shiny surface C4140 10 C4140 Limited number of regions of oxide discoloration on front side C4140 Front Oxide nodules over entire front surface. No nodules on back side C4340 1-4 N/A No visible corrosion; shiny surface N/
5、A No visual corrosion; shiny surface 410 1-4 N/A No visible corrosion; shiny surface N/A No visible corrosion; shiny surface STP-NU-068: Corrosion of A193 Grade B7 Bolt Material in BWR Sodium Pentaborate Solutions 12 Figure 3-8: Coupon Weight Changes after 20 and 60 Day Exposure to 12% Sodium Pentab
6、orate Solution at 95F Alloy S/N Weight, g Weight loss, mg Weight loss, mg/dm-mo 0 days 20 days 60 days 20 days 60 days 20 days 60 days C1010 1 10.6694 10.6656 10.6696 3.8 -0.2 26.1 -0.5 C1010 2 10.5072 10.5004 10.5051 6.8 2.1 46.7 4.8 C1010 3 10.6370 10.6275 10.6378 9.5 -0.8 65.3 -1.8 C1010 4 10.846
7、5 10.8408 10.8457 5.7 0.8 39.2 1.8 C4140 7 14.1215 14.1215 14.1222 0 -0.7 0.0 -1.6 C4140 8 14.3101 14.3132 14.3101 -3.1 0 -21.3 0.0 C4140 9 14.2528 14.2532 14.2531 -0.4 -0.3 -2.7 -0.7 C4140 10 14.2675 14.2586 14.2693 8.9 -1.8 61.2 -4.1 C4340 1 12.3828 12.3806 12.3842 2.2 -1.4 15.1 -3.2 C4340 2 12.56
8、15 12.5604 12.5620 1.1 -0.5 7.6 -1.1 C4340 3 12.6120 12.6120 12.6126 0 -0.6 0.0 -1.4 C4340 4 12.5844 12.5829 12.5850 1.5 -0.6 10.3 -1.4 410 1 10.3230 10.3247 10.3232 -1.7 -0.2 -11.7 -0.5 410 2 10.1903 10.1858 10.1906 4.5 -0.3 30.9 -0.7 410 3 10.1710 10.1693 10.1709 1.7 0.1 11.7 0.2 410 4 10.2213 10.
9、2198 10.2214 1.5 -0.1 10.3 -0.2 3.2 Bolt Exposure at 95oF When it became apparent that the C4140 coupons were exhibiting minimal corrosion in the 12% NaPB solution at 95oF, an A193 Grade B7 bolt was suspended in a 600 ml beaker containing a 12% NaPB solution. A second bolt was suspended in a beaker
10、containing demineralized water, and the beakers placed in the coupon exposure oven. After only one day, a rust colored oxide film had formed on the bolt in the demineralized water, and the solution had become discolored. No corrosion of the bolt in the NaPB solution was observed. After several days
11、of exposure, the demineralized water solution was rust-colored indicating formation and release of hydrated iron oxides. The NaPB solution remained clear. The bolts were removed for inspection after two months of exposure. After drying the bolts, they were weighed, rinsed with demineralized water, r
12、eweighed, brushed, rinsed again and reweighed. The rinse solutions were filtered through a 0.22 micron filters which were then dried and weighed. Results are summarized in Figure 3-9. There was no measurable corrosion of the bolt submerged in the 12% NaPB solution. However, the bolt submerged in dem
13、ineralized water had a weight loss of approximately 180 mg/dm2-month corresponding to a metal loss of approximately 1.1 mils per year. The bolt surface area was estimated to be 0.40 dm2. The total amount of iron oxide/hydroxide collected by filtering the rinse solutions from the demineralized water
14、bolt was 0.189 mg. This corresponds to a metal release of 0.119 grams (assuming that the iron was present as FeOOH) compared to a measured weight loss of 0.142 grams. The amount of material collected by filtration of the rinse solutions for the bolt suspended in the NaPB solution was near the detect
15、ion level. STP-NU-068: Corrosion of A193 Grade B7 Bolt Material in BWR Sodium Pentaborate Solutions 13 Figure 3-9: Table 3:1 Corrosion of A193 Grade B7 Bolts during Two Month Exposure at 95F Bolt ID 9 7 Solution Deionized Water 12% Sodium Pentaborate Initial Weight, g 66.5085 66.4271 Dry Weight afte
