Damage analysis in Fe–Cr–Ni centrifugally cast alloy tubes for reforming furnaces

•Damage during service of HP grade tubes, modified with Nb and Ti addition.•Laser-Optic Tube Inspection System (LOTIS) measurements performed in situ.•Softening effects at high temperature are highlighted by tensile and creep tests.•Tubes are put out of service when their deformation become not acceptable.

Reformer furnaces tubes work under high temperature and pressure for a long time, which are very critical conditions for creep deformation and life of most common materials. Cast austenitic Fe–Cr–Ni alloys in the widely know HP grades are used for reformer tubes to allow a good service at temperatures that can be close to 1000 °C. This paper reports a study devoted to the damage analysis of reformer furnace tubes after more than 100,000 h of service. Tubes, made of a HP grade modified with Nb and Ti additions, were inspected in situ by a laser optic system to measure their internal diameter and evaluate creep deformation. With the aim of developing a criterion for deciding the substitution of components, samples of as cast material and samples, cut from the most deformed tubes put out of service, were considered to check changes of mechanical properties and metallurgical characteristics. Tensile and creep tests were carried out; moreover the metallographic observations included optical and scanning electron microscopy and energy dispersive X-ray microanalysis in order to measure locally the chemical composition.