INTRODUCTION
In fertilizer production, storage and handling, corrosion inhibitors play a very important role in ensuring the durability of the equipment and plant structures. The plants handle very corrosive raw materials and several corrosive intermediates and by-products under operating conditions. Fluid velocity and high temperatures and pressures compound the corrosion problems. In this paper an attempt is made to review the materials commonly utilized in the fertilizer plants and the role of inhibitors in mitigating various corrosion problems encounter~ based on the chemicals commonly handled and the products generated and distributed. Corrosion inhibitors for liquid ammonium nitrate-urea fertilizer are described in detail.
As in many other industries, corrosion inhibitors (CIS) are also used in the fertilizer industry to protect equipment and structures from corrosion. The problem of protecting the equipment used in storing and dispersing the fertilizers also impacts the ultimate customer. The strategy adopted in ensuring durability and safety of installations and equipment involves a judicious compromise between the selection of fully corrosion resistant materials and the utilization of relatively less corrosion resistant materials with adequate protective measures. The latter generally involve cathodic protection, protective coatings and inhibitor systems. CIS may sometimes be ignored by the plant personnel due to the unfamiliarity with the chemicals, or processes involved. Only in cases where the inhibitor application is the only viable corrosion protection method, is the prescription followed earnestly.
During fertilizer production, virtually all kinds of corrosion problems are encountered14, under the prevalent conditions of elevated temperatures and pressures, the presence of very corrosive chemicals and the by-products handled, high fluid velocities, and abrasion, erosion, etc. Though all the corrosion problems cannot be solved using inhibitors alone, many of the CIS used in other industries can be used in the fertilizer industry as welL5. To combat stress corrosion, erosion corrosion, cavitation, etc. industrial problems by applying inhibitors alone is difficult, and practical experience needs to be relied upon heavily. For normal corrosive situations, recommendations for the optimum choice of materials for handling different products, with or without additional corrosion protection measures, are available in the literature,&9 along with the specifications for optimum inhibitor systems. Since the raw materials utilized and the products generated and handled are known, the problem of selection of the inhibitor system may appear to be simple and straight-forward. However, in practice, the choice and application of the proper CI system is not that simple, for the working conditions are severe and varied. A brief summary of the raw chemicals and the fertilizer products handled and the materials of construction utilized 10>1?is presented first. A review of the CIS used at various stages of fertilizer production is presented further. Experiences reported on the effectiveness of different types of CI formulations in the fertilizer industry are discussed and an attempt is being made in this paper to identify the areas where the problems still persist and how further research and development might stimulate the development of new inhibitor systems for application in the field of fertilizer systems.
