Heat exchanger failure investigation report

Technical Report from the year 2013 in the subject Materials Science, grade: B, Robert Gordon University Aberdeen, course: MSc Oil and Gas Engineering, language: English, abstract: A high pressure gas cooler located in an offshore platform have been operating for more than 10 years. Throughout that period the gas cooler have been subjected to several tube failures, the failures have caused gas leak from the tube side. Several materials upgrades have been used to contain the tube failure. The last choice was to use a more corrosion resistant material Hastelloy C22. Crevice corrosion has been reported as the primary failure mechanism. The tube and tube plate joined surfaces have been exposed to high temperature which is relatively higher than the critical crevice temperature of Hastelloy C22. There was a poor heat transfer between the shell side fluid and tube side due to a small heat transfer area and low fluid velocity in the affected zone. Stress corrosion and fatigue corrosion accounted for the secondary failure mechanism which ultimately caused a crack in the tubes. Other possible reason identified to cause crevice corrosion was the mechanical rolling expansion technique. Oftentimes it creates rear crevices on the tubes with enough geometry to develop crevice chemistry. Mitigation methods such as hydraulic expansion technique, heat treatment for residual stresses and baffle design enhancements have been proposed in this report.

Key words: shell and tube heat exchanger failure; Hastelloy C22 material; tube failure; localized corrosion; crevice corrosion; internal pitting corrosion