KN Series: Tear-down Report
Despite the fact that KN-Series boilers produce efficiencies upward of 99%, many still believe that condensing cast iron is a bit of an oxymoron. To finally put the naysayers to rest, the KN-Series team went straight to the source to investigate the true effects of cast iron in condensing boiler applications.
Two different KN-20 boilers in full operation were removed from their job sites solely to examine their heat exchangers and to verify their thermal efficiency. Boiler 1 (Serial #: KN-HL-07-1059) and Boiler 2 (Serial #: KN-HL-07-1068) were installed in extremely harsh operating conditions with low operating temperatures and non-stop condensing performance. While these types of applications exist globally, they are not the norm and are the ultimate test for any condensing boiler.
Observations & Findings
Prior to disassembly, both Boiler 1 and Boiler 2 were hydrostatically tested for leaks, with no leaks found.
An internal view of the heat exchanger’s bottom pan showed an even distribution of iron oxide, with no indication of corrosion beyond the surface level. Consistent loss of metal across the entire exchanger stems from even gas and water distribution across the entire unit and is an expected result.
Boiler 1 and 2 were then disassembled, and four sections from each unit were sandblasted for a clearer look at the cast iron surface.
All sections showed nearly identical levels of wear, which proved inconsequential. When compared side-by-side with a new heat exchanger, it was hard to see any significant differences in the surface between the new and returned sections.
Areas that were expected to have the highest levels of wear were cut down even further for a more detailed examination of the metal.
The areas exhibiting the most corrosion were then milled until the surface was free from pits and revealed clean cast iron. Together, the weight of the removed castings and the extent of surface pitting indicated a 1 – 2% loss of cast iron throughout Boiler 1 and 2’s life cycles.
Based on the amount of material lost and overall condition of the heat exchangers in our comparison, it can be concluded that both sample boilers could run an additional 38,000 – 44,000 hours in full condensing mode, before reaching the ASME minimal wall thickness standards for performance.
In addition, certified efficiency decreased less than 1% from the original 92.7% using the standard BTS-2000 testing protocol. More importantly, there was a less than .3% thermal efficiency performance change at part load firing rates using a 30° ΔT, which is indicative of today’s modern boiler application parameters.
The calculated remaining lifecycle is estimated at an additional 19 - 22 years when used in the same full-condensing operating condition.
With these numbers in mind, its easy to see that cast iron is an ideal material for condensing boiler applications.
It’s durable. It’s efficient. It’s made to last the long haul.
Colorado and Wyoming Engineers, Contractors, and Wholesalers:
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