The joining of aluminum is commonly performed by arc welding technique which easily induces severe weld defects and distortion. The friction stir welding (FSW) technique offers excellent mechanical properties and environmental-friendly process. In this proposal, we intend to study the application of FSW on tubular components. FSW of small diameter aluminum pipes is a relatively new application thus presents a unique challenge requires the use of specialized techniques and equipment. Significant amounts of residual stresses are generated during welding and result in critical degradation of the structural integrity and performance of components. Residual stress mapping of the FSW components by neutron diffraction will provide the necessary insights to the effects of the welding parameters and provide guidance on the limits of these process parameters for manufacturing FSW aluminum pipes.