|Best Practices: The Engineering Approach for Industrial Boilers - Page 4|
|Written by Natalie Blake|
|Tuesday, 08 June 2010 11:08|
Page 4 of 4
Iron and Copper Corrosion in a Condensate System
A plant on the West Coast was experiencing corrosion in their condensate system. The system is primarily mild steel, although there are copper containing portions. Due to plant operation, there are constant steam load swings resulting in pH swings in the condensate system. Both copper and mild steel corrosion were detected.
The operators adjusted the condensate treatment (neutralizing amine) to maintain acceptable pH to minimize corrosion, with the focus on mild steel.
Again, a mechanical survey was done of the condensate system, followed by looking at all the data. Steam load swings were correlated with pH swings and corrosion results. A chemical survey was also performed which looked at the particular neutralizing amine chosen, its application point, the average dosage, and the frequency of changes in dosage to maintain minimized mild steel corrosion (optimized pH). The historical copper and iron levels in the condensate were also analyzed.
The surveys indicated that no mechanical changes were needed, and that all testing procedures, equipment, calibrations, and frequency of testing were all acceptable.
When system operation was analyzed, it became apparent that the pH swings that were causing the problem would continue, and the system would continue to have sections that were at low pH (5.5-7). More neutralizing amine could not simply be added to increase the pH as this would unacceptably raise the pH elsewhere in the boiler system. This restriction needed to be taken into account in examination of the system. The chemical program chosen was not capable of properly protecting the system under the given conditions. As the operation could not change, changes to the chemical program were considered.
After careful examination of a variety of neutralizing amines (different blends, different neutralizing ability), a supplemental program was suggested. The original neutralizing amine was retained, and a new nonamine film former was chosen as a supplement in the low pH areas of the system. The product works in the pH range of 5-7, which will meet the system’s mild steel protection needs in the low pH regions, but will not raise pH in other areas of the system, protecting the copper areas.
Within twenty-four hours of implementing the chemical program, both iron and copper levels in the condensate dropped dramatically. In fact plant personnel commented on the Millipore pads, and how clean they looked through the first day—from almost black, to grey, to almost clean!
Again, through a careful examination of all potential factors, a solution was arrived at that met the needs of the plant, with good results. If the operational information had not been analyzed, it is possible that the chosen solution might have been just to feed more neutralizing amine, definitely the wrong long-term overall solution.
There are many opportunities to improve overall plant as well as boiler system performance, efficiency, and safety while reducing the total cost of operations. Boiler best practices and the Engineering Approach provide useful tools to achieve these goals, and make sure that no stone is left unturned in making the system reliable. By looking at mechanical, operational, and chemical aspects of the systems, all potential problems and opportunities for improvement can be identified, whether in performance, total cost of operation, profitability, or safety.
Incorporating all aspects of the system provides a comprehensive approach. Regardless of the source, problems can be solved/prevented without creating others in other parts of the system. In fact, often starting with a mechanical survey, followed by statistical analysis of operational data, will eliminate problems that may be masking issues with the chemical treatment. Costs associated with improvements (chemical, capital, operational) can then be determined/ justified, and agreement obtained from management to prioritize projects, and then track and complete them.
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