Gas-Fired Boiler Tube Thickness Surveys

[Sharik]

Does anyone know of any good, important reasons to complete tube thickness surveys in gas-fired watertube power boilers? I can understand the need in coal, oil, black liquor, etc. fired boilers but I don't see the need in gas-fired boilers. These new 150 MW, 2,000 psig, 1100F boilers are fed with very controlled and tested demineralized, deaerated boiler feedwater so where would the tube metal losses occur, internally and/or externally? I am inclined to have baseline thickness and tube OD measurements completed and then trended on the superheater and reheater tubes only and not on the waterwall or generating tubes. Unlike our coal fired boilers where we have thickness surveys completed and trended throughout the boilers.

For these gas-fired boilers in the future, regular scheduled internal and external inspections and pressure tests will be completed and we'll probably do some random UT on the waterwalls, as well as cutting out tube pup pieces for gram loading and analysis.

So would complete waterwall and generating section thickness surveys be recommended?

Thanks

 

[davefitz]

You would not have the external erosion/corrosion issues associated with firing the other fuels, so no loss in OD material is expected. However, water side problems do not dicriminate based on fuel fired, so the normal removal of tube samples during major maintenance overhauls to determine if a waterside issue is developing is still required.

 

[rmw]

Do the boilers have low NOX burners? If so, there can be problems in areas adjacent to burners near the walls.

rmw

 

[eyec]

lo nox burners usually create a reduced atmosphere in the lower elevations of the boiler closer to the upbend of the lower slope so this area needs investigation