# A Case Study of Floating Offshore Super-Long Steel Pipeline Combing with Field Monitoring
## 4 Analysis of Monitoring Results  
### Strain Monitoring Results  
The pipeline body followed the direction of the flow before the floating movement began. After the floating movement started, the pipeline body was rotated counterclockwise at a speed of about \(2^{\circ}/\min\). It rotated to the direction perpendicular to the flow at 45 min, and to the designated position at 110 min, with the strain value tending to be stable. Figure 8 shows the strain during the floating movement process of pipeline Section 1. The maximum tension strain at the point 1-1 facing the water surface is 99.1 \(\mu\epsilon\), and the maximum pressure strain is \(-122.3\)\(\mu\epsilon\); at the top measuring point 1-2, the maximum tensile strain is \(55.4\)\(\mu\epsilon\), and the maximum pressure strain is \(-48.6\)\(\mu\epsilon\); the maximum tensile strain is \(150.9\)\(\mu\epsilon\) and the maximum pressure strain is \(-52.4\)\(\mu\epsilon\) at the backwater detection point 1-3. The measuring point 2-1 was located at the corner outside the surface of the water. It used a unidirectional strain gauge and the maximum strain was along the axis of the straight pipeline section. The maximum tension strain is \(57.9\)\(\mu\epsilon\), and the maximum pressure strain is \(-100.4\)\(\mu\epsilon\). The measuring point 2-2 was at the top, the main stress direction is clear, and the right-angle strain flower is adopted, \(0^{\circ}\) along the axis direction and \(90^{\circ}\) vertical pipeline axis direction. The maximum tensile strain of \(0^{\circ}\) is \(44.5\)\(\mu\epsilon\), and the maximum pressure strain is \(-78.4\)\(\mu\epsilon\). The maximum tensile strain of \(90^{\circ}\) is \(87.7\)\(\mu\epsilon\), and the maximum pressure strain is \(-60.2\)\(\mu\epsilon\). Measuring points 2-3 at the angle of the backwater, the direction of principal stress was unknown, so the tri-directional strain flower  
Figure 7: Arrangement of strain and modal measuring points. (**a**) Section arrangement of pipeline. (**b**) Point arrangement of section. is adopted. The maximum tensile strain of 0\({}^{\circ}\) is 177.9 \(\mu\epsilon\), and the maximum pressure strain is \(-\)99.9 \(\mu\epsilon\). The maximum tensile strain of 45\({}^{\circ}\) is 60.4 \(\mu\epsilon\), and the maximum pressure strain is \(-\)24.5 \(\mu\epsilon\). The maximum tensile strain of 90\({}^{\circ}\) is 44.7 \(\mu\epsilon\), and the maximum pressure strain is \(-\)135.7 \(\mu\epsilon\). The maximum tensile strain at the facing water surface measuring point 3-1 is 66.9 \(\mu\epsilon\), and the maximum pressure strain is \(-\)130.6 \(\mu\epsilon\). The maximum tension strain at the top measuring point 3-2 is 14.5 \(\mu\epsilon\), and the maximum pressure strain is \(-\)68.2 \(\mu\epsilon\). The maximum tension strain at the backwater detection point 3-3 is 85.3 \(\mu\epsilon\), and the maximum pressure strain is \(-\)53.1 \(\mu\epsilon\). The cables of measuring points 3-1 and 3-2 were pulled during floating transportation, and the strain curve shows a downward trend. In the early stage of floating transport of pipeline segment 1, the pipeline rotated from downstream to cross-flow, and the middle tugboat had a large jacking force to correct it, so there was a short tension stage on the upstream and a short compression stage on the water-carrying side. At the time of floating transport of 72 min, a strong wind suddenly blew on the sea surface, causing an abrupt increase in the strain of the pipeline. In general, the strain in the floating transportation of pipeline Section 1 does not exceed the warning value. The steel pipeline is pressed against the surface of the water or pulled away from the surface of the water, and the strain curve is anti-symmetric. The strain of the windward side and the dorsal side of pipeline Section 1 is significantly greater than that of the top.