(40b) Cold Box Pipe Leak Due to Erosion from Flashing Liquid

On March 25, 2002, a leak was discovered after 10 years of service on the Large Cold Box at DuPont's Sabine River Works Ethylene Plant. The large cold box consists of a highly, internally insulated shell (insulated with perlite) containing 4 series-aligned brazed aluminum plate heat exchangers, three separators, and associated aluminum and stainless steel piping. The cold box uses successively lower heat exchanger temperatures and Joule-Thompson expansion to liquefy and separate all other components from hydrogen. The outer shell is 12 ft OD x 63 ft high. The leak (¾? hole) was located on a 3? aluminum pipe elbow on the downstream side of control valve that lets liquid methane down from 480 psig to 12 psig. Analysis of the failure revealed a combination of internal impingement and cavitation in a highly localized area, which was determined to be associated with the flashing that occurs during the pressure let down of the liquid methane. Computational fluid dynamic modeling was conducted to replicate the failure and propose piping modifications to prevent future failures. This paper discusses the findings, repairs, and CFD analysis results, along with proposed piping changes to prevent reoccurrence.