Large-diameter piping used in the petrochemical,oil and gas,steel plant and power industries often carry toxic fluids and can pose significant safety hazards.Their stability and reliability are important while they operate under external pressure loading due to vacuum formation or any other external load that can potentially collapse the piping system.Major piping codes,such as the ASME B31 pressure piping series,refer pressure vessel codes for the design of piping subjected to external pressure.However,piping and pressure vessel configurations are usually different,and a pressure vessel external pressure design approach should be carefully considered when applied to piping.In the author's experience,a design by rule(DBR)approach as stipulated in various pressure vessel codes is conservative in nature;those rules are conservatively applied to a specific piping system without due consideration of its actual geometry,pipe support location and configuration.However,these aspects have considerable impact on the external allowable pressure/loading capacity of a piping system.
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