SOME CASE-STUDIES OF FAILED AUSTENITIC DRILLCOLLARS

Non-magnetic austenitic Cr-Mn-Ni steels with high N content are used f or drillcollars in a high-strength cold worked condition. The dominant strengthening mechanisms are solid solution hardening from Cr, Mn and N, and strain hardening due to cold working. It is the need for high- strength (yield strength greater than or equal to 800 MPa) and non-mag netic (mu(r) less than or equal to 1.001) steel for some bottom hole a ssembly components which has led to the development and widespread use of these steels. Case studies from a selection of recent investigatio ns of failed pin connections serve to illustrate the common failure mo des encountered. Examples of fatigue, ductile fracture and stress corr osion cracking are considered in detail. Instances are reported of str ess corrosion cracking where overload yielding or bore wear has remove d the effectiveness of the hammer peened layer in the bore. Copyright (C) 1996 Elsevier Science Ltd.