การวิเคราะห์ความเสียหายของก้านเจาะหินปูน ด้วยการตรวจสอบพื้นผิวการแตกหัก

Abstract

This research studied on a failure cause determination of limestone drill rod using fractography investigation with failure analysis method. Five samples of drill rods, damaged during December 2014 – November 2015, were used in this study. Drilling Rods were tool steels with low alloys, DIN 1.6659 Standard, grade 31NiCrMo13-4 and carburized surface hardening. From hardness testing Results, it was found that outside surface hardness was similar and chemical composition was normal. From data of the 5 drill rods uses, the average of use duration was 36 days per rod and the average drilling depth per rod was 3671 meters, maximum drilling depth was 4,629 meters and minimum drilling depth was 2,505 meters because drill head fracture. The surface fractography analysis revealed that the fractures initiation of the drill rods started at the outer surface, especially at joint between drill rod and drill head. The mode of failure was found to be fatigue. Propagation of fracture was beach mark over the surface fracture appears, resulting from continuous low nominal stress. This was mainly origin fracture caused by a stress concentration, the joint or groove of screw, and impact force. Finally, a failure prevention guideline was proposed.