Boiler Water Temperature

[aida2011]

Hi

My watertube boiler is working at 20 bar, so the saturated temperature is 215 deg. C.

One boiler designer recently talked to me about the importance of keeping the metal tube temperature (low C steel) below 400 deg.C to prevent creep. What confused me was when he further said the tube metal temperature is always almost the same with the saturated temperature.

Following this logic, in no circumstances that the tube temperature can exceed 400 deg.C because it works only at 215 deg.C and it takes a 219 bar boiler (almost super-critical) to obtain at least 373 deg. C, which is still below 400 deg.C.

Is there any instance in the boiler that the metal temperature can approach 400 deg.C?

Thanks.

Miss Ida

 

[metengr]

Yes, if scale deposits on the tube ID surface which can be common for watertube boilers with little or no feedwater treatment. The scale acts as an insulator increasing the tube metal temperature.

 

[EdStainless]

And there is some temp gradient in the tube wall.
But fouling is the biggest issue by far.
I have seen boiler tubes with multiple layers of scale on the ID from swings in water treatment.
Then it is a race to see which happens first, the inability to make steam or the failure of tubes.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[chicopee]

Scale is not the only condition that will increase tube temperature, fuel oil that leaks back into water space and coats the water side sufaces will have the same effect. I have seen that.