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Overview of Buoyancy & Stretch Properties

Due to the difference in modulus of elasticity of aluminum compared to steel, an aluminum drill string will exhibit more stretch than a steel string in air.  In a liquid, an aluminum string will develop greater buoyancy than steel, which will nullify a portion of the aluminum string weight, thereby reducing the stretch of the string.
 
The difference in length of a steel string, compared to an aluminum string in a liquid, depends on several factors:
  • String length
  • Weight of drill collars
  • Weight of other bottom hole assemblies in use (pipe sizes, mud weight, and straightness of the hole)
 
Arconic aluminum drill pipe, under its own weight without collars, etc., has less stretch in 10 lb. mud (or a heavier mud) than a comparable steel string.
 
Aluminum drill pipe users have reported no problems associated with stretch.  Although aluminum drill pipe strings exhibit more axial displacement than steel drill pipe on a pull, no cases of stretched pipe (permanent axial elongation of the joints) have been observed or reported on strings in service.
 

Effect of Stretch and Buoyancy on Length

Drill Pipe Size4 1/2 in5 in5 1/2 in5 7/8 in6 5/8 in
In Air
Hook Load (lbf)143,000167,333176,333187,502229,150
String Lengtd (ft)10,31010,31010,31010,30910,309
In 10lb/gal Mud
Hook Load (lbf)97,935113,740119,782126,190153,394
String Load (ft)10,30710,30610,30610,30610,305
In 12lb/gal Mud
Hook Load (lbf)88,922103,021108,471113,928138,243
String Load (ft)10,30610,30510,30510,30510,305
In 14lb/gal Mud
Hook Load (lbf)79,90992,20397,161101,665123,092
String Load (ft)10,30510,30510,30510,30410,304


Stretch – Arconic Drill Pipe Per 1000 Ft Per 1000 Lb Load

Drill Pipe Size-In.4 1/2 in5 in5 1/2 in5 7/8 in6 5/8 in
In-Air-Ft..0129.0108.0102.0091.0073


Fatigue Endurance of Aluminum Alloy Drill Pipe at Various Temperatures


Buoyancy of Aluminum and Steel Drill Pipe (weight per foot)


Depth to Sticking Point vs. Stretch


Contact Information

Alcoa Oil and Gas
7211 Spring Cypress Rd
Spring, TX 77379
United States
1 866 385 2137
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