Swivel joints on fracturing trucks work under severe pressure pulsation and high-cycle loading. A burst failure normally results from a combination of stress concentration, fatigue crack growth, overload, corrosion, or manufacturing defects.
The first step in analysis is to identify the fracture origin. Cracks often initiate at thread roots, transition radii, seal grooves, ball races, or impact-damaged areas. Fracture morphology, beach marks, and local deformation help distinguish fatigue failure from overload rupture.
Material verification should include chemical composition, mechanical properties, heat-treatment condition, hardness, and metallographic examination. For high-pressure service, insufficient toughness or excessive hardness can significantly reduce fatigue resistance.
Dimensional inspection is also necessary. Sharp transitions, undersized wall thickness, poor thread form, and nonconforming seal grooves can increase local stress. Pressure testing alone cannot replace dimensional and nondestructive examination.
To reduce burst risk, swivel joints should be selected according to actual working pressure, pressure cycle, medium, temperature, and connection type. Components showing leakage, abnormal wear, visible cracks, or impact deformation must be removed from service.
