Drill Pipe and Tubulars

How drill pipe carries load

A drill pipe joint is a seamless tube with upset ends and a tool joint friction welded to each upset. The tube carries tension and torsion. The tool joints carry make-up torque, take the elevator load on their 18 degree shoulder and give room for recuts. Fatigue concentrates where stiffness changes, at the internal upset taper and in the slip area just above the pin.

HWDP has a thick-wall tube, extra-long tool joints and a centre wear pad. It sits between collars and drill pipe to smooth the stiffness change, and in high-angle wells it often carries weight on bit in compression. Tubing work strings are API Spec 5CT tubing used for completion and workover jobs. They have no tool joints, so their torque limit is set by the coupling or premium connection.

Configurations

• Sizes from 2-3/8 in to 6-5/8 in OD. Offshore strings are usually 5 in, 5-1/2 in or 5-7/8 in.
• Grades E75, X95, G105 and S135, where the number is minimum yield in ksi (517, 655, 724 and 931 MPa).
• Range 2 joints of 27 to 30 ft (8.2 to 9.1 m) and Range 3 joints of 38 to 45 ft (11.6 to 13.7 m).
• API connections such as NC38, NC46, NC50 and 5-1/2 FH, or proprietary double-shoulder connections for higher torque.
• Landing strings, which are heavy-wall, high-grade pipe for running heavy casing and subsea completions, with slip-crushing limits that govern their rating.

Key specifications

Inspection classes and standards

API RP 7G-2 and DS-1 class the tube by remaining wall. Premium pipe keeps at least 80 percent of nominal wall and Class 2 at least 70 percent. API RP 7G publishes tension, torsion, burst and collapse ratings for premium and Class 2 pipe, and those are lower than the new figures for the same size and grade. Premium pipe carries two white paint bands near the pin tool joint, and Class 2 pipe one yellow band.

Tool joints are classed separately. Their OD and the box shoulder width decide whether the joint still matches the torsional strength of the premium tube.

Failure modes and inspection

• Fatigue cracks at the internal upset taper and in the slip area, which grow into washouts. Full-length EMI, ultrasonic wall checks and magnetic particle inspection of the upsets find them.
• Wall loss from OD wear, and pitting under failed internal plastic coating. Look inside with a borescope or lamp.
• Slip cuts and crushing marks, which DS-1 limits by depth.
• Tool joint OD wear, box swell and pin stretch from over-torque, and galled or flattened shoulders.
• Cracked or spalled hardbanding, which can damage casing.

Ask which DS-1 category was run. Category 4 or 5 adds the slip-area and connection work that a basic rack inspection skips.

Documentation that makes a lot credible

• Mill certificates by heat, showing grade, PSL, chemistry and impact tests.
• The latest inspection report with the standard, category and result for every joint.
• Tool joint dimensions per joint, including tong space and any recut history.
• Hardbanding type and internal coating records.
• Run history: rotating hours, dogleg severity and any sour or high-chloride exposure.

Integration with your rig

Check the tool joint OD against your elevators, slips, iron roughneck and pipe handler gripping ranges. Match the connection to the top drive saver sub and your crossover kit. Proprietary double-shoulder connections need the licensee's gauges, thread compound guidance and a licensed shop for every recut. Heavy strings may need long slips or a slip-crush check against the hook load. For elevators and slips that fit the tool joint, see Elevators and Slips.

Refurbishment and when to buy what

A shop can recut tool joints if tong space remains, reface shoulders, apply new hardbanding and recoat the bore after blasting. Nothing restores lost tube wall, so a string's class only moves down over its life. Unused surplus pipe with mill paperwork suits critical wells. Premium used pipe suits development work with known loads. Class 2 pipe only fits light, shallow duty. For the heavier members below the pipe, see Drill Collars.