Citation: Wang, P.; Hao, W.; Xie, J.;
He, F.; Wang, F.; Huo, C. Stress
Triaxial Constraint and Fracture
Toughness Properties of X90 Pipeline
Steel. Metals 2022, 12, 72. https://
doi.org/10.3390/met12010072
Academic Editors:
Alberto Campagnolo and
Alberto Sapora
Received: 28 November 2021
Accepted: 29 December 2021
Published: 2 January 2022
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Article
Stress Triaxial Constraint and Fracture Toughness Properties of
X90 Pipeline Steel
Peng Wang
1,2
, Wenqian Hao
3
, Jiamiao Xie
3
, Fang He
1
, Fenghui Wang
1,
* and Chunyong Huo
2,
*
1
Bi-Inspired and Advanced Energy Research Center, Department of Engineering Mechanics, Northwestern
Polytechnical University, Xi’an 710129, China; wangpeng013@cnpc.com.cn (P.W.);
he_fang@mail.nwpu.edu.cn (F.H.)
2
Tubular Goods Research Institute, China National Petroleum Corporation, Xi’an 710065, China
3
The College of Mechatronic Engineering, North University of China, Taiyuan 030051, China;
wqhao@nuc.edu.cn (W.H.); jmxie@nuc.edu.cn (J.X.)
* Correspondence: fhwang@nwpu.edu.cn (F.W.); huochunyong@cnpc.com.cn (C.H.)
Abstract:
The X90 pipeline steel with high-strength and high-toughness become the most popular
pipeline steel. Due to the stress triaxial constraint and fracture toughness properties are the key
factors for the stable work of pipeline steel, the research on the fracture toughness of X90 is a great
significance to promote the engineering application of high-strength pipeline steel. In order to
investigate the stress triaxial constraint and fracture toughness properties of X90 pipeline steel, the
experimental rules with different grooves size are proposed using the common toughness experiment
and the corresponding numerical models are established in this paper. The resistance curves and
fracture toughness of each type of specimens are obtained and compared with that of finite element
analysis. Furthermore, the stress distribution, J-integral distribution and stress triaxial constraint
of the specimen are analyzed, as well as the influence of side grooves size on the determination of
fracture toughness is also discussed. The results obtained from the study will provide a reference to
the fracture toughness evaluation research and application of X90 pipeline steel.
Keywords:
X90 pipeline steel; stress triaxial constraint; fracture toughness; fatigue crack; side grooves;
J-integral
1. Introduction
With the advantages of large transportation volume, strong economy and high safety,
pipeline transportation has become the main transportation mode of oil and natural gas [
1
].
Due to the long distance and complex terrain of pipeline transportation, the high toughness,
fatigue resistance, corrosion resistance and fracture resistance are the necessary properties
of pipeline steel. The research shows that improving the grade of pipeline steel is the most
effective way to increase the oil and gas transport capacity and reduce the cost of pipeline
construction and transportation [
2
–
4
]. The reason for this is that upgrading the grade of
pipeline steel, such as X70 to X80, can reduce the amount of pipeline steel by 8% to 12%
when the transmission pressure and diameter are determined. At present, X90, X100 and
X120 have been successfully trial produced. In fact, X100 and X120 have made very slow
progress in industrial application due to their high requirements for strength and toughness.
Compared with X80, the strength and toughness of X90 pipeline steel have been improved,
and the span is relatively moderate, so it has become an excellent breakthrough point to
stride into ultra-high strength steel [
5
]. Given that the fracture toughness is one of the key
factors for the stable work of pipeline steel, the research on the fracture toughness of X90 is
of great significance to promote the engineering application of high-strength pipeline steel.
Many investigations have been conducted to study in depth the fracture toughness of
various grades of pipeline steels, including the influence of hydrogen, long term ageing,
temperature, thickness, pre-strain and so on [
6
–
14
]. The static and dynamic fracture
Metals 2022, 12, 72. https://doi.org/10.3390/met12010072 https://www.mdpi.com/journal/metals
