NACE SP0189

Abstract

<strong>General</strong> <br>The purpose of this standard is to describe technologies applicable to the online monitoring of cooling water systems. The standard focuses on those technologies that provide data on a short-term basis (minutes to hours) and provide output in a form that may be used by the operator to deal with changing conditions in real time. <br>For the purpose of this standard, an online monitor for a cooling water system is defined as a device, or combination of devices, that measures corrosion rates and determines changes in heat transfer coefficients (fouling factors) by measuring pertinent parameters under steady-state conditions that simulate critical conditions in an operating heat exchanger in a reliable and objective manner and with acceptable precision and accuracy. <br>References to Existing Publications <br>ASTM(1) G 961 covers two techniques for monitoring the corrosion rates of metals&#8212;(1) electrical resistance method, and (2) linear polarization resistance (LPR) method. Of the two, the LPR method, which determines instantaneous corrosion rates, has found considerable acceptance compared with other methods for monitoring corrosion rates of metals exposed to cooling waters. <br>NACE Publication 3T199² covers techniques for both direct and indirect monitoring of corrosion and related parameters in field applications. <br>EPRI(2) Report TR-112024³ covers online monitoring techniques used by utility end users. <br>This standard covers simulation of plant heat exchangers with cooling water on the tube side where the monitor incorporates (1) a test surface heated by high-purity steam or an electrical resistance heater of constant heat flux, or (2) pressure-drop methodology, generally unheated to evaluate microbiological growth. However, other heating media such as hot water or a heat transfer fluid have been used as the heat source. When numerical results are given for fouling, they represent only what occurred under a specific set of heat exchanger operating conditions and cooling water quality. Online monitors, such as those covered in this standard, are not designed to model operational problems such as localized hot spots, changing heat flux, localized low-velocity areas, hydraulic shocks, or mechanical cleaning that may occur in operating plant heat exchangers. As with most process modeling, online monitors cannot replicate the total process heat exchanger at one time. Thus, the user must choose the section of the heat exchanger (e.g., inlet, middle, outlet) to be modeled. <br>Appendix A (nonmandatory) includes heat transfer nomenclature and equations used in this standard.