How to use API 650 ANNEX M.4.2 formulation

[inammanj123]

Dear All,
M.4.2 says that if all criterias of either condition a or b are met, cyclic design life evaluation need not to be made. Condition b, says that 0.3(Dt)^0.5 is normally maintained in tank. My question is this that the value which comes out from this formula needs to be compared with which liquid level: "high liquid level" or "low liquid level" or "low low liquid level"?

Regards
Inam

 

[JStephen]

It is to be the minimum level maintained in the tank, and may or may not coincide with any of the control set points.

 

[inammanj123]

O.K let say if both these criteria are not met, than we have to go to calculate Check for equality of "S", Calculate "S", and than calculate "K". My question is what is the purpose of calculation "S" & "K". Like how will they can control my annular plate or first shell course thickness. I think that the purpose of this calucation os to make sure than "K" remain below 1300. So it means that we play with the annulat plate thickness so that "K" comes out to be less than 1300. Is my point true or not?

Regards,
Inam

 

[JStephen]

You're calculating estimated number of cycles to failure based on the construction. If that estimate comes out more than 1,300, it is not considered a concern.

 

[inammanj123]

ok but if it comes out to be less than 1300, than we will to increase annular thickness or first shell course, so the the value of "K" comes to be less than 1300?

 

[JStephen]

"K" is the stress concentration factor, and is either 2 or 4.
"N" is the estimated number of cycles. If the tank is not operated under exemption (a) or (b), then the bottom/annular plate/shell need to be adjusted so that N calculates to be greater than 1300.

 

[inammanj123]

OK Thx got it