Hydrogen Damage in Transfer Line Exchanger Tubes

Abstract

Abstract This paper presents the analysis of a Transfer Line Exchanger (TLE) tube, which ruptured from hydrogen damage on the steam side. Hydrogen damage occurs where corrosion reactions result in the production of atomic hydrogen. Atomic hydrogen combines at grain boundaries or inclusions in the steel to produce molecular hydrogen. Hydrogen may also react with iron carbides (Fe3C) in the metal to produce methane (CH4). As a result, intergranular microfissures will form, linking to form larger microcracks and leading to eventual through-wall failure. Decarburization might also occur near the tube surface. TLEs are heat exchangers designed to operate at extreme temperatures. In the exchanger design included in this study, pyrolysis furnace effluent gases enter the inner tubes at over 1500°F (815°C). The heat is then removed by water, which is supplied to concentric outer tubes, to generate steam. It is common for water-side damage in TLEs to occur at the tubesheet, where solids from boiler water are known to deposit and inhibit heat transfer. The nature of the rupture under discussion in this paper differs, because the location of the rupture was not near the tubesheet. Metallurgical analysis confirmed indications that the tube failure is attributed to hydrogen damage.