Foreign pipe or tube determining method

A foreign pipe or tube determining method carried out in a pipe or tube production process including a rolling step and an actual weighing and length measuring step for measuring weight and length of each pipe or tube rolled in the rolling step, comprising:

• a size measuring step for measuring outside diameter, wall thickness, and length of each pipe or tube after the rolling step and before the actual weighing and length measuring step;
• a weight calculating step for calculating weight of each pipe or tube based on the outside diameter, wall thickness, and length of pipe or tube measured in the size measuring step;
• a material determining step for determining material of each pipe or tube after the rolling step;
• and
• a foreign pipe or tube determining step for determining the presence of a foreign pipe or tube, wherein
• the foreign pipe or tube determining step comprises
• a step for determining the presence of a foreign pipe or tube by comparing the length of pipe or tube measured in the size measuring step with the length of pipe or tube measured in the actual weighing and length measuring step, which is associated with the pipe or tube in the size measuring step;
• a step for determining the presence of a foreign pipe or tube by comparing the weight of pipe or tube calculated in the weight calculating step with the weight of pipe or tube measured in the actual weighing and length measuring step, which is associated with the pipe or tube in the weight calculating step;
• and
• a step for determining the presence of a foreign pipe or tube based on the material of pipe or tube determined in the material determining step.