Analytical Method for Evaluating a 4-Piece Retaining Ring

Abstract

Valves used for nuclear power applications are designed according to the rules in the ASME Section III Code [1]. A review of the applicable rules governing valve design (i.e. NC-3500) reveals that the Code favors valve body designs with very conventional shapes and elements. The nuclear supplier base has contracted over the past few decades and there are significantly fewer vendors that maintain nuclear QA programs than in the past. As a result, there has been an increasing trend toward using commercial grade dedication (CGD) methods to enable the use of valves successfully deployed in other applications for use as replacement parts, or as part of plant modifications, in nuclear power plants. This paper discusses the qualification of a check valve for a Section III application that had previously been used in other industries. The valve was designed with a split ring that retained the bonnet instead of a more traditional flanged cover. The split ring design is logical from a commercial perspective — it is faster to assemble and maintain the valve, and therefore less expensive to manufacture. However, the ASME Section III Code does not contemplate a split retaining ring in the standard design elements explicitly covered by the Code. This paper provides information about the split ring design and the analytical methods we developed to conservatively evaluate the as part of the valve pressure boundary.