Assessment of remaining service life of 1Cr-0.5Mo steam piping

摘要

A Savannah River Site power plant has been in operation for 40 years, producing electricity and process steam for the site. This coal-fired plant employs lCr-0.5Mo steam piping which is exposed to temperatures up to about 500(degree)C in service. With applied loads on the order of 69 MPa (10 ksi), this pipe is at the lower bound of conditions that might lead to service-induced creep damage. Efforts to characterize the creep damage to date and predict the remaining service life are two-fold, employing microstructural characterization (through the use of in-situ metallography) and analytic predictions based on constitutive equations and creep data available in the literature. This effort is part of an overall program to evaluate life extension of this power plant versus new construction. The literature contains many examples of efforts to correlate microstructural changes to the extent of creep damage and remaining service life. A brief review identified examples as far back as the 1950s. The concepts and techniques involved have matured to the point where this means of life prediction can be considered a standard tool in the engineer's arsenal. In this regard, a comparison is made between this approach to life extension and an analytical approach based on basic creep data and constitutive equations. Possible pitfalls of each method are discussed. It is concluded that both approaches can offer valuable insights depending on the circumstances of the situation at hand.