Annular Plate 1

[curlyjackme]

There is a discussion in the office here on the requirements of the annular when A516-70 material is used for the shell and bottom for a tank. In API 650 section 5.5 the code says that if the material is designed using the allowable stress for materials from groups IV, IVA, V, or VI, then a butt-welded annular shall be used. Then is states that materials from these groups is used and the maximum product stress for the first shell course is less than equal to 23,200 psi or the maximum hydrostatic test stress for the first shell course is lass than equal to 24,900 psi, a lap-welded bottom may be used in lieu of a butt-welded annular plates. If this is done with A516-70 plate then you are using the allowable stress for A36 to design the tank. Does this mean that regardless of the material used in groups IV, IVA, V, or VI that the allowable stress' can be lowered to omit the annular ring requirement? Is the intent of API 650?

 

[IFRs]

I read it to say that when the design stress in the shell is high then an annular plate is required. If the shell stress is low then you don't need butt welded annular plates. If you design using a lower stress but use high strength steel you still don't need butt welded annular plates because the design criteria is stress. You can use any design stress you want to, I guess, but I have never found it to be economically justified to design to a lower stress than the material can withstand.

 

[IFRs]

Also, it may be used in conjunction with 4.1.5

 

[curlyjackme]

Thanks!