API650 Tank Tolerances

[magmath]

Dear Experts.

We are constructing a 28.4 mtr dia x 17.7mtr hight CS Fixed roof storage tank. Construction is done using Jacking method oe top to bottom construction.

I would like to seek your advise on the Roundness Tolerance. As per API 650 for the size of this tank roundness tolerance is +/- 19mm. As the roundness is measured 300mm from the tank floor on the first strake, we are just checking the radius of each course at 10deg intervals.

My question is if radius of each courses checked outside the tolerance limit the is it still acceptable? as API 650 does not give any roundness tolerance for individual courses?

Thanks in advance

 

[JStephen]

The roundness is only checked at the 300mm level as you note. Roundness of shell above that point is actually checked with the plumbness measurements.

 

[magmath]

Thanks JStephen,

Referring the API650 on the plumbness, tolerance given in 1/200 of the total height. So if I am doing the top to bottom construction and to check the plumbness at any time during construction is it measured 1/200 of the height of the tank constructed? or is it something else? (Also API 650 indicates plumbness of individual course is limited to flatness and waviness of plate as per ASTM A6M/..... and checking that for 8mm thick x 2400mm wide plate it is around 35mm, but if I go with 1/200 x 2400 which is only 12mm....so I am confused which is right way)

 

[JStephen]

It's 1/200 of the final shell height for overall plumbness.

 

[ll23]

I don't see any problem to measure the roundness in each course, as matter of fact its convenient matter for construction, the tolerance for plumbness in a individual plate course is in ASTM 6m, and check the peaking and banding before you raise each course.