7.5.5 Foundation

[MohammedSheikh]

7.5.5.2 Where foundations true to a horizontal plane are specified, tolerances shall be as follows:
a. Where a concrete ring wall is provided under the shell, the top of the ring wall shall be level within ±3 mm (1/8 in.) in any 9 m
(30 ft) of the circumference and within ±6 mm (1/4 in.) in the total circumference measured from the average elevation.

Hello everyone,
I am little confused about the explanation given by API 650 section 7.5.5.2 (above).
I took reading of the elevation for ring wall foundation of tank 22.5 Dia every 50 cm and i separated each 9 m .
could anyone please explain to me how to exactly calculate to get the differences between all points according to API.

 

[BAretired]

API is specifying a tolerance from true level. Ideally, all points around the circumference would be at the same elevation but in practice, this cannot happen. I would interpret API to mean that in any 9m length of arc, the deviation shall be no greater than 3mm from the average. In the entire circumference, the deviation shall be no greater than 6mm from the average or a maximum difference of 12mm from high point to low point.

BA

 

[JStephen]

I would have to check, but I don't think that "from the average elevation" used to be in there, and that changes it somewhat. From the wording quoted, it is not clear if both tolerances are from the average or just the second tolerance.