I'm guessing that M_l = longitudinal and M_c = circumferential, but I don't know what M_t means. Does the program documentation expand these abbreviations?

? tangential (would be same as circumferential - so go figure)

From reading around in the internet, the Mt is the Torsional Moment, the Ml is the Longitudinal Moment, and the Mc is the Circumferential Moment. In a computer printout I saw online Mt was also referred to as MX, Mc was MY, and Ml was MZ; thus yielding X, Y, and Z. Hope this helps.

actually the problem is that the analysis software has its own global co-ordinate system, but the the alignment of Mt, Mc & Ml is diffrent for diffrent vessel and nozzle axis. let us say if the vessel is vertical and there is nozzle on top of the vessel, what will be the directions of Mt, Mc, & Ml in that case???

thank you for the extremely useful diagram. but i have 1 more doubt, when the axis of nozzle and the longitudinal axis of vessel are same, then what will be the orientation of Ml & Mc??

thank you very much.