Elongation analysis of coiled tubing

It is easy for Coiled Tubing (CT) to deform a plastic elongation because of many factors, such as the residual stress etc, in the process of coiled tubing service. The paper analyses the cause of coiled tubing plastic elongation and explains the principle of the same elongation. Coiled tubing plastic elongation has four mainly reasons: axial load causes plastic elongation, thermal causes plastic elongation, pressure difference causes plastic elongation, helical buckling causes elongation. The theoretical calculation formula and calculation method for CT plastic elongation are summarized. Calculation examples about CT plastic elongation give some basic CT plastic elongation conclusions by comparative analysis of relation curve on calculated value. The CT plastic elongation is more complicated and more obvious than conventional tube. The elongation caused by axial load and the shortening caused by helical buckling are larger than others and should be focused on the need to consider in the progress of coiled tubing service. The thermal expansion and the elongation caused by pressure difference are smaller than above all and should be given due consideration in the progress of coiled tubing service. Total elongation deformation is made up of four parts: the plastic elongation caused by axial load, thermal expansion, plastic elongation caused by pressure difference and the shortening caused by helical buckling. The four elongations may cancel partially each other, so the total elongation deformation generally is smaller than every single elongation.