The three-layer polyethylene (3PE) anti-corrosion coating has been widely used in the oil pipeline industry for its good corrosion resistance, water vapor permeability resistance, and mechanical properties. This anti-corrosion steel pipe end is susceptible to the problem of edging due to corrosion.
According to the analysis, when the 3PE anticorrosive steel pipe is used to polish the reserved section of the polyethylene layer, the remaining height of the pipe end weld is not repaired or the grinding is not smooth, which will cause the epoxy powder on the polyethylene bottom of the protruding part of the weld to be worn off. In the case that the anticorrosion pipe is stored in the open air for a long time, the metal on the surface of the weld will be corroded first, which will lead to the appearance of edge-up in the 3PE anti-corrosion layer.
The measures to avoid the occurrence of edging on the tube end of the 3PE coating are:
1. Without affecting the welding of the nozzle, the reserved length of the epoxy powder at the end of the polyethylene layer should be appropriately increased to prevent the 3PE anti-corrosion and edge-up due to the long time for the steel pipe to be stacked and the serious metal corrosion at the pipe end.
2. When the anti-corrosion pipe is stored in the open air for a long time, it should be covered at the pipe end to prevent rain erosion and cause serious corrosion at the pipe end.
3. If the pipeline has a long construction period on site, it can be painted with solderable anti-rust paint on the bare metal of the pipe end to prevent corrosion of the 3PE anti-corrosion layer caused by corrosion of the anti-corrosion pipe during storage.
4. Strictly control the grinding quality of the weld seam at the reserved area of the pipe end. In the weld seam outside the polyethylene groove and other parts of the pipe body, so that the epoxy powder retention length> 20mm, in order to prevent the epoxy powder at the weld at the bottom of the first corrosion caused by 3PE coating layer Alice. Pipe end weld grinding should pay attention to:
1) From the beginning of the weld repair to the polyethylene chamfer, there should be a 10-20mm flattened section of the polyethylene layer with no seam height, to ensure that the pipe end is pressed and bonded at the polyethylene groove. quality.
2) The remaining height of the welded joint should be flush with the pipe body as far as possible, and there should be no obvious excess height, so as to prevent the epoxy powder from being polished together when grinding the polyethylene layer chamfer.
3) The chamfer of the transition between the untrimmed end of the weld and the dressing is also to be the same as the chamfer of the polyethylene layer (≤30°) so that the pressing force of the pressing roller can be uniformly applied to the polyethylene layer. In order to prevent the polyethylene layer from curling due to poor adhesion of the coating at the groove.
5, only a complete protection of the reserved section of epoxy powder coating can play a role in delaying the edge of the tube caused by corrosion. The domestic pipe-end polyethylene groove processing is carried out by the wire wheel grinding method, which will damage the epoxy powder coating. The machined groove should be used instead. The cutting edge of the knife edge should be limited to control the depth of the tool, so as not to hurt the epoxy powder coating.