Development of Lightweight Steel Drillpipe With a 165-ksi Yield Strength
- Yasushi Tsukano (Nippon Steel Corp.) | Masakatsu Ueno (Nippon Steel Corp.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- September 1991
- Document Type
- Journal Paper
- 209 - 214
- 1991. Society of Petroleum Engineers
- 4.2.3 Materials and Corrosion, 1.6 Drilling Operations, 1.10 Drilling Equipment
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This paper describes the development of a lightweight steel drillpipe with a 165-ksi (1137-MPa) yield strength. The drillpipe was developed according to three design objectives and verified by full-size and material-evaluation tests. The lightweight steel drillpipe has two advantages over standard API G-105 pipe with the same pipe-body OD-it weighs 25% less and has a 20% lower hydraulic loss (loss of pipe-body OD-it weighs 25% less and has a 20% lower hydraulic loss (loss of fluid pressure)-but maintains a performance level comparable with that of G-105 pipe.
Wider application of horizontal and extended-reach drilling has in-creased the need for lightweight drillpipe to reduce the greater torque and drag caused by increasing hole angles. Lightweight aluminum and titanium drillpipes were developed but are not widely used because they are much more costly than heavier steel drillpipe. Therefore, from an economic viewpoint, lightweight steel drillpipe is the best type of pipe for horizontal and extended-reach applications.
The weight of steel drillpipe is reduced by decreasing the pipe's wall thickness. Performance is maintained by use of high-strength steel. This is the ordinary way to design a lightweight pipe; how-ever, in the case of drillpipe, it is only the starting point of development. For example, the upset configuration must be designed so that it can be fitted to the thin pipe body. The tool joint also needs to be selected on the basis of its adaptability to the upset. Furthermore, both designs should minimize hydraulic loss in the drillpipe.
We established three design objectives.
1. The ID had to be as large as possible to mi hydraulic loss.
2. The stress concentration at upset transitions had to be reduced to prevent fatigue failures.
3. The upset had to be as thin as possible on the basis of the allowable section modulus. The allowable section modulus was calculated with the following equation:
Zu=Zp(Hp/Hu) ................................... (1)
where Zu =the allowable section modulus of upset, ZP =the section modulus of pipe body, Hp = the Vickers hardness of pipe body, and Hu = the lowest Vickers hardness in upset.
Pipe Body. A pipe OD of 5 in. [127 mm] was selected because Pipe Body. A pipe OD of 5 in. [127 mm] was selected because it is common in drilling. The pipe body was 0.256 [6.5 mm] thick for practical reasons. The yield strength was 165 ksi [1137 MPa], the highest commercial grade.
Upset. External upset initially was used as the upset type for the lightweight drillpipe because the large ID effectively reduced hydraulic loss; however, stress was concentrated at the external upset transition (see Fig. 1). To lessen the stress concentration, the pipe thickness at the external transition was increased slightly by use of pipe thickness at the external transition was increased slightly by use of the internal upset. Fig. 2 shows the final upset design.
Fig. 3 shows the upset's bending stress contours. Because the stress concentrations at the upset transitions were reduced effectively, the maximum stress was not observed at either the external or internal upset transitions.
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