BOILER OPERATIO PRESSURE

[hyl]

Hello members
I want some advice how to caculate the operation pressure of boiler .my task is that we have boiler design pressure is(257kg/cm^2)and operation pressure is (140kg/cm^2) after 25 year of operation we get areduction in thickness from 6mm to 4mm in the tubes .we have no time for retubing now but we want to reduce the operation pressure.According to the asme section one we use the thickness equation to caculate the pressure according to tensile stress at operation temperture .We get the result of (120kg/cm^2).
my question is that .
1-Isthat result is operation pressure if not how to calculate the operation pressure.
2-what is the relation between operation pressure and design pressure.
3-how to caculate the test pressure with the age of the boiler i mean after 5year 10 year 15 year and so on .
thank you very much and god bless .

 

[davefitz]

You will need to discuss it with your local nat'l board inspector, but I am aware of cases in the past where no reduction in op pressure was required if only tubes within the setting were eroded/corroded on only 1 side of the tube, up to a 50% wall reduction. This typically may happen in the burner zone.

tubes and piping outside of the setting are a different story- a recent set of failures related to caustic erosion corrosion of wet steam and feedwater piping at elbows and tees implies discovery of such wall thinning requires immediate repair.