Fire tube boiler pitting

[Cowtown]

Pitting is usually a sign of O2 content, is there any other factors I should consider?

 

[Ahmedv]

Hi
Please provide more details.
Is it the water side you are having problems with?
Chemical treatment, pressure, temp fuel type , Steaming rate etc

Regards

 

[TTT]

If the pitting is on the inside of the fire tubes, have u used a sulphur fuel? Where are pits?

 

[TBP]

Pitting on the water side is normally from oxygen. You can also suffer pitting from dissolved copper coming back with condensate. This can (not nearly always, but can) be the result of copper condensate piping, etc. The dissolved copper winds up back in the boiler, where it plates-out, creating a cell.

Something like copper condensate lines, in and of themselves, won't necessarily cause problems. You need another factor to be present, such as a serious carry-over problem from the boiler, etc.

 

[rustbuster]

Water side pitting may be as decribed prior, O2, Copper. It may also be due to improper lay-up during outages. If the pitting does not propogate during operation this is likely, if it does propogate it is likely due to water chemistry.

 

[countryham]

Oxygen pitting is usually caused from lack of a good operating deaerator and/or a chemical oxygen scavenger residual in the feedwater upon exiting the deaerator (chemical feed is always advisable in the deaerator storage section).Another thing that almost no one knows is that sulfites are more rapidly reacting than any other scavenger but in many (IF NOT MOST)CASES,CATALYZED SULFITES may not perform any better than those that are not!There are chemical kinetics involved in the sulfite-oxygen reaction that are never addresed by vendors.Your deaerator should be producing water with dissolved oxygen content (absent chemicals) no greater than 7ppb (parts per billion-not parts per million)....Industrial deaerators always have the potential for malfunction and under periods are known to produce exit waters with up to 100ppb........A boilerwater sulfite residual needs to be maintained always as high as possible to "catch" these excursions when they occur.The maximum residual is dependent upon pressure,i.e. the higher pressure ,the lower the residual.......Unless you are operating above 400psig you should be carrying around 25ppb sulfite.......Note that I said SULFITE NOT SODIUM SULFITE.....Generally the "wet" test is for sulfite concentration...NOT for sodium sulfite.There is only 63.5%sulfite in pure sodium sulfite......You generally buy sodium sulfite in the dry form which is generally about 95% active so you have to add ,by weight, about 35% more based upon water to be treated and tested as sulfite.....Bet no one ever told you about such things before...