There are some formulas in Roarks you can use to approximate but usually I find you need to model the situation in an FEA package to include the affects of the shell radius and doubler plates etc. I dont think there are any nice "deemed to comply" hand calcs out there for tank attachments but if there are please post the links here>

 

Pressure Vessel Design Manual by Dennis Moss has a method of converting the equivalent areas of several strucural shapes into regular shapes that can be used with WRC-107.

Crusader...

Generally speaking, tank attachments fall into two categoreies....nozzles and clips.

Nozzles, and the sometimes required reinforcement, are to be handled in accordance with the code of construction ... i.e. API-650

Smaller clips (flat plate attachments) can be handled via company standards, Roark "Fomulas for Stress and Strain", Bldogett or similar handbooks.

Larger attachments, if necessary, should be configured either as reinforced trunions or competely rethought...

My opinion only

-MJC

   

I can certainly calculate the loads from Roark's, but what is the allowable stress?  I'm thinking that in this case what will govern is the amount of deflection in the wall of the tank.  In other words, long before failure there is enough deflection in the tank wall under load that the platform doesn't feel right when walking on it.  How can I quantify this?