The demand for hydroprocessing reactors has increased dramatically in recent years. In addition, reactor size and thickness has also increased. New materials with higher allowable stresses have been introduced. Lead times and prices for vessels have increased for many reasons, one of which is because of the limited number of mills that are capable of producing advanced materials for the higher thicknesses required. For many years, layered design was successfully used for high pressure vessels including hydroprocessing reactors, including some that have 40 years of service history. Yet, recent history shows that hydroprocessing reactors are exclusively built using solid wall design. This paper discusses the advantages and disadvantages of using layered construction for hydroprocessing reactors. Consideration is given to mechanical properties, venting of diffused hydrogen, thermal conductivity differences between the layered parts and solid sections, and non-destructive examination. Specific design issues related to bed support design, nozzle to shell, and head to shell connection construction are discussed. As a part of the evaluation, finite element analysis has been recommended to study critical areas for layered design assessment. An industry survey of layered reactor service is suggested as well.

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