1, the pipe can be judged by the echo. Knock on each tube and listen to the echo at the mouth of the tube. If the echo is higher and sharper, it has been annealed. Because the crystal structure of the annealed parts is more uniform and denser, the echo with higher pitch can be produced. Due to the more defects of the structure, the part of the UN annealed parts can absorb part of the acoustic energy, so the tone is low and stuffy at the mouth. If there is a condition, sonar can be used to detect it.

2, use a good digital multimeter to measure the resistance per unit length (such as 2 meters) of each branch. The resistance of stainless steel is large and should be measured. The resistance of annealed steel parts is smaller than that without annealing. Dry before the test, no liquid.