# Test System Development and Experimental Study on the Fatigue of a Full-Scale Steel Catenary Riser

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## Abstract

**:**

## 1. Introduction

## 2. Development of the Counterforce Frame

#### 2.1. Main Components of Counterforce Frame

#### 2.2. Force Analysis of the Counterforce Frame

## 3. Development of the Loading System

#### 3.1. Internal Hydraulic Loading System

#### 3.2. Servo Mechanism for Axial Tension/Compression Loading and Torsion Bidirectional Loading

#### 3.3. Four-Point Bending Moment Bidirectional Loading Servo Mechanism

#### 3.4. Hydraulic Loading Servo System

- (1)
- The full size of the test system (main body of the system) was 26 m, the size of the counterforce frame was 24 m, and the longest size of the test pipe section was 22 m;
- (2)
- The maximum loading capacity of the test system was designed to be 3000 kN dynamic axial force, 1300 kN·m dynamic bending moment loading, 200 kN·m torque loading, and 60 MPa internal water pressure loading, with a loading frequency of 30 Hz.

## 4. Full-Scale Riser Fatigue Test

#### 4.1. The Test Process

- The first-order frequency of the filling riser was 3.4 Hz, and the effect of the rising water pressure on the first-order frequency could be ignored;
- Under a loading of 48 MPa internal pressure, the axial displacement changed by 8.9 mm, and 732 kN axial tension continued to be applied. The overall axial displacement changed by 2.3 mm. The total change in pipeline displacement was 11.2 mm;
- On the basis of 48 MPa internal pressure and 732 kN axial tension, when the axial tension was applied at 2900 kN, the axial displacement increased by 7 mm, and the pipeline displacement reached 18.2 mm. The stress value reached the maximum stress value in the high-stress experiment;
- On the basis of 48 MPa internal pressure and 732 kN axial tension, when the axial pressure was applied at −1500 kN, the axial displacement decreased by 7 mm, and the pipeline displacement reached 4.2 mm. The stress value reached the minimum stress value in the high-stress experiment.

- (1)
- An internal pressure of 48 MPa was applied;
- (2)
- A fixed axial tension of 732 kN was applied, and the average stress reached 138 MPa;
- (3)
- A cyclic axial force between −1500 and 2900 kN was applied. The cyclic range of axial displacement was ±7 mm, meeting 172 MPa (±86 MPa) of cyclic stress.

#### 4.2. Weld Test Results

#### 4.3. Fatigue Analysis Based on BS7608

_{0}is the correlation constant of the average S–N curve, D is the standard deviation below the mean, $\sigma $ is the relative standard deviation of N, and m is the reverse slope of the S–N curve under a double logarithm.

_{B}is the equivalent stress of the joint fatigue strength using the basic curve, t is the actual plate thickness when the thickness is greater than 16 mm, and t

_{B}is the maximum plate thickness corresponding to the basic S–N curve, which is 16 mm.

#### 4.4. S–N Curve Selection and Riser Thickness Correction

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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Internal Pressure Loading Control System for the Specimen | |||||||
---|---|---|---|---|---|---|---|

Loading Pressure Range | Maximum Loading Speed | Load Function | Pressure Control Accuracy | Pressure of the Pipeline and Valve | Environmental Conditions | ||

0.5~60 MPa | 10 MPa/min | Single linear loading or low-frequency cyclic fatigue loading | Lifting and lowering accuracy: less than ±0.2 MPa under 5 MPa; | Pressure load retention accuracy: less than ±0.5 MPa | ≥70 MPa | Temperature: −5 °C~+40 °C; | Medium: tap water or 3.5% saltwater |

Size of Specimen | Axial Force | Bending Moment | Torque | Internal Pressure MPa |
---|---|---|---|---|

L ≤ 22 m D < 609.6 mm | 3000 kN | 1300 kN·m Loading schedule ± 150 mm | 200 kN·m | 60 |

**Table 3.**Weld inspection of the full-scale domestic steel catenary riser in a high-stress fatigue test.

The Weld Number | Test Results | Types of Crack | |||||
---|---|---|---|---|---|---|---|

Defect Wave Reflection Region | Defect Location (mm) | Defect Indication Length (mm) | Defect Levels | ||||

L1 | L2 | Depth | |||||

G1 | III | 57 | 318 | 3.1~27 | 261 | III | Weld fatigue stress crack |

III | 531 | 855 | Through-wall crack | 324 | |||

G2 | III | 114 | 327 | 6.2~27 | 213 | III | |

III | 605 | 797 | 5.6~27 | 192 | III | ||

G3 | III | 24 | 270 | Through-wall crack | 246 | III | |

III | 449 | 735 | 2.3~27 | 286 | III | ||

III | 897 | 989 | 7.3~27 | 92 | III |

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## Share and Cite

**MDPI and ACS Style**

Yu, J.; Wang, F.; Yu, Y.; Liu, X.; Liu, P.; Su, Y.
Test System Development and Experimental Study on the Fatigue of a Full-Scale Steel Catenary Riser. *J. Mar. Sci. Eng.* **2022**, *10*, 1325.
https://doi.org/10.3390/jmse10091325

**AMA Style**

Yu J, Wang F, Yu Y, Liu X, Liu P, Su Y.
Test System Development and Experimental Study on the Fatigue of a Full-Scale Steel Catenary Riser. *Journal of Marine Science and Engineering*. 2022; 10(9):1325.
https://doi.org/10.3390/jmse10091325

**Chicago/Turabian Style**

Yu, Jianxing, Fucheng Wang, Yang Yu, Xin Liu, Pengfei Liu, and Yefan Su.
2022. "Test System Development and Experimental Study on the Fatigue of a Full-Scale Steel Catenary Riser" *Journal of Marine Science and Engineering* 10, no. 9: 1325.
https://doi.org/10.3390/jmse10091325