Hi everyone, To begin, sorry for my english....:S I try to calcualte inner/outer surface stresses on a pipe submitted to instanatenous temperature variation on the OUTER SURFACE. I know the Roark's formua giving the stresses but with an instantaneous temperature variation on the INNER SURFACE. My question is: can i apply theses formulas to my case (but with a Delta T on the outer surface, not on the inner surface)? For me, the Roark formulas is the combination result of the temperature formula on the thickness with the Hook formulas. Temperature/thickness formula: => Hook formula: So, to my mind, i can apply it to my case, it is just the results sign which change (tension stresses in outer surface area and compression stresses in inner surface area for a outer negative tempeature variation). Thanks a lot. Bruno.