Fatigue Life Evaluation: A Key to Avoid Drillpipe Failure Due to Die-marks

Abstract

Slips and tongs produce permanent marks on pipe body and tool joints. Such marks develop high stress concentration that reduces strength of pipes. The remaining strength of pipes often falls below the pipe stresses which can lead to tubular failure. Slim pipes are most susceptables to failure due to die- marks. In many instances, slim pipes are handled using double elevator system to reduce pipe failure. In this paper, results of a recent study of various die-mark related failures of drill pipes under different loading conditions, with particular emphasis on fatigue damage are presented. Stress concentration due to die-marks is characterised by finite element analyses as a function of mark sizes to cover various gripping systems available in the market. Then a methodology is presented for the prediction of failure due to cumulative fatigue damage. Effect of stress concentration arising from die-marks is taken into account in the analysis. Results of this study suggest that the effect of stress concentration on the cumulative fatigue damage may be significant depending on particular gripping system in use. In most cases, the fatigue life evaluation based on conventional assumption of smooth pipe surface is found to be very unsafe. Thus, a new approach is proposed in this paper for prediction of true safe life of marked drillpipes against fatigue failure. Fatigue damage results are presented in graphical forms. Calculation of cumulative fatigue damage of drillpipes used in a number of drilling events is then presented systematically in tabular form to assist drilling engineers in the evaluation of actual remaining fatigue life of drillpipes for the target drilling event using a particular gripping system. P. 125

Finite Element Modeling of Slip Insert Geometric Grip Optimization for Oil Well Drill Pipes

“…Looking at the results of the present literature survey in more detail, most of the identified publications were focused on the crushing force or handling limitation of the slip [24,25]. e structure or geometry of the slip insert undoubtedly has a considerable influence on the mechanical behavior of the DP because permanent marks are produced on the pipe body [26,27]. As a result, conducting researches on optimization of the slip insert is of great significance.…”

Finite Element Analysis of Drill Pipe-Slip System

“…After reviewing and analyzing the existing literature, it has been understood that the current efforts are focused on calculating the slip crushing load or the clamping limits of the slip (Zhang et al, 2010;Tikhonov et al, 2017;Paslay et al, 2006), whereas the sensitivity of the slip insert structure and geometric parameters has rarely been analyzed. Since the slip insert creates permanent die marks on the DP, the structure of the slip insert is of great importance (Hossain et al, 1998;Bordet et al, 2016). However, the cost for carrying out experimental tests for the purpose of optimizing the structure of slip insert is almost prohibitive, as it requires the multiscale high fidelity computations using Finite Element Methods (FEMs) (see e.g.…”