16、r exposure, g 66.4033 66.4299 Weight change, g -0.1052 +0.0028 Weight after brushing, g 66.3669 66.4271 Oxide Removed by brushing, g 0.0364 0.0028 Total Metal Loss, g 0.1416 0 Weight Loss, mg/dm2-mo* 180 0 Collected Oxide/Hydroxide, g 0.1890 0.0013 Collected Metal Based on FeOOH, g 0.119 0.001 *Esti
17、mated bolt area of 0.40 dm2 3.3 Coupon Tests at 185F 3.3.1 Visual Observations Coupon tests of C1010 (carbon steel), C4340 and C4140 low alloy steels and 410 stainless steel at 185F in NaPB solutions were initiated on June 25, 2013. Four coupons of each alloy were suspended by nylon lines in separat
18、e 800 ml polycarbonate beakers covered with a polycarbonate sheet to minimize evaporation. Beakers were placed in a stainless steel oven. The coupons were initially submerged in 12% NaPB solutions which were air saturated. Temperature was measured with a calibrated thermocouple immersed in a polysty
19、rene flask filled with water and located in the center of the oven and by a thermocouple in the oven atmosphere. Evaporative losses from the beakers during the 185F tests were significant. These losses were initially compensated for by addition of a 12% NaPB solution. This led to an increase in the
20、NaPB concentration from 12% to 18% over the first 10 days of testing. At that time, the solution concentration was adjusted to 12%, and demineralized water was subsequently added to compensate for water losses. The solution concentration remained at 12% for the remainder of the test. Visual observat
21、ions of the coupons throughout the exposure indicated minimum corrosion of all materials. All solutions remained clear. Coupons were initially removed for inspection on July 17 after 22 days of exposure. They were rinsed with demineralized water (0.1 S/cm) and then air dried for several hours before
22、 visual inspection and weighing. There was no visual indication of corrosion on any of the coupons, and the coupons were not photographed. They were again removed after two months of exposure, weighed, visually inspected and photographed (Figure 3-7 to Figure 3-10). There were no indications of gene
23、ral or localized corrosion on the surfaces of any of the materials. However, there was a slight dulling of the C4140 coupon surfaces. 3.3.2 Weight Measurements After rinsing and drying, each coupon was weighed, and the changes in weight during each exposure period were determined. Coupons were not d
24、escaled. After the initial exposure period, visual inspection and weighing, the coupons were returned to the same test beaker which contained the original NaPB solution. Coupon weight losses and estimated corrosion rates expressed as milligrams of weight loss per dm2 per month (mg/dm2-mo) are given
25、in Figure 3-14. Results are graphically summarized in Figure 3-11, Figure 3-12 and Figure 3-13. The total coupon area (0.194 dm2) was used for this calculation. Note that the STP-NU-068: Corrosion of A193 Grade B7 Bolt Material in BWR Sodium Pentaborate Solutions 14 corrosion rate calculated in this
26、 manner is an average value for the total coupon surface and is based on the assumption that 100% of the oxidized material is released to the solution. Observations of coupon weight gains (negative values of weight loss) indicate that a portion of the oxide formed during the corrosion process has be
27、en retained on the surface. Most coupons exhibited a weight gain during the initial 20 days of exposure. After two months of exposure, the coupon weights were generally very similar to those of the initial non-exposed coupons. Weight losses (or gains) were all 2 mg/dm2-month. To put this value into
