Residual Stress Surface Treatments for the Bore of Nonmagnetic Drill Collars

In the early 1980’s, the directional drilling industry relied on nonmagnetic drill collars as an essential tool.  These tools frequently failed due to stress corrosion cracking that started on the bore surface.  A partial solution was developing mechanical treatments that produce a thick compressive residual stress layer on the bore surface.   Since then, compressive stress layers have proven to be an effective means to prevent bore cracking and thick compressive layers have proven 100 % effective.   Furthermore, compressive residual stress treatments are now standard on the bore of nonmagnetic drill collars and, consequently, bore cracking has almost disappeared.  Bore treatments for nonmagnetic drill collars will be reviewed, including some details of current bore treatment specifications.  A pending American Petroleum Institute (API) specification for bore treatment of nonmagnetic drill collars will be mentioned.

Bore treatment technology has had a greater impact than simply preventing stress corrosion cracking problems that existed 25 years ago.  Since commercial introduction of bore treatments in 1983, a lot more nonmagnetic directional drilling equipment now exists for two reasons.

a. In the decade of the1980’s, horizontal drilling technology was developed and, in 2008 there were 600 rigs drilling horizontal wells in the United States with directional drilling equipment.

b. From a beginning in 1978, Measurement While Drilling (MWD) technology has been growing.  Many nonmagnetic tools with a bore treatment are used within MWD systems.