Cooldown of Large Pipes During the Commissioning Phase of Cryogenic Facilities

Cryogenic facilities such as LNG receiving terminals operate at temperatures as low as -260F. During day to day operations, the temperature in the pipes of the facility is relatively uniform, leading to low material stresses in the pipes. However, during exceptional operations, such as the initial cooldown of the facility performed during the commissioning phase, high temperature gradients exist in every pipe. The cooldown procedure is therefore a critical aspect of the design process and needs to be carefully scheduled to ensure the integrity of the piping. The present study quantifies the material stresses reached during a cooldown procedure for different pipe sizes and pipe support spacing. A model to estimate the cooldown front speed when the cryogenic liquid is first introduced in a pipe is presented. This model also estimates the height of the cryogenic liquid behind the cooldown front and accounts for cryogenic liquid evaporation both in the film and nucleate regimes. Cooldown strategies such as shock cooling with cryogenic liquid and precooling with vapor are also discussed.