Analysis and Prevention of Corrosion-Related Failures S.R. Freeman, Millennium Metallurgy Ltd Examples of Corrosion Failure Analy Example 1: Analysis of Pitting and MIC of Stainless Steel Piping. Type S31603)austenitic stainless steel piping was installed as part of a collection system for a storm nt system used in a manufacturing facility. Within six months of start-up, leaks were discovered On-Site Examination. A of tests were performed on site to eliminate stray currents as a possible cause of failure in the piping system. The piping system was inspected for possible sources of ac or dc current flow.An external battery was used to impress a voltage. Voltage and current were recorded with the external power supply applied and removed There was no evidence of stray currents or electrical discharge It was noted that the ambient temperature and slow or stagnant flow conditions present in the piping were ideal for bacteria growth On-Site Sampling. Water samples were obtained for corrosivity and MIC testing. Commercially available field MIC kits were used. Samples of the damaged pipe were removed total dissolved solids level of 10,000 ppm was also high. The MIC water samples were shipped to the laboratory within 24 h of removal for viable culture testing. The testing showed high levels of aerobic, acid producing, and low-nutrient bacteria Laboratory Examination. Perforated pipe samples were provided for metallurgical evaluation. Figure 2(a) shows the leak area as viewed from the outside-diameter surface. The sample was cut dry to avoid contamination. The inside-diameter surface is shown in Fig. 2(b). The pit appeared larger on the inside diameter surface, indicating pit initiation occurred at the inside surface and at the bottom of the pipe. a rusty discoloration was apparent along the bottom length of the pipe. This discoloration corresponded to the area of the pitting. There was no corrosion deposit associated with the pitting. The discolored areas and other areas were evaluated using EDs. The EDS revealed contaminants consisting of chlorine, sulfur, sodium, silicon, and potassium. The area of discoloration revealed iron and oxygen only Fig. 2 Pitting corrosion of 316L stainless steel pipe. (a) view of pitting on the outside- diameter surface at the leak location.(b) View of the inside-diameter surface where the pit size was larger at the leak location. There was a rusty discoloration along the bottom of the pipe. (c) Cross section of pipe wall through the perforation. The sample was etched in AstM 89 reagent to delineate the microstructure. Uniform wall thickness is approximately 2.9 mm(0.1l in. ) 5x Courtesy of s.R. Freeman, Millennium Metallurgy, Ltd A metallurgical cross section was prepared through the pitted region. Figure 2(c)shows a 10X magnification of the cross section through the pitted region after etching with AStM 89 reagent. The pit was not associated with a welded region, and the microstructure appeared normal. There was no evidence of general wall loss(uniform corrosion)Analysis and Prevention of Corrosion-Related Failures S.R. Freeman, Millennium Metallurgy, Ltd. Examples of Corrosion Failure Analysis Example 1: Analysis of Pitting and MIC of Stainless Steel Piping. Type 316L (UNS S31603) austenitic stainless steel piping was installed as part of a collection system for a storm sewer treatment system used in a manufacturing facility. Within six months of start-up, leaks were discovered. On-Site Examination. A series of tests were performed on site to eliminate stray currents as a possible cause of failure in the piping system. The piping system was inspected for possible sources of ac or dc current flow. An external battery was used to impress a voltage. Voltage and current were recorded with the external power supply applied and removed. There was no evidence of stray currents or electrical discharge. It was noted that the ambient temperature and slow or stagnant flow conditions present in the piping were ideal for bacteria growth. On-Site Sampling. Water samples were obtained for corrosivity and MIC testing. Commercially available field MIC kits were used. Samples of the damaged pipe were removed. Laboratory Testing. High levels of chlorides, as high as 20,000 ppm, were reported in the water sample. The total dissolved solids level of 10,000 ppm was also high. The MIC water samples were shipped to the laboratory within 24 h of removal for viable culture testing. The testing showed high levels of aerobic, acid￾producing, and low-nutrient bacteria. Laboratory Examination. Perforated pipe samples were provided for metallurgical evaluation. Figure 2(a) shows the leak area as viewed from the outside-diameter surface. The sample was cut dry to avoid contamination. The inside-diameter surface is shown in Fig. 2(b). The pit appeared larger on the inside￾diameter surface, indicating pit initiation occurred at the inside surface and at the bottom of the pipe. A rusty discoloration was apparent along the bottom length of the pipe. This discoloration corresponded to the area of the pitting. There was no corrosion deposit associated with the pitting. The discolored areas and other areas were evaluated using EDS. The EDS revealed contaminants consisting of chlorine, sulfur, sodium, silicon, and potassium. The area of discoloration revealed iron and oxygen only. Fig. 2 Pitting corrosion of 316L stainless steel pipe. (a) View of pitting on the outside￾diameter surface at the leak location. (b) View of the inside-diameter surface, where the pit size was larger at the leak location. There was a rusty discoloration along the bottom of the pipe. (c) Cross section of pipe wall through the perforation. The sample was etched in ASTM 89 reagent to delineate the microstructure. Uniform wall thickness is approximately 2.9 mm (0.11 in.). 5×. Courtesy of S.R. Freeman, Millennium Metallurgy, Ltd. A metallurgical cross section was prepared through the pitted region. Figure 2(c) shows a 10× magnification of the cross section through the pitted region after etching with ASTM 89 reagent. The pit was not associated with a welded region, and the microstructure appeared normal. There was no evidence of general wall loss (uniform corrosion)