Probabilistic characterization of primary stress index B<inf>2</inf> for nuclear pipe bends subjected to in-plane opening moment

Probabilistic Characterization of an Allowable Design Moment in a Piping Elbow

Journal of Pressure Vessel Technology ◽

10.1115/1.4042907 ◽

2019 ◽

Vol 141 (3) ◽

Author(s):

Yonghee Ryu ◽

Abhinav Gupta ◽

Bu Seog Ju

Keyword(s):

Nuclear Power ◽

Stress Index ◽

Design Equation ◽

Design Code ◽

Straight Pipe ◽

Reliability Level ◽

Reliability Based Design ◽

Probabilistic Characterization ◽

Definition Of

The design of a nuclear power plant piping requires consideration of the effects of pressure and moment loads according to the appropriate design equation, which is Piping design equation (9) in NC/ND-3600, Section III of the ASME Boiler and Pressure Vessel Code. The design moment is influenced significantly by the definition of the B2 stress index in piping elbows. This paper presents a study on reliability-based design for piping elbows on the level D service limit in the design code. Probability density functions (PDFs) of the design moment were calculated using the ASME equation and modified B2 equations. The PDFs of the design moment were evaluated by the collapse moment using the closed-form equations. The probability distribution of the design moment using the modified B2 equation was closer to the distributions of the collapse moment than its design moment using the ASME B2 equation. Probabilistic analyses were conducted to evaluate reliability levels in straight pipe as well as piping elbows using the ASME and modified B2 equations. It was observed that the minimum reliability level (MRL) of the design equation for the straight pipe was slightly higher than the MRL of the elbow. The MRLs of the design equation using the ASME and modified B2 equations were similar for the same values of bend parameter h, and the MRL of the design equation did not show influence of changes in bend parameter, piping type, and B2 stress index.

Download Full-text

Fabrication Uncertainty in B2 for Nuclear Pipe Bends Subjected to In-Plane Opening Moment

Journal of Pressure Vessel Technology ◽

10.1115/1.4007470 ◽

2012 ◽

Vol 135 (1) ◽

Cited By ~ 3

Author(s):

Pronab Roy ◽

Siddhartha Ghosh

Keyword(s):

Random Variable ◽

Nonlinear Finite Element ◽

Conservative Estimate ◽

Element Analysis ◽

Stress Indices ◽

Primary Stress ◽

Reliability Based Design ◽

Probabilistic Characterization ◽

Geometric Uncertainty

For reliability-based design of pipe bends and elbows, a probabilistic characterization of the primary stress indices (B1 and B2) is essential. This paper aims at the characterization of the fabrication/geometric uncertainty in B2, for thin stainless steel long radius pipe bends, subjected to in-plane opening moment. This characterization is performed in a framework based on Monte Carlo simulation and nonlinear finite element analysis. A revision of the code-based expression for B2 is proposed where a random variable K replaces the constant numerator in this expression. The statistics for K are provided for different pipe nominal dimensions, which indicates that the existing provision gives a very conservative estimate of the plastic collapse moment for pipe bends subjected to in-plane opening flexure.

Download Full-text