Threaded Pipe Connections
Dimitrios Katsareas
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 2 padpad horizontalhorizontal oiloil drillingdrilling
modern method of drilling for oil, where from a single point on the surface, up to 8 holes are drilled, vertically and then horizontally Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 3 oil country tubular goods OCTG
drill bit
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 4 drill pipe threaded connection
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 5 bolt / nut - threaded pipe analogy
in drill pipe connections, shoulder contact is identical to the hexagonal head contact when we pre-load a cap screw
the only differences are: (1) the thread profile and (2) the fact that both the “screw” and the “nut” are hollow, in the case of the drill pipe
in both cases the theory is the same
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 6 bolt preloading additional torque to compensate for the additional friction between the “nut” top surface and the bolt head bottom surface Ff d T C C C 2 additional torque to compensate for the additional friction between the “nut” top surface and the bolt head bottom surface
Fdm l fdm sec FfC dC TR 2 dm fl sec 2 Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 7 preloading simplified Fdm l cos fdm FfdC TR 2 dm cos fl 2 for lubricated threads, f x l is a very small number and can be neglected
l cos fdm dC TR F f 2 cos 2
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 8 designing preloaded threaded connections
l fdm fdC TR F 2 2cos 2 assuming Acr is the area of the cross-section where the connection will fail and substituting the mean thread diameter dm and the “nut” contact mean diameter dC with the corresponding radii
l Rt f TR AcrYS Rs f 2 cos where YS is the Yield Strength of the threaded connection material, Rt is the mean thread radius and Rs is the mean radius of the “bolt” / “nut” contact area
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 9 yield torque of a threaded pipe connection according to standards: API RP 7G: Recommended Practice for Drill Stem Design and Operating Limits, of the American Petroleum Institute (API) and, ISO/CD 10407-1: Petroleum and Natural Gas Industries – Drilling and Production Equipment – Part 1: Drill Stem Design and Operating Limits, of the International Organization for Standardization (ISO)
Ym A p Rt f Ty Rs f 12 2 cos
where, Ty=TR/12 is the Yield Torque (ft-lbf), Ym=YS is the Yield Strength (PSI) of the connection material, p=l is the pitch (inches), A=Acr is the area (sq.in.) of the cross-section where the connection will fail (or critical area) and θ=α is the thread angle (o). The rest of the nomenclature remains the same as in the previous slide. Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 10 rotary shouldered connection geometry
Rt dm 2
RS OD QC 4
A OD2 Q2 B 4 C
2 A d B ID2 for API round thread, B H 2s P 4 m rs Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 11 designing a drill pipe connection
Calculate the yield torque Ty (ft-lbf) of the following drill pipe connection. The connection has a so-called “torque shoulder” (that is a step in the male-thread pipe) for preloading.
The thread is straight (not tapered), which means that the pitch diameter is dm is constant. The thread form or profile is the API V-38 round thread (see next two slides for data). Assume API drill pipe tool joint material, with a minimum yield
strength Ym of 120,000 PSI. Assume lubricated friction coefficient f=0.08 (API). Connection inner diameter ID=3.5”, connection outer diameter OD=6-5/8”, box (or
nut) counterbore QC=5.312”, pin (or screw) pitch diameter
dm=4.920”. Calculate also the make-up torque (screwing torque), which according to API, should not exceed 60% of the minimum
yield strength Ym of the material. Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 12 the V-38 round thread profile (API)
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 13 round thread dimensions (API)
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 14 homework Optimize the design of the drill pipe connection, studied in slide 11, by: 1) “balancing” the connection
(making AP=AB) and 2) using different thread profiles (see following slides for other thread profiles, but also find others in the literature). The objective of the optimization is to maximize the yield torque Ty of the connection. Report deadline 2 weeks.
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 15 the V-40 and V-50 round thread profile (API)
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 16 the V-55 round thread profile (API)
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 17 the metric thread profile (ISO)
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 18 metric thread dimensions (ISO)
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 19 unified screw thread dimensions (ANSI)
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018 Threaded Pipe Connections 20 rotary shouldered connection geometry (API)
Mechanical Engineering & Aeronautics Department, University of Patras, March 2018