An efficient method for estimation of reduction of welding residual stresses from stress-relief annealing. Report 4: Applicability of the method for stress-relief annealing of thick welded joints

Abstract

Stress-relief annealing (SR treatment) is included in the fabrication process of welded structures such as pressure vessels. This study aims to develop a simple analytical method to facilitate the calculation of transient and residual stresses during SR treatment, in order to easily determine the reasonable conditions for SR treatment of recent large-size structures of high-quality thick plates. In the first report, estimation equations for uniaxial stress state were formulated for relaxation tests at changing and constant temperatures. In the second report, the stresses relaxed by SR treatments in thick welded joints were analyzed accurately by the finite element method based on thermal elastic-plastic creep theory. The characteristics of the changes in the welding residual stresses in multiaxial stress states were studied in detail. In the third report, estimation equations for multiaxial stress state were developed for thick welded joints, based on the above characteristics. In this report, the stress relaxation phenomena of thick welded joints during SR treatment are analyzed by applying the estimation equations. The accuracy of the method is investigated, comparing the results with ones by FEM.

圧力容器のような溶接構造物作成では、応力緩和焼鈍(SR処理)は工程の一部に組み込まれている。本研究の目的は、SR処理中の過渡応力と残留応力の計算を容易にする簡略な解析法を開発して、最近の高品質厚板より成る大型構造物のSR処理の経済的条件を簡単に決定することができるようにすることである。第1法では、温度を変化させた場合と、一定温度の場合とでの応力緩和試験について、1軸応力状態での推定式を定式化した。第2報では、厚い溶接継手のSR処理によって緩和した応力を、熱弾塑性クリープ理論に基づいて有限要素法でより正確に解析した。多軸応力状態での溶接残留応力の変化の特徴を詳細に検討した。第3報では、上述の特徴に基づいて、多軸応力状態の推定式を、厚い溶接継手について展開した。本報では、SR処理中の厚い溶接継手の応力緩和現象を、推定式を応用して解析する。本方法の精度を調べ、有限要素法による方法での結果と比較する。