The working condition of drillpipe is very serious, especially in the dogleg or build section.Large alterative bending stress gives rise to the fatigue failure of drillpipe.

• 钻柱工作条件恶劣 ,尤其在狗腿或弯曲井段时 ,较大交变弯曲应力常造成钻柱疲劳破坏 ,计算钻柱疲劳寿命可以为钻柱使用和管理提供依据。