Experimental results of nine branch-pipe tee connections and two plain pipes are reported.The models were exposed to individual loadings: internal pressure and external couples and their combination.The loads were applied well beyond the elastic limit, and the elasto-plastic response of the models are discussed.Experimental limit or yield-point load of each model is determined, and the interaction curves are plotted.For the individual loadings, the out-of-plane couple is the critical case.However, presence of the internal pressure increases the resistance to the external couple.Normalized limit couple (out-of-plane or in-plane) decreases with the increase of diameter ratio.All models showed considerable reserve capacity beyond the experimentally determined limit loads.