A Serviceability Approach for Carbon Steel Piping to Intermittent High Temperatures

Abstract

Carbon steel piping (e.g., ASME SA-106, SA-53), is installed in many industrial applications (i.e., diesel generator exhaust manifold) where the internal gas flow subjects the piping to successive short time exposures at elevated temperatures up to 1100°F. A typical design of this piping without consideration for creep-fatigue cumulative damage is at least incomplete if not inappropriate. Also, a design for creep-fatigue, usually employed for long-term exposure to elevated temperatures, would be too conservative and will impose replacement of the carbon steel piping with heat-resistant CrMo steel piping. The existing ASME Standard procedures do not explicitly provide acceptance criteria for the design qualification to withstand these intermittent exposures to elevated temperatures. The serviceability qualification proposed is based on the evaluation of equivalent full temperature cycles which are presumed/expected to be experienced by the exhaust piping during the design operating life of the diesel engine. The proposed serviceability analysis consists of: (a ) determination of the permissible stress at elevated temperatures, and (b ) estimation of creep-fatigue damage for the total expected cycles of elevated temperature exposures following the procedure provided in ASME Code Cases N-253-6 and N-47-28.