Automatic free span assessment for subsea pipelines using static strain data

Abstract

Free-spanning of subsea pipelines is a common problem that may threaten structural health. Free span assessment using online measurements could benefit the integrity management of subsea pipelines. However, existing approaches have the limitation that the required vibration data is difficult to collect. This study presents an automatic free span assessment method using only static strain measurement. The premise is that the assessment only needs to be valid in some typical load conditions, allowing us to exclude the scenarios with dramatic and nonlinear responses so that the ill-posed problem is simplified. First, a batch-mode inverse finite element method (iFEM) is proposed to reconstruct the full-field deformation using noisy static strain data. Second, a model updating procedure is conducted to find the best predictions on the free span length. Validations against numerical simulations of single-span pipelines indicates the present batch iFEM has higher accuracy and superior noise robustness than the standard iFEM and conventional modal superposition (MS) method. The estimation of free span length achieves higher accuracy than the spatial resolution of sensors. However, further investigation is required to make this approach compatible with more complicated multi-span conditions and load cases.