BOILERS CONDUCTIVITY CORROSION MONITORING POWER SAMPLING STEAM

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Abstract

Editor’s note: Welcome to a technical article from our library of more than 2,100 technical and water business articles published since 1984. This article by Otakar Jonas, PhD, and Joyce M. Mancini was published in the December 2006 issue of Ultrapure Water Journal. It looks at steam sampling practices.

Many utility and industrial steam plants do not have a properly designed and operated sampling system to monitor water and steam chemistry. As a result, operating decisions are based on bad data, which can have sampling errors as high as 1,000%. This article describes the principles that must be considered when designing a good water or steam sampling system.

Steam and water sampling in utility and industrial steam cycles is necessary to monitor:

• Cycle chemistry control.
• Sources of impurities (e.g., condenser tube leaks).
• Corrosion products, their transport, and deposition around the cycle.
• Impurities in the steam that could damage equipment (e.g., steam turbines).

Corrosion in boilers and steam turbines is among the most expensive causes of outages in utility and industrial power plants, and deposit and scale buildup causes a reduction of efficiency and megawatt (MW) capacity in many units. In water chemistry and corrosion control audits, sampling problems were found in approximately 70% of the plants. Many samples have a concentration of impurities in the low parts per billion range, and any deposition or chemical reactions in the sampling system or non-representative sample withdraw can lead to large sampling errors.  

Sampling and analysis of water and steam can be separated into three parts: extracting a representative sample, transporting the sample, and the analysis itself.  However, a meticulously performed analysis is of no value if a non-representative sample is used. This article will focus on properly obtaining and transporting the sample.     

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