定ピッチスパン法による簡易配管設計のための新手法提案: オーバーハング手法と理論解に基づいた許容支持間隔

摘要

In nuclear power plants, the allowable support span method is frequently used as a simplified structural evaluation method of piping systems. The method is suitable for small－bore piping, which is used in relatively lower range of the maximum operating temperature and in condition that are less susceptible conditions to stress induced by thermal expansion, and for piping of Classes 2 and 3 ， which is defined by the classification of safety function of the mechanical equipment and components - A new allowable support span method which has different features from the conventional methods was proposed by developing a design method using simple models. The method has versatility and clearness to allow application to the whole field of plant piping installation taking into account the consistency of the conventional methods but not depeding on empirical knowledge such as practical findings. In this paper. first development of the piping design method using a theoretical solution based on beam bending theory was done. This clarified the engineering process to derive the allowable pipe support span. Next, the overhanging technique was proposed to determine support Locations easily for piping systems with complex geometry. Finally ， the proposed allowable support span method was validated by application to design of actual piping system. Comparison of results between the proposed method and the finite element analysis, demonstrated the former offered easy determination of piping support locations suited for design conditions and practical use.%原子力発電プラントでは，安全機能の重要度分類により区分されたクラス2および3の小口径配管のうち，最高使用温度が比較的低温かつ熱膨張による応力が低い配管に対して,簡易な構造評価手法である定ピッチスパン法が一般に用いられている.プラント配管設備分野全般に適用できる汎用性と説明性を重視して，従来の方法も尊重するが慣例等に依存しない説明性の高いモデルを用いて設計手法を新しく作成することで,従来法とは特長の異なる新しい定ピツチスパン法を提案した.本論文では，まず，基本的な形状の配管系に対して，梁の曲げ理論に基づく理論解を用いて直管部に対する配管支持間隔比の導出に至る技術的プロセスを明確にした方法を提案した.次に,複雑形状の配管系に対しても特別なノウハウに頼らないで容易に支持位置を決定できるようにオーバーハング手法を提案した.最後に,提案した定ピッチスパン法を実際の配管系に適用した結果と有限要素法による解析結果との比較から，設計条件を満たす配管支持位置を容易に決定できることと実際の設計へ活用できることを明らかにした.