Flatness 1

[Tzzadik]

Hi
How do you guys meassure flatness on the walls of an API 650 tank? ASTM A6/6M?

 

[Bonswa]

if you're talking about plumbness, normally we use a plumb-bob. Just drip a line over the edge of the roof and measure the distance from the shell to the line at a preferred interval. usually we measure the top, middle, and bottom of each course. if we cant use a manlift in the area, the we've just measured the bottom for an overall.

if it's just a local area, then follow this from 650:

7.5.4 Local Deviations
Local deviations from the theoretical shape (for example, weld discontinuities and flat spots) shall be limited as follows:
a. Deviations (peaking) at vertical weld joints shall not exceed 13 mm (1/2 in.). Peaking at vertical weld joints shall be determined using a horizontal sweep board 900 mm (36 in.) long. The sweep board shall be made to the nominal radius of the tank.
b. Deviations (banding) at horizontal weld joints shall not exceed 13 mm (1/2 in.). Banding at horizontal weld joints shall be determined using a straight edge vertical sweep board 900 mm (36 in.) long.
c. Flat spots measured in the vertical plane shall not exceed the appropriate plate flatness and waviness requirements given in 7.5.2.

 

[Tzzadik]

We are also through the same matter, and if we measure in the morning the flatness of the shell is ok, but in the afternoon it doesn´t, the code does not say what time is recomended to do this, what would it be?

 

[IFRs]

I have used a plumb bob to measure lots of tanks from top to bottom by hand,inside and out. It's easy and simple. The code does not recognize time of day for measurements. I'd measure the tank at the worst time. Is the difference from solar heating? Perhaps the tank should be painted a light color? If the tank will be mostly full of liquid, will that moderate the temperature? Unless the tank has a floating roof, the deformations may have no real impact.

 

[Tzzadik]

Thanks IFRs, I just convinced the contractor by looking at your thread that it´s the supervisor the one who decides the time to make the meassures. This tank has no floating roof but the look is not satisfactory.