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Monitor pH value within boiler to avoid system corrosion

Tools that allow you to detect any pH changes and modify ammonia and sodium hydroxide dosages

The steam which goes to the turbines has to be pure water. It is normal practice to keep the pH value of feed water at alkaline levels as it helps to minimize the corrosion of the pipe work and other equipment, thus preventing unscheduled downtime.

Keeping the pH value of feed-water at slight alkaline levels

pH value monitoring to avoid system corrosion in steam circuit ©Endress+Hauser

The pH value is an important parameter to monitor in order to avoid equipment corrosion. The value varies depending on the location in the water/ steam circuit: high pressure heaters, make-up water, Condensate Extraction Pump Discharge.

There are two modes for pH conditioning depending on the existing materials in your plant: universal mode and alkaline mode. Nevertheless, it is common practice to keep the pH value of feed-water at slight alkaline levels to prevent corrosion.

How to control the pH value: universal mode

  • Two different pH ranges depending on the existing materials in your plant

  • Conditioning with ammonia hydroxide

  • This mode is used for plants with copper and steel piping ammonia hydroxide to control pH values between 8 and 9 to protect copper materials

  • The lowest corrosion rate for copper is pH <8.8

  • Corrosion rate is between 3 and 7µg/l total Fe.

  • Online measurement of ammonia is necessary

How to control the pH value: alkaline mode

  • Conditioning with sodium hydroxide and sodium phosphate as buffers to stabilize the pH value

  • This mode is used only for stainless steel materials (No copper materials in the plant)

  • To control pH values between 9-10

  • The lowest corrosion rate for stainless steel is for pH >9.1

  • Corrosion rate is between 2 and 5µg/l total Fe.

  • The cation conductivity must be less than 0.15 µS/cm

  • Online measurement of sodium, phosphate, conductivity and cation conductivity is necessary

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Endress+Hauser (Ireland) Ltd.
Embassy Office Park Exchequer House Kill County Kildare , Ireland
Tel.: +353 (45) 98 92 00
Fax: +353 (45) 86 81 82
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References

  • Hitachi Power Europe GmbH (HPE), a subsidiary of Hitachi, Ltd., designs and constructs fossil-fired power plants. The plant constructor also supplies key components such as utility steam generators, environmental engineering equipment, turbines and pulverizers. Including subsidiaries, approx. 2000 staff is on the company's payroll (as of May 2013).

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