The Tank › Tank longevity
- February 23, 2008 at 3:29 pm #8248
Hello Randy and Larry,
Well, what an idiot I was for not knowing about anodes!, :(, so I can see that I should get a new tank with hex head anode + install a back up combo anode and curved dip tube,+flush regular. My question is–Is their any other factor that wears a tank out besides electrolysis and/or scale build up and is it possible to achieve a 50 year old tank simply with timely anode changes and muriatic cleansing for scale? Does an anode stop all corrosion,regardless?. For instance, I have seen vaque inferences that high heat itself will diminish tank life, but it is unclear if this because of heat stress on steel or some other factor. If you think this is true, then the implication is that a 30 gallon tank kept at the highest temp will die before a larger tank that can be kept at a lower temp(Because don’t need to mix in cold). Clearly higher temps increase electrolysis, rust, but this should not not matter, it seems, if one relaces anodes in time. Nor should cracks in the lining matter for the same reason. So what do you think, eternal tank?, and if not , why not.? And heh, what about this story that I can’t live forever? 😀
TonyFebruary 23, 2008 at 5:06 pm #8250
There are indeed other things that can wreck water heaters, but rusting is the most common one. It is possible for a tank to turn on and off so many times that the expansion-contraction of heating and cooling stresses the steel welds to the breaking point, but that is more likely on a commercial tank serving a lot of people and even then, I’ve seen commercial tanks that were 30 years old, so it’s just a possibility, not a certainty.
But a big, hidden danger is pressure and thermal expansion. You can test for that pretty easily with a pressure gauge. Pressure should never be more than 80 psi. I’ve seen thermal expansion make it spike to 150 psi. This was in an apartment complex where the water heaters seldom made it past the warranty period.
And then there is stray current, if a tank is not well-grounded.
Also, corrosive air, where chlorine and the like are stored and used near the water heater so that the combustion air is acidic.
But as I said, it’s usually rust.
Randy SchuylerFebruary 23, 2008 at 10:30 pm #8254
But I thought anodes prevented rust. Are you saying they do this only partially?
And what causes this thermal expansion and/or pressure that you mention. How can there be too much heat with a thermostat?February 23, 2008 at 10:52 pm #8255
Anodes do prevent rust, but most people don’t know they exist, so don’t change them and when the anode is gone, so is the water heater.
As for thermal expansion, time to read up a bit. Go to the entry Temperature/Pressure Relief Valves under Tanklets to find out about that one.
Randy SchuylerFebruary 24, 2008 at 5:31 pm #8257Larry WeingartenParticipant
Hello: I’ll add that rusting can happen from the inside out or the outside in. Anodes can stop the internal rusting, but corrosive flue gasses and external leaks… even rain coming down the flue pipe when the cap gets blown off, all can contribute to external rusting. The outside of the tank is bare steel and rusts easily. Tanks do not tolerate water on the outside well at all.
Sediment buildup prevents rapid heat transfer in gas heaters and makes the bottom of the tank overheat. This ruins the glass lining, exposing more bare steel to the water. Then the anode either cannot keep up or is worn out quickly and not replaced often enough.
So you see, there is more to it than simply checking the anode 😉
Yours, LarryFebruary 24, 2008 at 11:48 pm #8260
Sure do appreciate the replies. The main thing I have learned here(that I should have got before) is that the more exposed metal there is in a tank the faster an anode will wear. Thanks Larry. I guess then that if the lining never changed then the amount of bare metal in the tank would be constant and the intervals for changing anodes would stay the same. Hope I got this right! All rust could be prevented. So what it is that wears out the lining is the important mystery, I guess, and maybe some linings are more durable then others
Sorry, but I still don’t understand your reference to tpr valves and thermal expansion/pressure diminishing tank life, since the tpr valve is for the rare extremes of thermostat failure. Do you think a tank kept at 160 degrees would not last as long as one at 120 degrees? Or maybe you mean that the cycling of a tank from cold to hot wears it out. Would the lining wear out quicker or the metal stress in some way in either of these two situations?
Boy I’m really a fun guy aren’t I? In addition to needing a new electric tank, I’m long range thinking about one of those Rheem external heat exchanger tanks for solar and man, you don’t want to wear one of those suckers out!!
Regards and cheers,
TonyFebruary 25, 2008 at 3:14 am #8261
What I mean about thermal expansion is that if a tank meant to function at 80 psi or below is continually subjected to 150 psi spikes, eventually, that is going to trash it, and probably the piping, too. Indeed, at the place I mentioned, the piping was falling apart as well as the water heaters. That has nothing to do with the temperature the tank is set at. Did you actually read the section in Tanklets about this that I mentioned?
Randy SchuylerFebruary 25, 2008 at 4:39 pm #8266Larry WeingartenParticipant
Hello: Being a little water heater crazy, I’ve collected sediment samples for years. Tanks that were subjected to high pressure often had flakes of the blue glass lining in the sediment. This is bad :X Steel tanks will stretch a bit with pressure, but the glass doesn’t. So, pressure fluctuation will damage the glass in addition to damage caused by overheating under sediment. The high pressure could be from the street or from thermal expansion in a “closed” system. Closed, means the system has a pressure reducer, backflow preventer or check valve which prevents any backflow. Hope that clarifies a bit.
Yours, LarryMarch 3, 2008 at 11:03 pm #8382
I stand corrected. While I was certainly in to studying the issue completely, I apparently did not look under the troubleshooting tab, or I would have noticed the “tanklets” reference. Simply looked for a tanklets tab on home page, did not see it, and thought it must be an old term now replaced by “knowhow and solutions” Re read these looking futily for thermal expansion. Incredible I know. Too many late nights.:(
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