The Simulation and Assessment of Compressed Natural Gas Storage Well With Defects

Abstract

Compressed natural gas (CNG) is a fossil fuel substitute for gasoline (petrol), diesel, or propane/LPG (liquefied petroleum gas). Nowadays, there are three ways used to store CNG: gas bottles group, jumbo tubes trailer, and CNG storage well. The technology of storage well came into use in the early 1990s in China and nowadays, there are more than 5000 CNG storage wells in use. In this paper, the CNG storage well is introduced with the structure, advantages, and the technology of construction. Compared with other CNG containers, storage well has the following advantages: safer and more reliable, accident-preventive, space-saving, and longer life expectancy. The feasibility of IRIS (internal rotary system) used for storage well NDT (Nondestructive testing) is also studied. And the CNG well with defects are assessed as well. To investigate the validity of IRIS in detecting the storage well, an interval casing with man-made defects is tested. FEM (finite element method), combined with the method in JB4732 (Chinese industry standard) is used to analyze the storage well with inner corrosion pits, and evaluate the fatigue life. The linear elastic FEA (finite element analysis) of storage with single, two, and three defects is performed. The limit load analysis is also discussed with two different iterative methods. The result shows that IRIS can be used in detecting internal and external defects and recording the information. The simulation indicates that the pit along the axis direction is more dangerous than the one on any other direction and the influence radius of pit is the length of defect. The two different iterative methods used in limit load analysis finally lead to a consensus. The IRIS can be adopted in storage well. It can detect the defects on the internal and external surface of casing and record the detailed information. A database should be built to record defect information for each storage well. On the basis of IRIS detection and FEM analysis, determines whether a well can survive or not until next detection carried on by the method proposed in this paper.