Abstract
Nonmagnetic drill collars and other structural components are used to provide a region in the bottom hole assembly near the bit in which sensitive magnetic measurements can be made. Beryllium copper, C17200, is paramagnetic with low magnetic permeability which makes it aptly suited for nonmagnetic components. Not only are the magnetic properties of the alloys for these components important, but the integrity of the alloys under dynamic loading in a range of hostile drilling fluids is critical as well. Chlorides in certain drilling muds can cause unpredictable stress corrosion cracking (SCC) of susceptible alloys. In a standard test for chloride SCC, ASTM G 36-73, beryllium copper, C17200, showed no failure after 1000 hr of exposure to boiling 45 weight percent magnesium chloride solution. The applied stresses were 100 percent of the 0.2 percent offset yield strength for the alloy. Failures for austenitic stainless steels generally occurred in less than 200 hr in this environment at applied stresses of 25 percent of the yield strength. Although benefits can be obtained by controlling the environment and introducing residual compressive stresses to austenitic stainless steel components, these remedies cannot permanently eliminate the underlying susceptibility of these alloys to chloride SCC. Beryllium copper is immune to chloride SCC.
