Tracking the bending and internal pressure history of coiled tubing (CT) at the reel and guide arch, as it is run in and out of wells during field operations, is accepted throughout the industry as the preferred method for predicting the fatigue damage distribution along the string throughout its life. A mathematical model, relating bending strain and hoop stress (from internal pressure) to cumulative fatigue damage can be applied to this recorded field loading history. Such models determine when tubing should be retired or when tubing cuts should be made in order to maximize the utilization of the pipe while minimizing the chance of pipe failure. The problem of CT fatigue has been studied extensively in the lab, using constant pressure bend cycling and/or axial coupon testing. However, models resulting from experimental programs have seldom been correlated in the literature with CT behavior under field loading conditions. This paper presents such validation by correlating the experimentally determined cycles to failure of CT samples which have had extensive use in field operations, to predictions from an advanced predictive fatigue algorithm. The string, from which the samples were taken, had been removed from service based on criteria specified by the operating company for which the CT work was being performed. This stated that strings were to be retired after a given value of "running meters" had been reached, rather than on the actual bending and internal pressure history. Excellent agreement is demonstrated between the actual remaining fatigue life of the tubing, determined experimentally, and the estimated cycles to failure predicted by the fatigue model. Therefore, it is shown that the string could have been safely utilized much longer than the current string retirement specification allows. Based on the results of this testing, the operating company has changed its criterion for CT string retirement to one that relies on tracking of bending and internal pressure history and subsequent predictive fatigue modeling based on this history.
Field Validation of a Coiled Tubing Fatigue Model
2003
6 Seiten, 13 Quellen
Conference paper
English
SAE Technical Papers | 1960
Full-scale coiled tubing fatigue tests with tubing pressures to 15,000 psi
Tema Archive | 1999
|Coiled tubing and vessel motions for riserless coiled tubing systems
Tema Archive | 2004
|Fatigue monitoring of coiled tubing in downline deployments
European Patent Office | 2023
|