Annular Bottom Plate API 650

[raisie]

Hi guys,

Quick question about tank bottom annular plates.
API 650 states (in section 5.5.1):
"When the bottom shell course is designed using the allowable stress for materials in Group IV, IVA, V, or VI, butt-welded annular bottom plates shall be used (see 5.1.5.6). When the bottom shell course is of a material in Group IV, IVA, V, or VI and the maximum product stress (see 5.6.2.1) for the first shell course is less than or equal to 160 MPa (23,200 lbf/in.2) or the maximum hydrostatic test stress (see 5.6.2.2) for the first shell course is less than or equal to 171 MPa (24,900 lbf/in.2), lap-welded bottom plates (see 5.1.5.4) may be used in lieu of butt-welded annular bottom plates."

The material I am considering is from Group I.. I have been searching for sections on materials from groups other than stated above but I haven't found anything.. I don't think I should assume that annular plates are NOT installed for tanks with a bottom shell course made from materials in groups other than IV, IVA, V or VI... Should I?
Does anyone have any advice/suggestions on this?
Thanks in advance!

 

[JStephen]

Annular rings are used for the material groups mentioned, for certain elevated-temperature tanks per Appendix M, for certain tanks in higher seismic zones per Appendix E. If there is not a specific requirement for an annular ring from one of these sections, it would not generally be used.