Distributed monitoring method for upheaval buckling in subsea pipelines with Brillouin optical time-domain analysis sensors

Abstract

A method for monitoring the upheaval buckling of subsea buried pipelines by distributed optical fiber sensors is introduced. The proposed method originates from the fact that the bucked pipe has the deterministic patterns of the bending-induced and axial force–induced strains, which can be used to identify the pre- and post-buckling states of the pipe. The challenge for utilizing these features is that the distributed fiber optic sensor can only measure the compound strain created by both bending and axial compression. A monitoring scheme by placing three sensors with [Formula: see text] space around the circumference of the pipeline was proposed in this article. An approach was presented to extract the bending-induced and axial force–induced strains from the longitudinal strains measured by the distributed fiber optic sensors. The experimental programs were then designed to investigate the feasibility of the proposed method. It is demonstrated that the proposed method is possible to detect the occurrence of buckling in the pipe. However, further research is necessary in order to examine the efficiency of the proposed approach under the complex loading patterns at subsea levels.

Laboratory Testing of FBGs for Pipeline Monitoring

“…If the strain energy is stored mostly as axial compression, it may be converted to bending during buckling. To bring about this transformation, significant deflections are needed [ 19 ]; as a consequence, the bending behavior is not necessarily indicative of buckling, being observable also in the phase preceding this event, which can nonetheless be unequivocally identified by distinctive trends of axial and bending strains, extracted from the measured longitudinal one: Condition 1, an increase in tensile strain or, correspondingly, a release of compression (geometric shortening – Section 2.1 ) within the bend; Condition 2, the generation of bending strain in the same tract [ 18 ]. …”

“…Feng et al [ 18 ] worked out a method based on DBFSs for detecting the upheaval buckling of buried subsea pipelines. The model pipe was made of polyvinyl chloride (the preference for PVC over steel was dictated by the small scale of the experiment: the lower the stiffness, the easier it will be to trigger buckling); its initial shape was not straight due to imperfect manufacturing.…”

“…Equation (1) contains three unknowns (namely the axial strain, the maximum bending strain and the angle) and can be solved if as many measurements of longitudinal strain per cross section are performed. The issue can be resolved as suggested by Feng et al [ 18 ], who proposed that sensors should be arranged at intervals of 120° around the circumference (that is to say, at 12, 4 and 8 o’clock). A (determined) system of three equations in three unknowns must be solved: …”

Inspection and monitoring systems subsea pipelines: A review paper

“…In a recent report, through the installation of three fibers distributed equally around the circumference of the pipeline, buckling and upheaval, along with the effects of the hydrostatic pressure from the water column onto the pipe shape, can be detected and estimated. 228 Pipeline corrosion and leakage can also be monitored using DSS 229 . On the other hand, distributed fiber sensors dedicated to distributed temperature sensing (DTS) have been used to detect thermal 217 (Bottom) Encapsulation to enhance and protect FBG sensors for leakage detection.…”

Definition of damageability of the sea buried pipeline by method of spectral summation of tension at vibrations caused by technological and casual seismic loadings

“…A relation linking tensor of the random strain with equivalent stress is called von Mises equation. [2][3][4] ( )…”