The Elongation and Diametral Growth JIP was completed in March of 1998. The project made some amazing discoveries about coiled tubing mechanics and resulted in a powerful, robust coiled tubing plasticity model as well as a unique experimental coiled tubing testing facility. The JIP accomplishments are summarized:

1. A coiled tubing test facility was designed and constructed. The fixture is capable of applying bending cycles and axial loading to pressurized CT samples up to 3.5 inches in diameter. The capacity of the machine is 120,000 lbs of axial force, 10,000 psi internal pressure and bending radii of 48 and 72 inches. Coiled tubing materials QT-800 and QT-1000 were studied in this project, with diameters of 1.25” (wall thicknesses of 0.095” and 0.156”) and 2.375” (wall thicknesses of 0.134” and 0.156”).

2. Important tensile data were generated at Quality Tubing Inc. following various amounts of fatigue testing at various pressures. These data provide insight on the effect of fatigue and internal pressure on yielding and tensile strength. (see attached powerpoint file – Partial Cycling & Tensile Testing)

3. Diametral growth data were collected during constant pressure fatigue tests and used to identify parameters in a new multiaxial cyclic plasticity model for coiled tubing. Based on this model, the CTDef Analytical Software package was developed to predict the mechanical response (elongation, diametral growth and wall thinning) of a tubing segment subject to any bending-straightening, pressure and axial load history.

4. The CTDef Software is also capable of examining the first order influence of tubing rotation on its elongation behavior. Examples are used to demonstrate the strong effect of rotation, although experimental investigation was not possible.

5. Elongation and diametral growth data were collected from complex load histories and compared to predictions made by the CTDef software. Good correlation is demonstrated between predictions and experimental data.

6. The model predicted mechanical behaviors that were not intuitively obvious: including the shortening of a segment under internal pressure due to bending cycles, and diametral shrinkage during cycling with moderate internal pressures. These behaviors were validated experimentally. The model predicted other subtle experimental trends, including slightly greater wall thinning at the compressive tube wall, relative to the tensile tube wall.

7. The model is robust enough to examine field loading sequences that have never before been considered, including the influence of back tension between the reel and injector, and reversed bending. Case studies are used to demonstrate the capabilities of the software.