This is the first research to investigate the Underwater
Friction Stir Welding of Pipes (UFSWoP). UFSWoP of
Al 1050 pipes was carried out successfully by designing a
new device that allows the underwater rotational motion of
the pipe to be friction stir welded. An important
consideration in the UFSWoP is the cooling effect on the
surrounding water during the process. The water-cooling
affects directly the mechanical properties of the produced
joint. A study is carried out to conclude and predict the
effects of the UFSWoP process parameters on the
mechanical properties of the welded joint. A Box Behnken
experimental design was employed with different levels of
tool rotational speed, traverse speed and tool diameter. The
corresponding response considered was the tensile strength
of the produced joints. Finally, a hybrid Response Surface
Methodology-Fuzzy based model was proposed and
evaluated for predicting the considered response of the
UFSWoP process. This model showed more accurate
predicted results than the Artificial Neural Network based

model.