API 650 Tank Settlement Allowances

[TarikY]

Do API 650 tanks have center-to-edge settlement allowances following erection/hydrotest?

In API 650 I have found the following:
1) 7.5.2 Plumbness: The maximum out-of-plumbness of the top of the shell relative to the bottom of the shell shall not exceed 1/200 of the total tank height.
2) 7.3.7.7 Hydrotest: If settlement measurements are specified by the Purchaser, any differential settlement greater than 1/2 in. per 32 ft of circumference or a uniform settlement over 52 in. shall be reported to the Purchaser for evaluation.
3) Annex O Underbottom connections: The recommendations of this Annex are intended for use only where significant foundation settlement is not expected. It is not possible to establish precise limits, but if predicted settlement exceeds 1/2 in., the recommendations should be subjected to detailed engineering review for possible additions, modifications, or elimination of bottom connections

 

[HTURKAK]

API 650 is silent for the allowable settlement at center of the tank. IMO , (based on experience ), the center settlement of the tank should not compromise the free flow at the bottom of the tank for the bottom slopes cone up to center and total settlement should be limited to 50 mm.



7.3.6.6 If settlement measurements are specified by the Purchaser, any differential settlement greater than 13 mm per 10 m
(1/2 in. per 32 ft) of circumference or a uniform settlement over 50 mm (2 in.) shall be reported to the Purchaser for evaluation.
Filling of the tank shall be stopped until cleared by the Purchaser.