Measures to avoid the edge of the pipe end of steel pipe 3PE anti-corrosion layer

The three-layer polyethylene (3PE) anticorrosive coating has been widely used in the petroleum pipeline industry due to its good corrosion resistance, water vapor permeability and mechanical properties. The end of the steel pipe of the anticorrosive layer is prone to the problem of warping caused by corrosion.

According to the analysis, when the 3PE anti-corrosion layer steel pipe is sanded in the reserved polyethylene layer groove, the residual height of the pipe end weld is not repaired or the unevenness is repaired, which will cause the epoxy powder at the bottom of the polyethylene portion of the weld be worn away. In the case where the anti-corrosion pipe is stacked for a long time in the open air, the surface metal of the weld bead is first corroded, which causes the 3PE anti-corrosion layer to be warped.

Measures to avoid the edge of the 3PE anti-corrosion layer 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 warping caused by the corrosion of the metal at the end of the pipe due to the long stacking time of the steel pipe.

2. When the anti-corrosion pipe is stored for a long time in the open air, it should be covered at the pipe end to prevent rainwater erosion and cause serious corrosion at the pipe end.

3. If the pipeline construction period is long, the weldable anti-rust paint can be painted on the bare metal of the pipe end to prevent the anti-corrosion pipe from being corroded due to corrosion during storage.

4. Strictly control the grinding quality of the weld height at the reserved end of the pipe end. Outside the polyethylene groove at the weld, the epoxy powder is retained to a length of >20 mm, so as to prevent the bottom of the epoxy powder at the weld from being corroded first, causing the 3PE anti-corrosion layer to be warped. Pipe end weld grinding should pay attention to:

1) From the beginning of the weld grinding to the polyethylene chamfering, there should be 10-20mm flat layer of polyethylene with the same weld height as the pipe body to ensure the extrusion bonding at the pipe end polyethylene groove quality.

2) The residual height after the weld is repaired should be as close as possible to the pipe body, and there should be no obvious residual height to prevent the epoxy powder from being polished together when the polyethylene layer is chamfered.

3) The chamfer of the transition between the unfinished tip of the weld and the dressing point should also be the same as the chamfer of the polyethylene layer (≤30°), so that the pressing force of the pressing roller is evenly pressed on the polyethylene layer. On the top, to prevent the polyethylene layer from curling due to the adhesion of the anti-corrosion layer at the groove.

5. The reserved epoxy powder coating can only be used to delay the edge of the tube due to corrosion. Domestic pipe end polyethylene groove processing is done by wire wheel grinding, which will damage the epoxy powder coating. The machined groove should be used instead, and the bottom layer of the knife edge should be limited to control the depth of the tool to avoid damage to the epoxy powder coating.