Replacement of Economiser 1

[cssmach]

We have been planning replacement of complete economizer banks in 500MW boiler of 25 years old. We planned sponge ball testing for thoroughness check of new coils before welding. Chemical flushing ( DM filling and ammonia dosing for up to 9.5 pH)of new banks after complete erection. Please discuss best methodology in this aspect.

 

[metengr]

As long as the replacement tube banks had been capped from the tube fabrication shop what you proposed seems acceptable. I would probably perform a borescope inspection on a random sampling of tubes after uncapping to ensure the ID surfaces are clean as well.

 

[cssmach]

Does steam blowing add any value

 

[metengr]

Only if, upon borescope inspection, you find trapped debris.

 

[cssmach]

What are the disadvantages, if we don't see in borescope and resort to steam blowing?

 

[EdStainless]

People often borescope so that they can examine the tie-in welds and internal surface condition.
It is good to know and record photos so that when you look again in 5 years you can see if it has changed.

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P.E. Metallurgy, Plymouth Tube

 

[Duwe6]

"What are the disadvantages, if we don't see in borescope and resort to steam blowing?"

None, other than the neighbors. Steam blow is LOUD if properly done. And you need to build and anchor the temporary discharge pipe. I prefer blowing, myself. Borescoping hundreds & hundreds of tubes is boring. If you get inattentive, or the snaky scope curls at the wrong moment, you could miss a nut or die-grinder bit. The steam misses nothing, assuming that the pressure & velocity are adequate.

 

[cssmach]

Thank you all for the discussion. Perfect cleaning is interesting but steam blowing with inadequate pressure and velocity can cause chemical corrosion due to the condensation and trapped debris if any. I feel sufficient airblowing and chemical flushing at 0.5pH will be better and effective.

The Coils are almost 12mt length and 10 bends/loops ( total length of 288mt each), which needs extra care in maintaining steam pressure and temperature. In addition the coils will be lifted for positioning and welding, where the debris generated from weld also react with the water entrapped.

Please discuss further.

 

[cssmach]

correction : each coil of 12mt length with 24bends ( total length of coil 288mt)

 

[cssmach]

correction 9.5pH

 

[Duwe6]

Inadequate compressed air volume & velocity is much more common & likely than inadequate steam.

 

[cssmach]

How to calculate steam source requirement?

 

[lilliput1]

Steam blowing of economizer tubes in service is recommended for oil fired or non-gas fuels. Feedwater piping to maintain follow is critical so feedwater in economizer does not boil. See attached.