28、perspective, a metal release rate of 160 mg/dm2-month corresponds to a metal loss rate of 1 mil/year for a material such as carbon steel. Based on the visual inspection results and weight change measurements, general and localized corrosion of all test materials was minimal in the 185F NaPB solution
29、. STP-NU-068: Corrosion of A193 Grade B7 Bolt Material in BWR Sodium Pentaborate Solutions 15 Figure 3-10: C410 Test Coupons 5, 6, 7 and 8 after Two Months of Exposure STP-NU-068: Corrosion of A193 Grade B7 Bolt Material in BWR Sodium Pentaborate Solutions 16 Figure 3-11: C1010 Test Coupons 5, 6, 7
30、and 8 after Two Months of Exposure STP-NU-068: Corrosion of A193 Grade B7 Bolt Material in BWR Sodium Pentaborate Solutions 17 Figure 3-12: C4140 Test Coupons 11, 12, 13 and 14 after Two Months of Exposure STP-NU-068: Corrosion of A193 Grade B7 Bolt Material in BWR Sodium Pentaborate Solutions 18 Fi
31、gure 3-13: C4340 Test Coupons 5, 6, 7 and 8 after Two Months of Exposure STP-NU-068: Corrosion of A193 Grade B7 Bolt Material in BWR Sodium Pentaborate Solutions 19 Figure 3-14: Coupon Weight Changes after Exposure to Sodium Pentaborate Solution at 185F Alloy Serial Number Weight, g Weight loss, mg
32、Weight loss, mg/dm -mo t = 0 days t = 22 days t = 60 days t = 22 days t = 60 days t = 22 days t = 60 days C4340 5 12.6504 12.6506 12.6504 -0.2 0 -1.4 0.0 C4340 6 12.5832 12.5829 12.5830 0.3 0.2 2.1 0.5 C4340 7 12.6568 12.6569 12.6571 -0.1 -0.3 -0.7 -0.7 C4340 8 12.4463 12.4464 12.4464 -0.1 -0.1 -0.7
33、 -0.2 410 5 10.2096 10.2093 10.2094 0.3 0.2 2.1 0.5 410 6 10.1389 10.1389 10.1390 0 -0.1 0.0 -0.2 410 7 10.1260 10.1260 10.1255 0 0.5 0.0 1.1 410 8 10.2494 10.2497 10.2490 -0.3 0.4 -2.1 0.9 C1010 5 10.8115 10.8127 10.8114 -1.2 0.1 -8.2 0.2 C1010 6 10.7481 10.7501 10.7486 -2 -0.5 -13.7 -1.1 C1010 7 1
34、0.8357 10.8371 10.8361 -1.4 -0.4 -9.6 -0.9 C1010 8 10.7273 10.7300 10.7273 -2.7 0 -18.6 0.0 C4140 11 14.2563 14.2584 14.2564 -2.1 -0.1 -14.4 -0.2 C4140 12 14.2200 14.2220 14.2207 -2 -0.7 -13.7 -1.6 C4140 13 14.3101 14.3129 14.3105 -2.8 -0.4 -19.2 -0.9 C4140 14 14.3419 14.3436 14.3420 -1.7 -0.1 -11.7
35、 -0.2 STP-NU-068: Corrosion of A193 Grade B7 Bolt Material in BWR Sodium Pentaborate Solutions 20 Figure 3-15: Effect of Exposure Time on Coupon Weight Loss (12% Sodium Pentaborate Solution at 185F) -3-2-1010 10 20 30 40 50 60Weight Loss,mg C1010-3-2.5-2-1.5-1-0.500 10 20 30 40 50 60Weight Loss,mg C
36、4140-0.4-0.200.20.40 10 20 30 40 50 60Weight Loss,mg C4340-0.4-0.200.20.40.60 10 20 30 40 50 60Weight Loss,mg 410STP-NU-068: Corrosion of A193 Grade B7 Bolt Material in BWR Sodium Pentaborate Solutions 21 Figure 3-16: Effect of Exposure Time on Coupon Weight Loss per Unit Area (12% Sodium Pentaborat
37、e Solution at 185F) -20-15-10-5050 10 20 30 40 50 60Weight loss,mg/dm-month C1010-25-20-15-10-5050 10 20 30 40 50 60Weight loss,mg/dm-month C4140-2-101230 10 20 30 40 50 60Weight loss,mg/dm-month C4340-3-2-101230 10 20 30 40 50 60Weight loss,mg/dm-month 410STP-NU-068: Corrosion of A193 Grade B7 Bolt
38、 Material in BWR Sodium Pentaborate Solutions 22 Figure 3-17: Effect of Exposure Time on Coupon Weight Change per Unit Area (12% Sodium Pentaborate Solution at 185F) -20-15-10-505C1010-5C1010-6C1010-7C1010-8C4140-11C4140-12C4140-13C4140-14C4340-5C4340-6C4340-7C4340-8410-5410-6410-7410-8Weight loss,m
