Effect of the Joule-Thomson Cooling on the Leak-Before-Break Approach

Abstract

The advantage of the new compressed natural gas (CNG) marine transportation technology is less investment in infrastructure and greater flexibility. It is highly competitive as compared to pipelines and liquefied natural gas (LNG) transport for distances of up to 2,500 – 3,000 nautical miles. Due to the high pressure inside CNG containers, its safety is the first important factor to be considered. Leak-before-break (LBB) is an important methodology of maintaining the integrity of pressure vessels. However, the Joule-Thomson (JT) cooling effect occurred during a leak may impact the validity of the LBB approach. In this paper, a looping model based on MATLAB software is developed starting with the gas at room temperature and 250bar at the entrance of the crack. From this, the pressure and JT temperature drop is calculated initially, which in turn affects the gas properties, such as viscosity, density, thermal conductivity and heat transfer coefficients. Heat transfer and FEA analysis using a 3D model of the plate with a central through-thickness crack are carried out. Under the internal pressure of 250bar, the temperature drop and the stress intensity factor in the vicinity of the crack is 59.7°C and 120 MPa· m1/2, respectively. The stress intensify factor obtained is higher than the fracture toughness of the material at the same low temperature. However, the structure may not experience a catastrophic failure. The reasons for this phenomenon are discussed in the paper.