API 650 Roof thickness 1

[Dream91]

As per API 650 , Nominal thickness of roof plate shall not be less than the greater of D/(4.8*SIN PH)*ROOT(B/2.2)+CA, D/(5.5*SIN PH)*ROOT(U/2.2)+CA , 5 mm

My question if 5 mm is the greater shall we add the corrosion allowance ( CA ) so it will become 8 mm?

 

[IFRs]

First - Please confirm that you are looking at a self-supported cone roof, not one of the other roof types.

Second - If your calculated nominal thickness including CA is less than 5mm you must use 5mm plate. Since you have already included the CA in your calculations, it is not necessary to add it to the 5mm. For some minor clarity, see section 3.22 where nominal thickness is defined.

Third - Please check your numbers - if your calculated thickness including 3mm CA is coming out to less than 5mm, your required thickness before CA is less than 2mm which can't support much load or span much distance.