Abstract: The TA31 alloy cold-rolled pipe fittings used in a certain petrochemical equipment exhibit abnormally low elongation after fracture. The reasons for the low elongation after fracture of the pipe fittings were analyzed using macroscopic observation, chemical composition analysis, mechanical property testing, scanning electron microscopy and energy spectrum analysis, metallographic examination. The results show that there were α layers and folding defects on the inner surface of the pipe fittings, which led to stress concentration and crack initiation on the surface of the specimen during the tensile test, changed the stress state of the specimen and ultimately resulted in a decrease in the elongation after fracture of the pipe fittings.