API 650 Tank - Stiffeners Shell for Fluid Pressure
API 650 Tank - Stiffeners Shell for Fluid Pressure
(OP)
I was brought into the design of a tank after a client ordered and began the erection of an ethanol processing tank. After running the numbers we realized the tank was not only build, but the shell thickness was to thin.
My question: Is it acceptable by API 650 to provide stiffeners to a shell for the purpose of resisting stresses due to fluid pressures (Circumferential Stresses). I need hard evidence, please no opinions. I need to have something in writing from API that states that this is an option. I have attempted to contact people at the API, however, I need an answer soon.
We developed a finite element model in order to design the "fluid bands".
Thanks
My question: Is it acceptable by API 650 to provide stiffeners to a shell for the purpose of resisting stresses due to fluid pressures (Circumferential Stresses). I need hard evidence, please no opinions. I need to have something in writing from API that states that this is an option. I have attempted to contact people at the API, however, I need an answer soon.
We developed a finite element model in order to design the "fluid bands".
Thanks





RE: API 650 Tank - Stiffeners Shell for Fluid Pressure
MMikola-
How do you expect someone to provide "hard evidence" that something does not exist?
jt
RE: API 650 Tank - Stiffeners Shell for Fluid Pressure
I'm not asking to provide evidence that something does not exist...I'm looking to an example where it (stiffening bands and FE analysis) has been done and the approval from API that states the method could be used.
mmikola
RE: API 650 Tank - Stiffeners Shell for Fluid Pressure
Joe Tank
RE: API 650 Tank - Stiffeners Shell for Fluid Pressure
Joe Tank
RE: API 650 Tank - Stiffeners Shell for Fluid Pressure
I know that API does not approve the tank, I just want to know if they approve of the method. Also, the shell thicknesses are adequate if stiffening bands are utilized. My client basically wants that warm and fuzzy feeling then when he signs his name to certify the tank is built according to the API 650 that it actually is designed acceptable by the API.
mmikola
RE: API 650 Tank - Stiffeners Shell for Fluid Pressure
However, I doubt this type of retrofit would be considered acceptable by API. (If so, it might be very useful for stainless tanks). An official interpretation would be the only way to confirm for sure. But certainly API doesn't address the issues of designing hoops for tension, welding and radiography of shell hoops, etc, that would be required to make this approach comparable to standard shell design.
RE: API 650 Tank - Stiffeners Shell for Fluid Pressure
They didn't carry an API data plate but were quite functional, built before FEA was invented.
I have also seen quite a few municipal water tanks built with reinforcing rings. You might try searching the AWWA for a standard with reinforcing ring details that your client, his underwriters, and the jurisdiction could find acceptable.
I have a sometimes foggy recollection that water and ethanol don't difer too much in specific gravity. (Lighter by 20%?). So a water tank-based beef-up should be conservative?
RE: API 650 Tank - Stiffeners Shell for Fluid Pressure
I've never seen a municipal tank built with rings for that reason. I've seen decorative rings on a few tanks, and seen one or two standpipes reinforced in that method when the height was extended- and that was probably a bad idea as well.
RE: API 650 Tank - Stiffeners Shell for Fluid Pressure
Joe Tank
RE: API 650 Tank - Stiffeners Shell for Fluid Pressure
RE: API 650 Tank - Stiffeners Shell for Fluid Pressure
I and others have used stiffening rings to reinforce tanks due to poor design, deterioration or changes in service. This method is not recogniozed by API-653 either. In fact it was rejected as a repair method in the early drafts of the document. So, in the end you are on your own. You cannot point to a recognized Code or Standard to rely upon to validate your actions. It does not mean that what you are doing is not adequate, but it is clearly none Code. there is of course a business risk to the owner to pursue this approach. If something went wrong (even unrelated to this issue) they will be be hung out to dry for not complying with recognized Codes and Standards. For example, how would you resolve non-compliance with NFPA-30 (which require tanks per UL, API or ASME) Ethanol is a flammable product and I am assuming that your state building Code references this document. As with many things the devil is in the details, so please put lots of control on the ring installation, tightness if fit, NDE, weld spacing. If they can't even design a tank correctly, are you sure the rest of the tank is right. Is the welding up to Code? Do you have the NDE records to verify that? Are the tanks within dimensional tolerances now? They will distort further when the rings are wellded on the shell. Well, I guess that's enough for now. Best wishes on this one.
Joe Tank