Determinación y análisis de variables críticas en el proceso de galvanizado de la tubería de acero a escala de laboratorio para su posterior optimización en planta

Abstract

The objective of this work is to determine the critical variable to effectively control the preparation of the surface of the steel pipeline in the company TUGALT S.A. and propose a chemical composition that allows optimization in the zinc bath process (zinc plating process). For this, a current evaluation of the plant was carried out, obtaining information on its parameters, evaluated by means of control letters over a period of seven weeks. The work was carried out on a laboratory scale with steel cylinder samples (JIS G3132 SPTH 1 specification) to manipulate the variables at each stage of the process (degreased, pickling, fluxing, and zinc plated): pH, concentration of the solutions used in the baths, temperature, immersion times and the optional working range to obtain a higher quality pipeline. For the zinc plated stage, work was carried out at a temperature of 450±1°C for an immersion time of the steel cylinder samples of 2, 4, 6 minutes, keeping the zinc composition at 98,5% W/W constant, varying the aluminum, bismuth, tin and nickel composition in the range of 0-1,5% by weight of the “Zn-Al-Bi-Sn-Ni” system, which was dosed by experimental design, to favor drainage and reduce the thickness of the steel cylinder samples, decrease zinc intake and avoid lumps. The coatings obtained were examined by means of: layer thickness measurements, metallographic analysis using an inverted microscope, salt spray chamber corrosion test and cross-method adherence; determining that experiment 1 (0,25A/0,05B/0,07C/0,025D-2minutes) meets the established specifications, provides a better finish (crystal formation) that makes the product visually accepted, with a layer thickness of 79,233 µm and formation of the four defined layers (alpha, beta, gamma and delta) that influence corrosion and a perfectly smooth finish