Corrosion Performance of Nickel Based Alloys in Highly Concentrated Hydrochloric Acid (2024)

ABSTRACT

Nickel alloys, especially the nickel(Ni)-chromium(Cr)-molybdenum(Mo) family, offer excellent resistance to hydrochloric acid. The objective of this paper is to study the corrosion performance of various Ni based alloys in high concentrations of HCl acids below the boiling point. In this work, the corrosion resistance of nickel-based alloys C- 276 (UNS N10276), C-22 (UNS N06022), C-2000 (UNS N06200), Hybrid-BC1 (UNS N10362) and B-3 (UNS N10675) in mill annealed condition were studied in highly concentrated (25-37wt.%) HCl solutions. Based on the available data, an attempt was made to draw iso-corrosion diagrams 10 mpy (0.25mm/y) and 20 mpy (0.5 mm/y) for selected alloys in the range 25 to 35 wt.% HCl.

Additionally, the corrosion rates of the above-mentioned alloys subjected to heat treatment (760°C/15 min/air cool) were studied via immersion and electrochemical linear polarization resistance (LPR) methods and compared to the corrosion rates obtained in mill annealed condition.

This study shows that heat treated alloys show relatively much higher corrosion rates when exposed to higher concentrated HCl solutions at higher temperatures.

INTRODUCTION

Hydrochloric (HCl) acid is a colorless liquid and very corrosive in nature and considered as a strong mineral acid. HCl is monoprotic, which means it has a high level of dissociation in water, this creates an overabundance of H⁺ ions in solution. The overabundance of H⁺ ions means it has a very low pH level of 0-1. This indicates that it is a highly corrosive substance, and only a few materials are resistant. Most of the commonly used metals and their alloys experience extensive general and/or localized corrosion attack in HCl. Further, the solution aggressiveness drastically changes depending on the concentration and temperature.

HCl is used in many different applications, from production of metals and chlorides to acid treatment of oil wells. Major applications include steel pickling, chemical cleaning, chemical processing, ore reduction, food processing and synthesis of vinyl chloride and alkyl chloride.¹