Takeo Miyamura

Studies on Influence of Tantalum Addition in TP310HCbN

SA-213/SA-213M TP310HCbN (UNS S31042) has excellent creep properties. The superior creep strength of this alloy is achieved by precipitation of fine niobium based Z-phase. It is well established that niobium and tantalum have similar physical and chemical properties. We evaluated mechanical properties of tantalum added TP310HCbN, to investigate whether tantalum could be substitute for niobium. It is concluded that niobium can be replaced by tantalum in TP310HCbN.Copyright

Development of Pressure Vessels Made of 9Cr-1Mo-V Steels for High-Temperature Processes in Refining Industries

Due to the increasing demands for light oil in newly industrializing countries and depletion of conventional oil resources, upgrading of heavy oil and coal-to-liquid processes have been a focus in recent years. The efficiency of these processes depends on temperature and pressure conditions, where a higher temperature, around 500°C, is likely to be used. However, 2¼Cr-1Mo-V steels which have been widely used for heavy-wall pressure vessels for many years cannot be applied to a high temperature process around 500°C since the design temperature of this material is limited to 482°C by ASME Code Section VIII, Division 2 [1].On the other hand, 9Cr-1Mo-V steels (Grade 91), which has an excellent performance at high temperature in mechanical properties and hydrogen resistance, has been used for tubing and piping materials in power industries and it can be a candidate material for the high temperature processes. However it has not been used for pressure vessels in refining industries.In order to manufacture heavy-wall pressure vessels using 9Cr-1Mo-V steels, essential techniques including manufacture of large forged shell rings, thick wall welding and overlay welding have been developed.Copyright

Fracture Toughness After Long-Term Aging in 9Cr-1Mo-V Steel for Pressure Vessels

9Cr-1Mo-V steel with excellent high temperature strength is one of candidate materials for advanced pressure vessels in oil-refining plants, whose process temperature is expected to be around 500°C. Although 9Cr-1Mo-V steel has been applied as boiler tube material in power generation for a few decades, it was reported that embrittlement occurred after long-term aging around 600°C which is accelerated condition for pressure vessel operation. Since pressure vessels are more sensitive in stress-concentration around crack tip than boiler tube because of its large wall thickness, fracture toughness is an important property of concern when 9Cr-1Mo-V steel is applied to pressure vessels. In this research, 9Cr-1Mo-V steel with tempered-martensitic microstructure was aged up to max. 10000 hr at 500, 550 and 600°C, and fracture toughness was evaluated after the aging by Charpy impact test.The influence of heat treatment conditions such as austenitizing, tempering and PWHT were also investigated, because the heat treatment conditions used in pressure vessels are different from those of boiler tube. In case of samples treated under the conditions for pressure vessels, Charpy impact values at 0°C were sufficient around 200J before aging, and decreased after aging depending on its conditions, and longer time and higher temperature led to more severe degradation. When the aging time at 550°C and 600°C was converted to the equivalent aging time at 500°C by Larson-Miller-equation, the impact value was estimated to keep over 50J after several decades at the operating temperature for pressure vessels. In contrast to the conditions for pressure vessels, the heat treatment conditions used in boiler tube made initial impact value decreased significantly, because tempering and PWHT were shorter than those of pressure vessels. Therefore, the samples heat treated under boiler tube conditions showed lower impact values around 50J in the earlier stage of aging. Considering all obtained results, it was suggested that the serious degradation of fracture toughness in 9Cr-1Mo-V after long term aging would not occur in actual service time for pressure vessels.Copyright