Boiler Tube Wastage Rates

[MechEng1995]

I am conducting a study of one of our power utility boilers (3,195,000lbs, 1005F, 2590psi) in order to determine the remaining life of the major components. My references for the study are past boiler inspection reports and life assessments. I have developed a tool to perform all of the basic boiler life calculations, however, it depends on knowing tube wastage and scale growth rates.

My problem:

On our much older boilers, there is ample tube wall thickness data where I can determine linear wastage rates from multiple years of tube wall UT Thickness and scale data at consistent tube locations. On this boiler, the thickenss and scale data is limited to one set of measurements per section (ex. I only have Water Wall tube thicknesses from a single year). I need more than one data point to determine a linear wastage rate for a specific section. Does anyone know of a usable method to determine tube wall wastage rate when you only have one wall thickness measurement? Note: The new tube wall thickness is not known. The only known is the specified minimum wall thickness.

Thanks,

MechEng1995

 

[metengr]

No. From my experience, I deal with a fleet of coal-fired boilers (subcritical, supercritical) supplied CE, B&W and FW and none of these animals are alike in terms of waterwall and steam circuit tube wastage rates. You need to obtain field inspection data for each boiler because of the complex variables related to the type of coal being burned, operation of the boiler and soot blowing cycles.

 

[rmw]

Metengr makes a good point. Building on that, is there any similarity in the boiler in question and the older boilers?

Do you have any other boilers in your system that are of a similar type and style as the boiler in question, and burning the same fuel?

That might give you a place to start or an approach to take.

I'm with Metengr when it comes to trying to compare different types and styles. But, now to discouage you, I've seen differeng wastage rates within the same boiler.

Not an easy thing you are trying to do.

rmw

 

[MechEng1995]

This boiler is the largest (3X the next largest)and only oil fired unit of the fleet. I have no similar boilers to compare it to. Obviously this adds to the challenge since oil ash is going to erode the tubes at a different rate than coal ash.

The intent of my original post was an attempt to find a way to determine remaining life when the as- built "original" wall dimension is not known.

A model was proposed in 1993 by Ellis and Tordonato, "Probabilistic Assessment For Waterwall Tubing," Service Experience and Life Management: Nuclear, Fossil, and Petrochemical Plants, ASME, 1993. This model apparantly utilizes the eccentric tube geometry and standard deviation to define the original tube thickness based on the specified minimum wall thickness.

Is anyone familiar with this method?

Thanks.

 

[rmw]

I would like to add another wrinkle to the discussion. Does this boiler have low NOx burners? If so, this can seriously throw off (as in accelerate) the predicted wastage rates, especially in the vicinity of the burners themselves.

rmw