Development of Titanium Drill Pipe for Short Radius Drilling
Authors: Smith Jackie E. , Schutz Ronald W. , Bailey Edmond I. 
Published: January 2008

Abstract
A need exists for drill pipe that offers improved reliability and extended life in re-entry drilling programs where the radius of curvature is less than 60ft (i.e., &gt;95-deg/100 ft). Steel, aluminum, and composite drill pipetraditionally utilized in these short radius drilling operations often exhibit abbreviated lives stemming from fatigue, wear, and/or physical damage.
With an elastic modulus of approximately 17 msi, titanium pipe offers enhanced flexibility and reduced fiber stresses compared to steel pipe when rotated in holes of high curvature. Utilization of the most widely used titanium alloy, Ti-6Al-4V, offers a high nominal yield strength of 120 ksi with a density 56% that of steel. Combined with good corrosion and fatigue resistance in drilling and down hole fluid environments, this titanium alloy isa lightweight, highly flexible, robust, and fatigue-resistant drill pipe material.
A practical and cost-optimized Ti drill pipe joint design consists of a seamless Ti-6Al-4V alloy pipe body, which is produced in standard API sizes and Range 2 and 3 lengths, to which steel tool joints are mechanically attached to the upset ends. The steel tool joints offer the advantages of lower tool joint costs, standard drill pipe make/break connection behaviour, the option for tooljoint hard banding, and elimination of welded joints.
Successful development of titanium drill pipe assemblies for short-radius drilling included appropriate conditioning of the OD and ID pipe body surfaces to maximize fatigue life, optimizing the pipe end upsetting procedure, establishing the tool joint-to-pipe attachment methodology, and design and testing of a high-integrity tool joint-to-pipe connection and tool joint for optimum fatigue performance. This paper overviews these developments and the laboratory test results used to establish critical performance behaviour and requirements for 2–7/8 in. OD titanium drill pipe for short-radius drilling. An update on recent field experience with titanium drill pipe utilization invarious short radius drilling programs is provided as well.

Introduction
This program was undertaken in late 1996 with the objective to develop titanium drill pipe for short radius drilling applications. The pipe size selected for this development was 2–7/8 in. × 2.151 in. ID with 3–5/8 in. OD × 1–3/4 in. ID NC26 tool joints. The pipe body is dimensionally the same as API2–7/8 10.40 lb/ft steel pipe which is widely used. The NC26 tool joint is a good match for the pipe and is also commonly used.
Titanium has five attributes that make it an attractive choice compared to steel for short radius drill pipe:*Titanium has a density of 0.160 lb/in3 compared to 0.283 lb/in3 for steel orit's about 43% lighter.*Titanium has an elastic modulus of 17 million psi compared to 30 million psifor steel or it is 57% as stiff as steel.*Titanium is more corrosion and erosion resistant than steel.*Titanium does not suffer corrosion fatigue. The fatigue performance in air issustained in the drilling environment.*Titanium pipe has a yield strength of 120,000 psi, which equates to a strength to weight ratio of 1.54 times that of S-135 steel pipe.
Even though all these attributes contribute directly to the pipe's attractiveness for short radius drilling, the low modulus is the primary characteristic that gives titanium the advantage over steel. It is desirable inthe industry to drill through a radius of curvature of 50 feet or less and have a service life greater than 500,000 cycles.