Minimum Thickness with changing radius

[daily123214]

I feel a bit silly asking this question:

how come for Tmin calculations, the radius or diameter isn't usually changed even when there is metal loss?

I worked at some companies where the design radius/diameter was used but that does change a little over time due to metal loss.

 

[SPDL310]

There are too many API standards to know which one you are talking about, but most of the valve codes do not prescribe a required wall calculation method. A corrosion allowance is normally applied to the calculations that I perform. For standards where a wall thickness calculation is given possibly for large storage tanks the change in diameter by even a 50% loss of thickness is a less than 1% change in diameter. Ie. a 48' Diameter tank with a .5" plate thickness losses a .25" wall thickness the change in diameter is a 0.17% increase in radius. The small corrosion losses are accounted for by plate tolerance and specification above minimum thickness.

 

[daily123214]

Sorry I was looking at API 510.

Based on what you just said it sounds like it doesn't make a difference since it's so small.