The Synergistic Effect of Thiourea and Surfactants on Corrosion Inhibition of Stainless Steel-316 in Hydrochloric acid Sami Ullah 1, a , Muhammad Nadeem 2, b , A.M. Shariff 1, c* , Faiz Ahmad 3, d , Shaukat Ali Shahid 4, e , M. Sagir 5, f Muhammad Rafi Raza Malik 3, g and Muhammad Mushtaq 5, h 1 Research Center for CO 2 Capture, 5 Department of Chemical Engineering Universiti Teknologi PETRONAS, Malaysia 2 PETRONAS Research Sdn Bhd, Kawasan Institusi Bangi, Selangor, Malaysia 3 Department of Mechanical Engineering Universiti Teknologi PETRONAS, Malaysia 4 Department of Physics University of Agriculture Faisalabad, Pakistan a samichemist1@gmail.com, b nadeem_waterchemist@yahoo.com, c azmish@petronas.com.my, d faizahmadster@gmail.com, e shaukatalishahidpy@yahoo.com, f sagir.utp@gmail.com, g rafirazamalik@gmail.com, h mmushtaq3@gmail.com Keywords: Corrosion inhibition, Thiourea, Surfactants, Stainless Steel 316 Abstract: Corrosion and scaling are the common problems to all the industries. A remedy of these problems was sought out through chemical treatment: indigenously available raw materials including thiourea, surfactants (cationic, anionic and nonionic containing pre, critical and post micellar concentration). Evaluation of corrosion inhibition properties stainless steel 316 by thiourea based inhibitor and its synergistic effect with cationic cetyl tri-methyl ammonium bromide (CTAB), anionic sodium dodecyl sulphate (SDS) and nonionic triton X-100 have been carried out by weight loss method as a function of concentration of thiourea and surfactants. These materials were applied to the coupons of stainless steel 316 in different acidic concentration. Corrosion rates were calculated using weight loss method. Excellent results were achieved regarding corrosion inhibition in the presence of thiourea and surfactants assuring the better performance of these chemicals. The results showed that corrosion rate was decreased from 90 mpy to 12.1 mpy after 720 hours by the addition of 200ppm thiourea in critical micellar concentration of SDS in 3M HCl acid solution. Introduction Evaluation of corrosion phenomenon and its inhibition in acidic environment for metal and metal alloys have got tremendous importance when viewed in terms of maintenance and repair costs of industrial systems associated with corrosion and material failure. Due to their heavyweight and mechanical strength, the alloys of stainless steel are used for industrial applications. The use of stainless steel arises from their significance in the current society [1-6]. The evaluation of corrosion coupons is one of the most traditional and reliable methods for corrosion monitoring. They yield exact information on the basis of average mass loss; extent and distribution of localized corrosion and can also provide further information regarding the nature of corrosion through analysis of their corrosion products. Corrosion of metals is the most important industrial problem that has attracted a lot of investigators in recent years [7-9]. In general, acid inhibitors are nitrogen (N), sulphur (S) oxygen (O) and phosphorus (P). These are organic based compound with the structure of triple bond. The value of inhibition of corrosion decreases according to the order O<N<S<P. The corrosion inhibition is a surface process, which involves the adsorption of the organic compounds on metallic substrate surface. The inhibition efficiency of organic compound relies on size of molecule, type of interaction with the metallic surface [9-12] . The adsorption primarily depends on the electronic configuration of molecule structure. Thiourea and three different types of surfactants (CTAB, SDS and Triton X–100) these compounds contain nitrogen and sulphur [13, 14]. Though, previous research on utilize of chelating agents as organic inhibitors particularly those bearing Advanced Materials Research Vol. 917 (2014) pp 28-34 © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.917.28 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 203.135.191.3, Universiti Technologi PETRONAS, Tronoh, Malaysia-10/04/14,03:06:22)