steam boiler water jacket crack.

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Old 11-23-08, 07:49 AM
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steam boiler water jacket crack.

my slant/fin jacket cracked pretty good. it does not have a hot water coil. I can actually see the crack from inside the water jacket where the hot water coil would go which means I can access it. I simply can't replace it right now and I only need to get a few more weeks out of it. my question is what are the temperatures on the inside of the water jacket filled with water as opposed to the outside where the burner is? is it possible to temporarily repair this crack with a high temp epoxy from the inside or should I just go ahead and weld it?
 
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Old 11-23-08, 09:21 AM
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The temperature of the metal in a clean boiler is almost equal on both the fire side and the water side.

If at all possible drill a small hole through the metal just beyond the crack on both ends, this will stop the crack from progressing. If you are really good at welding and you use a high nickel content electrode you might be able to weld the crack. You might also try something like JB Weld.
 
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Old 11-23-08, 12:51 PM
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I have been looking at different types of high temp epoxies like JB weld but I'm not sure how hot the metal gets. I did pick up some cast iron specific brazing rods. was just hoping to not put so much work (such as welding or brazing) into a temporary situation.
 
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Old 11-23-08, 01:05 PM
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The temperature of the metal will be nearly the same as the water temperature.

I doubt that you would be able to braze or torch weld the cast iron. Arc welding using AC and nickel rods is much more likely to work because in torch welding you cannot concentrate the heat as well and this leads to uneven heating and even more cracking. Ideally you should use DC welding with stainless steel electrodes but even that takes a great deal of skill. This is one reason that I do not like cast iron boilers, they are difficult to repair if they crack and they will crack much more easily than a steel boiler. If you do try to weld it weld only about a one inch bead and then using a ball-peen or cross-peen hammer, peen the weld metal immediately after welding to help relieve stresses. After the metal is cool enough to hold your hand on it go to the other end of the crack and do the same. Alternate on both ends welding towards the middle. Be sure to completely clean all slag from the weld metal before moving on to the next weld.

I think the JB Weld is your best bet. I still would drill the ends of the crack before using the JB Weld.

Good luck.
 
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Old 11-23-08, 02:38 PM
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The fireside of the heat exchanger will see temperatures well above the water temp. Whatever the flue gasses touch will be above water temp. The water side will see water temp and if any gets inside the crack it will see water temp. I have never tried JB Weld but it may be worth a try but I have my doubt's.
 
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Old 11-24-08, 09:27 PM
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Yes, the metal on the fireside will "see" the higher temperature of combustion but the metal itself will be nearly the same temperature as the water unless (a) the metal is covered with soot on the fireside, or (b) the metal is covered with scale on the water side.
 
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