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Posted by den on January 12, 2012 at 21:21:07:
we have 2 CB 800 fire tube boilers that have generated massive hot spots on the front 4to 6 ribs of the morrison tubes(next to the fire brick). this happened in the # one boiler first and while it was down the # 2 boiler developed them.The factory claims it is due to flame impingement the hot spots are on the bottom center line of the morrison tube with the closest rib to the brick ring suffering the most damage and the hot spots get smaller as you go down the tube away from the burner end. the metal has flaked off parts of these spots as much as 0.030 in. I am worried as to the decision of putting another row of brick down and putting them back in service. a test was down to the metal that indicated a deterioration in the tensil strenght of the hot spots, but we were told that the boiler is not under tensil stress but rather compressive stress , therefore there should be no issue with the the concerned hot spots. The solution is to install an additional row of brick and tighten up the flame so it will not impinge on the tube. Is it possible that film boiling could be the cause? The only thing that has change with our system is the water quality is poor. Chemically it is ok but we have alot of iron in the boiler water this year and the apperance of the water could be mistaken for a strong glass of ice tea(without the ice). We have always struggled with fluctuating water levels but this year it has been severe in nature(as much as 4in). If you have seen something like this I will appreciate any and all feed back.