Shakedown, ratchet, and limit analyses of 90° back-to-back pipe bends under cyclic in-plane opening bending and steady internal pressure

Abstract

A 90° back-to-back pipe bend structure subjected to cyclic in-plane bending moment and steady internal pressures is analysed by means of the Linear Matching Method (LMM) in order to create the limit, shakedown, and ratchet boundaries. The analyses performed in this work demonstrate that the cyclic moment has a more significant impact upon the structural integrity of the pipe bend than the constant pressure. Full cyclic incremental analyses are used to verify the structural responses either side of each boundary and confirm correct responses. In addition, the shakedown boundary produced by the LMM is compared to another shakedown boundary of an identical pipe bend computed by the simplified technique and it is shown that the LMM calculates results more accurately. Parametric studies involving a change of geometry of the pipe bends and loading type are carried out. From the studies of the geometry, two semi-empirical equations are derived from correlations of the reverse plasticity limit and the limit pressure with the bend characteristic. Finally, the results presented in this paper provide a comprehensive understanding of post-yield behaviours of the 90° back-to-back pipe structure under the combined loading as well as offering essential points to be concerned for the life assessment of the piping system.

Investigating the Effects of Cyclic Thermo-Mechanical Loading on Cyclic Plastic Behavior of a Ninety-Degree Back-to-Back Pipe Bend System

“…Journal . Compared to the previous study [18], cyclic out-of-plane bending generates a larger elastic shakedown limit boundary but smaller reverse plasticity zone.…”

“…Journal ratchet limit boundary as a conservative manner. It is noteworthy that the previous study [18] shows that the pipe system under cyclic in-plane bending has a completely different shape of the shakedown limit boundary from the one under cyclic out-of-plane bending. The cyclic in-plane bending produced the boundary which is very similar to Bree-like diagram with large margins between the limit load and the shakedown boundaries.…”

“…The material investigated is type 304 stainless steel, previously considered in [18]. Young's modulus is 193.74 GPa and Poisson's ratio is 0.2642.…”

“…From the numerical results in Figure 11, we develop another relationships between the bend characteristic h and reverse plasticity limit ) and by adopting the Quadratic Regression method as given Eq. (18) and Eq. (19)…”

Cyclic Plasticity Behavior of 90° Back-to-Back Pipe Bends Under Cyclic Bending and Steady Pressure

“…Quadratic relationships between RPIP and the bend characteristic h are derived for a single pipe elbow [7]. Recently Cho and Chen introduced a correlation between RPIP and LP with h for the same back-to-back pipe bends being used in this paper [16]. Utilizing the Quadratic Regression method, two quadratic equations between RPOP and h and between RT and h are developed.…”