This paper considers a real case study of the bellows instability (squirm) observed in a pressure balanced universal expansion joint within a power plant during hydrostatic tests conducted immediately after piping installation. The investigation aims to identify the root causes of this instability by considering potential modes of failure in the universal expansion joint. The analysis takes into consideration the impact of actual piping stiffness on critical pressure, along with additional lateral stiffness occurred when the tie rods of the expansion joint are inclined. The critical pressure values obtained through this study are then compared against stability requirements outlined in EJMA standard.