API TR 934-D:2010

This API document provides background information and guidance on the implementation of API 934-C, Materials and Fabrication of 11/4Cr-1/2Mo Steel Heavy Wall Pressure Vessels for High Pressure Hydrogen Service Operating at Temperatures at or Below 825 °C (426 °C) and API RP 934E, Materials and Fabrication of 11/4Cr-1/2Mo Steel Heavy Wall Pressure Vessels for High Temperature Service Operating Above 825 °C (426 °C), and should be used as a supplement to these recommended practices. In recent years it has been recognized that there are important distinctions that need to be considered for 11/4/1Cr-1/ 2Mo steels. Whereas API 934-A continues to provide materials and fabrication requirements for new 21/4/3Cr-1Mo and 21/4/3Cr-1Mo-1/4V steel heavy wall pressure vessels in high temperature, high pressure hydrogen service, different material, and fabrication requirements have been developed for 11/4/1Cr-1/2Mo steel heavy wall pressure vessels. These requirements are covered in RP 934-C and 934-E. This document contains a description of key damage mechanisms that relate specifically to 11/4/1Cr-1/2Mo pressure vessels used in a variety of services. These damage mechanisms include elevated temperature damage mechanisms such as 'reheat cracking' or 'creep embrittlement' as well as other damage mechanisms that may occur at lower temperatures. Not all services are affected by the same damage mechanisms due to significant differences in service conditions. For example, Hydrofiner Reactors tend to operate at lower temperatures and higher pressures than Catalytic Reformer Reactors, and Coke Drums and FCC Reactors do not see hydrogen service. Also, as a result of the different services causing different damage mechanisms, the fabrication requirements also differ. To this end, API has developed two separate recommended practices to take this into account: API 934-C and 934-E. Accordingly, background information and guidance on the implementation of these two new documents are needed. This document provides information and guidance on successful practices for fabrication of 11/4/1Cr-1/2Mo steel heavy wall pressure vessels for the intended services of both API 934-C and 934-E. The survey of steel producers and vessel fabricators (Annex 1) indicates that there is a need to evaluate the effect of heat treat cycles on materials properties (CVN toughness, tensile and yield strength). For this reason the connection of the Larson-Miller parameter is emphasized to better align the user needs with fabrication requirements. However, detailed attention is still needed to implement this approach for individual cases, as there are many secondary variables, such as heating and cooling rates that need to be considered and discussed between the user and the fabricator. The areas of fabrication that are covered in this document include steel making as related to chemical composition, heat treatment, forming, and welding.