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ASME STP/NU-068
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ASME STP/NU-068 2014 Edition, March 14, 2014 CORROSION OF A193 GRADE B7 BOLT MATERIAL IN BWR SODIUM PENTABORATE SOLUTIONS
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Description / Abstract:
INTRODUCTION
To better determine the impacts of using A193 Grade B7 bolts in stainless steel flanges installed in a Boiler Water Reactor (BWR) sodium pentaborate (NaPB) systems, quantification of the corrosion rates of this material in NaPB solutions was investigated. Two types of tests were performed. First, coupons of 4140 (the base material for A193 Grade B7), C4340 low alloy steel, C1010 carbon steel and 410 stainless steel were immersed in a 12% NaPB solution at ~95°F and a 12 to 20% solution at ~185°F. An A193 Grade B7 bolt was also immersed in a 12% NaPB solution and in demineralized water at 95oF. Coupons and bolts were intermittently examined and photographed, and weight change measurements were made to assess corrosion rates after three weeks and two months of exposure.
Second, tests to assess corrosion of A193 Grade B7 bolts when leakage occurs across stainless steel flange seal surfaces were performed. The test flanges had a 4-inch diameter and a bolt circle diameter of ~3 inches. Three flanges were exposed at ~99ºF, and one flange was exposed at ~203ºF. Leakage of the NaPB solution was simulated by injecting a 12 weight percent NaPB solution through a small diameter Teflon tube onto one of the four bolts in each flange at a rate of ~0.1 ml per minute. One flange was allowed to accumulate borate salts as a result of the leakage. The exterior surface of the other flange was brushed clean approximately every two weeks. The third 100ºF flange was insulated with NUKONTM and was not cleaned during the test period. The 203ºF flange was not insulated and was allowed to accumulate borate salts over the test period. Flanges were exposed for approximately two months.
After the nearly two month exposures, the flanges were disassembled, and the bolts and flanges were photographed and inspected. The bolts were rinsed of borate salts, weighed, de-scaled, and reweighed to determine metal loss. Local corrosion depths were estimated based on the weight losses.
Test methodology is summarized in Section 2. Coupon test results are summarized in Section 3. Flange bolt testing is summarized in Section 4.
To better determine the impacts of using A193 Grade B7 bolts in stainless steel flanges installed in a Boiler Water Reactor (BWR) sodium pentaborate (NaPB) systems, quantification of the corrosion rates of this material in NaPB solutions was investigated. Two types of tests were performed. First, coupons of 4140 (the base material for A193 Grade B7), C4340 low alloy steel, C1010 carbon steel and 410 stainless steel were immersed in a 12% NaPB solution at ~95°F and a 12 to 20% solution at ~185°F. An A193 Grade B7 bolt was also immersed in a 12% NaPB solution and in demineralized water at 95oF. Coupons and bolts were intermittently examined and photographed, and weight change measurements were made to assess corrosion rates after three weeks and two months of exposure.
Second, tests to assess corrosion of A193 Grade B7 bolts when leakage occurs across stainless steel flange seal surfaces were performed. The test flanges had a 4-inch diameter and a bolt circle diameter of ~3 inches. Three flanges were exposed at ~99ºF, and one flange was exposed at ~203ºF. Leakage of the NaPB solution was simulated by injecting a 12 weight percent NaPB solution through a small diameter Teflon tube onto one of the four bolts in each flange at a rate of ~0.1 ml per minute. One flange was allowed to accumulate borate salts as a result of the leakage. The exterior surface of the other flange was brushed clean approximately every two weeks. The third 100ºF flange was insulated with NUKONTM and was not cleaned during the test period. The 203ºF flange was not insulated and was allowed to accumulate borate salts over the test period. Flanges were exposed for approximately two months.
After the nearly two month exposures, the flanges were disassembled, and the bolts and flanges were photographed and inspected. The bolts were rinsed of borate salts, weighed, de-scaled, and reweighed to determine metal loss. Local corrosion depths were estimated based on the weight losses.
Test methodology is summarized in Section 2. Coupon test results are summarized in Section 3. Flange bolt testing is summarized in Section 4.