Annular bottom plate thickness per API 650
Annular bottom plate thickness per API 650
(OP)
hello,
while calculating the thickness of annular bottom plates, i needed to determine the stress in first shell course which can be calculated using the formula in table 5.1a (5.1b).
the formula in table 5.1a (5.1b) states two thicknesses in both product and hydrostatic test stress
Question:
i can't figure out the which thickness to use, apparently there are both the same, which does not make sense
thank you in advance for your help
while calculating the thickness of annular bottom plates, i needed to determine the stress in first shell course which can be calculated using the formula in table 5.1a (5.1b).
the formula in table 5.1a (5.1b) states two thicknesses in both product and hydrostatic test stress
Question:
i can't figure out the which thickness to use, apparently there are both the same, which does not make sense
thank you in advance for your help





RE: Annular bottom plate thickness per API 650
RE: Annular bottom plate thickness per API 650
RE: Annular bottom plate thickness per API 650
i did read the note B in table 5.1, it didn't clear anything up:
for example:
product stress= (td - CA/corroded t)*(Sd)
i can't determine the difference between : (td-CA) and (corroded t), aren't they the same thing ? if not could you please explain!!
thank you
RE: Annular bottom plate thickness per API 650
RE: Annular bottom plate thickness per API 650
whatever was my question, you are always there !! i can't thank you enough,
i really apreciate your help !!
thank you
RE: Annular bottom plate thickness per API 650
We can say that td-CA corresponds mathematically to Sd stress.
t_ordered is the thickness ordered for plate; in my example it could be 20 mm.
t_ordered-CA= t_corroded corresponds to the "Product Stress" in your tank, in the end of the tank life.
By mathematical structure of the hoop stress ("Stress" is proportional with inverse of "t") it follows that
Product Stress= [(td-CA)/(t_ordered-CA)]*Sd= [(td-CA)/t_corroded]*Sd
RE: Annular bottom plate thickness per API 650
i.e. product stress = [(calculated design thickness 'td' - C.A) / (ordered plate thickness - C.A)] x Sd
Also take note with regards to the placement of the brackets in the formula between the 11th Edition and the latest API 650 12th edition...
11th Edition shows...............Product Stress = (td-CA/corroded t)(Sd)
12th Edition has corrected this to.........Product Stress = ((td-CA)/corroded t)(Sd)