Tower Axial Alignment of Shell Courses 3

[MikeL3]

Is there any specific reference or language in Sect.VIII Div.1 that addresses the axial (longitudinal) alignment of shell courses (cans)?

We have a small vertical tower (60'L X 12' diameter) that appears to have a minimal dip or sway midspan of the vessel that just arrived on site, and I could not find any specific language in the code that address this issue.

This is a fabrication question at this point and not a wind load issue because the vessel has not been set.

Any input would be appreciated.

 

[gr2vessels]

Mike,
Look for ASME Y14.5 Geometric Dimensioning and Tolerancing.
cheers,
gr2vessels

 

[vesselfab]

i am not sure that ASME Y14.5 really applies, as it is a guideline for dimensioning and I think it is for APPLYING tolerances.

I am at home currently and no code book here, but I do not remember the ASME code addressing this directly.

Our shop standard is 1/16" off in 10 feet with a max of 1/2" in 100 feet. This is about half of what most users require which is 1/8" in 10 feet or max of 1" in 100 feet

look in your written specifications sent to your fabricator and see if there was not a tolerance sheet sent.

also look at your inspector's reports. There should be a "final dimensional report" or something of that nature in there.

finally, if no tolerances were specified and/or your inspector did not check the tower, you may have problems. This is hard to fix after the fact.

Do you need help in determining the amount of "dip" or "banana" you may have in the vessel?

 

[CodeRef]

Read the following National Board Classic Series article regarding dimensional inspections.

http://www.nationalboard.org/nationalboard/articles/classics/classic54.aspx

In short, and taken from this article,.......... Dimensional requirements are translated from code and design calculations to fabrication drawings. Therefore the drawing requirements become code requirements. The ability of the completed component to safely operate during its required design condition is directly dependent upon conformance with the dimensional requirements and tolerances given in the construction code and those based upon the design calculation.

You had better call out the tolerance in the fabrication drawing, otherwise it may be assumed to not have any tolerance at all and subject to the AI's acceptance or rejection.



There are three kinds of people in this world; those who can Google and those who can't.

 

[MikeL3]

Thanks everyone for the very informative responses.

 

[jte]

Mike-

You state that the vessel "just arrived on site", and "...has not been set." Out of curiosity, are you measuring the "dip" with the vessel in the horizontal position, and if so, how does the measured dip compare with the calculated mid-span deflection? For the calc, since the "beam" is relatively short and fat (L/D = 5), consider that most beam equations will only consider deflection due to bending but you'll have a bit more since shear may also be significant for a "beam" of these dimensions.

jt