API DRILL PIPES DESCRIPTIONS
The longest section of the Drill String is the Drill Pipe. Each joint of drill pipe consists of the tube body and the Tool Joint (connection). Drill pipe joints are available in three length ranges:
Range Length, ft
Range 2 is the most common.
Drill pipe is generally described by tube OD, nominal weight, pipe grade, type tool joint, thread connection and classification. For example, a 5" drill pipe can be described as,
5'' 19.5 Grade ''E'' XH NC50 Premium
tube OD Nominal Minimum Upset Connection Classification
Weight Yield strength Tool Joint thread (wear)
Each description item is explained in more detail below.
Drill Pipe OD
- Which is simply the plain end (tube) outside diameter.
Drill Pipe Nominal Weight
- Which is the weight per foot including the weight of an API regular connection. The number serves no real purpose other than identification because drill pipe does not have API regular connection.
- The actual weight depends on the type of connection and pipe grade. As the grade (minimum yield strength) increases the actual weight increases because the upset has more metal in it.
- The actual weight of the 5'' drill pipe in the above example is 20.89 lb/ft. The actual weight for grade G pipe is 21.92 lb/ft.
The Pipe Grade
- states the minimum yield strength of the metal which is the tensile stress that will result in 0.5% strain. Grade E drill pipe has a yield strength of 75,000 psi.
- The minimum strength can be converted to a more usable strength in pounds by multiplying the minimum yield in psi by the cross-sectional area of the metal.
The tool joint and type of upsetWhich are part of the drill pipe description. Tool joints are screw-type connectors that join the individual joints of drill pipe. Each joint of drill pipe is fitted with a pin (male thread) and box (female threads) tool joints or connectors.
Drill Pipes Tool Joints Types / Upset Types
- IEU (Internal-External Upset) - The tool joint OD is larger than the OD of the drillpipe and the tool joint ID is less than the ID of the drillpipe. Generally, IEU tool joints are the strongest available. The large OD and small ID of the tool joint cause relatively high external and internal pressure losses.
- IF (External Upset) - The tool joint ID is the same as the ID of the drill pipe to minimize internal pressure losses. The upset is on the OD of the tool joint.
- IU (Internal Upset) - The tool joint ID is less than that of the drill pipe. The small ID causes relatively higher internal pressure losses. The tool joint OD is the same as the OD of the drill pipe. This type is called slim-hole drill pipe because of the small OD.
The type of connection
- Which is designated by the API NC number which is a two-digit number of the pitch diameter taken at the pin gauge point .
- Gauge point pitch diameter is the distance at gauge point measured to imaginary lines that bisect the thread halfway between crest and root. For example, for pitch diameters of 5.042'' and 4.628'' the NC numbers are NC 50 and NC 46 respectively.
The classification of drill pipe is based on wear.
- As new drill pipe is rotated in the hole it wears and, therefore, it must be reclassified according to its wear.
- Exterior wear includes OD wear, dents and mashes, slip area crushing, cuts, pitting and corrosion. The working strength is reduced because of loss in cross-sectional area.
- The drill pipe is inspected periodically to detect cracks, pits, reduction in wall thickness and other defects. Inspection methods include electromagnetic inspection of pipe body to locate cracks and pits, sonic inspection to measure wall thickness, visual inspection to detect mashes and caliper measurements.
API Drill Pipes ClassificationsThe API has established guidelines for pipe classes in API RP7G. The classes are summarized as follows:
New:- No wear and has never been used.
Premium:- Uniform wear and a minimum wall thickness of 80% of original wall thickness.
Class 2:- Allows drillpipe with a minimum wall thickness of 65% with all wear on one side so long as the cross-sectional area is the same as premium class, that is to say, based on not more than 20% uniform wall reduction.
Class 3:- Allows drillpipe with a minimum wall thickness of 55% with all wear on one side.