During commissioning of Industrial Cooling Water Systems, when make-up water is first circulated through equipments, the initial damage which occurs on metallic heat transfer surface is corrosion or flash corrosion. The flash corrosion must be controlled to prevent uneven growth of corrosion products else these will promote, in chains, layers of uneven corrosion product deposit, scale, foulants and microbiological foulants leading to choking and under deposit corrosion. The corrosion or flash corrosion in open recirculating cooling systems is prevented by a rigid, impervious and protective film. The concept of film formation versus film maintenance prevails since long in the field of Cooling Water Treatment Programme. Film formation (Pretreatment) is achieved by high level of chemical inhibitors/additives and film maintenance by low level of inhibitors (Regular Treatment). Based on experimental and field data new phosphate based Pretreatment and Regular Treatment have been developed and applied successfully to several Industrial Cooling Water Systems. The paper describes the Pretreatment and Regular Treatment process and field experience on their performance.
Phosphate based cooling system inhibitors are still popular for treating industrial cooling waters. Combination of phosphates along with polymers and zinc provide acceptable protection and still considered environmentally acceptable inhibitor systems. The Mechanism of Corrosion Inhibition by Phosphate based Cooling System Corrosion Inhibitors, was published1 by the author in "CORROSION (NACE) April 1986"1. 'Studies on the Corrosion and Scale Inhibiting capability of Phosphate based Inhibitors' was presented by author in "Corrosion-89, New Orleans".2 Thereafter, similar studies have been carried out in Israel, (published in August 1999)3 and in Greece (published in January 2006)4. In the author's study there were two important observations; that Hydroxyethylidine Diphosponic acid (HEDP) is the most effective scale inhibitor and iron sequestrant and Sodium Hexametaphosphate (SHMP) is an effective industrially viable corrosion inhibitor. Based on the experimental data in combination with field experience, two new cooling water treatment schemes were developed: I) On-stream cleaning cum passivation (Pretreatment) of cooling system equipments with high concentration of HEDP + an 'Ethylene Oxide based non-ionic surfactant' and moderate concentration of SHMP & ii) A Regular Cooling Water Treatment Programme with low concentration of HEDP, SHMP and Zinc, with or without polymer.
Both the schemes were implemented in a number of refinery and 'gas processing unit' cooling systems. Field performance of both the schemes were satisfactory when implemented properly,however, in a number of cases extended standardization was required. The paper describes the technical specifications of the two schemes developed and glimpse of their field performance.
The Pre-treatment: The new process was developed using laboratory, field and published data. Essentially the application of Pretreatment increases the life expectancy of cooling system equipments through chemical conditioning practice prior to cooling water exposure. The Pretreatment applies to all metals but primarily directed toward low carbon steel equipment. The initial conditioning may be applied to an entire cooling water system or individual exchanger unit. The new pretreatment process developed was for the entire cooling water system or individual exchangers by connecting in close loop circuit.