Effects of Crack Tip Constraint on the Fracture Toughness Assessment of 9% Ni Steel for Cryogenic Application in Liquefied Natural Gas Storage Tanks.

Young Kyun Kim,Jae Hoon Kim,Byung Taek Oh

doi:10.3390/ma13225250

Young Kyun Kim, Jae Hoon Kim + Show 1 more

Open Access

https://doi.org/10.3390/ma13225250

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Abstract

Recently, increasing demand for the accurate assessment of the structural integrity and fitness-for-service (FFS) analysis of engineering structures has elevated constraint effects to one of the most important issues in fracture mechanics and structural integrity research. In this paper, the effect of crack tip constraints are investigated on the fracture toughness assessment of 9% Ni steel for application in liquefied natural gas storage tanks. Crack tip opening displacement (CTOD) tests were conducted using both conventional standard three-point bending (3PB) and wide plate (WP) specimens at a cryogenic temperature of −196 °C. The distribution of the stress and strain fields near the crack tip in the 3PB and WP specimens were then obtained by FE (Finite Elements) analysis. Based on both the experimental and numerical results, the parameters of the Weibull distribution were obtained to evaluate the critical Weibull stress at brittle fracture. The equivalent CTOD ratio β is defined as the ratio of the CTOD of the 3PB specimen to the CTOD of the WP specimen at the same Weibull stress. The application of the proposed CTOD toughness correction method to the WP results was then demonstrated in the context of a failure assessment diagram (FAD). It was determined that the conventional evaluation yields an excessively conservative result for WP specimens, but can be reasonably reduced by applying β.

Highlights

Global demand for natural gas is continuously increasing due to its convenience and status as an environmentally friendly energy source with a high energy density
The application of the proposed Crack tip opening displacement (CTOD) toughness correction method to the wide plate (WP) results was demonstrated in the context of a failure assessment diagram (FAD)
The present study focused on the effect of crack tip constraint on the fracture assessment of 9% Ni steel for application in liquefied natural gas (LNG) storage tanks using CTOD tests conducted using both conventional standard three-point bending (3PB) and WP specimens under a cryogenic temperature of

Summary

Introduction

Global demand for natural gas is continuously increasing due to its convenience and status as an environmentally friendly energy source with a high energy density. The integrity assessment of engineering structures such as the 9% Ni steel inner wall of an LNG storage tank is typically performed using fracture mechanics parameters such as the stress intensity factor K, crack tip opening displacement (CTOD), and the J integral. These conventional standard test methods have gained credibility over a long period of time by using deep notched specimens subjected to predominantly bending loads. The present study focused on the effect of crack tip constraint on the fracture assessment of 9% Ni steel for application in LNG storage tanks using CTOD tests conducted using both conventional standard three-point bending (3PB) and WP specimens under a cryogenic temperature of. It was demonstrated possible to perform a more carefully adjusted, less conservative assessment by incorporating the CTOD correction for constraint loss in the 9% Ni steel structure of an LNG storage tank

Experiments

Evaluation of Fracture Toughness Using the Local Approach

Finite

Weibull Stress Criterion

Failure Assessment and Constraint Loss Correction Using Equivalent CTOD Ratio

Conclusions