The hydrocarbon and chemical processing industries operate a large number of low and medium
pressure industrial and waste heat recovery steam generators. They are typically in the 150 to
600 psig range, while some may be as high as 900 psig. For simplicity we will define medium
pressure as 600 to 900 psig and low pressure less than 600 psig. As the feedwater impurity
concentrations increase and cycled percent recovery of said impurities decrease in the boiler
water, the potential for tube metal overheating, resulting in reduced efficiency and eventual
metallurgical failure increases. Some failures can be catastrophic, while others result in very
costly forced outages. The former is related to increasing the total operating cost (TOC) of the
thermal process, while the later results in much higher lost opportunity costs. It is these two costs
that make up the total cost of ownership (TCO) associated with the forced outage failure. Most
low and medium pressure steam systems suffer from poor quality feedwaters that are associated
with:

❖ Chemical and physical corrosion within the condensate and feedwater system.
❖ Condensate process inleakage
❖ Poorly operated:
▪ Thermal-mechanical deaeration equipment
▪ Clarification and filtration equipment
▪ Ion exchange equipment

An assessment method to predict a time for a scheduled outage that would be used for chemical
cleaning of the generator based upon the actual operating feedwater quality is required to avoid
forced outage repairs. Should feedwater impurity concentrations be inconsistent and variable,
due to the nature of the upsets, then the assessment becomes somewhat difficult. Therefore, a
risk-based assessment that is applied to the poor feedwater quality that can be experienced over
the operating period of a steam generator would be useful. This paper will provide and discuss an
assessment method to predict when to schedule a chemical cleaning of steam generators to avoid
tube failures and forced outages.

KEY WORDS: Steam Generators, low pressure steam, medium pressure steam, cycled feedwater
impurity recovery, condensate process in-leakage, pre-treatment performance, make-up water
quality, types of failures, operating assessment, impurity limit setting, contingency plans, time to
clean methodology, American Society of Mechanical Engineers (ASME), American Boiler
Manufacturers’ Association (ABMA), Technical Association of the Pulp and Paper Industry
(TAPPI), deposit weight density (DWD), specific conductivity, cation conductivity, degassed
cation conductivity, oil, hydrocarbons, total organic carbon, non-volatile organic carbon,
hardness, iron, impurity and chemistry limit setting, Babcock and Wilcox (B&W), Combustion
Engineering (CE).