https://orcid.org/0000-0003-3761-4260
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ABSTRACT
Initial geometric imperfections and corrosion defects were considered as two of the most common imperfections for subsea pipes, which could lead to an inevitable reduction of collapse capacity. In this study, the coupling effect of both types of defects on the collapse performance was investigated numerically, with a particular focus on the relative corrosion position as described by defect location angle (DLA). A customised numerical framework was established to efficiently build FE models with various corrosion defects and imperfect geometry. Verification of the finite element (FE) model was performed using existing experiments in the open literature. In addition, extensive sensitivity studies were then conducted for several key problem parameters, including defect length, width, depth, initial ovality, and DLA. The variation of normalised collapse pressure with DLA exhibits two types of trajectories, namely ‘Minor Decrease’ and ‘Constant-Decrease-Constant’ responses. In the first, the normalised collapse pressure decreases slightly with increasing DLA. Among these cases, if the ratio stays above or close to 1.0, the collapse takes the form of classical ovalization mode. In contrast, for cases below 1.0, the collapse occurs in the corroded region. For the latter type of trajectory, the normalised collapse pressure follows a ‘Constant-Decrease-Constant’ path, and the collapse mode involves ovalization, anti-ovalization, non-symmetrical and U-shaped pattern. Subsequently, a series of empirical formulas were proposed upon extensive simulation results to predict the collapse pressure of non-symmetrical defect pipes.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the National Natural Science Foundation of China [grant numbers 52071290, 51779223].
Nomenclature
| c | = | circumferential width of the defect |
| d | = | maximum depth of the defect |
| D | = | outer diameter of the pipe |
| E | = | Young's modulus |
| E’ | = | strain hardening modulus |
| l | = | maximum length of the defect |
| L | = | length of the pipe |
| n | = | parameter of material strain hardening |
| PCO | = | collapse pressure of intact pipe with 0.1% initial ovality |
| PCOR-α | = | collapse pressure of non-symmetrical defect pipe |
| PCOR-90 | = | collapse pressure of non-symmetrical defect pipe with DLA α=90° |
| t | = | wall thickness of the pipe |
| U1, U2, U3 | = | displacement in x, y, z axes |
| x, y, z | = | Cartesian coordinates |
| Δ0 | = | initial ovality of the pipe |
| α | = | defect location angle DLA |
| σ0.5 | = | yield stress at a strain of 0.5% |
| σy | = | effective yield stress |