Effect of Stress Ratio on the Corrosion Fatigue Crack Growth Rate of X56 Steel After Service

被引：0
|
作者：
Gao X. [1 ]
Shao Y. [1 ,2 ]
Guo Y. [2 ]
Zhong Y. [2 ]
Luo X. [1 ]
机构：
[1] School of Mechatronic Engineering, Southwest Petroleum University, Chengdu
[2] School of Civil Engineering and Geomatics, Southwest Petroleum University, Chengdu
来源：
Cailiao Daobao/Materials Reports | 2022年 / 36卷 / 15期
基金：
中国国家自然科学基金;
关键词：
fatigue crack growth rate; Paris law; pipe-in-pipe; seawater; stress ratio; X56; steel;
D O I：
10.11896/cldb.21040303
中图分类号：
学科分类号：
摘要：
To study the corrosion fatigue crack growth rate (FCGR) of the API 5L X56 pipe-in-pipe submarine pipeline after service, fatigue crack growth (FCG) tests with different stress ratios (R = 0.1, 0.2, 0.3, 0.4, 0.5) were carried out on standard compact tensile (CT) specimens taken from the pipeline in seawater and air, respectively. At the initial stage of stable crack growth, within a given stress intensity factor range (ΔK = 35 MPa·m0.5), the fatigue crack growth rate (da/dN) of the X56 steel after service in seawater is about 1.64 times that in air, and with the increase of ΔK, the influence of seawater decreases gradually. A comprehensive analysis of the effect of stress ratio on the fatigue crack growth curves of the X56 steel in seawater is conducted. It is found that stress ratio has a great influence on the FCGR in the initial stage of stable crack growth. A low-stress ratio (R = 0.1, 0.2, 0.3) has little effect on the fatigue crack growth rate in the intermediate stable stage of stable crack growth, while a high-stress ratio (R = 0.4, 0.5) increases the fatigue crack growth rate in the whole stage of stable crack growth. The fatigue fracture faces of different CT specimens observed by scanning electron microscopes are all transcrystalline fractures. In seawater, as stress ratio increases, the crystal face area and the height difference of the cleavage step formed by cleavage fracture gradually decrease and the fatigue fracture face becomes flatter. Accordingly, the fatigue crack propagation mode changes from tearing to cleaving. © 2022 Cailiao Daobaoshe/ Materials Review. All rights reserved.
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