Materials Performance

OCT 2017

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

Issue link: http://mp.epubxp.com/i/879896

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17 NACE INTERNATIONAL: VOL. 56, NO. 10 MATERIALS PERFORMANCE OCTOBER 2017 Information on corrosion control and prevention Continued on page 18 CVD WC coatings can be applied to both internal and external surfaces and complex geometries. Photo courtesy of Hardide Coatings. Samples of three different coatings after salt spray corrosion tests: HVOF after 480 h (left), HCP after 288 h (center), and CVD WC Type T coating after 480 h (right). Photos courtesy of Hardide Coatings. Nanostructured Tungsten Carbide Coatings Protect Against Corrosion I n industries characterized by extreme operating environments that push materials, components, equipment, and tools to the edge of their design capabili- ties, companies are challenged to contin- ually seek economically viable ways to improve performance, safety, and competitiveness. The oil and gas industry, for example, is faced with mitigating the impact of corrosion—which reduces the life of components such as drilling tools and pipeline valves—in ever-challenging environments such as sour service and ultra-deep water. Sour oil and gas containing hydrogen sulf ide (H 2 S) can cause sulf ide stress cracking, which inf licts signif icant damage on valves, pumps, and seals. Seawater, acidic media, carbon dioxide (CO 2 ), and other aggres- sive media can cause a variety of corro- sive attacks, including metal loss and pitting. Corrosive attacks can be especially quick and damaging when combined with abrasion or erosion, which removes the steel's protective passive surface layers and can signif icantly accel- erate corrosion. Hard chrome plating (HCP) has been widely used for many years to success- fully increase the life of tools and critical components; however, its manufacturing was banned in the European Union (EU) in September 2017 (unless authorized by the EU Commission), as it uses carcino- genic hexavalent chromium salts in its production. In the United States, the Occupational Safety and Health Adminis- tration is imposing increasingly tighter restrictions. Existing HCP alternatives include high velocity oxy-fuel (H VOF) and physi- cal vapor deposition (PV D) techniques, as well as emerging processes such as elec- troless-nickel composite plating and explosive bonding. A lthough successful in some applications, each has its limita- tions. H VOF coatings can create a very thick and durable layer, but cannot be applied to internal surfaces. They are rough and porous and often require post- coat grinding, which is not possible on intricate shapes. PV D coatings can pro- duce an extremely hard layer with an accurately controlled thickness, but are very thin (ty pically <4 µm) and have lim- ited abrasive/erosive resistance and load- bearing capacity. Various wet electroplat- ing and electroless coatings are more suitable for internal surfaces and com- plex shaped parts, but have lower hard- ness than HCP and less wear resistance. Extensive testing of chemical vapor deposition (CV D) tungsten carbide (WC) coatings developed by Hardide Coatings Limited (Oxfordshire, United K ingdom) has proven that low-temperature CV D coatings can be tough and provide a Material Matters continued f rom page 16

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