How is corrosion protection typically applied to the welds of epoxy coal tar pitch anti-corrosion pipes?
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This post was last edited by gqsh618 on 2011-11-17 at 17:45. Some of the buried pipes are coated with epoxy coal tar pitch for corrosion protection as required by the design. In this case, is it possible to simply purchase pipes that already have this corrosion protection applied, place them in the trench, and then carry out welding? How is the area around the welded joints treated? I would like to ask again: what method is used for corrosion protection at the welded joints?
After performing a pressure test on the weld area and applying anti-corrosion treatment, it can then be buried in the ground.
Reply to 1# gqsh618: “Is this situation where pre-treated pipes are purchased directly, then placed in a pit before welding?” Yes, that’s generally how it’s done. The subsequent processing of the welding area includes: 1. The weld appearance meets the requirements, and non-destructive testing is successful. 2. The pipes are thoroughly cleaned, and the hydrostatic test is successful. 3. Rust removal and anti-corrosion treatment are carried out on the welding area, with the results meeting the acceptance criteria. 4. Finally, the area is covered with soil
Generally, the anti-corrosion requirements for the welds of buried pipelines should be the same as those of the pipelines themselves. However, since the welds represent weak points, a higher level of anti-corrosion protection is typically applied during construction compared to that required for the pipelines. For example, anti-corrosion paint requires a higher-grade paint, or an additional coat of anti-corrosion paint is applied during construction. The pipes you mentioned are protected using epoxy coal tar pitch, which indicates that the level of corrosion protection is not high; presumably the environment in which the pipes are buried is not highly corrosive. The same standards of corrosion protection apply to the welding areas as well as to the pipes themselves. It is important to ensure proper bonding between the welding area and the original corrosion protection layer, in order to maintain continuity and sealing. The anti-corrosion coating in the welding area should pass an electric spark test before it can be approved.
For pipelines, the first thing to consider is the geological conditions of the area in question; different geological conditions require different anti-corrosion grades. For example, in saline-alkali soil layers, an anti-corrosion structure consisting of four layers of oil and three layers of fabric is used.