Introduction
Drill rods for geological operations consist of one end threaded internally to form a pin, and the other end threaded externally to form a box. The 3.1m long rods are fit together to provide the length needed for drilling. Originally, these AISI 4130 steel drill rods were imported. It was then decided to manufacture these locally by threading rods imported from India. These rods began seizing prematurely in the field
Scope of Investigation
Two batches of rods were imported from India. A sample of the original rod and one from each batch from India were sent for spectrographic analysis to determine material composition. Further samples were sectioned for metallographic examination and hardness testing.
Findings – Root Cause Failure Investigation
The original rods, as well as both batches from India, are AISI 4130 steel, as specified. The hardness results and microstructural analysis show the following:
- In the original setup, only the pin thread has been hardened, to 320 HV, by quenching and tempering. No heat treatment has been applied to the base material and box thread, which remain in the normalised condition.
- There is a difference in hardness and microstructure between Batch 1 and 2.
- The sample from Batch 1 has been quenched and tempered, resulting in a higher hardness (290 HV) than Batch 2 samples. However, this treatment does not match that of the original pin thread.
- The Batch 2 samples are in the normalised condition with a hardness of 255 HV.
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