A Novel Proof of Concept Experimental Setup for Seabed-Pipe Interface Friction Measurements

Abstract

Offshore hydrocarbon pipelines operate at relatively high pressures and temperatures. These conditions lead to their expansion and contraction and ultimately result in pipeline buckling or “walking” after multiple cycles of operation. Such movements are typically opposed by the axial resistance of the pipe-soil interface, which has to be accurately evaluated to optimize the engineering performance of the pipelines while minimizing testing and construction costs. To date, different testing techniques have been adopted to evaluate this resistance throughout the pipeline operational life. These include laboratory soil element testing, laboratory model testing, and in situ testing using specialized, complex, and costly devices. Despite being the most reliable testing technique, in situ tests are limited by the very small number of available specialized field equipment, e.g., the Fugro SMARTPIPE and the recently developed “pipe-like” penetrometers, both of which suffer from some drawbacks related to high costs, practicality, and testing conditions. This paper presents an attempt at addressing most of the limitations that were identified in the currently available methods, leading to the development of a new in situ, cost-effective apparatus for measuring axial pipeline resistance. A laboratory proof of concept experimental setup that could be adapted in future work to become an autonomous field apparatus was designed, produced, deployed on a clay bed and tested under normal stresses in the low-pressure range. The prototype reliably captured the effects of normal stress on the drained interface resistance. It produced accurate interface friction factors that are comparable to those obtained from the direct shear tests on the same soil and interface. The results obtained are very promising and confirmed the practicality and functionality of the proposed prototype. Some areas of improvement that would enhance the efficiency and reliability of the test were identified and will be applied to future versions of the device.