Implementation of linear, double-linear, and nonlinear fatigue damage accumulation rules for fatigue life prediction of offshore drilling top-drive tie-rods

J E Inoma,J Zec,D G Pavlou

doi:10.1088/1757-899x/700/1/012025

Abstract

The offshore oil and gas industry has been exposed to major challenges over the last decade, particularly demanding cost cuts and more effective technical solutions. Predictive systems and remaining life assessments for both machine and structural components are known to be one of the core areas that has gathered much attention lately. This paper focuses on multiaxial fatigue that is a problem in number of engineering structures and equipment. The ability to properly assess and quantify multiaxial fatigue of offshore equipment and structures has major benefits for owners of engineering assets both in terms of technical and safety integrity. Traditionally, Palmgren-Miner’s damage rule is used for life estimation involving multiaxial fatigue due to its ease of use. There are however some known shortcomings with Palmgren-Miner’s rule namely: it does not consider the loading sequences. This for instance can result in overestimation of fatigue life in scenarios where stress amplitudes are decreasing, and moreover underestimation of fatigue life in scenarios where stress amplitudes increase. This research work thus involves closely studying the application of Palmgren-Miner’s linear damage rule, Manson’s double linear damage rule, and Subramanyan’s non-linear damage rule for the purpose of enhancing the predictability of damage as well as accuracy of fatigue life assessments. Each of these techniques were applied for tie-rods of an offshore drilling top-drive having a known stress history. The loading histories were provided by a drilling company. The torque and axial force values are transformed to stress components for the corresponding critical spots. The “rainflow” counting technique is applied to the obtained stress histories and the mean stress effect is considered for the damage accumulation calculations. The fatigue life prediction of the three models are justified and discussed. This research work was aimed at contributing towards the utilization of more robust fatigue life estimation techniques such as Manson’s double linear damage rule and simplified non-linear damage rules which capture the true nature of the fatigue that equipment’s are subjected to, and thus to improve the reliability of the fatigue life predictions.

Highlights

Condition monitoring and equipment maintenance are essential activities which must be carried out by managers of modern engineering assets, equipment and infrastructure
This is so important because using wrong models and assumptions will result in scheduled maintenance or replacement being initiated for equipment which could have been used for many more years without failure or can underestimate the fatigue damage increasing the risk when using such equipment
The damage accumulation results obtained from the selected models show that Miner’s rule was consistently less conservative in its prediction for the accumulated damage in comparison to Manson’s double linear damage rule and Subramanyan’s non-linear damage rule

Summary

Introduction

Condition monitoring and equipment maintenance are essential activities which must be carried out by managers of modern engineering assets, equipment and infrastructure. To fully harness the advantages of condition monitoring, correct models need to be used to determine the structural integrity of equipment and infrastructure that are being utilised for operations. This is so important because using wrong models and assumptions will result in scheduled maintenance or replacement being initiated for equipment which could have been used for many more years without failure or can underestimate the fatigue damage increasing the risk when using such equipment

Objectives

Results

Conclusion