29 Journal of New Materials for Electrochemical Systems Vol.24, No.1, January 2021, pp. 29-33 http://new-mat.org http://iieta.org/journals/jnmes Performance of Propargyl Alcohol as Corrosion Inhibitor for Electroless Nickel- Phosphorus (NiP) Coating in Hydrochloric Acid Solution Fernando B. Mainier * , Thiago Theobaldo da Silva and Fabio P. D. de Araujo Escola de Engenharia, Universidade Federal Fluminense , Niterói, Rio de Janeiro, Brazil *Corresponding Author Email: fmainier@uol.com.br ABSTRACT The electroless nickel-phosphorus (NiP) coatings have been used with great success in oil production equipment and accessories, such as pipes, valves, pumps, adapters, rings, connectors and various types of special tools. In the acidification or acid stimulation of oil wells, to increase their productivity, a hydrochloric acid (HCl) solution is preferably injected from concentrations of 5 to 28%, aiming at the dissolution of a reservoir rock constituted of limestone and dolomite. In addition, the HCl solutions are also used to remove lime scale adhering to carbon steel pipes, where propargyl alcohol as a corrosion inhibitor, has shown good anticorrosion protection. The aim of this work is centred on the laboratory evaluation of NiP coating in 5% and 10 % HCl solution, and addition of propargyl alcohol as a corrosion inhibitor. The mass loss and polarisation curves proved to be very promising with propargyl alcohol as a corrosion inhibitor. Keywords: Electroless NiP coating, propargyl alcohol, corrosion inhibitor, hydrochloric acid, acid stimulation Received: October-26-2020, Accepted: November-18-2020, https://doi.org/10.14447/jnmes.v24i1.a05 1. INTRODUCTION The autocatalytic chemical deposition of nickel (Ni) and phosphorus (P) on carbon steel surface, without external current application, is performed by cathodic reduction with the atomic hydrogen (H), from the hydrolysis of hypophosphite (H2PO2 - ) and nickel salts (Ni 2+ ), as shown in Figure 1. Figure 1. Scheme of formation of NiP coating and scanning electron microscopy (SEM) image with X 800 In addition, pH regulators, complexing agents and other additives are added to ensure a good adhesion of the NiP layer to the metal surface. The resistance to corrosion and abrasion of this coating depends on the content of Ni and P present in the layer deposited, and the increase of the P content favours the anticorrosive protection. The co-deposition of NiP has the behaviour of a crystalline or amorphous alloy, which depends on the mass ratio of Ni and P. For severe operating conditions, the P content must not be less than 10% by mass [1-6]. The justifications for the evaluation of NiP coating in the solutions of HCl, with and without the addition of corrosion inhibitors, are based on the acid stimulation process, which consists of the injection of HCl in the limestone or dolomite reservoir rock to increase the productivity in oil and natural gas production [7, 8]. The HCl reacts easily with limestones (CaCO3) or dolomites (CaCO3.MgCO3) by solubilizing the rocks in soluble chlorides (CaCl2 and MgCl2) and carbon dioxide (CO2), increasing permeation, not forming tampons or restrictions, and consequently increasing oil production. The propargyl alcohol is a corrosion inhibitor, soluble in the acid medium that has been used in these petroleum operations with good performance, for both carbon steel and stainless steels [9 - 13]. 2. MATERIALS AND METHODS The rectangular coupons (35.5mm x 15mm x 4mm) of mild steel were used as the substrate material for the preparation of electroless NiP coatings. These coupons were immersed in a commercial acidic sodium hypophosphite bath, kept thermostatically at 90°C, consisting basically of sodium hypophosphite, nickel chloride, complexing agents and pH regulating substances, to form a coating with 10.39% phosphorus and in the following NiP thicknesses: 10.37 μm, 38.39 μm and 67.40 μm. The theoretical NiP mass of each coupon, in function of its thickness, can be determined by the following equation: m=ρ.S.e where, m = mass of NiP coating (g), S = surface area (cm 2 ), e = NiP thicknesses (mm) and ρ = density of NiP coating (7.95 g/cm 3 ), calculated on the basis of the work carried out by Parkinson [14] and Umapathi et al.[15]. On average, the theoretical NiP mass relative to the thicknesses of 10.37 μm, 38.39 μm and 67.40 μm are 90 mg, 260 mg and 570 mg, respectively. The corrosive medium used in the tests was 5 to 10% (by volume) of high purity HCl. The corrosion inhibitor used was