IN UG 27 - Formula given for thickness calculation with internal pressure where input we need is internal diameter of the vessel. Which is generally available.
In Mandatory appendix 1, formula given for thickness calculation with internal pressure but in terms of outside diameter.
What is the purpose of formula given in Appendix -1 (ie formula in terms of outside diameter) Where one can apply this formula? As generally inputs are internal diameter. How one can first decide outside diameter if thickness is unknown?