The Most Common Boiler Tube Failures

Probably because that's where most of the sludge collects, impeding heat transfer to the water, resulting in overheated pipes. Water treatment chemicals will do their job of precipitating the Mg and Ca salts, as phosphates, in a flocculated form, but still settle to the bottom.

Are you blowing down often enough to get rid of the sludge? It may seem to be a wasteful process, but the alternative (blown tubes and downtime) is a lot more costly.

Dear Friend,

The bottom zone air bubble formation will be more than at the top, and gets localised heating more , raising the skin temp or metal temp and prone to fail.

Pl. study the details, for HEAT TRANSFER during how air bubble is formed while boiling as given in the Book, NUCLEAR POWER ENGINEERING by Mr. ELWAKIL.

I have the book and I will try to to scan and post.

DHAYANANDHAN.S

Do you not mean steam bubbles, rather than air bubbles. If indeed air bubbles are forming, there is an entirely separate issue of water treatment to be dealt with here.

Once again, the OP does not provide sufficient information to really provide a coherent answer. If the boiler is a type that has a sludge (mud) drum (A config or D config), then unless the amount of sludge is way out of control, he should seek another answer. If there is no mud drum, then one should expect more corrosion in the bottom tube header(s), especially if blow-down is not continuous, and with initermittant bottom blow-down being applied. Another factor is the actual heat flow pattern in the boiler, or if this is a water tube boiler or a fire tube boiler, none was specified.

Without further information, we can state simply the bottom tubes fail because trolls live under the bridge, and gremlins seek their own level (at the bottom).