API 571 Certification (Corrosion & Materials) Practice Test

Alloy C-276 is listed as the most resistant to hydrofluoric acid (HF) corrosion among the options provided. This superalloy, mainly consisting of nickel, molybdenum, chromium, and tungsten, demonstrates exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking in severe environments, including acidic conditions such as those presented by HF. HF is a highly corrosive acid that can aggressively attack many metals; however, C-276's unique composition enhances its ability to withstand such corrosive assaults. The molybdenum and tungsten in the alloy contribute to its overall corrosion resistance by forming stable oxide layers that protect the underlying metal from acid attack. In contrast, carbon steel is generally unsuitable for application in environments exposed to HF due to its vulnerability to rapid corrosion and failure. Alloy 400 and Cu-Ni alloys, while providing some level of corrosion resistance, do not match the performance of Alloy C-276 in HF environments. Thus, Alloy C-276 stands out as the most corrosion-resistant option available for such applications.