A New Automated Tool-Joint Inspection System To Reduce Drillstring Failures
- Bruce McPherson (Inspectorate/OIS) | Paul Dutton (Inspectorate/OIS) | B.A. Dale (Exxon Production Research Co.) | T.S. Chilton (Esso E and P U.K.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- June 1991
- Document Type
- Journal Paper
- 153 - 159
- 1991. Society of Petroleum Engineers
- 5.5.2 Core Analysis, 1.10 Drilling Equipment, 4.2.3 Materials and Corrosion, 2.4.5 Gravel pack design & evaluation, 2.2.2 Perforating, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.6.1 Drilling Operation Management, 1.6 Drilling Operations
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Drillstring connection failures continue to be a costly problem for the oil industry. To reduce the occurrence of these failures, operators and drilling contractors typically specify periodic nondestructive inspections to remove damaged tubulars from service. Conventional inspections generally involve the use of magnetic particles, and performance is highly dependent on human factors, which can result in errors by inspectors. This paper describes the development of a new automated tool-joint inspection system (ATIS) based on electromagnetic-flux-leakage principles to detect common service-induced flaws reliably, such as fatigue cracks, stretched threads, and mechanical damage. ATIS is capable of inspecting common connections on drillpipe and drill collars in the pipeyard and at the drillsite. Laboratory testing and field experience show that ATIS limits the probability of human error and thus reduces the occurrence of costly drillstring failures.
Drillstring failure is a serious problem that has troubled the petroleum industry for many years, often resulting in lost rig time and petroleum industry for many years, often resulting in lost rig time and damaged tubular goods and occasionally in abandoned or side-tracked wells. Despite the many advances that have been made in drilling since the development of the first rotary drilling rigs, drillstring failures are still common. Operators and drilling contractors try to prevent these costly failures by performing periodic nondestructive inspections to remove damaged tubulars from service. A large proportion of these failures occur in the drillstring connections, typically in the second or third thread root from the shoulder on the pin and in the threads just outside the makeup area on the box (Fig. 1).
It is generally agreed that most drillstring failures are caused by some form of metal fatigue and/or associated corrosion. To guard against these failures, the industry uses periodic nondestructive testing (NDT) to check for fatigue cracks and other potentially serious imperfections, such as pin stretch and thread damage.
Previous fatigue studies proved that fatigue-crack growth can constitute a significant portion of the total fatigue life for drillstring tubulars and that it was feasible to establish inspections on this basis. Other studies, however, indicated that the reliability of the NDT techniques typically used for drillstring connection inspection was often limited by human factors, such as the skill, patience, and visual acuity of the inspector, and by the high level of cleanliness required by NDT techniques involving the use of magnetic particles. In the early 1980's, Exxon developed a prototype inspection particles. In the early 1980's, Exxon developed a prototype inspection device that demonstrated that the inspection of drillstring connection could be successfully automated. This paper describes the design, construction, use, and performance testing of an enhanced system based on this early prototype.
New Inspection System
ATIS is based on the theories of electromagnetic-flux-leakage inspection (EMI). The method analyzes the disturbances (i.e., leakage flux) with an active or a residual magnetic field caused by a flaw or discontinuity. The method is well established and applied extensively in equipment used for the inspection of oil-country tubular goods (OCTG). ATIS consists of two detector heads that engage the pin and box threads, an electronic console that controls the system's operation and output, and associated detector-head handling equipment. Figs. 2 and 3 illustrate the general arrangement of the detector heads. Each detector head contains a magnetizing coil that induces a closed-loop longitudinal magnetic field in the connection being inspected. Magnetic flux leakage is detected by a probe containing two Hall elements mounted directly above two adjacent thread crests. The probe is driven around the critical thread area in a helical path with the same pitch as the threads being inspected, thus maintaining the position of the Hall elements directly over the thread crests position of the Hall elements directly over the thread crests throughout the scan. A thin-wall nonmagnetic conical sleeve fitted between the probe and the threads protects the probe and internal parts from the connection. Thus, only minimal cleaning of the threads is required before an inspection.
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