Experimental study on the influence of bending and straightening cycles for non-destructive and destructive coiled tubing. (May 2021)

• Record Type: Journal Article
• Authors: Qian bei, Yue; Guohao, Sun; Gang, Wang; Jubao, Liu; Ming, Yang; Qiang, Zhang
• Is Part Of: Engineering failure analysis. Volume 123(2021)
• Publication Date: 2021-05
• Subjects: Coiled tubing -- Ellipse -- Scratches -- Internal pressure -- Bending and straightening; System failures (Engineering) -- Periodicals; Fracture mechanics -- Periodicals; Reliability (Engineering) -- Periodicals; Pannes -- Périodiques; Rupture, Mécanique de la -- Périodiques; Fiabilité -- Périodiques; Fracture mechanics; Reliability (Engineering); System failures (Engineering); Periodicals; Electronic journals; 620.112
• DOI: 10.1016/j.engfailanal.2021.105218
• Languages: English
• ISSNs: 1350-6307

Abstract

Highlights: The non-destructive and destructive specimen are carried out cyclic experiments. The internal pressure with 40 MPa is a critical pressure for the of underground operations. If the internal pressure and ellipse exist simultaneously, the ellipse can neglect. The influence of circumferential scratches on the fatigue life is greater for the coiled tubing. The formula of fatigue life is established for destructive coiled tubing. Abstract: During each operation in wells, the coiled tubing has to undergo three straightening-bending-straightening plastic deformations, causing different damages on coiled tubing (ellipse, scratches on the surface), which results in low cycle fatigue failure occurring frequently. According to the failure shapes and causes of the coiled tubing, the described damage forms of coiled tubing are: ellipticity, axial scratches, circumferential scratches and square pits. A special fatigue experimental device is designed and built under the electronic universal tensile testing machine CMT5105 in the laboratory, and the commonly used 2–3/8″ coiled tubing is selected. The non-destructive and destructive coiled tubing with ellipse and scratches are carried out cyclic bending-straightening experiments. The experimental results show that: (1) When the internal pressure of the coiled tubing is less than 40 MPa, it does not affect the number of underground operations for the coiled tubing, but the applied internal pressure is equal to or greater than 40 MPa, the number of underground operations is significantly reduced. (2) If the internal pressure and ellipse exist simultaneously on the coiled tubing, the ellipse has little effect on the number of operations. (3) The influence of circumferential scratches on the fatigue life is greater for the coiled tubing, while the axial and square pits have less effect on the cyclic numbers. (4) The formula of fatigue life is established for destructive coiled tubing, which can provide theoretical basis for the failure prediction and control for coiled tubing in engineering.