Evaluation of creep damage of INCOLOY 800HT pigtails in a refinery steam reformer unit

• Creep strains in pigtails have been predicted with FEM calculations.
• Critical areas in terms of maximum creep strains have been identified.
• Effect of temperature, thickness and counterweights has been assessed.
• Metallurgical evaluation of creep damage has been performed.

Pigtail tubes constitute a critical component of the outlet system of steam reformer units for hydrogen production in refineries. Creep failure of pigtails is a common cause of downtime and potential risk to plant personnel. In this paper, finite element analyses are combined with experimental techniques in order to evaluate creep damage in INCOLOY 800HT pigtails of a reformer unit. A finite element model has been developed in order to investigate the creep behavior of pigtails under various operating conditions. A metallurgical evaluation of creep damage has been performed on pigtail samples removed after 8.5 years of operation. The results indicate that the most important parameters affecting the structural behavior of pigtails are the operating temperature, reduction of thickness, magnitude of counterweights and grain size of the alloy. A comparison between the numerical calculations and the metallurgical evaluation is also reported.