Coiled Tubing is developing into a multi-talented work horse. Efforts to use the technology in high pressure deep wells, horizontal drilling and production logging require a better understanding of the mechanical properties of the tubing material. The basic design of any Coiled Tubing system causes the tubing to experience bending strains beyond the material's Yield Point when passing between the reel and the wellhead equipment. It is widely expected that such levels of cyclic straining will cause work softening of the tubing material. This paper describes a series of experiments to investigate the effects of plastic levels of strain on the Yield Point and Young's Modulus. A modified method of performing full body uniaxial tensile tests is described.
Further tests were conducted to demonstrate whether any evidence of anisotropy between the material properties in the axial and hoop directions could be found. The use of linear elastic theory to predict the stability of Coiled Tubing during well operations is acceptable in the presence of small degrees of anisotropy.