intermediate wind girder API 650

[judge503]

to calculate if we need intermediate wind girder or not according to API650

5.9.7 Intermediate Wind Girders
5.9.7.1 to calculate the maximum height of the unstiffened shell

t = as ordered thickness, unless otherwise specified, of the top shell course (mm)

5.9.7.2 to calculate the height of the transformed shell

t= as ordered thickness

I think that we have to calculate according to corroded thickness as it is the worst case.

Please advise.

 

[fegenbush]

You are reading from the 2nd Addendum of the 11th edition (at the latest), since the wording was changed to "nominal thickness" in the 3rd Addendum. I see the fact that the committee did not change the calculation when they changed the wording as a confirmation of the method. In addition, Note 1 to 5.9.7.1 states that unless specified to calculate buckling in the corroded condition on the data report, the calculation is to be done in the nominal condition.

 

[judge503]

thank you for your reply

what do you mean by nominal thickness?

i noticed unless other thing specified , but i think that we have to calculate in the worst case .
as i have to revise a document from a contractor and he calculated using uncorroded thickness. by this way we don't have to use intermediate wind girder.

but if we used corroded thickness, we have to use intermediate wind girder.

 

[JStephen]

The default requirement is to use as-built or nominal thicknesses. The idea is that corrosion occurring is not a uniform metal loss over the entire surface. If the owner desires to base the calculation on corroded thickness, that is an option. It is an extra-cost requirement in many cases, and should be specified in the data sheets or other specifications furnished to the contractor.

 

[Duwe6]

"The idea is that corrosion occurring is not a uniform metal loss over the entire surface."

And it doesn't. Typically, the significant corrosion is confined to the vapor space; or the floor and first 1 to 2-feet of the shell. I have never seen, or even heard of, structurally significant corrosion occurring half-way up a shell, assuming the floor and vapor space were both sound.