Abstract

The Ni-based corrosion resistant alloys are known to exhibit high resistance to hydrochloric and sulfuric acids over wide concentration and temperature ranges. Pipe and tube materials are widely used in chemical process industry (CPI) and various other industries. The common tubing forms include seamless, as-welded, welded bead-worked, and welded fully cold-reduced. Many of the Ni-Based product types are produced according to ASTM and ASME (B622, B626, B619) (1) specifications. Commercial UNS N10675 (HASTELLOY® B-3®) (2), UNS N10276 (HASTELLOY® C-276) (2), UNS N06200 (HASTELLOY® C-2000 ®) (2), UNS N06022 (HASTELLOY® C-22®) (2) and UNS N10362 (HASTELLOY® HYBRID-BC1®) (2) alloys with the above-mentioned forms of tubing materials were studied in this paper. UNS N10362 tubes showed excellent general corrosion and pitting resistance compared to other C-type alloy tubes in selected test environments. C-type alloy welded tubes sensitization behavior was studied in ASTM standard G28A(3)and G28B (3) solutions. From testing it was concluded that welded and fully cold-reduced tubing has similar corrosion resistance to that of seamless tubing, while as-welded and welded bead-worked tubing underwent localized corrosion.

Introduction

Nickel-based corrosion-resistant alloys are vitally important materials in chemical processing, petrochemical, agrichemical and pharmaceutical industries. When aggressive process streams are involved, corrosion-resistant alloys are selected for applications such as heat exchangers, reactors, pressure vessels and/or other process equipment in various industry sectors.1 The Ni-Mo alloys provide excellent resistance to reducing hydrochloric and sulfuric acids over large ranges of concentration and temperature. They also resist pure hydrobromic acid, hydrofluoric acid and other non-oxidizing halide salt solutions.1 The primary limitation of the Ni-Mo alloys is that they cannot tolerate either oxidizing acids, such as nitric, or acids that contain oxidizing species. Such species include oxygen, hydrogen peroxide, chlorine, bromine, ferric ions and cupric ions.1

The Ni-Cr-Mo alloys provide both excellent general corrosion and localized corrosion resistance, such as stress corrosion cracking, pitting and crevice corrosion, when they are exposed to highly corrosive reducing or oxidizing acids. Chromium induces passivation in oxidizing acids, Molybdenum provides resistance to reducing acids, in particular hydrochloric acid.1

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