Effect of residual stress on ACFM crack measurements in drill collar threaded connections

M. J. Knight, F. P. Brennan, W. D. Dover

Research output: Contribution to journalArticlepeer-review

34 Citations (Scopus)


The drill collar threaded connection of the type used in hydrocarbon exploration is a critical component of the drillstring that is highly susceptible to fatigue damage. In an attempt to reduce costly downhole failures the connections are cold rolled to introduce compressive residual stress, and when in service the connections are routinely inspected. The Alternating Current Field Measurement (ACFM) technique is an increasingly popular method of thread inspection, however, results have indicated that the ACFM defect sizing capability may be compromised when it is used to inspect recently cold rolled connections. If a connection is cold rolled without first being defect free, subsequent inspections may under estimate crack depth with the standard interpretation. Inspection before rolling is therefore necessary.

Original languageEnglish
Pages (from-to)337-343
Number of pages7
JournalNDT and E International
Issue number5
Publication statusPublished - 1 Jul 2004


  • alternating current field measurement
  • crack sizing
  • residual stress
  • thread root cold rolling

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