External Pressure Charts for Carbon and Low Alloy Steels in the Creep Range

External pressure charts of ASME Boiler & Pressure Vessel Code do not account for reduction of buckling strength due to creep under long-term loads at elevated temperatures. This restricts the design of ASME boiler and pressure vessel components in the creep range. Although the design factors and equations for creep buckling are available in various other literatures, the external pressure charts in the creep range are not available at present time. External pressure charts are developed for most commonly used elevated temperature materials (Carbon & 1.25Cr-0.5Mo and 2.25Cr-1Mo low alloy steels) in the refinery and petrochemical industry up to a temperature of 550 °C. API 579-1/ASME FFS-1 isochronous stress-strain curves from Omega model, which does not include the effects of plasticity and primary creep, are used. Thus adjustment factors are proposed based on available isochronous stress-strain curves which considers the plasticity and primary creep effects. The developed external pressure chart for 2.25Cr-1Mo steel at 538 °C is validated with ASME B&PV Code Case 2676. The loads and load combinations to be considered in the design and examples illustrating the application of the developed external pressure charts in the creep range are presented.