Connection Fatigue Modeling with Large IDs: How Large of an ID Can Support a SRG?
- Grant Pettit (T H Hill Associates) | Kang Lee (T H Hill Associates)
- Document ID
- Society of Petroleum Engineers
- IADC/SPE International Drilling Conference and Exhibition, 3-5 March, Galveston, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2020. IADC/SPE International Drilling Conference and Exhibition
- Stress Relief Groove, Fatigue, MWD/LWD, Inspection, Stress Relief Features
- 1 in the last 30 days
- 85 since 2007
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Drilling specialty tools and accessories are often machined with large Inside Diameters (IDs) so that the necessary electronic packages can fit within the component. As the ID of the component increases, the wall thickness of the pin connection is reduced. It has been established that the machining of a Stress Relief Groove (SRG) on the pin connection with a standard-sized ID will greatly improve the fatigue performance of that connection. However, no such consensus has been reached regarding the machining of SRGs on the pin connections of these special-purpose tools with large IDs.
The common concern is that the wall thickness of the pin connection has been reduced so much by the large ID that the machining of a SRG would drastically deteriorate the performance of the connection. This paper addresses that concern by providing in-depth analysis of various API connection sizes tested over a broad range of IDs. Finite Element Analysis (FEA) was used to quantify the difference in fatigue life between connections with stress relief features versus without stress relief features. Additionally, calculations were performed to understand the reduction in the capacity of the connection that results due to machining stress relief features.
This paper gives the comparative fatigue life for each of the connections modeled where the API recommended Make-Up Torque (MUT) is adjusted to compensate for the increasing ID of the connection. In every case, the benefits of machining SRGs on large ID connections are significant. Allowing larger IDs in connections where SRGs are required will bring the technical benefit of allowing larger electronics packages to fit within the bore and increased hydraulic performance, among other benefits. Additionally, the drawbacks to SRGs are considered and quantified whenever possible. Possible solutions to these drawbacks are proposed as a way to lessen their effects so the full benefit of cutting the SRGs can be realized.
In total, by looking at the potential gain in fatigue life against the trade off in lost capacity, this paper provides operators with the ability to determine the suitability of stress relief features on their components with large IDs. For those connections where a SRG is required, this paper provides guidance as to the connection's performance at various large IDs.
|File Size||764 KB||Number of Pages||5|
Ellis, S., Reynolds, N., Lee, K. 2004. Use NC56 Connections on 8? Drill Collars and Cut 1? or 3/4? Pin Stress Relief Grooves on Rotated BHA Connections NC38 and Larger. Paper presented at the IADC/SPE Drilling Conference, Dallas, TX, USA, 2-4 March. IADC/SPE 87191. https://doi.org/10.2118/87191-MS.