If misoperation happened in production of HDPE Pipe, such like workers’immature technology, raw materials, and malfunction in the machine , which could caused many kinds of problem that could affect the quality of pipe. Today we are trying to talk about the SPOT on HDPE Pipe: 1.Blocking of the cooling water channel in the calibration die, that could give regular distribution of spot on pipe. We could try to clean the water channel,to ensure the regular cooling water film, and to avoid the spot. 2.Too much heating time for raw materials in machine nose or barrel,some dirty in the nose and barrel, too higher heating temperature,or damage in the screw, all of which could burn-in the raw materials,then spot occured。After the 1.5hrs of the machine stopped working,stop the recycled HDPE raw materials into machine. More importantly,reduce the heating temperature immediately to 150-200℃ if the machine will stop for more than 4 hrs. 3.Un-regular cooling water quantity in the calibration die also could give spot on the pipe, especially for the Φ315 pipe or more,because it will need more cooling water to ensure the water film,but the more gravity of water will be a resistance. So please try to give more water to the upside of calibration die, or increase the water flow at weakness water channel. 4.The un-plastify impurity in raw material also could give spot in the pipe. You could watch the impurity if spot is big. Try to increase the temperature, adopt screen filter, or change materials. 5.The humidity in the raw materials will produce bubble in the surface of pipe,then the spot will be there after calibration. Also you will find a small tail in the negative extrusion direction,and you need to dry the raw materials. 6.Too much water flow could give spot in the pipe surface. Especially for the hole-type calibration die,where there is no partition for the water channel, the bottom water pressure is bigger, but surface of pipe is soft, it is easy to get spot in the bottom.