The cleaning of HVAC and industrial cooling systems is a complex process that requires careful planning. The presence of large quantities of deposits in pipes and equipment, or the appearance of leaks, is usually the driving force for considering a cleaning program. However, the choice between cleaning and pipe replacement, the further choice between online and off-line cleaning, and the selection of the specific cleaning program to be used, all depend upon detailed knowledge of the systems involved. Some of the factors that must be considered include: deposit composition; the condition of the pipes to be cleaned; and the design of the system, including circulation patterns, flow rates, metallurgy, etc. Also important are the possibilities for removing suspended solids from the circulating water and for isolating equipment to be cleaned; the water treatment history of the system; and system operational requirements. These can include, for example, a need to maintain continuous system operations while cleaning, or to provide specific windows of time during which the system can be off-line. Other factors specific to individual systems can also be critically important. Methods for evaluating the progress of the cleaning process and for determining when cleaning is complete must also be carefully planned. This paper examines several detailed case histories of on-line and off-line cleaning of condenser water systems. The amount of advance preparation, the selection of the cleaning method, the specific chemical program, and the degree of performance monitoring are all shown to critically affect the success of the program.
INTRODUCTION
Water piping systems in commercial buildings and industrial plants often become fouled with deposits that can seriously compromise performance. Mineral scales, such as calcium carbonate and calcium phosphate, metal oxide corrosion products, microbiological slimes and general system dirt can all reduce water flow in pipes and interfere with heat transfer in condensers and other heat exchangers.
Water treatment programs are intended to prevent these deposits from accumulating. However, for many reasons involving improper program selection and application, poor control of water chemistry and operational factors, deposits may accumulate to the point that an open or closed water system can no longer function properly. Also, localized under-deposit corrosion (pitting) may lead to through-wall failures that can make an entire piping system unusable.
This paper considers the problems involved in removing deposits from piping systems in order to restore performance and protect the systems From further corrosion damage. NACE International Recommended Practice RPOI 82-85, states in Paragraph 5.1.1, that: Corrosion inhibitors require clean metal surfaces for proper film formation and metal protection.
The intent of this statement is clear: metal surfaces must be clean to allow corrosion protection programs to operate properly. Ideally, then, cleaning a piping system implies returning the internal pipe surfaces to new metal condition. However, this may not always be practical. Loose bulky deposits that interfere with flow and provide sites for under-deposit corrosion must always be removed. Depending upon the cleaning method, the cleaning chemicals and the time available for cleaning, some thin hard adherent oxides or organic deposits may remain in place after the cleaning process has been completed. Deposits that do not interfere with water flow and heat transfer, and that provide corrosion protection rather than sites for future under-deposit corrosion, can usually be allowed to remain in the system. Therefore, the pr
Case histories of on-line and off-line cleaning of HVAC piping systems (Conference) | OSTI.GOV
Case Histories of On-Lone and Off-Line Cleaning of HVAC Piping Systems | NACE CORROSION | OnePetro