Expansion joint are the most basic parts of piping systems that are used in various industries such as powerhouses, petrochemical and aerospace industries. The expansion joint is used for absorption of mechanical and thermal displacements in piping systems. Bellows is the main part of an expansion joint. Bellows are essentially flexible elements of expansion joints. These are usually made from austenitic stainless steels that show good weldability, formability, creep and corrosion resistance, strength and fracture toughness. The bellows can be made by various methods such as hydroforming, punch and roll forming methods. In roll forming, the tube is held by three rollers, two on the outside and one on the inside of the tube. The tube is rotated and the rollers are driven radially and axially towards each other, thus forming the convolution. The main purpose in this research is study of effective parameters on bellows roll forming of large diameter bellows and reducing their forming defects such as wrinkles or other undesirable shapes in the manufactured bellows. Some factors of roll forming process such as position of guide rollers, axial feeding or geometrical parameters of bellows such as pitch and depth of convolution, thickness, can affect the final quality of produced bellows. In this thesis first explains various types of expansion joints and their application. Then is past research on bellows are reviewed. In the next chapters of this thesis various forming method of bellows are described and also their advantages and disadvantages are explained. Then attention is paid on roll forming method of large bellows and effective parameters on this method are focused. Finally different methods for making bellows with more than one convolution are presented. The finite element model has been used to simulate roll forming of bellows. The model has been confirmed by experimental results with respect to thickness at the cross section of a convolution in the axial direction. The simulation results showed good agreement with experimental test. Then effective parameters on bellows roll forming process were explained using FEM results. The simulation model also showed instability in forming that also happens in practice. Consequently in this thesis various strategies for reduction of instability in forming process has been presented. During bellows roll forming wrinkling might occur, that often are located in rim of bellows and in root of convolution. The wrinkles in the rim of bellows depend on various factors such as position and type of guide rollers in forming process, pitch and depth of convolution, thickness, type of loading of the rollers. Various techniques to reduce or eliminate the wrinkles that might occur at the rim are explained. In bellows roll forming, bellows diameter is reduced in the root of convolution, thus can create wrinkles in this area. The wrinkle in root is increased by decreasing initial thickness of bellows. Another important parameter in bellows is thickness of convolution after forming. The thickness depends on friction coefficient and axial feeding in forming process.The convolution wall thickness is increased by axial feeding in roll forming process. In the crests of a convolution thickness is increased by increasing the friction coefficient. Keywords : Bellows, Expansion Joint, Roll Forming, Finit Element Method