A dive into the friction performance of polyurethane tensioner pads used in offshore pipe laying

Master thesis (2023)

Authors

M.J. Schuijt Mechanical Engineering

Contributors

A. Cabboi Mechanics and Physics of Structures - CEG (supervisor 1)
E. Sulollari Mechanics and Physics of Structures - CEG (coach)
A. Grammatikopoulos Ship and Offshore Structures - Mechanical, Maritime and Materials Engineering (coach)
J. Breukels Allseas Engineering (coach)
Faculty
Mechanical Engineering
Copyright: © 2023 Rinus Schuijt
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Published Date

08-06-2023

Language

English

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Faculty

Mechanical Engineering

Abstract

In this thesis, the friction performance of polyurethane tensioner pads used in offshore pipe-laying was investigated. Tensioner pads are used in pipe-lay to create tension in a pipe. The need to understand the pads better is because of the increased use of pipe coatings and pipe lay in deeper waters. Deep water leads to more pipe tension, and polymeric coating reduces friction.

A literature review was conducted on the friction of polyurethane. From the literature review, a few variables that influence polyurethane friction behaviour were summarised into the following research question: What is the influence of normal force on the pads, pad hardness, pad geometry, and pad temperature on the friction performance of polyurethane tensioner pads?

Experiments were performed at a full-scale setup. Polyurethane has a nonlinear coefficient of friction, making it difficult to upscale results from laboratory testing. In the full-scale setup, existing pads can be tested to find the influence of the different variables from the research question. The test setup was found to be flawed. Not only did it deform due to the massive forces, but the data gathered from the hydraulic pressures was not robust and accurate enough to estimate the static coefficient of friction, which is important in tensioners. Therefore, only trends in the pad behaviour were observed.

Increased normal force on the pads was found to increase the coefficient of friction. This contradicted the literature but was likely due to the geometry of flat pads versus round pipes, where the contact surface increased when the pads were loaded. Softer pads were found to yield higher friction than pads made from harder grades of polyurethane. This effect was also found in the literature. The influence of temperature was difficult to test. Since the pads could only be heated externally before testing, temperatures were inconsistent, and test results were inaccurate. The temperature did affect the friction significantly, though, so some newly produced pads were fitted with internal heating.

Next to the experiments, different pad geometries were tested in finite element analysis. A new pad shape was found that decreased stresses, leading to higher friction.

Next to the variables of the polyurethane itself, the relative humidity was recorded. The relative humidity changed significantly during the different tests, and it was found to affect friction more than anticipated.

Three sets of new pads were produced for future testing to validate the influence of geometry and further investigate the influence of the pad temperature. Moreover, a new test setup was designed to test the coefficient of friction more accurately.