39、g/dm-month20 Days-2-1.5-1-0.500.511.5C1010-5C1010-6C1010-7C1010-8C4140-11C4140-12C4140-13C4140-14C4340-5C4340-6C4340-7C4340-8410-5410-6410-7410-8Weight loss,mg/dm-month60 DaysSTP-NU-068: Corrosion of A193 Grade B7 Bolt Material in BWR Sodium Pentaborate Solutions 23 4 FLANGE TESTS 4.1 Flange Tests a
40、t 99F The test flange configuration with the 1/16-inch ID Teflon tube in place for NaPB injection is shown in Figure 2-4. As indicated in Section 2, three flanges were exposed at 99F. Flanges 1 and 2 were not insulated. Flange 1 was allowed to accumulate borate salts that developed as a result of le
41、akage. Flange 2 was cleaned intermittently. Flange 3 was insulated with NUKONTM and was allowed to accumulate borate salts during the test period. The orientation of the bolts installed in each flange is shown in Figure 4-3 to Figure 4-5. Upon receipt, bolts were rinsed with acetone, cleaned with RB
42、S-35 solution (a mildly basic surfactant containing anionic and nonionic detergents) in an ultrasonic bath, rinsed with DI water and then air dried. Testing began on September 3, 2013. The temperature during the test was 99.3 2.7F. Since mockup tests had indicated that all bolts would be exposed to
43、the NaPB solution at an injection flow rate of 0.5 g/minute, and it was desired to limit the exposure to primarily one bolt, the injection flow rate target was set at 0.1 g/minute. Initially, injection was performed at 0.3 g/min using a peristaltic pump. Flow was then decreased to 0.06 g/min by chan
44、ging the pump tubing size. On September 5, the bolts were removed from the three flanges, rinsed with acetone to assure the absence of any organic residual and reweighed. Injection was reestablished at 11:10 on the same day at 0.06 ml/minute. A final flow adjustment was made on September 10. Thereaf
45、ter, the flow rates varied from 0.08-0.14 g/min through the remainder of the test (Figure 4-6). Flange 2 was periodically cleaned using a wire brush to remove salts accumulated during testing. Cleanings were performed at 17 days, 27 days and 45 days during the test. Photographs of Flange 2 before an
46、d after removing salts at day 27 are shown in Figure 4-7 and Figure 4-8. There was no evidence of the NaPB solution reaching the outside surface of the Flange 3 NUKONTM insulation. Flow was terminated, and the oven was shut off on October 30 at 16:10 after approximately two months of exposure. The b
47、olts and flanges were allowed to dry overnight. Bolts were removed on October 31. After disassembly of the flanges, bolts were weighed and then soaked in 2.5% NaPB solution to dissolve readily soluble salts, dried, weighed, rinsed with demineralized water, brushed with a soft bristle brush, dried an
48、d reweighed. Initial and final weights of the bolts exposed for approximately two months to the 12% NaPB solution at 95oF are given in Figure 4-1. General corrosion rates were estimated from the weight decrease of each specimen. No residual oxide generally appeared present on the specimens following
49、 brushing and rinsing. Results can be summarized as follows: In Flanges 1 and 2, which were not insulated, the bolts onto which the NaPB solution was injected had significantly greater metal losses than the other bolts in these flanges. Note that the velocity of the solution impinging on the bolt was very low (0.003 ft/s) so the effect was not a result of erosion-corrosion. It was related to the local solution chemistry that developed on the bolt surface as the water evaporated and the borate salts crystallized. In the insulated flange, Bolt 9 on
