A Perspective on the Failure Rates of Long Seam-Welded Low Alloy Steel High Energy Piping

For over three decades, the long seam-welded low alloy steel, Grades 11 and 22, high energy piping in fossil power plants has been considered at risk of premature damage and failure. The experience with piping damage and failures has been documented and extensively studied, but there remains a lack of perspective on how the overall experience with such piping, including that of the large “survivor” population, compares with what one may expect with the design rules used in their construction. Such a perspective can be useful in helping decide on suitable design rules for this class of piping. This paper focuses on an aggregate, global, semi-quantitative evaluation of the damage and failure experience in fossil plant low alloy steel long seam-welded piping in terms of a rate of failure measured against the performance of the overall population. A key aspect of the evaluation is the consideration of the survivor population, particularly important since the documented cases of failure and damage represent a very small fraction of the population of relevant components. The damage and failure rates have been derived from the Electric Power Research Institute database, using an exposure parameter represented by the product of operating time and length of piping. The rates are viewed against the backdrop of the statistical scatter band of base metal stress rupture data used in development of the ASME Code design allowable stresses and against the weld strength reduction factors recently adopted by the ASME Boiler Pressure Vessel Code, Section I and the Power Piping Code, B31.1.