The electrofusion welding is a joining procedure which is relatively simple to do, besides of being efficient and, in comparison to the others, a little expensive. However, it is important to do each of the steps with extreme caution and knowing very well that a mistake in any of them could produce a bad joining. In this article we are going to focus on one of the first steps of the welding, the scraping.
It is important to remember that the surface of the pipe should be always clean with a clean and dry cellulose paper, even though, in appearance, it is already free of dirt. It is a way to reduce the possible risk of pollution of the part we are going to weld.
Occasionally we can use water for this operation, using rags or paper towels which don’t leave any remain and always before doing the scraping. One of the obligatory propositions is to keep dry the area prepared for the welding. The presence of humidity can mean that bubbles appear during the joining, what would suppose an important problem.
The aim of the scraping is to eliminate the little oxidation of the superficial layer that there is in the polyethylene (PE) pipes. The scraping is always done towards the end of the pipe. After the cleanness with the mentioned paper, it is essential not to touch the surface of the pipe after that.
>>> IMPORTANT: We should take into account that neither sandpaper nor abrasive papers are apt to prepare the surface of the welding, as not only they don’t eliminate material, but also they damage the surface of the pipe and they leave particles on the surface.
We differentiate between manual scrapers and mechanical scrapers. These last ones control the surface of penetration and eliminate a uniform layer of material. The manual scrapers, on the contrary, are directly handled by a worker.
The best thing is to use marking techniques to delimit the area that we want to scratch, like to use a marker of a visible colour to mark the area that has to be scratched. Erasing these lines will mean that it has been scratched the area we wanted.
We should not forget that, in any case, the efficacy of the manual scraping depends on the worker’s experience and skill.
In the case of the PE 100 pipes, the most advisable thing is to use a mechanical scraper due to the hardness of the surface, something that it is not necessary in the PE 80 pipes.
One of the mistakes that occurs in some occasions is to give too much width between the welded fitting and the pipe, and it is a consequence of having scraping too much and eliminated an excessive quantity of material. This would produce a creep of the melted PE towards outside of the fitting.
Another mistake that occurs in some occasions is to use rags soaked in alcohol on the scratched area, something that can add pollution because if this isn’t very well evaporated, it could produce volatile matters which will damage the welding procedure. In the case the welding is being done outdoors there is a risk that the scratched area gets dirty, like if the fitting has stayed outside of the bag. Only in this case it is recommended to clean the area with paper and isopropanol.