ABSTRACT
The outlet system of a steam methane reforming unit, depending on design, normally consists of a combination of wrought components and cast components used in a welded construction. Proper functioning of the outlet unit is dependent on the in-service performance of these components. Both cast (UNS N08151) and wrought (UNS N08810/N08811) metallurgies have been used for outlet components. Based on a literature survey, the microstructural features responsible for material performance, the various microstructural alterations occurring in service and its impact on serviceability as well as repair weldability as well as examples of failures are reviewed. Some of the potential areas for further technical improvements are identified and summarized.
INTRODUCTION
Steam methane reforming (SMR) has firmly established itself as the leading process technology for the production of synthesis gas.1,2 The typical SMR unit consists of a furnace in which series of tubes are vertically held and connected to a manifold which then collects the reformed gas from the various tubes and transfers the same to downstream processing units. SMR process involves tube metal temperatures ranging from 850 to 1000°C with inside pressure ranging from 1 to 5 MPa.2 It is estimated that the cost of a catalyst tube assembly along with manifold is a very significant part of the total cost of the furnace.3 Proper materials selection is a key aspect to be considered since it has an impact on the operation, reliability and economics of the SMR unit. Fe-Cr-Ni alloys are used as material of choice for catalyst tubes and manifold.4 Experience has proven that these alloys are able to resist deformation and corrosion at high temperature and pressure due to their excellent properties. Material property requirements are based on service conditions of the component of the SMR furnace.4 For example catalyst tubes are fired from outside. Hence, oxidation resistance, high temperature creep, and stress rupture properties are prime requirements.4 In case of manifold components, ductility and toughness needs to be considered in addition to strength since these components need to move unhindered during the numerous start/stop cycles which is part of the normal furnace operation.4
