Reasons for the fracture of the sucker rod

The sucker rod in a certain oilfield frequently fractured. The causes of the fracture of the sucker rod were analyzed using methods such as macroscopic observation, chemical composition analysis, mechanical property testing, metallographic examination, scanning electron microscopy and energy spectrum analysis. The results show that the fracture property of the sucker rod was corrosion fatigue fracture. After adopting deep pumping process, the sucker rod was subjected to a larger tensile load, which increased the average stress of the sucker rod and shortened its fatigue life. The oil well contained hydrogen sulfide, which caused corrosion on the outer wall of the sucker rod, led to the formation of corrosion pits on the outer wall of the sucker rod. The stress concentration at the bottom of the corrosion pit was relatively high. Under the action of alternating loads, micro cracks were generated at the bottom of the corrosion pit, which continuously expanded and ultimately caused the sucker rod to fracture.