CoatingsPro Magazine

MAR 2016

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Page 64 of 84

64 MARCH 2016 COATINGSPROMAG.COM material and carbon from the epoxy were also detected in the base metal. Te results were otherwise typical for Type 316 stainless steel, which is the specifed material for the tubes. Analysis of the copper layer revealed primarily copper with a lesser amount of carbon and small to trace amounts of iron, chromium, nickel, aluminum, silicon, and oxygen. Te iron, chromium, and nickel were judged to be smeared from the base metal. Te carbon and oxygen were judged to be from the epoxy. Te nickel layer consisted primarily of nickel with a lesser amount of carbon and small to trace amounts of iron, chromium, aluminum, copper, phosphorus, and oxygen. Phosphorus is commonly added to nickel coatings to improve their strength and hardness. Te dark features were analyzed via EDS to determine the relative composition of the contaminants. Te results were similar in compar- ison to each other, and the features consisted primarily of aluminum and oxygen with lesser amounts of carbon, iron, and nickel along with small to trace amounts of chromium, copper, titanium, and phosphorus. Te general composition of the features was consis- tent with aluminum oxide. A luminum oxide is commonly used in grit blast- ing media to remove scale and other contaminants from the surface of a part. So what does that all mean? Analyzing the Evidence Te darker areas on the tubes were judged to have, as their source, grit blasting media. Te presence of grit blasting media along the surface of the steel can interrupt the plating process and result in plating holidays. After all the information is collected and the analysis is complete, a fnal conclusion can be made based on the evidence available. Te investi- gation can be thought of as a forensic puzzle. Te more pieces of the puzzle that are in place, the more conclusive the investigation will become. It is often tempting to ask the metallurgist to minimize the amount of testing performed to save time and money. In this case, the evidence showed that the coating delamination could be attributed to improper cleaning of the abrasive blast material. Te blast material that had been used had embedded into the steel substrate and interrupted the bond between the nickel plating and the tube. Applying the blast media with less force or less angular media could have prevented the embedding of the particles. Collaboration Necessary Before you need to get to an inves- tigation, you may ask, " W hy should we plan and budget for SEM-EDS work? Isn't that expensive? " As the results of this investigation showed, the SEM-EDS work was critical in determining the source of the contam- ination that was present beneath the nickel layer of coating. It may also be tempting to withhold background information, such as steps in the process, process changes, vendor changes, etc., about the part for fear of biasing the metal- lurgist's fnal conclusion. It should be understood, though, that restricting the amount of testing and withholding important information will efectively take away pieces of the puzzle that can prove critical to achieving the correct fnal conclusion. If the reasons for a failure are not properly understood, corrective actions to prevent future failures may be inefec- tive. When the investigation is complete, it is often up to the parties involved to collectively determine the best course of corrective action to prevent similar events from occurring again. CP Check out more of the visual support for the case of this Never Again online at Nickel-Plating-Case-Photo-Evidence Craig J. Schroeder, P.E ., Senior Eng ineer, Meta l lurg y for Element Mater ia ls Technolog y, has his Bachelor and Master of Science f rom t he Universit y of Wisconsin. Schroeder has severa l publ ished work s and has g iven severa l presenta- t ions over t he years. For more infor mat ion, contact: Element Mater ia ls Technolog y, w w Table 1: EDS Results, Invner Tube (Relative Weight Percent --- = Not Detected) Flaked Nickel Plating Element Epoxy Base Metal Copper Layer Nickel Layer Area 1 Area 2 Area 3 Figure No. None 11 11 11 11 11 11 Iron 0.7 60.3 3 3.8 6.4 8.9 12.5 Manganese --- 1.8 --- --- --- --- --- Chromium --- 13.8 1 1.2 1.7 2.7 3.3 Nickel --- 1.7 66.6 2.1 14.3 11 Molybdenum --- 1.2 --- --- --- --- --- Silicon --- 0.1 0.3 --- --- --- --- Aluminum --- --- 0.3 0.6 40.2 29.8 26.5 Copper --- 1.6 77.1 2.6 1.1 1.7 2 Titanium --- --- --- --- 0.3 0.4 1.7 Phosphorus --- --- --- 7.2 0.2 1.4 1.1 Chlorine 0.3 --- --- --- --- --- --- Carbon 69.6 11.9 15.4 16.3 13.1 13.7 15.8 Oxygen 29.4 --- 1.1 1.6 34.9 27.2 26.2

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